Help with motor drift

[Robiscool]

Hello, I’m having an issue with motor drift where in both autonomous and driver control the whole drivetrain appears to drift to the left and this is annoying to deal with especially in autonomous so any help would be appreciated.

[u89djt]

Hi there, (your post should probably be under drivetrain and building tips) you need to provide more information about your robot. A photograph of the underside would probably be quickest so we can see what the drivetrain layout looks like.
But, I’m going to make a guess: you’ve got omniwheels in line with each other on the left and right of your base. In this case, there’s nothing stopping it drifting sideways because the omniwheels don’t provide lateral constraint. Push it sideways while it’s supposed to be stationary and you’ll see. In this case, minor distortions in the build either as static structure errors or bending during application of forces can deflect the drive of the wheels slightly and allow that free sideways mode to go wherever it conspires.
There are a million ways you can go to fix it, too, and assessing that would take more information from you anyway, so go ahead and post pics and description

[663J_Jellybotz]

2 really simple things

1. Your shafts may not be in the motors. Go to devices and run each motor to check.
2. One side may have a lot of friction. There are lots of reasons for this. EX: shaft collars too tight, no bearings, etc.

[Gigahertz.t]

This is almost always due to friction, seeing as it happens both during your driver control and autonomous (assuming you didn’t copy and paste). Here are a few forum posts about it:

Unexplained pauses during autonomous

If it is a build problem, then it is most likely bad build quality due to: Friction, caused by too many spacers or shaft collars rubbing against structure Unsquared chasis Bad gear mesh Lack of or improper bracing, usually you would see the drivetrain bending outwards if you look at it from the front Since your drivetrain is swerving slightly, then that is a sign of too much friction on the same side as the turn direction (right turn–> right side for example) Could we see a few pictures of y…

Tournament Feedback?

I second this. This year was my first year building a competition bot, and I did this. The c-channels ended up flexing outwards like this / \ and created a lot of friction. It also led to gear mesh problems. Use standoffs and some c-channels to brace your drivetrain [20240115_090223]

Motor issues in drivetrain

That means it is probably a build issue. Do you notice your drivetrain drifting to one side? Then it is friction. If not, try swapping the motors on the sides (right motors to the left side and vice versa). If the same side is getting hot, it is friction. If not, then it is a motor problem and you need to replace the motors. But yes, like @Micahy321 said, a picture of your bot will really help

Flywheel speed and motor Speed

Yeah, adding on to @JoBro and @Wesley13406D , this meqns it is probably a mechanical issue. Could we have a picture of your flywheel setup? Also, like @Penguin1 said, a 600 rpm motor is best for flywheels as it reduces the amount of gears, and hence friction, involved. Before you post your picture though, try removing the motor and then spinning each axle individually to see where the problem child is.

A picture of your drivetrain would help us out though.

[4233XBen]

This won’t fix the driving but in auton you could use a angle correction pid something like this :

@4233XBen

This works well for making my drive pid go straight mine is more like this:

This is just eyeballed so the straightness of these is not 100% accurate but close.

@Bubski

Are you using the built in Vex drivetrain controller in your code? If not, and you have your own drive PID, I’d recommend including a second PID controller into the function that holds the robot at the angle it starts at.

It really does make a difference and the code is pretty simple to implement ours is something around this

double LError = Rabsoulute-Labsoulute ;
double LDerivative = LError - LprevError;
LIntergal = LIntergal + LTotalError;
if (fabs(LError) > .2){
LmotorPower = (LError * dLkp + LDerivative  * dLkd + LIntergal * dLki) + RmotorPower;
}
else{
  LmotorPower = RmotorPower;
}

It only changes the Lmotorpower based on the difference in motor sides. This keeps it mostly straight It has some flaws like you have to give it a 200 millisecond delay between turns and driving or else it corrects the turns overshoot (it causes it to go slightly not as far).

[Mano]

Our team has come across this problem before, and here are some tips that could help you.

1. Check if all the motors are working. If one of the motors is slow, then it’s probably because it’s too hot. If it’s not moving the drive train at all, then check if the shaft is in all the way.
2. Check the drive train’s angle. If the left side of your drive train is slightly angled to the left, then that could’ve made your robot move towards the left. To fix this, just make sure that both sides of the drive train are parallel to each other, and then are braced together well.
3. Make sure that the friction is the same on both sides. If the left side of your drive train has more friction than the other, then that is probably the reason why the left side is a lot slower, causing the robot to drift in that direction.
4. Make sure that no shafts are bent, each axle is free to move, and that the bearing flats aren’t trapping the axle in anyway.
5. Check if the motors on the left side of your drive train are hot. If they are, then that means the left side does have a lot of friction.

[Robiscool]

Update: My team is just scraping the current design. But keep posting solutions so others with the same problem can see.