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A Customer Asked:
Hello,
I spoke with someone on the phone a little while ago concerning the speed control of the robots. Specifically, we were talking about the IG32-DM model. I have a customer that has the following specifications that need to be met and I wanted to make sure your robot could meet these performance specs:
1. Ability to set the speed of the robot between 0.1 and 2.0 m/s with a resolution of 0.1 m/s.
2. Ability to maintain speed within 0.05m/s of set point.
3. Turn radius of 4 feet or less, 2 feet or less is desired.
4. Ability to follow a taped course with a maximum axis displacement of +/- 1 inch.From previous discussions I’ve had with folks at your facility, it was my understanding that with the 256 rpm motors and 6 inch wheels, we would have not trouble with getting up to the 2 m/s speed. It’s the resolution and control that I’m wondering about. All the videos I see seem to show the robots traveling at a constant speed and not really doing any variable speeds.
You will want to read our blog posts on encoders. https://sdrobots.com/encoder-support-overview/ There are also a bunch of links about encoders and speed control at the bottom of the page. You will definitely need to implement speed control and you need to use encoders for that. We would recommend a roboteQ controller. The tires may prove to be too inconsistent, you can try them, but you may want to just get us to put set of solid tires on it that are machined and true (this is a custom feature and not a stock item). Not sure where you got 256 RPM from, we do not have any IG32 motors with that speed. You can use the calculator here for speed of the robot https://www.superdroidrobots.com/shop/custom.aspx/how-to-build-a-robot/70/#motors The IG32P 265 RPM motors will give you 127 meters/minute. https://www.superdroidrobots.com/shop/item.aspx/ig32p-24vdc-265-rpm-gear-motor-with-encoder/998/ but they have a 1:19 gear ratio. With quadrature encoder readings you will be getting 19*28CPR for 532 CPR of the wheel. So you will have to do the math from there to see if you can get the resolution you want. The RoboteQ will let you implement speed control and tune the PID to try to keep the desired speed based on the encoder input.
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