Absoloute Potentiometer for swerve drive

[buildmaster5000]

My team is prototyping a swerve drive this fall and is having trouble finding a sensor for determining the posistion of a wheel. We are using the WildSwerve modules forom Team 221 which have .25" shafts for sensors. The KOP encoders seem to offer a good degree of accuracy (360 degrees), but they do not have an absoloute zero. From what I know, this means they would re-zero themselves every time we turn the robot on, which is not ideal.

Any advice on the problem in general or a specific sensor would be greatly appreciated!!

Thanks in advance

[Don Wright]

http://www.usdigital.com/products/en...ary/shaft/ma3/

[JewishDan18]

Team 20 considered normal encoders, absolute encoders, and ten turn potentiometers. We decided the zeroing made the normal encoders not worth using. We wanted to get be able to make more than one full twist of the modules, which the magnetic encoders are able to do, but the zeroing once again becomes an issue. So, we went with the ten turn potentiometer, and it worked well.

[EricVanWyk]

The magnetic encoders provided by Austria Microsystems in the 2010KoP would do nicely here. They are absolute within one revolution, and can handle continuous rotation. I believe them to be ideally suited for this purpose*.




* Which is why I introduced AMS to FRC in the first place.

[buildmaster5000]

Thanks!!!!!!

[ajlapp]

The MA3 that Don mentioned from US Digital has worked well for us in the past.

Our current demo bot uses them. We are able to have continuous rotation and the data seems quite robust.

[Alan Anderson]

Originally Posted by JewishDan18

We wanted to get be able to make more than one full twist of the modules, which the magnetic encoders are able to do, but the zeroing once again becomes an issue.

Depending on how the rotation motor is connected to the module, there are several possible ways to get multiple turns of the module to correspond to a single turn of the sensor. If you use chain, it's easy to put the sensor on an appropriately-sized "idler" sprocket.

There is also a software solution. Each time the swerve module makes a full rotation, save the "twist number" to a file. When initializing the system, read that file. This does fail if someone turns the module too far by hand while the robot is not powered off.

The simplest answer is to make the modules capable of rotating without limit so you don't need to keep track of how many full turns they've made. That's not necessarily the easiest answer, though.

[JewishDan18]

Originally Posted by Alan Anderson

Depending on how the rotation motor is connected to the module, there are several possible ways to get multiple turns of the module to correspond to a single turn of the sensor. If you use chain, it's easy to put the sensor on an appropriately-sized "idler" sprocket.

There is also a software solution. Each time the swerve module makes a full rotation, save the "twist number" to a file. When initializing the system, read that file. This does fail if someone turns the module too far by hand while the robot is not powered off.

The simplest answer is to make the modules capable of rotating without limit so you don't need to keep track of how many full turns they've made. That's not necessarily the easiest answer, though.

Yes, we considered saving the number of turns to a file, but we didn't want some I/O error breaking the robot in competition. We actually had plans to use slip rings along with magnetic encoders (which is ideal), but slip rings were banned this year

[PAR_WIG1350]

Membrane potentiometers might work, but their reliability in competition is questionable:
<Link> or <Link>
I am currently doing research to investigate their suitability for the task, but at the rate it is going, I'll be lucky to finish by build season.