Robot help!

So are robot’s drive train isnt working, it is a four motor drive train and on both sides the motors are on different size gears so will that effect what is happening? What is happening is that are robot can go forwards and back, But can not turn at all, so is there a way to fix this? And does the motor positions effect what is happening?

(Note: I don’t own a phone so I cant send any pictures, later today I may ask one of my friends who has a phone to take a picture of it)

A photo would really help, make sure to get that photo from your friend. However, if you could provide a sketch on google slides or something, especially of the wheel configuration, we might be able to help.

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There is a google slides image of it

(dont mind the highlighted blue, doesn’t mean anything)

If one motor is on a 60 tooth gear and the other is on an 84 tooth gear then they will be conflicting with each other, because they are both trying to rotate the wheels at different speeds. Assuming you are using blue cartridges and the wheels are on the 84 tooth gears, the motor on the 60 tooth gear will be trying to rotate the wheels at around 430 rpm, and the motor on the 84 tooth gear will be trying to rotate the wheels at 600 rpm. You need both motors to be on the same gear size for them to try to rotate the wheels at the same speed and not conflict.

Also I’m guessing you’re using 4 inch wheels because those are the only wheels bigger then 84 tooth gears, which makes your drivetrain’s max speed almost 90 inches per second if you’re using blue cartridges or around 30 inches per second if you’re using a green cartridge (for reference my team’s drivetrain is 61 in/s). The speed with blue cartridges is way too fast, and the speed with green cartridges is too slow, so I would recommend potentially switching out the gears on your robot so you have a more balanced speed. This post has a good list of drivetrain gearings: Catalogue of Drive Gearings


Thats my same drive train but instead of it being 2 motors its 1 motors

Ok, But what would fix the not being able to turn the bot?

If you want to fix it you would need to move the motor on the 84 tooth gear to the 60 tooth gear so they spin at the same speed.

Since you guys are going for a torque and not a speed approach, move the motor that is on the 84 tooth gear to the other 60 tooth gear.

OK THANK YOU GUYS SO MUCH!!! But i have a new problem, after setting up the drive train in a new way that works, for some reason are bot is drifting to the left without any input? So what is the deal with that?

One side probably has more tension than the other so the wheels aren’t spinning at the same speed. To fix this you will have to loosen the tension on the side that the robot it driving toward.
It also may have to much slip on the 60 tooth gear (I’m guessing that’s where your motor is are. If not then that’s not your issue).
If that doesn’t fix it, it may be that the motor(s) is burnt out.

Robot drift can be the result of a variety of things, such as:

  1. Uneven friction - If, for any reason, one side of the drive base has more friction than the other, this could lead to one side moving faster and drifting towards the other side. In your case, I would recommend ensuring that both sides of the drive base are symmetrical.

  2. Motors - Some motors are older than others and are more burnt out than others; if one side of the drive base is slower than the other, you’re bound to have drift.

  3. Curved c-channel - From what I can see, this is relatively uncommon, but this happened to my team last year. One of the c-channels on our drive base was curved, causing drift.

  4. Un-squared drive base - If your drive base isn’t square, then there is a high probability that that is the cause behind your drift. I would recommend watching episode 3 of Ryan Liao’s “Build Masterclass”: VEX Build Masterclass #3 - Squaring

Hope this helps!


Turn on your brain, go to devices, then run each motor individually. By doing this, you can see if one motor is slower than the others. To run each motor individually, click on the motor in the device section, then click the arrows.

That sounds like controller drift to me.

Differential gear sizes may affect turning. Check motor connections, gear alignment, and code for differential power distribution to troubleshoot the turning issue in your four-motor drive train.