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Originally Posted by Gary Dillard
Mount/fix the motor so the shaft is horizontal and up in the air, like up on a table. Put a spool or pulley on the output shaft and attach a string or cord to the spool with a weight on the end. Apply voltage to the motor and determine the speed of the motor using a tachometer or by timing the speed that the weight moves up and dividing by the circumference. The torque is the weight times the radius of the spool. Change the weight and you will have several points on the speed curve - they should be linear (theoretically they are).
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That is exactly what I want to do but electronically. I know there are expensive torque sensors that do this but I am looking for a neat idea to do this on the cheap.
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Originally Posted by Gary Dillard
Now, if you want something you could do on the robot that correlates to torque, you could measure the current because it is linear with speed as well. But you would still need to know what torque correlates to what current.
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The "what torque correlates to what current" is the part I am trying to get to (I think).
So here's the deal. I stumbled across these:
http://www.medusaproducts.com/Other/...rs/PA-Main.htm Particularly the new "Pro" model which is due out next month. These are really nifty power analyzers used by the R/C airplane folks that hook up between your power source (battery) and load (speed controller & motor) and display voltage, current, power, amp-hours, and watt-hours. The Plus will connect to a PC and graph. The new Pro will also measure RPM, temperature, and thrust using a digital scale. Do any teams use these? So I emailed the company and it turns out the scale is just hooked up to an aux input which can accept any 0-2.6V signal. It seems to me that if a proper inexpensive "torque sensor" could be found and the right circuit developed this thing would be a really nice addition to a FIRST team tool box. I just don't know enough about electronic torque measurement to know where to start. I wonder if there is someone here on CD that would like a summer project.
-Chuck