swerve drive alinement question
 

In a swerve drive system how do we know what direction our wheels are pointing when we start the bot, so the wheels are all facing the correct directions, I know with rotery encoders position is relitive to the starting position. I am sure that this is not a problem, because I have seen bots with swerve drive, so I know there is a solution, I just cannot find it.

Thanks in advanced for any help.
Mark

Re: swerve drive alinement question
 

We use the ma3 absolute encoders, the fact they're absolute means they keep the same 0.

Re: swerve drive alinement question
 

We use Cherry magnetic sensors. If you look at the DEWBOT VI steering you can see the sensor mounted on the drive motor. There is a link on that page to the sensor specs.

Re: swerve drive alinement question
 

There are three possible solutions:
1. add a set point, something like a microswitch being pressed when the wheel is at angle 0. For this solution the wheels would have to do an initialization process on the beginning of each match (turn around until microswitch is pressed).
2. Save your wheels last positions in the cRio memory, possible, but not really a good solution.
3. Third time's the charm - use absolute sensors (not incremental encoders) such as Potentiometers (one or multiple) or absolute encoders (see http://usdigital.com/ for MA3 or MAE3).

have fun programming.

Re: swerve drive alinement question
 

1640 used the Cherry AN8 series absolute non-contact rotary sensors. We have been very pleased with the performance. Note that several teams have had problems with the US Digital absolute encoders. Several teams suspect electrostatic discharge to be the problem. The Cherry sensors are automotive qualified and IP67 rated. Perfect for our robot environment. The availability of the Cherry sensors is spotty and is a problem. Many other companies will be bringing absolute magnetic sensors to the market in the future. Robot teams should watch their development and possible robot applications. The potentiometer is loosing it's place on our robots.

Re: swerve drive alinement question
 

Team 2423 used hall-effect sensors on our robot last year. When we turned on our robot, the wheels would spin until our sensors told us the wheels were facing forward.

Re: swerve drive alinement question
 

Not all encoders are relative. Some are absolute, like the austriamicrosystems magnetic encoder that came with the 2010 KoP.


~

Re: swerve drive alinement question
 

We used one of the Kit Magnetic encoders for our swerve drive this year. They have a digital interface, so you can read them without any encoding error and without having to worry about calibrating the limits of an analog output to avoid a deadzone. You can get similar sensors with higher accuracy if you need it.

Re: swerve drive alinement question
 

potentiometers. We used them on our swerve drive this year, along with encoders on each of the wheel axles. That coupled with a MEMS gyro and good coding and a camera, and you can position yourself for nearly everything.

Re: swerve drive alinement question
 

Aside from electronic sensoring....

Many swerve systems, including Wild Swerve, have mechanical features that allow you to fine tune each module without tweaking your steering sensors.

For instance, I have seen teams put radial slots in their steering chain mounts. The slots allow them to loosen their transmissions and make slight adjustments to the alignment, or compensate for chain that won't hit a center distance number and also line up properly.