Combat robot R/C and electrical system questions and answers from Team Run Amok.

A: Do not switch the polarity of the servo - instant fried electronics. Almost all hobby R/C transmitters have a 'servo reverse' switch or function that will invert the servo direction. Use that! You can also buy a tiny 'electronic servo reverser' that plugs in between the receiver and servo -- websearch!

You can wire two servos in parallel and plug them into a single receiver output. Your local hobby shop can provide a 'Y-connector' for that purpose, or you can splice the wires yourself.

A: Mark J. here: Some readers may wonder why you want to do this. Servos can be 'hacked' to provide continuous rotation and used as drive motors. 'Overvolting' the servo will provide more speed and power at the cost of reduced lifespan. Many receivers and other R/C electronics, however, are very sensitive to increased voltage and can fail or malfunction if pushed to higher voltages. The trick is to run the receiver at a correct voltage while providing higher voltage to the servo.

A servo lead has three wires:

Note: although extensively used in the past, servos are inferior to other insect class drivetrains. I don't recommend them.

A: Gyros don't prevent the death spin, they CAUSE the death spin if they invert. See the gyro guide for info. I don't know of any event which has either required or disallowed the use of gyros.

A: Mark J. here: the inexpensive Gardner crimper is best used with the 30 amp Anderson Powerpole connectors. The contacts for the 15, 30, and 45 amp connectors are the same, so actual power capacity of the connectors are also the same -- about 100 amps. The difference is in the size of wire the connectors will accept. The 30 amp powerpoles will accept up to 10 gauge wire (really). You may want to solder the 45 amp connectors rather than trying to crimp them. See: this archived article for instructions on crimping with the Gardner tool.

A: Sure. Most teams have only a single transmitter that they use for all of their 'bots. One word of caution: at some large tournaments the insect classes run in a small arena at the same time that the larger 'bots are fighting in the big arena. In that case you may need a backup driver and a spare transmitter. Same deal if you have more than one 'bot entered in a single weight class -- you may end up fighting yourself!

Q: If you end up fighting yourself, can't you forfeit one of ur bots and still win?

A: Mark J. here: --- WEAK! ---

If you enter a robot in a tournament you should be prepared to fight it under any and all circumstances; if not for your pride then for the benefit of the spectators. Allowing such a forfeit would be at the discretion of the event organizer. I'd throw both your 'bots out.

A: If a radio system has failsafe capability, it will say so somewhere in the descriptive text -- it's a feature they want you to know about! AM and regular FM (PMM) systems generally do not failsafe. Coded FM (PCM or IPD), 900 MHz, and 2.4 GHz systems may failsafe.

Part of the problem you're having is that Robot Marketplace currently sells only one radio system under $200 that is full failsafe: the 'Spektrum DX6 2.4 GHz with BR6000 receiver'.

Note: All Spektrum 2.4 GHz systems failsafe, but systems with the AR6000 receiver fail to the last speed setting received from the transmitter. This is not legal for robot combat which requires drive and weapon systems to stop on signal loss. The Spektrum BR6000 receiver corrected this problem.

A: Mark J. here: lots of variables! Rule of thumb: a typical spinner adds about 40% to the capacity needed for the drive motors.

If you're determined to go thru some rough calculations, you can use the Team Run Amok Spinning Weapon Excel Spreadsheet to calculate the energy capacity of your weapon in joules. Each time the weapon is depleted and must spin up it will consume approximately:

A: The current RFL rules require all robots with active weapons to have fail-safe electronics which will stop all robot motion if the radio signal is lost. Robots weighing 12 pounds or above must use FM radio with PCM or IPD coding, or digital 900 MHz or 2.4 GHz systems.

The GWS GWT-4A does not meet any of these requirements. It may be used for passive weapon robots up to 12 pounds, or for active weapon robots up to 6 pounds if add-on fail-safes are included.

Note that a few tournaments now require digital 900 MHz or 2.4 GHz systems for all robots. Check with the specific event organizer to be sure.

A: Yes. The 'Spektrum DX6' is a full-featured R/C system. It has multiple pre-set and custom programmable mixes and couplings built in. A full description is in the owners manual.

So, would I be able to use a normal FM system with my Antweight?

A: Mark J. here: From the discussion on the on-line forums, I think the intent is to require ALL combat robots at Robogames to run 'spread spectrum' radio systems -- sections 4.4.4 thru 4.4.6 should have been removed. However, I've always had trouble with Dave Calkins' logic. Write to him for clarification: dcalkins@robotics-society.org. Dave sometimes ignores his email, so 'cc' a copy of your question to Simone Davalos: simone@robotics-society.org.

Q: I talked to Dave Calkins. He told me:

A: Six words? I guess that helps a little, but it still leaves beetles, sublights, and AM radio uncertain. Robogames was once a popular and well-run event. I'm sorry to see it fall into confusion.

