robot turns to the left?

hey i’m part of a rookie team 4976. our bot seems to turn to the left when driving forward but going back it moves to the right. we have discovered it is not a mechanical problem by switching the motors and motor controllers. so i was just wondering if any older teams have experienced this problem before what or could it be? We have as well checked voltage all were 12.04v when moving straight Thanks

Four motors or two? If 4 one motor may not be getting power and/or PWM signal. Check for a reversed PWM cable.

We had that problem last year and it was caused by a pinched bearing. Double check your bearings as well as your spacers (Spacers were too tight for us). Also you may need to calibrate your motor controllers. Based on our controllers (Vex Victors)… you need to push the small pin near the heat sink until the lights start flashing (red or green I believe) and then drive Up 5 seconds, down 5 seconds, right 5 seconds and left 5 seconds. Hoped that helped, PM me if you need further assistance.

Four motors,we found out the arcade drive is the problem by switching outputs on the side car from 1,2,3,4 to,4,3,2,1 and the problem switched so the bot turns to the right going forward and the left going back does any one have experience with arcade drive not working any suggestions?

When you say to the robot is moving right while moving the joysticks going forward, do you mean the robot is spinning in place?
If so it might be a good idea to try switching motor polarities on two of the jaguars that control the same side of the robot. (i.e. swap polarities at the jaguar on the two motors that drive the left side of the robot, and then see the response from the robot)

Informing us of what the jaguar indicator lights do while you are moving forward may help us diagnose with you as well.

If you are doing this, make sure your motors aren’t fighting each other in the gearbox. Be absolutely sure when you do this that the two motor controllers controlling the motors in one gearbox are flashing the same color light. If you have motors working against one another, it can trip the overcurrent protection in the controllers and have symptoms of what you are describing.

Are you sure you’re not accidentally commanding the robot to turn? Using a single joystick for Arcade Drive, it’s very hard to control forward and backward without getting a tiny bit of X-axis involved at the same time.

Are you inverting any of the motors? In a normal wheel setup, going forward is different for the wheels on each side.

When you turn left, the left wheels are going backward and the right wheels are going forward. So I would assume that because that is happening when you drive forward, you need to invert the left wheels.

In java this is as simple as:

RobotDrive.setInvertedMotor(RobotDrive.m_frontLeftMotor , true);
RobotDrive.setInvertedMotor(RobotDrive.m_rearLeftMotor , true);

Thanks to all who responded, we will try all of the ideas desperate to get this thing moving. I’ll give an up date Saturday on what we did (hopefully fixing it) thanks for the ideas!

Be sure that your speed controllers are calibrated as well. This method causes the controllers to interpret the joystick for full throttle forward and reverse. A good indication that you need this is that the motors creep when the robot is lifted off the floor. Another quick check while you have the robot up is to command it to full throttle forward and check the indicators on your speed controllers. They should all reach full and all at approximately the same joystick position. Repeat for full throttle reverse.