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Privacy Policy
Even small combat robots can be dangerous! Learn proper construction and safety techniques before attempting to build and operate a combat robot. Do not operate combat robots without proper safeguards.
Ask Aaron is a simple little question and answer page. People ask questions about combat robots and we do our best to answer them.
Recently I've received some messages where the bulk of the text is used to express views or opinions that would be better suited as social media posts. Although I found the topics of these messages personally interesting, I did not publish them and I will continue to reject submittals of this type. I won't have Ask Aaron turned into Reddit. Let's keep it to combat robot questions, please. Adjust Size as Needed
Q: what wheels to use
A: [Mark J.]
If you give me no information about your robot, I can give you no guidance on components.
It's Just Too Much
Q: I'm using a Flysky i6x transmitter with a Malenki Nano receiver/ESC in my fairyweight, but the turning is too fast. How do I turn it down? [Social Media]
A: [Mark J.] The easiest and most flexible solution is to assign a 'Dual Rate' for CH1:
Q: Could you set 'End Points' for Ch1 to get the same steering sensitivity adjustment?
A: The short answer in this particular case is 'Yes', but it is preferable to use a 'Dual Rate'.
Longest Internal Diagonal
Q: Can my 30lb thwack bot be 6 feet long in NHRL? I heard that the longest it could be was 3 feet but I don’t know if I read it right so I’m super confused. [Social Media]
A: [Mark J.] Just to make things complicated, the NHRL has a 'cube rule' for dimensions: "12lb and 30lb robots must be able to fit into a 36 x 36 x 36-inch box."
The 'bot does not have to sit flat on the box floor -- design your 'bot to fit into into the longest internal diagonal of the box and it could have a maximum dimension up to ( 32 + 32 + 32 ) 0.5 ≈ 5.2 feet. Plus, there is a loophole that allows even greater length:
"Once the match begins, robots are allowed to expand or contract to any size."
If your 'bot can unfold of otherwise expand when it starts moving it can become much longer.
Machinations
Q: Did NHRL ever announce if/when they would release the teams tournament special on YouTube? I’m asking because I need footage of the event for a video I’m working on.
-sincerely, Iceywave
A: [Mark J.] I no longer care to discuss machinations of the National Havoc Robot League. Rodger the Web Gerbil has relatives in Connecticut and has been asking for more editorial responsibility, so I'll let him handle this topic.
My cousin Sidney in Norwalk tells me that the ESPN TV networks have exclusive rights to all video footage from the NHRL Teams Tournament Finals thru the end of August. NHRL says they will release full coverage of the event on their YouTube channel in September.
A Job With Benefits
Q: I hope Roger the Web Gerbil enjoyed his vacation. I also have a couple favors to ask him.
In the Robotica Competitor Gallery, 'Ill Tempered Mutt' and 'PSHHHT!' have incorrect links for their wiki pages. I've attached the correct links. A: [Mark J.] Hey, you're pretty good at this. I could sack that annoying rodent and give you his job. It comes with a water bottle, an exercise wheel, and a fresh scoop of alfalfa pellets every other day -- but you have to clean your own cage. Interested?
Q: And a commenter on Ill Tempered Mutt's page said that a robot of the same name tried to enter Robot Wars in 2017 but failed to qualify. I’ve never heard of this supposed robot before. Have you?
-sincerely, Iceywave A: The Robot Wars Wiki lists an 'Ill Tempered Mutt' from Team Underdog that attempted to qualify for both the 9th and 10th Wars. It was a thwackbot with a horizontal circular saw in its long tail.
"And yes, we were inspired by the robot of the same name from Robotica 2.0. There needs to be more canine machines."
- Matt Robinson, Team Underdog on Facebook So Very Many Types
Q: What type of battle robot weapons are there, and what are the different categories that deal the most damage? [ATT Network]
A: [Mark J.] The Wikipedia article on Robot Combat has a extensive section on "combat robot weaponry and design" that includes a very long list of weapon types with a discussion of each type.
I will point out that the most damaging weapons are not the most successful in winning matches, particularly for new builders. Take a look at Frequently Asked Questions #8 and What Weapons Win.
For Accuracy's Sake
Q: Because I’m a stickler for details, I have a couple of questions about two Robotica season 1 competitors before I finish their virtual Robot Arena 2 models.
-sincerely, Iceywave
A: [Mark J.] For the sake of accuracy:
Q: The final season one robots are ready! I didn’t think I was going to make my own deadline, but I did it! I noticed you grouped Jeff Haas' Run Amok model with my Robotica replicas. I thought having it next to the 11 other robots I built felt a bit out of place, so I modified Jeff’s replica to have better ground clearance! I’m REALLY proud of how this batch turned out. Look out for season two bots coming later in August. A: Thanks for the 'Run Amok' update. I wanted to drop it in to complete the set of Robotica 'Fight to the Finish' competitors so your version is most welcome. This group of Robotica 'bots does look great! P.S. I noticed that my model of 'Run Away' can do the iconic 'gyro dance'. Could the real life bot do that?