A: The AstroFlight 110D can charge up to 24 NiCad or NiMHd cells in series. That's a nominal 28.8 volts. A single 12 volt pack can be charged at up to 8 amps, but the maximum charge rate starts to drop above 14.4 volts. A single 24 volt pack (or two 12 volt packs in series) can be charged at a maximum 5 amps.

It's possible to charge multiple packs in parallel, but the charge amperage gets split between the packs. Two 24 volt packs charging in parallel would each charge at only 2.5 amps maximum. That won't save any time compared to charging each pack by itself.

If you need to charge higher voltage packs or multiple packs in series, pay a few extra dollars for the AstroFlight 112D. It can charge up to 40 cells in series (48 volts nominal), can pump 8 amps into a single 12 or 24 volt pack, and can charge two 24 volt packs in series at 4 amps.

You might also consider the ElectriFly Triton2 charger [discontinued].

A: Each time the transmitter is turned on it 'listens' to radio activity on the 2.4 GHz band, selects an unused channel, and transmits a code to the receiver to tell it what channel to use. Your 900 MHz or 2.4 GHz wireless phone works pretty much the same way.

More information at Spektrum R/C.

Q: So from what you're saying, the 2.4Ghz radio only works with the receiver it comes with? If not, do you have to sync it with a receiver?

A: When a 2.4 GHz receiver is used for the first time with a transmitter it has to be 'taught' the receiver's code in a process called 'binding'. You only need to do that once, and you can bind multiple receivers to the same transmitter.

A: For a start, browse:

• Pololu Robotics
• Dr. Robot
• Robot Shop.

Q: After seeing Team Tentacle's 'Thinkling' I've decided to go with the Baby Orangutan MCU and two Devantech SRF08 ultrasonic rangefinders. How do I wire all of this? Is there anything else I need for the electronics? Thanks.

A: Mark J. here: hold on there, Cowboy... I'd say you were more than a little ahead of yourself. Nobody who's ready to build an autonomous combat robot is going to write to me and ask how it all gets wired up. Even if you can get your sensors, MCU, motors, weapon (you're missing a weapon controller), and remote activation R/C (you're missing that, too) wired correctly, the robot is just going to sit there without software. How are your programming skills?

Sit down with a good book on autonomous robots, like Robot Programming: A Practical Guide to Behavior-Based Robotics by Joe Jones. Technical information on how to communicate with the SRF08 is at the Devantech website, and the Pololu website has links to documentation for the Baby Orangutang.

Once you're confident that you can 'wire up' and program the robot controller and peripherals, write back and we can discuss design issues and combat theory.

A: Mark J. here: it isn't quite that simple. AM systems are incompatible with FM systems. 'Negative shift' coding (Futaba, Hitec) is not compatible with 'positive shift' (Airtronics and JR). Some 'third party' receivers can use either shift pattern. If the transmitter and receiver have the same coding, operate on the same frequency band (27/49/50/53/75/900/2400 MHz), and use the same modulation (AM or FM) then yes, matched frequency crystals (75 MHz and lower) will probably make them compatible. The 900 and 2400 MHz radios do not use crystals.

Stick with a single manufacturer for transmitters and receivers and you should be OK.

A: For your first R/C system, you can:

• Start with something simple and upgrade when you need to, or

• Start with a system that will handle your future needs and save the trouble (and expense) of a later upgrade.

The GWS GWT-4A has no fail safe capability, no channel mixing, no dual rates, no exponential response, no receiver battery pack, and it will require at least one extra set of frequency crystals for competition use. Just plain vanilla R/C. It's cheap to purchase (a little over $100, with listed options), but it's also gonna return little of the purchase price when you go to sell it -- and you're gonna need a better system as soon as you move up past the hobbyweight class or go to an active weapon.

For less than $200 you can purchase a system like the 'Spektrum DX6' with the BR6000 receiver. You'll get all the features you're gonna need for any practical combat robot in any weight class. It requires no extra crystals, has full fail-safes, three channel mixes, dual rates, exponential response, a receiver battery pack, and four micro servos that you don't need and can sell on EBay to further reduce the price. If you should decide that combat robots aren't your thing, you can sell the Spektrum for a good price to someone who made the $100 mistake of buying a cheap system for their first robot.

A: Sure -- the 2007 RFL Standard Extensible Rule Set allows use of any ground-legal frequency (27/49/50/53/75/900/2400 MHz in the United States) in any weight class. See the #18 for specific fail-safe requirements.

A. The usual solution is to use one transmitter and two receivers all on the same frequency. Put one receiver in each articulated section, plug the local ESC or weapon controller into the appropriate output slot and you're set. It's more reliable than running long extension leads from one side to the other and risking failure from flexed and twisted wires.

Some non-articulated 'bots also use two receivers for redundant back-up. JuggerBot / Tricerabot used twin receivers for separate dual-channel front and rear speed controllers. If either receiver or ESC failed, they could continue the match with at least partial power.

