[FTC]: 2 vs 4 Tetrix Motor Encoders?

[Just_In_Time]

Hello. My team is using motor encoders for the first time this year, and we're unsure about how many we will need. We currently have a 4-motor drive train with each motor separately powering each of the 4 wheels of our drive train. We were wondering if we need to use 4 motor encoders for it to work properly, or is there a way to only use 2 by putting one motor encoder on each side of the drive train? Any help is greatly appreciated. Thanks.

JIT

[FTC4211]

Your options depend partially on how you have the motors wired into the motor controllers. If you have both motors from one side of the drive going into the same motor port on the motor controller then you have to use only one encoder per side of the robot. If each drive motor has its own motor port then you can use either two or four encoders.

More broadly most teams can use only two encoders and be perfectly fine. When driving in a straight line where wheel slippage is minimal, two encoders work just as well as four encoders. The only spot you may see a difference is during turning. With four encoders you have the option to check for and account for potential wheel slippage, but requires much more software to actually achieve significantly noticeable advantages over only two encoders.

My suggestion would be to start with only two encoders, placed on the wheels with the most traction (tetrix rubber wheel before an omni wheel, or the wheels with the most weight over them) as this will provide the best representation of the overall drive train with only the two encoders. Fewer encoders means less software, and one less thing to fail. If the two encoders are not providing the accuracy that you looking for, then add the other two encoders. Generally the less there is to worry about the more reliable it is.

Team 4211

[maths222]

One other reason to use 4 is that 4 allows for PID to be enabled in autonomous. I find that that makes autonomous routines much more repeatable.

[Just_In_Time]

Thank you all very much for your help. 4 seems like it will work better in the end for improved accuracy. Thanks again.

JIT

[Sasha]

We are actually using just 1 encoder (and a gyro and IR sensors) - and it works fine for us, too. Robot motion is accurate to within 1 inch.

[mikets]

It also depends on what kind of wheels you have. If you are using mecanum wheels, you need all 4 encoders to figure out x and y displacements. If your robot can only go forward and backward but not sideways, then 2 are probably just fine. Our robot is 4-wheel swerve drive each with an independent motor and encoder. So our code can keep track of both x and y displacements.