A: Gyro dances are annoying -- I try to avoid them. 'Run Away' has a single electric motor chain driving a differential gearset that allots power to the two rear wheels. If either rear wheel lifts, the differential will cut power to the other wheel and drop the 'bot back onto a level footing. No 'gyro dance' is possible -- even with a monster spinner weapon.
NOTE: A gyro dance lifts the OUTSIDE wheels in a turn. Run Away appears to be lifting the inside wheels. Is this a flaw in the RA2 simulation engine? Is the 'bot backing up? Regardless, Run Away can't hold a lifted wheel.
A: [Mark J.] What is it that is done to arrange words into a beautiful sonnet? There is no one thing done to enable precision control and pushing power on a two-wheeled 'bot -- there is a long list, and you have to get everything on that list right. Here is part of that list:
A: [Mark J.] I see two problems in adapting any of the Four Spring Flipper Designs to power a 4-bar flipper:
A: [Mark J.] I'm wondering how you decided on two KingMax servos.
Overvolting There is no 'standard' used by servo manufacturers to determine a maximum allowable voltage, and there is no agreement on a safety margin. Some servos are limited by the voltage ratings of their electronics, while others may establish a voltage limit to remain under the current capacity of the electronics or motor when stalled. Running a servo at a voltage above the stated limit may:
Battery Tap You can tap into the balance connector on your 3S LiPo to feed 7.4 volts direct to your servo while still supplying 11.1 volts to your motors. The amount of current used by the servos is small relative to the drive motors -- just balance charge the LiPos every time to keep the cells happy. If your receiver can run at 7.4 volts, clip the red receiver wires on the tinyESCs and the wiring diagram (which shows a single dual-channel ESC) looks like this:
If the receiver needs a lower voltage, leave the tinyESC leads alone and run the servo power and ground direct to the 7.4 volts:
If you still want to use a UBEC, the voltage regulator, battery, and servo are wired in like this, with power and ground (red and black) wires running to the ESCs and the signal wire (white) going to the receiver:
I decided upon using a KingMax KM1203MD servo because I used the desired stall torque formula from the Electric Lifter FAQ, multiplying the theoretical blade length, opponent weight, and the 1.67 factor together. I was unaware that the formula is different for cam lifters. Having extra torque is good, but my initial choice was absolutely overkill.
Response: [Mark J.] Aha! Cam lifters were not a thing when the lifter FAQ was written. "Length" in the above formula refers to the maximum distance perpendicular to the axis of rotation at which your opponent might be lifted -- which in the case of a cam lifter will generally refer to the width of the blade rather than the length that gets shoved under them. I've added a section on cam lifters to the lifter FAQ.
Q: Additionally, I didn't consider that the blades could be run off a single servo. What kind of linkage system would you recommend for this application? Upon digging through Wikipedia and remembering an old Youtube video, my best guess would be some sort of modified "Watt linkage", but I would like to hear your thoughts.
A: A Watt's linkage is tricky to get to work for this application, and it isn't needed. Although 'Supreme Ruler' and 'Needle/Ace' rotate their blades in opposing directions it's more efficient to rotate them in the same direction to avoid scraping them across the underside of the opponent as the edges converge. A simple linkage setting a tie rod between two "steering" arms and running a drag link to the servo will work nicely. As the blades draw closer to vertical the torque requirement is reduced, so you don't need to get fancy. I leave trigonometry behind this as an exercise for the reader. Crude animation:
There are some refinements available, but it's late and it's been a long day.
Addendum: Your wiring diagrams were extremely helpful, and your suggestions will certainly help me lower the amount of weight I need for electronics.
A: [Mark J.] I'm going to interpret "ants making a simple hub motor mount for weapons" as an antweight direct-drive weapon hub rather than a mount for a weapon hub motor made by ants. Tell me if I'm wrong.
I don't believe I've seen a good match for what you describe. I've seen soft and squishy TPU sandwiched between motor/hub and around the mounting screws to cushion the motor from impact shock, but I can't recall seeing a single-piece TPU weapon hub. I can tell you:
Q: Specifically I'm talking about this one horizontal spinner named Cheesecake. I know he has a lot of videos posted on his channel but I haven't found one yet explaining the hub. I was just hoping to see if you had any insight thanks.
A: That gives me something to work with. I wrote to the builder of 'Cheesecake' and asked for some details on the weapon hub. Alex F. was kind enough to write back quickly and confirm my assumption that the hub bolts to the top of the weapon motor, but the design has a very clever method of locking the weapon blade in place:
A very few minutes later...
Here's a cross section of the hub. It pushes down onto the motor, is held down by three screws, and the act of pushing it down onto the motor causes the collet to flare out, clamping onto the inner diameter of the weapon bar.