A: The Vex Robotics System radio control gear has a different data format than hobby R/C systems. It is not compatible with standard combat robot components. Use the HiTec!

Comment: I have some information to add to your answer to the question about the Vex radio system. The Vex transmitter uses pretty much standard Futaba data encoding, it's the receiver that's the problem. If you replace the receiver the system works just fine with standard R/C equipment.

I've tested the Vex transmitter with Microbotparts and Futaba AS receivers. They work well and can even use the Vex crystals. Microbotparts have a 6 channel receiver available for $29.95, though it is not on the webite -- just ask. I've also used the Vex transmitter with the Sombra Shadow 3 and Polk Hobbies' Seeker 6 synthesized receivers.

Great site, keep up the good work. [Wreno - North Texas Battle Group - BattleBots on the water with a WW2 theme]

Reply: Thanks, Wreno. I knew the data outputs of the Vex system weren't compatible with standard R/C, but didn't know the source of the problem. A 6-channel transmitter with crystals for that price is a bargain, but robot guys should be aware that the Vex transmitter has only primitive channel mixing and no ATV, fail safes, exponential response, or dual rates.

A: A pistol grip radio will work, but we use standard twin-stick transmitters: left stick forward and back for the speed controller, right stick 'side to side' controls the steering servo. No mixing required. You could put both throttle and steering on one stick, but we like them separate.

We set up our differential steering 'bots the same way, throttle on left stick and steering on the right, using elevon mixing. See our transmitter programming guide for more info on channel mixing.

A: Mark J. here: when an invertible robot is flipped upside down, left / right steering response remains correct but the throttle response is reversed; a forward transmitter command will back the robot up and vice versa. An 'inverted' switch reverses the response of your throttle to compensate for this, but you don't usually add-on an inverted switch -- it's already there:

1. Many twin-stick transmitters will have a toggle switch that controls channel 5, or channel 3 on pistol style radios. Some speed controllers (like the Scorpion HX) and some on-board mixers have an extra input lead that will reverse throttle response. Plug that lead into appropriate channel on your receiver and the toggle on your transmitter becomes an inverted switch. The Scorpion HX ESC can also reverse throttle automatically in response to a 'gravity switch' on the robot itself, but there is too much vibration on a combat robot for me to recommend that.

2. If you have a computerized transmitter with user-defined functions, you may be able to assign a custom function to one of the available switches on the transmitter to reverse the throttle response. See my tutorial on Programming the Futaba 6XAPs for Combat Robotics for more information on computerized transmitters.

3. Non-computerized transmitters usually have a mechanical 'servo reversing' slide switch for each channel. You can simply flick the reversing switch for your throttle channel when inverted. You may want to fasten an extension onto the small reversing switch to make it easier to find in combat. I suppose you could replace the small slide switch with a larger toggle switch if you really want to do a mod.

A: Mark J. here: the Robot Fighting League accepts use of 27/49/50/53/75/900/2400 MHz radio systems for combat robot control in the USA, as long as the radio system has the required failsafe protocol for your weight class and weapon type. However, you must have an amateur radio operator license to legally operate a radio transmitter on either 50 or 53 MHz.

Be sure to check with the event organizer to make certain they don't require some specific radio type. Some events are talking about going to only 2.4 gHz 'spread spectrum' radios.

Q: How come a 72 MHz radio is not legal to use on ground-based vehicles?

A: Model aircraft are particularly sensitive to interference because their altitude gives them increased 'line of sight' reception. The Federal Communications Commission (FCC) made 72 MHz 'airborne only' to assure R/C pilots of clear channels without interference from somebody playing with an R/C dune buggy in a backyard miles away. To even things out, 75 MHz is restricted to 'surface only' uses. All other approved R/C frequencies may be used for either surface or air.

A: You have to pretty much fully enclose an antenna in a box of metal or other conductive material to block the radio signal by forming a Faraday cage. You'll want to keep your antenna spaced away from the metal surfaces and any source of electrical 'noise', but the signal will be able to penetrate thru the plastic sidewalls. Check the Ask Aaron Radio Reception Problems page for more info.

A: The 2007 RFL Ruleset says:

So, digital 2.4 GHz and 900 MHz radio systems are cleared to control any weight class 'bot with either active or inactive weaponry -- equivalent to coded FM.

A: Non-conductive materials like wood, glass fiber composites, and plastics are transparent to commonly used R/C radio frequencies.

A: The Vex Robotics System radio control gear has a non-standard data output format from the receiver. It is not compatible with standard combat robot components. Use the HiTec!

A: Both metal and carbon fiber block radio signals. If the metal or carbon armor completely encloses the 'bot, the radio antenna must stick out thru the armor, or be mounted under a radio-transparent 'window'. See the Ask Aaron Radio Reception Problems page for more info.

