I second the idea of buying a servo tester. They’re super inexpensive and very handy. The cheap ones ship from China and take a few weeks to arrive, though, which may not be helpful for your immediate needs.
I would recommend building a control systems tester/trainer on a piece of plywood. You could start with a motor controller and a PWM signal generator on a board with a circuit breaker and battery connector. This would allow you to test motors and gearboxes in isolation, and it would also be useful if you wanted to prototype things like shooters.
My team invested in a full control system (RoboRio, PDP, radio, compressor, etc.) laid out on a plywood board so that students can learn how to program and use individual devices like motor controllers or limit switches without requiring access to the robot. It is also a great way to train your electrical students.
Well first of, make sure that you have terminals on your frc batteries. Then make a “connector wire” that converts the main frc battery terminal into something like an anderson power pole. Connect the anderson power poles to the power side of the spark (I personally didn’t bother with a fuse) (make sure you don’t hook it up backwards (negative to positive and vice versa) I did that with one of our talon sr’s accidentally, and boom came the magic smoke.)
Then make a pwm cable connecting the red to 5v on your arduino, the black to ground, and the white to a digital port on the arduino.
Additionally hook up a standard potentiometer to your arduino. I included the code I made for my motor test box below. Let me know if you need more details (I know I was a bit vague).
#include <Servo.h> //This comes with the Arduino
int talon_pin = 3;
Servo talon;
/* The 'Servo.h' library allows you to control motors and servos by passing any value between
0 and 180 into the "write" method (talon.write() in this program).
For a motor: 0 is full power in one direction,
180 is full direction in the opposite direction,
90 is stop.
For a servo: 0 is all the way one direction,
180 is all the way in the opposite direction,
90 is the middle.
*/
int talon_max_forward = 130; //this might not actually be forward
int talon_max_reverse = 50; //this might not actually be reverse
int talon_stop = 95; //this is definitely stop (if the Talon is calibrated right)
void setup() {
talon.attach(talon_pin); //This tells the arduino to control this pin like it's a servo/motor
}
void loop() {
int potValue = analogRead(A0);
int speedValue = map(potValue, 0, 1023, 95, 180);
talon.write(speedValue); //full power one way
}
Get a 1/2 hex nut driver and run the output shaft with a drill. The 30 minutes don’t need to be perfectly uninterrupted to swap out batteries or hands.
Personally we don’t run in the TB mini but we do have a Thrifty Throttle from AndyMark and a set up with a motor controller that we use for testing purposes that certainly could be used for break in.
You don’t really need both a main breaker and a breaker for the individual circuit(s).
Alternatively you can use one of these https://www.delcity.net/store/Manual-Reset-Circuit-Breakers/p_198672.h_201365 and cover it with the insulators linked to on that page. You can get those stud type circuit breakers at many auto parts stores but they are usually the auto reset style. For this application I prefer the manual reset so if something goes wrong and it causes the breaker to trip it doesn’t cycle back on like it will with an auto reset style breaker.
Back to the original problem - if you are significantly heating the CIM running the gearbox with no load other than break-in, you have a mechanical issue in the gearbox - something binding or a gear upside down (bosses on the gears should be against the bearings, flat sides to the center of the gearbox). We break in our gearboxes at full voltage (no controller, just a switch and breaker) and have never had heating problems. Of course, if the gearbox makes too much noise when we start it, we shut down and break it back down to find the issue.
So you dont spark, always put the red wire on first, and then black. We do that if we want to run a motor without an entire setup. We only had one issue, where a freshman connected the two wires and shorted the battery.
Why would closing the circuit on the negative terminal be better than closing it on the positive terminal? I’m wondering why it would make a difference because I’ve never heard this before and it doesn’t fit with my understanding of how electricity works.
This is good advice for automobiles, which use the chassis as a negative return, provided you do the black wire connection at the chassis, away from batteries and other components. On an FRC-legal robot (isolated chassis), no difference.
For cars and other systems with grounded frames (ie one leg of the battery connected to the frame) it makes sense. If you hit the frame with your tool while connecting the isolated lead, it will not short if the grounded lead is not connected. For isolated systems it doesn’t matter. For certain British cars the recommendation was to connect the negative lead first. But then they are always doing things backwards over there. :]
As a teenager replacing the starter motor on my 68 Camaro, I forgot to disconnect the battery first. Don’t know the exact sequence of events, but the metal band on my watch exploded and wound up on pieces on the driveway.
Did you get things figured out? If not pm me and I may be able to help you sort out your issue if it turns out your team needs a hand in person. Even If you have feel free to stop buy our pit in Orlando and we can give you a few pointers on test kits, common practices, or if you need a hand at the event. You have done better than most new teams in finding and posting on chiefdelphi. There are tons of people on here and in the first community in general that are just itching to help out. The point is never be afraid to ask for a hand and learn something along the way. We got your back, all started at the same place your at.
Honestly if it turns fine now, it wouldn’t be the end of the world to just grease them now and run them without breaking them in. It’ll just draw a bit more current and have a bit more friction. If you can break them in first, do that, but if you can’t it’s not going to be a season-ending issue.
Um…Um…Um… now that I think of it you don’t need to provide 5v. I was just trying to replicate the roborio pins, without actually thinking about it . Oh well either way doesn’t matter, not going to rip apart my box now to remove that wire :D.
We break in our gear boxes dry. In a perfect world they get mounted on a chassis and driven around under load, with the chassis weighted out to 120 lb. In the real world (when build runs late and we run out of time) we have just direct connected the motors to a battery (in a safe, insulated, switchoffable manner… ) and just run them at full speed.
With a bad tolerance gearbox, running at full speed with a fast gear ratio powered by 2 CIMs, the motors get warm. If they are getting hot quickly, you either have a bad motor, a bad gearbox, of something is assembled wrong.
Even with the worse (very noticeable rough/tight spots when turning it with a wrench on the output shaft) of the 4 gearboxes we broke in this year (the static break in resulted in a very noticeable accumulation of metal dust under the gearbox) the motors are not overheating after running for 15 minutes.
. Oh well either way doesn’t matter, not going to rip apart my box now to remove that wire :D.