Converting FRC Bot to RC

We have an older drivetrain of ours that we converted into a T-Shirt cannon. We would like to convert it over to more of an RC style control system like you see on Battlebots that way we don’t have to carry a laptop with us to events. We would prefer to just turn on the robot and the remote and be up and running. I have seen options to use a VEX controller and cortex but was thinking of something more robust/commercial than the VEX cortex. Any suggestions on how to tackle this? We have 4 NEO motors on the drivetrain, 4 solenoids and 1- 12V train horn.

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As it turns out, I’m in the middle of a similar project.

I’m using a FlySky controller with a 10-channel FlySky R/C receiver. PWM to the speed controllers works fine, but I’m running into issues with the solenoids–Spikes don’t play nicely with PWM signals, and when I put PWM relays on to control those solenoids I got some interesting crosstalk that I haven’t solved yet (the relay with the lowest number activates with the rest when they’re active, if that makes sense).

My top Thing to Do is to get another stick spring and make the left stick self-centering.

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I’ve gotten away with just using motor controllers as relays, depending on how your TX lets you program the outputs. Not the most cost or space effective, but that’s usually not an issue with Victor SPs.

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Not very well… that’s the problem I have on the relays. Can’t program them to not react multiple at a time when one is active.

Though you do have a point on trying the speed controllers. Using them to trip pneumatic solenoids might be interesting… (Wouldn’t use Victor SPs, though. Gotta stick with what’s available. 883s and 884s anybody? or Talon, original form factor.)

My team actually built a robot for marketing use during Covid that works off RC. We used a Teensy microcontroller and Arduino to achieve this. We used PPM and a Flysky fs-i6x. This method takes a lot of programming work as you have to learn c++ and arduino if you dont know it already. The best thing with this setup is that it is cheap and modular. Teensys are ~20$ and we have one on the chassis of our bot that feeds signal to another on the T shirt cannon mounted on top. We can take off the t shirt cannon and replace it with another module, a led screen and speakers for example.

How complex do you want to go? I assume there will be a bit of logic with the T-shirt cannon robot?

You can do a CTRE Hero board if you want to do some logic. You can also use a Raspberry Pi.

The advantage with the Hero board (and RPi if you tinker enough) is that you can use CAN

Otherwise, you can use arduino for some logic if you need.

If you don’t need any logic, you can use just a regular receiver. There is also a thing called a PixHawx which used to be good for drones, rc cars, helis, and boats, and came with a nice set of software. Maybe check that one out too?

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Would using a standard RC servo to operate a switch work for your application? You may have to choose the switch to make sure it doesn’t require too much force i.e. common toggle switches have some of the highest operating forces.

If you need to switch large D.C. currents, you may want to use the switch to control the current to the coil of an automotive relay. They are inexpensive, widely available locally and can have high D.C. current ratings for their contacts so they won’t weld.

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+1 On the Hero. You can plug a wireless dongle for a wireless game pad into it. You can use a PCM and canbus or PWM motor controllers on it. It can disable itself if it loses contact with the game-pad.

We turned our Stronghold chassis into our T-Shirt shooter (https://www.instagram.com/p/CT8e-M0gdel/).

We replaced the RoboRio with a Hero board which has CAN, so the drivetrain remained intact. We designed/built the new top section.

We use this controller (https://www.amazon.com/Tronsmart-Ergonomic-Wireless-Gamepad-Controller-pc/dp/B00ZFF75OE/ref=sr_1_4?crid=BKP3183VJTDN&keywords=tronsmart+controller&qid=1646061126&sprefix=tronsmart+controller%2Caps%2C80&sr=8-4), but any wireless usb controller should work.

Then we wrote code using C#; this was pretty straight forward.

@zebracorns have a nice whitepaper detailing how to go forward with this solution (https://drive.google.com/file/d/0B7SC9BMzdll7NkNvNW0xOVdKQWc/view?resourcekey=0-hj8WAnNcO0ZkFv0JOXJFZg).

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Be careful doing this. Motor controllers have an internal maximum duty cycle that caps at around 98-99%, so a solenoid could see some serious supply ripple or even switching.

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If one can get the output of the motor controller to over 90%, the relay should stay in it’s energized state.

The response time of small, reed relays is in the order of 2-3 msec. Larger relays like those the OP is likely to use will have longer response times.

As long as the output modulation frequency of the motor controller is above around 10 Hz, the relay will not respond to the 1-2% off-time at the motor controller output.

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And if it does, a capacitor in parallel with the coil should do the trick.

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We have a servo that is setup to toggle limit switches that in turn trigger solenoids.

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We just had microswitches because the current draw isn’t too much for the solenoids.

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Tons of great information here for our team to work with. Thanks for all of the prompt responses and knowledge shared!

What kind of range do you get with the wireless USB controller?

I have probably spent at least 30 hours with this solution in mind while I continuously refuse to implement it and try and make directly actuating a relay work work.

Two versions on the old t-shirt robot.

We converted our 2013 robot to RC control for demos, and so we could recover the expensive hardware from it for use on FRC legal robots.

There’s a full BOM and wiring diagram here:

We also put an Arduino in the loop (between the RX and TX) to add in some safety features (like disabling the hardware on comms loss and having some safe speed limits). I think you can get this kind of functionality implemented on many modern Transmitters now so that side of things may not be necessary, but code is there if you want to go that route.

@CoachZM They are rated for 10 meters and I’d say we’ve been about that far away before, but normally we are much closer to the robot since there are usually other people around, so we want a good view of the robot and be able to answer questions. They are nice in that they are rechargeable and in a pinch we’ve used a portable power bank when the charge was down.

We use this controller on other demo robots that we have as well. The only issue is they interfere with each other, so we run one at a time.