A: The 'C' relates to the capacity of the battery pack: a pack with a capacity of 3000 mAh has a 'C' of 3000 mA, or 3 amps. If the maximum discharge rate for that pack is given as '20C', it would be 20 times 3 amps = 60 amps. If you exceed the maximum discharge rate you will risk overheating and damaging the pack, and even setting the pack on fire!

A: Robotlogic.com makes a three-wheel omni mixer called the OMX-3. They also make a Mecanum mixer for four-wheeled Mecanum omnibots.

With the mixer installed, you may assign any stick axis you like for forward / reverse, left / right, and rotate. Search the Ask Aaron archive for more information on omnibots.

A: All freshly charged rechargeable battery packs will read a higher resting voltage than their rating. When placed under load, the voltage will drop down toward the rated voltage. Hitec says the servo will run on a 7.4 volt LiPoly, so don't worry about the extra volt in the resting state -- run it!

A: Mark J. here: a three-cell lithium polymer battery can be safely drained down to 8.4 volts, so running into the 9 volt cutoff is fine. The usual cause of damage to Lipoly batteries is overheating caused by too high a discharge rate. Temperatures over 140 degrees can damage or destroy the pack. Leave some space around the battery for cooling air circulation and keep the discharge rate within the manufacturer's spec. A well cared for Lipoly battery can exceed 1000 charge/discharge cycles. Check the Electrifly Lipoly Manual for more tips on care and disposal.

A: You can mix channels with a computerized transmitter, a plug-in electronic mixer, or a twin-channel controller with built-in mixing. All of them produce the same control style: one control channel (stick axis or throttle trigger) moves the 'bot forward and back, while a second channel (stick axis or wheel) controls turning. If you activate only the turning channel, the 'bot will spin in place without moving forward or back -- just like throwing the control sticks in opposite directions when working tank-style.

A: Mark J. here: even small combat robots don't use alkaline batteries! Alkalines are designed to operate in devices with a low current requirement. They cannot provide anywhere near the peak current that NiCad or NiMHd rechargeable batteries can, and in a permanent magnet DC motor current equals torque.

A typical alkaline 9-volt battery can provide just over 1 amp of current, and will last a VERY short time at that current draw. Your screwdriver motors will need at least 5 amps each to develop their full pushing torque potential. A sumo robot that can't push is pretty useless.

A modern AA size NiCad or NiMHd cell can pump out 8 to 10 amps of torque-grinding current and keep it up long enough for a full sumo match. An 8-cell pack will give you a nominal 8.4 volts and would be a far better choice for your 'bot than 9-volt alkalines. Simple chargers for NiCad / NiMHd packs are inexpensive and the charging process is uncomplicated.

Your other choice is a lithium polymer battery. LiPolys are very light and compact for their power capacity, but are more expensive and have lower peak current capacity than NiCads or NiMHd packs of equivalent amp/hour rating. LiPolys also require a different type of charger than other rechargeable packs -- never try to charge a LiPoly battery with a charger not specifically designed for the purpose. A good article on LiPoly care can be found at electrifly.com

A: Twist three wires together, solder, and insulate with heat-shrink tubing. Do not use 'bullet crimp' or 'twist' connectors on a combat robot -- they can fail under impact and vibration. Use stranded wire instead of solid-core for the same reason.

Q: Could I make a 'Y' shape in my wire with 3 ring terminal conectors held together with a nut and bolt?

A: Don't do that! You'd have three 'crimp' connections each subject to failure, plus a nut and bolt that could vibrate loose. It would also be heavy and bulky. Even though I don't like them, you'd be better off using a 'wire nut' twist connector to hold your three wires together. Best solution: learn to solder.

Q: Hi Aaron. I want to build a two-wheeled robot with a gyro, but I'm having a bit of trouble understanding how that all fits together. Is there a specific type of ESC that I'll have to use to get this to work properly?

Will I be able to use just one control stick (forward, backward, left, right) to control the movement of my robot, or will I have to use two sticks, one for each motor? Thanks!

A: Take a look at my dad's Beginners guide to combat robot gyros page.

R/C gyros are NOT COMPATIBLE with either two-stick (tank style) steering or transmitter mixed single-stick steering. If you're using a gyro, you'll need to use either a stand-alone plug-in electronic channel mixer between your gyro and the ESC, or use an ESC with built-in mixing. Either of these will give you single-stick control.

Many dual-channel ESCs offer built-in mixing: Barello ANT, SOZBots M, Scorpion XL, Vantec RDFR, etc. Check before you buy.

A: Most combat robots turn by 'skid steering' where the wheels on one side of the 'bot turn at a different speed and/or in a different direction than the wheels on the other side. This requires independent control of drive motors on each side of the 'bot. You can operate this type of 'bot by controlling the two sides of the 'bot with vertical motion of the two control sticks on a 'stick' style R/C transmitter (called 'tank steering') but most drivers prefer forward/reverse speed control with vertical motion of one stick and steering with horizontal motion of either the same or the second stick.

