Pot Gyro

Posted by Jason294 at 2/13/2001 11:36 AM EST

Other on team #294, Beach Cities Robotics, from Mira Costa and Redondo Union and TRW.

Just wondering if anyone had fooled around with this idea. I attached about a 4 inch long piece of aluminum bar with a small weight on the end to a pot and used the feed back as a good gyro that dosent tax the robot controller like the quartz gyro with the kit. Anyone working on differant algorithims to auto-balance the ramp… I know im close, just wondering if you guys had thought of this. I’m sure it will be helpfull to someone. If u want to contact me e-mail [email protected]

Posted by Thomas A. Frank at 2/13/2001 3:24 PM EST

Engineer on team #121, The Islanders/Rhode Warrior, from Middletown (RI) High School and Naval Undersea Warfare Center.

In Reply to: Pot Gyro
Posted by Jason294 on 2/13/2001 11:36 AM EST:

: Just wondering if anyone had fooled around with this idea. I attached about a 4 inch long piece of aluminum bar with a small weight on the end to a pot and used the feed back as a good gyro

Actually, it’s called a pendulum, not a gyro. That is in fact important, because you will need to look at the speed of response of your sensor (see below).

I am looking at it, but I’m not sure it is worth the trouble/risk, as the drivers are doing fine without any artificial aids, and the risks associated with complex software are perhaps not worth the benefit.

Please prove me wrong :slight_smile:

Please remember that there is a time constant associated with a pendulum:

time/swing T = pi * sqrt of (length/g), units having to be consistant (ie: meters and 9.8 m/sec^2). A 1 meter pendulum rod is the classic one second beat clock. So if you make the rod 0.1 meters long, you have a 0.317 second pendulum, which results in some interesting results if you look at the possibility of oscillation.

Also keep in mind that the above equation assumes a massless rod - the Cg of the system is in the bob. If not, then the whole thing appears “shorter”, with a resulting higher frequency.

Hope that was helpful.

Tom Frank

Posted by Tim Gates at 2/14/2001 9:04 AM EST

Engineer on team #288, RoboDawgs, from Grandville High School and X-Rite/Delphi.

In Reply to: Pot Gyro
Posted by Jason294 on 2/13/2001 11:36 AM EST:

Jason294;

We designed and built an inclinometer as a backup for the gyro-chip as a result of damaging the first one banging up and over the ramp. Our current gyro-chip will be shock mounted to prevent a repeat. The short shaft 100K pot recieved in your freebies requires
6 oz./in. to overcome friction between the wiper arm and resistive compound in the pot. I don’t know if that is static or dynamic coefficient of friction. A ten to one gear ratio will match the 280 degree sweep of the pot with the +/- 14 degrees of the ramp, but will bottom out so to speak. We used an eight to one (120/15 tooth) gear ratio which results in three in./lbs. to overcome the base friction. In retrospect, the high gear ratio gave us better resolution but resulted in needing more than three in./lbs. to get acceptable response. We only need to sense when the ramp starts rotation and are not concerned with oscillation when the mass on the end of the pendelum relaxes to a balance. Because the RoboDawg travels through the barrier, height is a consideration and the shorter the robot the more precious real estate becomes in the chassis. Don’t hesitate to try it, every learning experience is of great value.

Tim Gates
Controls Engineer
Team #288 RoboDawgs