Run Amok Combat Robotics
Tips and tricks for robot pneumatic weapon systems
The Team DaVinci pneumatics guide has long been the recognized authority on combat robot pneumatics, but 'Buzz' and 'Zander' didn't tip all their secrets. I think it's time for a few more tricks to see the light of day.

The Basics

Let's start with the basic pneumatic system diagram from the Team DaVinci pneumatic tutorial:

  • High-pressure gas flows from the storage tank to a regulator that reduces the pressure to a safe level for the rest of the system.

  • The reduced pressure gas flows at a moderate rate (due to flow restriction in the regulator) into the buffer tank, which holds a sufficient quantity of gas ready to quickly flow into the pneumatic ram.

  • The 5-port solenoid valve directs pressurized gas into either the 'extend' (push) or 'retract' (pull) side of the ram, venting the gas from the other side of the ram to allow motion.

  • The 'bottleneck' in this type of system is typically the 5-port valve, which is often too restrictive of gas flow to allow effective flipper motion.

This system provides efficient and controlled high-force movement of the ram in both directions -- but the speed of operation can be improved...
Two Things at Once

Two things happen simultaneously when a 5-port solenoid valve is powered:

  • Pressurized gas flows into the 'extend' side of the ram; and
  • The gas pressure holding the 'retract' side of the ram is vented.
Pressure builds in the ram to extend to flipper mechanism, but flipper motion is impeded by residual pressure on the retract side of the cylinder. The faster the pressure from the retract side is vented, the quicker than more powerful is the flipper extension. There are several ways to improve exhaust efficiency.
Quick Exhaust Valves

The Quick Exhaust Valve (QEV) is typically mounted right on the ram retract port. It passively allows gas to flow into the cylinder to retract the ram, but as soon as the gas pressure in the line from the solenoid valve drops below the pressure in the ram the QEV pops open a BIG port for the gas to rush out.

Adding a QEV is simple and effective. The valve is powered entirely by gas pressure differential and requires no external power or control.


Gravity Retract

If the retract side of your ram is never pressurized, you don't need to worry about pulling pressure out of it. Many flipper styles will retract from gravity when the 'extend' side is vented, and many more will retract with a little assist from a spring or even a bungee cord.

Replace the 5-port solenoid valve with a 3-port solenoid valve, and leave the retreact port on the ram open to the air. Since the retract side of the ram is never pressurized you can drill additional vents on that end of the ram to let the air exit even quicker.


Drop-Pressure Trigger Systems

Paintball guns use a QEV to store a fixed volume of pressurized gas in a buffer tank and then release it to fire a paintball. This makes for economical use of the gas supply and a quick exit of gas from the buffer. This same method can be used to dump gas from a buffer tank into a pneumatic ram faster than a conventional solenoid valve.

The set-up moves the buffer tank downstream from your solenoid valve and attaches a QEV to the tank in the same way it usually attaches to the ram retract port. The QEV holds presurized gas in the buffer tank until the solenoid vents, then it very rapidly dumps the pressurized gas directly into the ram for explosive flipping power. A small poppet valve vents the ram.

De-pressurizing at the end of the match is a little tricky. The pressure vent valve must be between the QEV and the buffer tank or the weapon will fire when you attempt to bleed off pressure. Some event organizers will require a second bleed valve between the pressure regulator and the solenoid valve.


Unregulated Poppet Valves with Leaky Rams

Commonly called a 'Full Pressure Insect Flipper', this is more like setting off a firecracker under a soup can than a real pneumatic system. A disposable CO2 cartridge attaches directly to a simple 2-port poppet valve that opens for just an instant and shoots a tiny squirt of high-pressure gas into a deliberately VERY leaky pneumatic ram. The gas blasts the flipper upward and quickly leaks out before pressure builds to explosive levels -- you hope (video).

Small high-pressure solenoid poppet valves are commercially available but the leaky ram is custom, and if you don't get the venting right the ram turns into a grenade. Very inefficient, very dangerous, and very not-legal in any tournament I know about.

Why mention this awful system here? There is a safe and legal use for a 'leaky' pneumatic ram and a poppet valve with regulated gas pressure. If your flipper design allows for a gravity-powered retraction, you can replace the solenoid valve in a conventional system with a high-flow poppet valve to get an improved flipper action. You shut the poppet valve off as soon as the flip is complete, and a small 'leak' anywhere downstream from the valve will allow the ram to 'leak down' for a slow retract.


Multi-Valve Systems

If your design does require a pressure-driven retract, there are several designs with multiple solenoid or poppet valves that allow each end of the ram to be independently pressureized and vented. Control of these systems is a bit more complex than a single-throw switch on your transmitter, but you gain maximum power and speed in both ram directions.

The pictured system uses twin 3-port solenoid valves. Triggering either will pressurize that end of the ram. As soon as current to the valve is removed the ram is vented, ready for a quick return when the other side is pressurized. Similar systems use four poppet valves -- two on each side.



More robot help: 4QD PRO-120 Speed Controller -- Peizo Gyros for Combat Robots -- Futaba T6XAPS Programming -- Ask Aaron - Combat Robot Q&A

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