By electronically 'mixing' the output of two R/C channels, you can have the vertical motion of one stick (or the throttle trigger on a 'pistol' style transmitter) instruct both drive motors to move the 'bot forward or backward, and the horizontal motion of a stick (or the 'pistol' steering knob) tell the motors to spin at different speeds. This is called 'differential steering'.

More expensive R/C equipment and some dual-channel motor controllers have channel mixing capability built-in. See our transmitter programming guide for more info on computerized radio transmitters, and our electronic gyro guide for help integrating mixers with gyros. If your equipment does not have mixing built in, you can buy a small electronic channel mixer that plugs into your system between the receiver and the speed controllers that will provide the same functions.

Thank You.

A: Thanks for your compliment about the site!

The short answer to your question is yes -- you can connect multiple Electronic Speed Controllers to a single battery if you connect them as parallel circuits. See the diagram and description of basic robot wiring in the Frequently Asked Questions section.

The longer answer involves the capacity of your battery to provide the current needed by your motors. Your battery must be able to supply enough current (not voltage) to meet the demands of all the motors at once. NiCad batteries can provide a lot of current to meet heavy load conditions, but if the load becomes too great the voltage output will drop. The Ant 100 ESC also supplies power to your radio receiver and if the voltage drops your receiver can start to 'glitch'. Other types of batteries are less able to meet high amperage drains. Lithium batteries can dangerously overheat if the current demand gets too high, resulting in damage to the battery and even fire!

Adding extra cells to your battery pack to raise the voltage is not a good solution. Higher voltage will create a demand by your motors for even more current and your voltage fluctuation will increase. Add up the maximum current consumption for all four of your motors and use a battery with enough capacity to meet that demand.

One last thing: I mentioned above that the Ant 100 supplies power to your radio receiver. Since you'll be using two Ant 100s, you might run into trouble with both of them trying to power the receiver. You'll want to remove both of the red wire connections from the receiver cables coming from one of the ESCs -- either one. You can clip the red wires, desolder them from the circuit board, or remove the connectors from the receiver plugs.

A: Mark J. here: a battery charging jack is a very useful addition to your 'bot. It will minimize charging mistakes in the pits and save critical time between matches.

Select a power plug and wires rated for at least the maximum output of your charger. Find a mounting spot protected from damage but with easy access. The jack will be 'live' to the main battery power, so protect it from accidental shorting!

The jack is wired into the main power cables, between the battery disconnect plug (optional, but handy) and the master power switch. See the diagram at right for details. Check the event rules to determine what type of master power switch is required for your weight class -- a 'removable link' disconnect may be required.

With this set-up, the battery may be charged with the master power switch 'off' for safety, and the battery may be quickly removed or replaced while the charging jack remains with the 'bot.

Q: What type of power plug do you recommend for a heavyweight 'bot charging jack?

A: I use Anderson PowerPole connectors for charger plugs on our larger 'bots. They are available in 15/30/45 amp ratings, have no exposed metal, may be crimped or soldered in place, and require no 'heat shrink' insulation. The PowerPole connectors are available at many hobby shops. Pre-assembled wire sets with PowerPole connectors are available thru 'Team Delta'.

A: Take a look at the diagram and description of basic robot wiring, Alan. Wire in your power switch where the removable power link is in the diagram -- combat robot tournaments often require a removable link instead of a switch. Your multiple lights will replace the single power indicator light in the diagram.

Q: Thanks for your advice. Just to clarify, do I attach three wires to each battery lead and run one + and one - to each ESC and the lights? Thank you very much for your reply.

A: That's right, Alan -- the ESCs and lights are connected in parallel to the battery. Don't forget to insert your switch between one battery lead and the device connections.

Q: I forgot to ask you this question last time. The different parts for my robot have wires of different gauges. Do I have to replace all the wires in one gauge? Will the robot function with wires in various gauges connecting together? Thanks for your reply.

A: Don't worry about the different wire gauges, Alan. The important thing is that the smallest wire in a given circuit is capable of carrying the largest expected current for that circuit. Bigger wire is OK, but smaller wire can overheat under the load, melt thru the insulation, and short out. As long as your robot components are operating within their rated voltage, you should be able to trust that the manufacturer has provided wire of adequate size. Hook 'em up and run 'em!

A: No -- American Wire Gauge (AWG) sizes measure the conductor only, not counting any insulation. The conductor diameter of 18 gauge wire is about 0.04 inch (1.02 mm).

A: Shortening the antenna that much will certainly reduce reception, but you may still have plenty of range. Give it a test run and see how it does.

If you decide to repair the antenna, you can just solder on a length of similar gauge insulated wire to restore the length. Cover the solder joint with heat shrink tubing or a flap of vinyl tape to prevent accidental grounding of the antenna. If you are comfortable soldering PC boards you can open the receiver case, remove the damaged antenna entirely, and solder on a new wire of the correct length.