I also found this side view of the weapon hub that shows the slots in the side of the hub that allow it to flex enough to 'click' down into the hole in the weapon blade before the assembly slides down over the rotor and is secured by screws into the top of the rotor:
I think that gives a good overview of the weapon hub design.
A: [Mark J.] See Frequently Asked Questions #2. Read the rest of the FAQ while you're there.
Reply: [Mark J.] Awesome, Icey!
For readers unfamiliar with the origin of the Iceywave era at "Ask Aaron", Icy decided to honor every single combat robot he could think of on his 2023 ballot to select members in the Combat Robot Hall of Fame. It was the largest ballot ever submitted, and it will remain the largest because it prompted me to institute "The Iceywave Rule" that will severely limit ballot size in future elections. For some reason Icey takes a great deal of pride in this accomplishment.
To celebrate the anniversary of his bloated ballot, Icy has gifted us the first season of Robotica 'Fight to the Finish' competitors in his new series of playable robots to upload into the popular Robot Arena 2: Design and Destroy action video game for Windows. The new robots may be downloaded from the Team Run Amok Robot Arena: Design and Destroy page, along with the thirty-seven robots from his previous three series. Looking forward to seeing the others in this set, Icey!
A: Rodger is out of control. The furry little bugger has taken to tacking his own opinions onto the end of some of my answers, and he has demanded a two-week vacation this year on very short notice. I gave him your ballot before he left with very clear instructions that it was to be uploaded before he could go, but I just now found it in the pile of litter next to his javascript manual.
I've personally uploaded your ballot and the link is now active and correct. I really must have a talk with Rodger when he returns.
A: Let not your left hand know what your right hand has given.
However, I will point out that shortly after he received his prize, Draco shuttered BattleBots Update and is rumored to have retired and moved to the south of France. Must have been some prize, huh?
A: [Mark J.] An internal memo to BattleBots staff from co-founder Trey Roski was leaked to the Las Vegas press and published on August 5th by Vital Vegas at Casino.org. Here is an excerpt from that memo:
Meanwhile I have been exploring the idea of an Internet show to see if there was potential value for us there. Unfortunately, the funding for that project has not yet materialized, and I'm not sure when or if it might become available.
Given these circumstances, along with other challenges like the upcoming F1 competition, I have had to make the difficult decision to put Destruct-A-Thon on hiatus. Our last show will be next Sunday August 10th, after which we will have a little pool party, and I hope to see you all there. Obviously I'm deeply disappointed and saddened, especially since we have made significant progress. For instance, I've been working on obtaining our liquor license for over a year, and we finally received it last Wednesday. I want to say I'm incredibly proud of Destruct-A-Thon and the show we have all created, and I'm so impressed by the effort many of you have put into exploring the potential for the Internet show...
A: A couple of the teams scheduled to compete in the Fall Faceoffs are reporting that the pre-qualifier tournament is still on, and a schedule for the event has been posted at BattleBots.com. Without a scheduled full tournament I'm not clear on why the Faceoffs pre-qualifier is needed, and the Horseshoe facility is quite expensive to continue renting. Maybe I'm missing something?
Skipping ahead...
In addition to the revamped live show, BattleBots also announced that many weekend performances of Destruct-A-Thon will include the new Fall FaceOff competition, featuring robots and teams from all over the United States, including many faces made famous by the BattleBots TV shows. The FaceOffs see four robots competing each weekend in a round robin competition. The fights will be shown on BattleBots’ hugely popular YouTube channel, enabling millions of viewers all over the world to stream and see the latest developments in robot combat. These FaceOffs will serve as pre-qualifying matches for the upcoming BattleBots World Championships, slated for filming in Las Vegas early 2025.
Tickets for the new look Destruct-A-Thon, including the special FaceOff weekends, are on sale now, with the first performance scheduled for Friday September 6th.
A: [Mark J.] The channel trims won't fix your problem. With channel mixing in place you need to tweek the individual receiver output ports using your FS-i6 sub-trims.
A: [Mark J.] See Frequently Asked Questions #17.
Mark is kinda touchy about questions that don't provide the silly little details that might give him a chance to come up with a quantified answer. This time though, I think he missed something. I have access to all of his notes and the exotic software that he doesn't share with the robot community, and I found this equation filed under "If All Else Fails":
The 'Ask Aaron' project was important to Aaron, and I continue the site in his memory.
Thank you for the many kind messages of sympathy and support that have found their way to me.
Aaron's obituary
Q: how can robots help us deal better with hurricanes and why? [Ontario, California]
A: [Aaron] Few people in Nebraska are threatened by hurricanes, so send a swarm of killer robots into low Atlantic and gulf coastal areas to drive the puny human inhabitants toward Nebraska. Problem solved.
Robot haiku:
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