Motors out of sync
 

We've finally recieved our two new CIM motors, and installed them on our robot. Our programming has a victor for each motor, as required, and is programmed so that each motor ought to run at the same speed as the one next to it, and all four should run at the same speed when the controller is pushed directly forward.

They don't. Not only do they not usually run at the same speed (at low speeds, especially, the robot will turn perpetually), but the motors mounted together in the gearboxes don't run at the same speed. We thought this was odd, but tried hooking it up for a few moments and running it with the wheels off the ground - it runs, even when on the ground, it will run fine, but it sounds so bad we took it back up on the cart. The problem is, we have NO IDEA how to get the motors to run in sync the way they should.

I hate to put it this way... but HELP!

Re: Motors out of sync
 

Are the two motors mounted so they will turn in the same direction, or opposite?

motors seldom run at the same speed in opposite directions.

If that is not the issue, could one of the motors be defective? running slower than it should?

are you sure the Victors for each motor have been calibrated, and you are always sending the same output to both victors?

Re: Motors out of sync
 

Exactly where I was headed too. Make sure to calibrate the Victors as pairs. Another idea to keep the paired motors sync'd is to use a "Y" PWM cable to run the pair from a single PWM output. That way, the code only has to support one PWM per motor pair.
Just a suggestion.

Re: Motors out of sync
 

I really don't understand this. Can you explain more?

If 2 motors are connected into the same gearbox how can they possibly be turning at different speeds? Aren't the physically coupled together so that a rotation on one MUST equal a rotation on the other?

Matt B.

Re: Motors out of sync
 

OK, if your drivetrain is making a sound kind of like that of a wounded bobcat at the YMCA, then that is a sure sign of something being wrong.

Some things to look for ( no matter how simple, they can still be overlooked :) )
1. One of the motors isn't hooked up backwards, the leads don't need to be reversed if you are using the kitbot Boxes.
2. check the RPM of each motor to make sure that they are all spinning the same without a load
3. if you've seel any magic smoke, check the brushes on the motor... in some cases they can be fixed, or defenately replaced
4. If you are using the kitbot boxes, make sure that no set screws have come loose
5. Make sure you are calibrating your Speed controlers correctly ( we had trouble with this a little)
6.As was said, Y cables are a good Idea, even if they do somewhat clutter your electronics up
7. If you are using the Kitboxes with two motors, try running them with only one.

Just definately make sure that your motors are spinning in the right direction and at the same speed, because if you pit CIM against CIM, one usually over powers the other, producing the terrible noise you might have heard when you put it on the ground and damaging stuff.

Sorry if this didn't help, I gave it my best shot :)





-CodyC

Re: Motors out of sync
 

Kenneth-

The CIM motors and the gearboxes are pretty consistently good quality, and the problem you are describing sounds fairly big, so I would suggest that you consider two possibilities:

1. There is some serious friction caused by parts sliding together somewhere in the driveline.

or

2. The PWM signal from the controller is not the same to each of your speed controllers.

If its number 2, you should be able to check what your program is doing to see if there is some calculation error, and you should be able to see quickly if the speed controllers are going "full throttle" by looking at the red and green lights that signal full-back and full-forward.

If it is number one (my guess is that it is), you should look for parts that are rubbing against each other. Usually they tend to make noise, and heat up if you run them at high speed. Look at every interface in the driveline - is there a washer rubbing up against a bearing, is there a gear thats rubbing against something? Look to see if the gearbox was assembled correctly - lots of teams use it so it should be pretty straightforward for you to make yours right. Put the bot up on blocks, turn the wheels with your hands, feel for odd resistance against turning. Pull a motor out - if everything is running on ball bearings (and now no motor to resist you turning the wheel) the driveline should run super-free. If you feel drag or hear crunchy sounding noises you are probably getting close to the problem. Be a detective - you'll find it. I've seen experienced robo-nuts take a loong time to figure out where the problem is, so don't give up easily.

This might be a problem that you only see under load (like when the robot is pushing against something, or when you turn and the wheels scrub sideways). If this is the case you need to look for deflections in your chassis - are they causing shafts to come out of alignment? If so, FIX IT, make your chassis stiffer, you'll be glad you did. Are the wheels sliding sideways and rubbing up against something?

If you post your findings (try to be clear and concise, and explain your methods) you'll see that people will be willing to help you solve it through this forum.

Hope this helps,
Ken

Re: Motors out of sync
 

we took the gearboxes apart and made sure they were lubricated well, and all the parts seem to mesh fairly smoothly. Also, we did check the motors against a strobe the other day, and most of them run within a few RPM of one another, but one is BADLY off. I'm hoping its not a parts defect, we'll have to try recalibrating the Victor

Re: Motors out of sync
 

Before you change anything, you can try swapping the "bad" motor with a good one. This will help identify if the issue is with the Victor or the motor.

Re: Motors out of sync
 

We don't have any more but the four we've got here... *sigh*

Ah well. We can try pulling one from the other box, I guess.

Re: Motors out of sync
 

Okay, the gearboxes check fine, and the no one has been able to find anything wrong with the programming... so now what? Becuase if it's just a bad motor, we're kinda SOL - takes too long to order another...

Re: Motors out of sync
 

what Mike was saying is, switch the wires between a good motor and the troubled motor, to the victors, to see if the problem follows the motors or the victors?

Re: Motors out of sync
 

Its the motor, as far as I can tell, but we've been using Easy C, and we can not figure out how to mess with the Victors at all using that program. So now we're trying to figure MP Lab out...