Q: What is impedance? I hear that even if I solder on a length of similar gauge insulated wire to restore the length, I need the correct impedance as well.

A: Mark J. here: Impedance is a measure of the opposition of an electrical component (like an antenna) to an alternating current (like a radio signal). A proper antenna must have its impedance match the other elements of the system to maximize signal strength.

The main factor determining the impedance of your simple wire antenna is length. Restoring the antenna length by soldering on a length of similar wire will restore the impedance to that of the original antenna.

A: Mark J. here: How quickly you throw the stick forward shouldn't matter to the radio system, so I don't think your problem is entirely with the transmitter set-up.

First, check the set-up procedure in the manual for your Electronic Speed Control (ESC) to make certain that the unit is correctly adjusted to work with your radio. An ESC requires careful adjustment to assure that the motors will respond correctly throughout the entire range of transmitter stick motion. Make certain that your transmitter trim settings are centered during ESC set-up.

Once the ESC is correctly set, the transmitter trim should be adjusted so that both wheels start turning at the same time when the stick is gently pushed forward or back. If you're still veering to one side, reduce the Adjustable Travel Volume (ATV) transmitter setting for the side of the 'bot that is running too fast.

If rapid acceleration is still a problem, check for equal weight on the drive wheels on both sides of the 'bot. If one side of the 'bot has more weight it will get better traction and can cause a spin under hard acceleration. You may need to move some components on the chassis to equalize weight. Backing up may mask the problem by reducing traction to both drive wheels.

For a 4-wheel 'bot, make sure all four wheels are in good contact when the 'bot is on a level surface. Adjust the chassis or motor mounts to correct if required.

For additional help on transmitter set-up, I suggest reading thru my guide to programming radio systems for combat robots. I wrote it with specific reference to Futaba systems, but the general tips are useful for any computer radio.

A: You probably saw the IFI Isaac Control System that is commonly used at the BattleBots IQ competitions. Some builders use this system at other competitions as well.

The IFI system accepts a variety of analog PC joysticks as external controllers. These are the same joysticks you can buy at your computer store. PC joysticks are not compatible with standard R/C transmitters.

A: Check the diagram at the right to see what gets connected to what. Solder the connections with rosin core solder and a non-acid flux. Watch out for sharp points on your connections that could poke thru insulation -- file smooth any rough edges. Large diameter 'heat shrink' plastic tubes are available at R/C hobby shops that will insulate the pack and hold it all together. Smaller diameter heat shrink does a great job of insulating the connector terminals.

A: NiCad or NiMHd cells come with or without metal tabs welded to either end. You can solder your wires to the tabs or directly to the cells. If you're soldering directly to the cell, you'll need a soldering iron with enough power to do the job quickly without heating up the whole cell -- maybe 25 watts. Use rosin core solder and a little non-acid flux.

A: Mark J. here: the operating frequency of your radio does not effect the ability of the system to accommodate a lifting servo. However, the 27 MHz band is used by both 'toy' radios and 'hobby-grade' radio systems. Toy radios are not compatible with hobby grade components like servos.

Toy radios in the USA are on either the 27 MHz or 49 MHz bands. Hobby grade radio systems are commonly available in the USA for the 27 MHz, 72 MHz (aircraft only), and 75 MHz (non-aircraft) frequency bands.

A: Mark J. here: We need to be careful not to mix apples and oranges:

AM (amplitude modulation)and FM (frequency modulation) are two methods of adding information onto a radio wave. All hobby radios are either AM or FM. Of those two methods, FM is less susceptible to electrical 'noise' interference.

PPM (pulse position modulation) and PCM (pulse code modulation) are two methods of encoding the information for radio control before it is added to the radio wave.

• PPM is an analog coding system with servo position represented by a time interval between two pulses. It is the standard system used on hobby radios.

• PCM is a digital coding system with servo position represented by a binary number. A computer in the receiver decodes the number and instructs the servo or speed controller. If no signal reaches the receiver, the computer can send a predetermined 'fail safe' position signal to the servo that can stop the robot and turn off weapons.

A: Mark J. here: Is that the middleweight flamethrower from Minnesota? I don't know about their radio, but the homebrew radio systems I've seen from the few other teams to try it were unreliable and had no advantages over off-the-shelf systems. If you just happen to have a degree in electrical engineering and a lot of time to spend designing, building, and de-bugging a radio system -- go for it. If you want something that works, stick with a professionally built system.

A: Critter Crunch has been fighting robots for a long time. Their first tournament was years before the first Robot Wars, but their rules are, ummmm... different. They do allow both 2 pound and 20 pound robots to operate with a wire cable instead of radio control. The circuit for each motor and weapon runs from the battery thru a long cable to a control box then back thru the cable to the motor/weapon. The control box has switches and maybe rheostats to control the motors. The cable wires have to be heavy enough to carry the motor current, and the robot has to drag the long, heavy cable behind it.

