Torque on motors

[Torboticsmember]

My team has been trying to find plans on the internet to find the torque and other specs of the motors we were given from the kit of parts. Does anybody know of or have plans to a tester like this; or have a mathematical equation to find torque with what each variable stands for. Thank you.

[AdamHeard]

The manuals section on usfirst.org has a document with the information in it. Under section 8, related document; tips and good practices.

[Kevin Sevcik]

If you want to determine it experimentally for the larger motors, you'd need a variable voltage or (better) variable current power supply and a high current multimeter. Then you just need to apply a known torque on the motor. The easiest way is to attach a bar to the end of the shaft and put a weight on it. Then you increase the voltage or current until the mass is just balanced 90* to the side. Measure the current and calculate the torque exerted by the weighted bar. And do this for 4-5 points. There's various other things you can do to make your own actual dynamometer to really measure this, but the above procedure works fairly well and is pretty easy.

Note it's only for the large motors. You probably can't reliably accurately load a small motor and stalling them at any current is dangerous besides.

[Al Skierkiewicz]

Originally Posted by Torboticsmember

My team has been trying to find plans on the internet to find the torque and other specs of the motors we were given from the kit of parts.

I have some spec lists from motors used in kits over the years. What motor sheets are you looking for?

As a general rule, teams should only use the specs as a starting point. The specs are tested under very strict conditions using well regulated voltage sources and low loss wiring. A motor will never perform on the robot as it is shown by the specifications. The variables of the condition of the battery, the wiring, and the speed controller all need to be accounted for in your design. Actual results will vary!

[Tristan Lall]

Originally Posted by AdamHeard

The manuals section on usfirst.org has a document with the information in it. Under section 8, related document; tips and good practices.

Note that there's an error on that spec sheet regarding the Fisher-Price (Johnson) 9012. The peak power is usually the mechanical power output; for that motor only, they've instead substituted the electrical power input, when the motor is at full power. The maximum mechanical output is actually 171 W. (See here.)

Originally Posted by Torboticsmember

My team has been trying to find plans on the internet to find the torque and other specs of the motors we were given from the kit of parts. Does anybody know of or have plans to a tester like this; or have a mathematical equation to find torque with what each variable stands for. Thank you.

Also, search ChiefDelphi for this stuff; it comes up frequently. (See here, for example; there's also a couple of equations for torque given there.) Just be sure to note the year of some of the threads, because the set of supplied motors frequently changes. For example, there are probably 7 different Fisher-Price RS-550 motors that have been in previous kits of parts—we don't know which ones (if any) will be legal next year.