Kilian's Robot Shop of Horrors - 03/23/2001

Subject: [TCRG] [RSOH] [FYI] [MOTORSPOWERANDTHINGS]
Date: Sun, 25 Mar 2001 19:55:11 -0600 (CST)
From: kilian@mail.ahc.umn.edu (Alan Kilian)
To: tcrobots@orbis.net (Twin Cities Robots group)

Last Friday I built a thing called a pony brake which is really just a long lever with a hole in one end that clamps onto a motor shaft but does not clamp tightly.

So the motor shaft can still slip inside the hole in the brake, and it develops torque which you can measure at the end of the lever.

So, you plop the end of the lever down on a scale and turn it on. Then you figure out some way to keep the motor body from turning and twisting up all your power supply wires.

Then you power it up again.

Then you reverse the power supply connections so the lever pushes DOWN on the scale instead of whipping up and clobbering you in the forehead.

Ahh, NOW you're in business. Luckily, this all happened before anyone showed up on Friday.

Here's the deal. You can measure the output power of a motor as follows:

HP = (T*RPM)/5252 Where T = Torque in Foot-Pounds.

Here are some numbers from our experiments:

Experiment #	Weight measured by the scale	RPS	Amps-in	Volts-in
1	170 Grams	8	3	34
2	300 Grams	5	4.7	33.7
3	340 Grams	4	5.3	33

So, converting from grams to foot-pounds went like this:

X Grams * (1 Ounce/28 Grams) * (1 Pound/16 Ounce) * 23 Inches * (1 Foot/12 Inch) = Torque in Foot-Pounds.

Y Revolutions per second * ( 1 Minute/60 Seconds) = RPM

A Amps-in * V Volts-in = W Watts in * (1 HP/746 Watts) = HP-in

Torque(foot-pounds) * RPM / 5252 = HP-out

Experiment #	HP-in	HP-out	Torque (ounce-Inch/Amp)
1	0.14	0.07	47
2	0.21	0.07	52
3	0.23	0.07	53

So, It looks like I get 0.07 HP out no matter what. The motor data sheet lists torque as 54 Ounce-Inches per Amp +/- 10% which is just what I got so at least THAT checks out.

Then we tried Jeff S's bigger AMETEK motor and got this:

Experiment #	Weight measured by the scale	RPM
1	200 Grams	1790

Which comes out to 0.29 Hp-out so it looks to me that a slow motor is not going to generate much horsepower out.

That's all the analysis I can stand for tonight.

-Alan

Motor experiments

Alan drilling an arm for the Pony Brake.	The small Ametek motor connected up.
The business end of the small Ametek motor.	Jeff's Dynetic Systems motor connected up.
Another shot of the Dynetic Systems motor.	The business end of the Dynetic Systems motor. You can see the keyway really chewed up the friction pad. (Alan's old belt.)

Brynn's Trycolps "eye" project

Brynn using a laser to adjust his mirrors.	The top is off the laser range finder.
Some drawings for a laser diode mount.	The lasers look like this in the dark.

Misc

Alan and Brynn took this linear pot apart.

A RSOH gremlin chasing a laser spot on the floor.

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