Critter Crunch also allows R/C robots, so why not build a 'bot that can enter other contests?

A: No functional difference. The only reason Robot Marketplace carries the discontinued Thor 883 is so builders who have a pair and smoke one can get an exact replacement.

A: Sure - as an expensive smoke bomb.

A: It would save time if people would check Robot Marketplace before asking me any question that starts with "Where can I buy a...".

Pretty much any place that sells R/C equipment will offer systems with computerized mixing. For a 'bot, you'll want a system on the 75MHz band. Guess what? Robot Marketplace sells a very nice [no longer available] 'Hitec Laser 6 FM System' for less than $135. Check with your local hobby shop as well.

You can also find Electronic Speed Controllers with built-in mixing at (wait for it...) Robot Marketplace.

A: Mark J. here: the IFI Isaac Control System has long been the mandatory R/C system for the BattleBots IQ competition. However, the system has been discontinued by IFI, and used systems are in short supply. BBIQ now strongly encourages the use of the Isaac system, but approves alternate systems on a case-by-case basis.

The Isaac controller is a 'smart' system that prevents radio interference and the need for frequency control and transmitter impound at tournaments. This makes things run much more smoothly for the tournament director. The Isaac also interfaces to the tournament computer and allows the director to remotely shut down power to all 'bots instantly - a big safety plus!

A: An ESC designed to interface with a hobby R/C receiver should have a plug already installed that will fit directly into the channel output socket of your choice on the receiver. See the 'bot wiring diagram. Ask the manufacturer of your ESC for additional info, if needed.

A: Mark J. here: radio systems are assigned to operate on specific frequency 'bands'. Both of the frequency bands you mention are available for use by R/C toys. MHz refers to how many million times per second the radio 'cycles' -- 27 million cycles per second for the 27 MHz radio.

Within each band are several specific frequencies to which a radio system may be tuned. A radio tuned to a specific frequency will not interfere with a radio operating on another frequency.

See also this earlier post.

A: You can scavenge the speed controller out of a toy or servos if you're really cheap, but remember: 'cheap' and 'combat robot' don't mix. If you're going to invest your time and effort, don't allow cheap components to let you down!

A: Two-wheeled robots can be difficult to drive in a straight line without veering to one side and they don't turn in a smooth arc. A piezo gyro senses turning motion, compares it the signal coming from the R/C receiver, and adjusts the signal to the electronic speed controller to keep the robot on the course the driver wants.

My dad has a whole webpage about gyros and combat robots that should answer any additional questions.

A: Mark J. here. The message doesn't seem to be getting thru: cheap and robot combat don't mix. You're going to spend a lot of time and effort building your 'bot and going to the tournament. When some component fails in combat and puts you out of the match, you're gonna wish you hadn't gone cheap.

That said, Tower Hobbies has a Hitec 3-channel pistol grip FM system for $69.99. You'll need either an ESC with built-in mixing or a separate elevon mixer to use it with a 'bot. Inertia Labs will sell you a GWS 4-channel twin-stick FM system for $89.90 (transmitter with crystal $59, micro receiver $21.95, receiver crystal $8.95) that does not require a mixer. Best luck.

A: Mark J. here: a piezoelectric crystal can be made to vary its electrical properties at a very precise frequency. When incorporated into a radio oscillator circuit, the crystal controls the frequency 'channel' on which the set operates. Hobby R/C systems have removable crystals in both the transmitter and receiver that can be replaced with crystals of a slightly different frequency to tune the system to a different channel and avoid interference from other radios.

R/C systems normally come with one set of crystals. Robot tournaments usually require that you have crystals for at least two different channels, so plan to buy a second set. There are different types of crystals for AM, FM single conversion, and FM double conversion -- make sure you get a set that matches your radio.

A: It doesn't take a whole hand to control a R/C channel -- you can easily control two with one finger. R/C airplane guys have to balance throttle, rudder, elevator, aileron, flaps, and landing gear controls. We've got it easy!

For a 'bot, throttle and steering take two sticks if you use simple tank-steer, but you can electronically 'mix' two channels and put both throttle and steering on a single stick operated by one thumb. The on/off control for the weapon can be assigned to a toggle switch that you can flip with an index finger. That leaves seven fingers and a thumb that aren't doing anything except holding the transmitter.

Different manufacturers have slightly different control layouts, but you can see a diagram of a typical Futaba transmitter and get more radio tips at my dad's page: Programming the Futaba 6XAPs for Combat Robotics. I usually run the weapon from the channel 5 toggle switch.

A: Mark J. here: LiPoly batteries have excellent charge retention and capacity recovery after storage. A LiPoly battery stored for six months at room temperature will recover about 95% of its capacity on the first charge cycle. It's still a good idea to discharge/charge cycle your rechargeable battery (LiPoly, NiCad, NiMHd) a couple of times before a competition to assure full capacity. Always follow the manufacturer's procedure for cycling.

