My robotics team has been chucking around a few ideas about a old t-shirt throwing cannon promo bot. We had a 10+ year old bot that had been sitting in storage for ages. We recently dug it out and wanted to perhaps replace some hardware, update everything and use it a bit for outreach.
To shoot the t shirts themselves it looks like we used Jar-topped sprinkler valves hooked up to something called a Vex Pro spike.
What in the world is a Vex Spike? From what I found online they were no longer legal as of 2014. What can I replace a vex spike with to make it semi- current day compatible?
Pictured below I have the sprinkler valve we used and the assembly on the robot for additional context.
Spikes are still legal in the current rules per R503 and R504.
If they still work, I wouldn’t recommend touching them just because there’s no harm in leaving them. If they don’t, you can replace them with either a CTRE PCM, REV PH, or multiple Automation Direct relay modules.
It is a relay. Actually a pair of relays setup up to make an H bridge. The Automation Direct solid state relay, available on First Choice can be used in its place to power a valve.
Keep in mind the sprinkler valves are not FRC legal.
Unlike the Spikes, these are wired such that they would break/complete the circuit along one of the wires going to your load. The input side would get wired to the signal and ground of a DIO port.
What is of real concern are those sprinkler valves. Do not use random plastic items for pneumatics! When something with under water pressure breaks, it leaks and maybe spews. Because air is compressible, when something under air pressure breaks, the air can push on those broken parts for a good distance, creating shrapnel. Only use air-rated pneumatics to carry or switch air under pressure. This is especially true as these valves are a decade old and have likely become brittle due to outgassing, UV exposure, or both.
Added: Here’s something similar to what 3946 used. You want one that’s normally closed, solenoid (vs motor) driven, and likely 12V. Solenoid, because you want it to open fast. Just don’t leave it open for long periods of time, or it will get hot. We found that 40-70 milliseconds was about right to launch a t-shirt with a 3/4" to 1" valve using 50-60psi.
We used Spike Relays we had lying around for our T-Shirt Robot last year, and they worked fine. I don’t see the point in swapping them out if they still work, especially since you won’t be spending more money/using motor controllers/relays you might use on your comp bot.
As @GeeTwo said, using sprinkler valves is not a good idea. If they break, you pretty much have a pipe bomb on your hands. You could replace em with some Solenoids from ESV (we got ours from ESV) and use a PWM motor controller you have lying around or the Spike to activate them.
