Shooting Motors and wheels

Our team is new to shooting high goal this year so we just wanted to know what to use for motors and wheels for an working shooter.

So far we have been using a 775 pro motor with a 5:1 gear ratio.
We used the kit of parts andymark wheels for the fly wheels

Trial and error.
If you can hook that 5:1 to a speed controller and a computer you can vary speeds and test distance.
Try varying the compression too. The balls will more than likely react a lot to pressure since they are hallow.

There are no instant solutions!

You’re on the right track!
775 Pro’s offer a high RPM, and are pretty useful when geared down, like you have.

As for wheels, experimentation is the key-- try using different size wheels, multiple wheels on the same axle (increase in contact surface area), higher traction, just play around with it!

Last year, we used 4’’ high traction wheels in a dual fly wheel set up… we had to play around with compression and speeds to get a consistent shot… this year’s a bit different so it’s hard to say what works and doesn’t.

As SensorZ pointed out, software control is integral in keeping consistent shooter. So I would encourage your programmers to modulate the speeds, and test out what happens!

Good luck!

As a follow-up to the question, does anyone know of any papers/guides on building high shooters?

The best guide for making new systems is to prototype a lot, and to take inspiration from past robots from previous years.

No paper will ever have the one answer for you, your team, and your needs.

I agree, and don’t forget kids, CHECK YOUR WIRING! :o)

Thanks for all the help, our prototype is shooting 6 out of 12 balls and the rest of overshooting. We r now just adjusting the compression and hood. As most of the comments said it’s just trial and error

How are you controlling your motor at the moment? If you’re not doing closed loop speed control, you’re going to have some difficulty getting good accuracy at a high rate of fire. If you ARE doing closed loop speed control, you want to set your gearing so the motor is spinning at about 50% max speed when you’re at your target speed for firing. That’ll give you the best control and recovery time.

We r just have it hooked from wires to battery

We do have vision tracking though if u that’s what you mean by a closed loop

You want to hook up a sensor (encoders, etc) to measure the RPM of your flywheel. Differing flywheel speeds will result in different shots.

It’s not. He’s talking about closed-loop speed control.

Open-loop speed control is what you have now. In short, it goes like this:
RIO tells motor: Go this fast

Closed-loop speed control is better for ranging accuracy. It goes like this:
RIO: Motor, go this fast.
Encoder: Hey, RIO, motor is going this fast.
RIO: checks number from encoder against commanded number Motor, I need more (or less) speed out of you.
Encoder: Hey, RIO, motor is going this fast.

Repeat.

The reason you want closed-loop is to keep the motor at shooting speed as much as possible–stuff being launched tends to slow wheeled shooters until it leaves the “muzzle”.

This is not ideal.

As a first whack, OK (despite the very big lack of safety), but now at least get a big fuse or circuit breaker in there.

Very much preferred at this stage - a week in - is to have the RoboRIO controlling it through a motor controller. This way you can:

  1. Adjust the speed very finely so accuracy is spot-on
  2. Use a speed sensor on the motor or wheel to (try to) keep the wheel speed constant, so ball 12 goes to the same spot as ball 1.
  3. Get a better idea of what you will see in reality when the robot is actually doing the controlling (The motor controller doesn’t give as much voltage to the motor as a direct connection might).

All of these point more towards success. Yes they require effort, but do you want to win or watch?

So looking up an encoder will control the speed of the wheels and motor which will help increase accuracy

775 pro motors are excellent motors for shooters. One very important thing about them is they need to be spinning for the fans to cool them. If they stall, they will fry in ~4 seconds according to Vex. They are high speed and high power, but keep them spinning! Even if you stall them for two or three seconds it may result in the motors having reduced power output or speed permanently. My team had some problems with our shooter shooting low last year and we found that our motors were partially damaged.

Tell us what language you plan to use to code your robot and you may get more detailed advice and help.

The first thing I would suggest is to take advantage of the Virtual KOP. In it you received a code for an encoder from Armabot that will attach directly to a 775 Pro. Use that with a Talon SRX, and you can have very stable, reliable control of your RPM in one afternoon.

Ye, last year we fried a couple of 775 pros last year and broke a fan blade on one of them, but other than that I love 775’s

We r using c++ most likely

For quick prototyping we wire up a motor controller in between the battery and the motor (and an in-line automotive fuse) and then use the thrifty throttle from Andymark to control the motor controller. This allows students to vary the speed of the motor to try various experiments. At $29 it’s a lot cheaper than tying up a robo-rio for this and it’s a lot quicker to set up.