A: Make sure the batteries in the car and the transmitter are fresh. If this doesn't help, as a last resort you might want to open up the car to expose the electronics board. There will be a couple of screw adjustments on the board, sealed with a thick, waxy material. Pick one adjuster, scrape away the wax, mark the starting position of the adjuster, and try turning the adjustment screw a little one way and the other to see if the range improves. If not, return it to the starting position and tweak another adjuster. Do NOT try this with the transmitter!

A: Mark J. here: In the USA the "AM Band" refers to commercial radio broadcast frequencies between 520 kHz and 1720 kHz -- a kilohertz is 1000 cycles per second. 49 MHz (49 million cycles per second) band is a 'public service' frequency range a little below VHF television broadcast. It's shared by older wireless phones, baby monitors, and five toy R/C channels. Other toy R/C systems operate on 27 MHz on six frequencies squeezed in between CB radio channels.

Toy R/C systems on 27 or 49 MHz use interference-prone Amplitude Modulation (AM) signals, but 'hobby grade' R/C gear on 27, 72, and 75 MHz use either AM or FM (Frequency Modulation) signals.

A: The Robot Marketplace and Tower Hobbies are both good on-line sources of 75 MHz 'ground frequency' radio systems, but don't forget to check with your local hobby shop!

It's also possible to have a 72 MHz radio converted to 75 MHz. Tower hobbies offers this service on new systems, and a web search will turn up other specialty shops that will do this.

A: Mark J. here: Micro receivers are 'single conversion' designs that are more sensitive to interference than the 'double conversion' design usually found in standard receivers, but if you're only getting 5 feet of reception distance you have problems other than your receiver. Electric motors create a lot of electrical 'noise' that can be a problem -- try adding anti R.F. capacitors across the motor leads. Position the receiver as far away from the motors and ESC as possible. Stretch out the receiver antenna and get it out in the open air, away from metal or carbon armor.

Check the Ask Radio Reception Problems page for more info on the topic.

A: Tech question, Mark J. here: You'll get a nice puff of smoke followed by a quick trip to the trash bin. Solid state switching controls are rated for a maximum amperage flow. Doubling the voltage to a motor also doubles the maximum amperage, so you've already taken the unit to twice it's design limit. I suspect that if you got into a pushing match you'd fry the controller as is. Bigger motor = more amperage = thermal meltdown. Note that not many R/C receivers can handle 12 volts -- try that at your own peril.

A: A remote control transmitter sends variable control signals for several `channels' based on stick, switch, and knob positions on the transmitter. The receiver deciphers the signal and sends separate signals to the channel ports. You can plug various devices into channel ports that read the signals and turn them into mechanical action (servos), variable current flow (electronic speed controllers), or on/off switches (R/C switches). Connect drive motors to the speed controllers, a lifter to the servo, and a weapon to the R/C switch and you've got control of your robot. For more on robot control systems, see: 4QD Robot Control website.

Date marker: February 2006

---

Q: Is any programming required for ESCs and the radio system?

A: Some combat robot ESCs have a short set-up process, but it isn't programming. Some brushless motor controllers have more elaborate programming capability, but most work fine with the default settings. More sophisticated radio systems can be programmed by selecting options from menus for things like channel mixing, but it isn't required to provide basic radio functions. See my dad's page on programming transmitters for details.

---

Q: Can I use 22 awg wire to connect electronic components in my antweight?

A: Tech question, Mark J. here: AWG wire sizes run opposite from the way you'd think, with larger numbers indicating smaller diameter wire. For small wire, amperage capacity approximately doubles with each decrease of three number sizes (thicker wire). A 22 gauge copper wire is conservatively rated to carry 7 amps in conditions found in a combat robot. You might get away with it, but I'd suggest 18 gauge for at least the battery to ESC hookup -- or you could use double strands of 22 gauge if that's what you have.

Always use 'multi-strand' wire in your robot, not solid-core. Solid core can break from repeated flexing and shock.

---

Q: Are there differences between micro receivers and standard receivers other than size?

A: Technical question - Mark J. here: Yes, there are a few:

• Some micro receivers are not compatible with 'pistol-grip' style transmitters.
• Most quality standard receivers use 'dual conversion' frequency crystals, while most micro receivers require 'single conversion' crystals. The two crystal types are not interchangeable.
• Different brands of transmitter have different signal formats -- Futaba and Hitec are 'negative shift', while Airtronics and JR are 'positive shift'. Make sure the micro receiver you buy is compatible with your brand of transmitter.

---

Q: What kind of cheap radio system do you recommend to control two motors and a spinning weapon?

A: Check with the event organizer before attempting to use any 'cheap' radio system in a 'bot with a spinning weapon. Many combat rules sets require specific safety measures for weapon safety that are not available in inexpensive radios. For robot combat it isn't smart to try to save money on your radio system.

---

Copyright 2006, 2020 by Mark Joerger -- all rights reserved.