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Unread 19-12-2007, 06:50
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Re: Torque vs. Speed

Don't forget to keep an eye on current. Your motor can vist 50 Amps, but it can't live there.

This presentation by Copoili & Patton covered most of the things in discussed here. http://www.chiefdelphi.com/media/papers/1682
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Unread 19-12-2007, 10:54
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Re: Torque vs. Speed

Personally, if i'm trying to make a nearly perfect gear reduction, I start out by making a rough mathematical model of the frictions that must be overcome by the robot, in other words, how much braking torque the robot has when its just moving along flat ground. Then, from this torque, I can figure what the top RPM of the motor will be about 12VDC.

If you don't want to make a mathematical model (it doesn't take long to make a rough one so i suggest you do) then you can just work your reductions out to hit normal load.

Now, this is all welll and good if your robot is going ONLY for top speed. If the pushing power of your robot at 40A (the power available through a victor for a limited but decent duty cycle) isn't enough for you, then you'll have to reach a compromise, change your requirements of your drivetrain, or use a multi-gear or continuously variable transmission.

I've attached the spec sheet for the 2.5" CIM motor. A few parting notes: Remember that when designing a transmission you can have more than one motor, so divide or multiply your torques accordingly. Also, a good figure to remember: A 2.5" CIM motor provides about 101.1oz-in torque @ 1564RPM when battery voltage is 12VDC and current is 40A (480Wi).

Questions? Comments? Post!

-q
Attached Files
File Type: pdf CIM.pdf (58.0 KB, 65 views)
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Unread 19-12-2007, 12:15
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Re: Torque vs. Speed

Just because you might be running your motors at half speed at the desired travel speed of the robot, that doesn't mean you are getting maximum power out. Unless you have a real load, it shouldn't take a full 12 volts to get there (the gas pedal analogy).
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Unread 19-12-2007, 16:11
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Re: Torque vs. Speed

Thanks for all the help. I'm pretty sure I understand now.

Quote:
Originally Posted by Hachiban VIII View Post
(apparently they don't like to run at this level or something??.. doesn't really make any sense to me, but then again I'm easily confused by electrical stuff).
What I mean't to say was...

Quote:
Originally Posted by Laura Rhodes View Post
When the operator is running the robot at a mid-joystick position, the Victor
speed controllers pulse the voltage applied to the
motor on and off rapidly (this is called pulse width modulation). This
effectively lowers the average voltage applied to the motor.
The torque and speed curves of the motor look similar at the lower voltages but
maximum no-load speed is slower and the stall torque
(when motor speed is zero) is lower. The Victor speed controllers have
limitations which make trying to control the speed of motors
at low speeds difficult.
I forgot this was how Victors worked. Silly me.
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