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#31




Re: Possible Issues with Feeding Voltage to a 775 Constantly?
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This answer deserves a "kudos". I couldn't have said it any better. A note i would add though. A motor is just a converter, from electrical to rotational. For every watt of input you'll get ~.7 watt of power. simple right. so keeping with electrical principles. If you give it steady voltage, you would get steady speed. but you don't want speed from the motor. I would try giving it constant current, which should give you constant torque to prevent back drive, also easier to do calculation on force it will exert in "hold" mode. just food for thought. best of luck and let CD know how it works 
#32




Re: Possible Issues with Feeding Voltage to a 775 Constantly?
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#33




Re: Possible Issues with Feeding Voltage to a 775 Constantly?
Please show how to calculate that.

#34




Re: Possible Issues with Feeding Voltage to a 775 Constantly?
There are measurements of the CIM power curve here. At zero speed and free speed, the CIM (as with any other motor) is producing to mechanical power, because power = torque * angular speed, and in each case, one of those is zero. Vex also has power curves for most of the other FRClegal motors linked from here.
When running at full throttle, a good approximation to these curves is to model the motor as a resistor and a generator which produces voltage proportional to rotational speed, in series with each other. You can get the resistance from the stall current: R = V/I = 12V / 131A = .092Ω. Then, you can calculate the generator ratio from that and the free speed. As the motor is drawing 2.7A, the voltage across the resistor is V = IR = 2.7A * 0.092Ω = .248 V. The generator ratio is therefore V/ω = (12V  0.248V) / 5330 rpm = 2.2mV/rpm. Note that due to the relatively flat efficiency in the upper third of the range, if running pretty fast but not free (35005100 rpm), 0.60 times the electrical power is a decent approximation to the mechanical power produced by a CIM  good to within 10%. Added: The BAG is the only motor listed there which reaches a 70% efficiency as claimed above. When doing output power computations, assuming that torque is proportional to current is a good approximation. Last edited by GeeTwo : 04092018 at 07:04 AM. 
#35




Re: Possible Issues with Feeding Voltage to a 775 Constantly?
Sure.
Here are the equations, if you want to learn to do it manually. Here is a simple motor calculator that has the above equations builtin. Just select a motor from the main menu, then select an operating point from the next menu. 
#36




Re: Possible Issues with Feeding Voltage to a 775 Constantly?
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I just uploaded a ZIP file containing specs for multimotor CIM, miniCIM, and 775Pro for use with the motor calculator. 
#37




Re: Possible Issues with Feeding Voltage to a 775 Constantly?
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For worlds I will test with the application of current )) Thanks 
#38




Re: Possible Issues with Feeding Voltage to a 775 Constantly?
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Perhaps I can use this to do actual calculations instead of taking the risk of damaging a motor. Last edited by Lesafian : 04162018 at 02:13 PM. 
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