What kind of sensor should we use?
 

We are using a windshield wiper DC motor to swing a rod for a set number of degrees.

We want a sensor that can give us the angle that our rod is at.

We are short on time, so something that is in our kit of parts would be ideal.

Our rod will be hitting frisbees pretty hard, and we want to avoid breaking any overly sensitive parts of the sensor on impact.

This is our first year, and we are a bit overwhelmed by the many different types of sensors, but we are looking primarily into optical or magnetic absolute encoders, and alternatively into potentiomenters.

We would appreciate any help we can get.
Thanks!

Re: What kind of sensor should we use?
 

Are you SURE that's an FRC legal motor? I don't see it in R32, which lists the only legal FRC motors. If it is not there, I'd suggest the throttle control motor or a window motor. Maybe a servo and set it to go to an angle--that's what they're designed to do--but that depends on how hefty the rod is.

You probably want a potentiometer with a sacrificial connection--that is, a connection that will break before the pot does. Butt up the ends of the pot shaft and another axle or shaft that is at the pivot point of the rod and rotating with it, then ziptie a short piece of surgical tubing around both. That connection will allow for shock absorption.

Re: What kind of sensor should we use?
 

Question: Do you REALLY need a sensor for this? Window lift motors are meant to be stalled without burning up or anything. It would be simpler and faster to put some physical stops in the system so that you're just running from one stop to another. Then you put in a little simple code to only run it for x.x seconds in one direction and y.y seconds in the other direction. Problem solved without sourcing a sensor or figuring out how to program it.

Re: What kind of sensor should we use?
 

For this application I would prefer something like a US Digital MA3 magnetic absolute angle sensor. It's physically a lot like a small potentiometer, and the signal it provides is also a lot like what you'd get from a pot.

If you're really short on time, you can probably find a 10k potentiometer at a local electronics shop.

Re: What kind of sensor should we use?
 

If it only sweeps between 2 positions, then 2 limit switches may work well. Make sure you use something other than the limit switch as the physical stop, apply the limit switch in a way that it has a little compliance. Often this can be accomplished by bending the limit switch tab into a shape that can flex.

If you need to stop at various angles, I would recommend a potentiometer. Be careful when installing as it is really easy to turn too far, and break them.

Re: What kind of sensor should we use?
 

If shock is an issue then a non-contacting absolute rotary position encoder would be good. A Cherry AN8 series is an example.
http://www.cherrycorp.com/english/se...sition/an8.htm

Re: What kind of sensor should we use?
 

If I'm not mistaken, the window motors will auto-protect if they trip the internal thermal limit. The software timer would definitely be a good idea in this case.

OP, can you provide a simple sketch of your mechanism?

Re: What kind of sensor should we use?
 

A roller type limit switch running on a disc with cam lobes would do the trick.

Re: What kind of sensor should we use?
 

teams 340's progs seem to be a big fan of vex encoders
at 14$ for a wired and enclosed encoder with 90 tick per rev you cant go wrong