Arduino Forum

Topics => Robotics => Topic started by: AndiJay on Jun 12, 2013, 01:38 am

Title: Two encoders on a 4 Wheel robot?
Post by: AndiJay on Jun 12, 2013, 01:38 am
Hello all,

I'm looking at buying a robot platform to work with. I don't understand why anyone would set a robot platform that has 4 motors with only two encoders. See the link below.

http://www.dfrobot.com/index.php?route=product/product&path=37_111&product_id=261#.UbezpJwQO64 (http://www.dfrobot.com/index.php?route=product/product&path=37_111&product_id=261#.UbezpJwQO64)

Does this make any sense to any of you?
Title: Re: Two encoders on a 4 Wheel robot?
Post by: drewdavis on Jun 12, 2013, 10:54 pm
What doesn't make sense? Why would you need for encoders? For most application both right wheels and both left wheels are going to be moving the same amount. What are you planning on building that would require separate encoders for each wheel? If you need more encoders, they sell them. 


I love their products including their rovers.

If you post what you plan to do with your robot we can recommend some platforms!
Title: Re: Two encoders on a 4 Wheel robot?
Post by: AndiJay on Jun 14, 2013, 05:12 am
Quote
What doesn't make sense? Why would you need for encoders? For most application both right wheels and both left wheels are going to be moving the same amount. What are you planning on building that would require separate encoders for each wheel? If you need more encoders, they sell them. 


It's wrong to assume that both right wheels will spin at the same rate. All four motors will be slightly different from each other, there is no way around this. If you want to precisely control the speed of a 4WD system, and ensure that thing will drive straight, you need to control all four motors independently. Only encoding two is kind of half assed, really.

Practically speaking, I'm sure you can get away with something like this, but I'd like to do some experiments with different drive control systems.

Anyway, I'm going with encoders for all four.