How will the final output here behave?

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    Horsepower Rpm Torque
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Discussion Overview

The discussion revolves around calculating the outputs of a system involving multiple DC brush motors, specifically focusing on final torque, RPM, and output shaft horsepower. Participants explore the implications of motor efficiency, potential issues in the setup, and methods for determining various electrical parameters.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the calculation of final torque, RPM, and output shaft horsepower, questioning whether these will simply be the sum of individual motor outputs and if efficiency scales linearly.
  • Another participant suggests that the torque output will be the sum of the torque from all motors, noting that torque is proportional to motor current and influenced by applied voltage, back EMF, and motor resistance.
  • A participant asks for guidance on calculating the applied voltage, back EMF, and resistance, indicating a need for further clarification on these parameters.
  • It is proposed that the method of powering the motors may affect calculations, and that operating the motor as a generator can help determine back EMF in relation to RPM.
  • Measuring winding resistance while manually turning the motor is suggested as a way to eliminate commutator bumps, which could affect resistance readings.
  • Another participant describes a method for calculating current and torque by measuring the back EMF and adjusting for terminal voltage.

Areas of Agreement / Disagreement

Participants express varying views on the calculations and methods for determining outputs, with no consensus reached on the best approach or the implications of efficiency scaling.

Contextual Notes

Participants highlight several assumptions, such as the type of motors used and the method of powering them, which may influence the calculations. There are also unresolved steps regarding the measurement of back EMF and resistance.

Who May Find This Useful

This discussion may be useful for individuals interested in motor control systems, electrical engineering, and those seeking to understand the dynamics of multiple motor setups.

seany
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TL;DR
If you have multiple motors adding to a shaft via bevel gear, will the output power be just the sum?
what about RPM? What are the problems the system can suffer from? e.g. backlash
Hi

I was watching this:



How will we calculate various outputs?


1 Final toruqe?
2 RPM
3 Output shaft horsepower?

Will it just be a sum of the individual motors, or will there be other things to keep in mind?

Does the efficiency scale linearly?

What issues will appear from a setup like this? gear mesh failure? Backlash?

I would be happy towards some general pointers, and if there are some technical papers i can read

Thank you.
 
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Assuming DC brush motors.
The torque output from the shaft will be the sum of the torque from all the motors.
The torque from a motor is proportional to the motor current.

The applied voltage, the back EMF from motor rotation, and the resistance of the motors, will set the operating point.

Backlash will be eliminated where two motors are opposed, with opposite currents and torque.
 
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Thank you

The applied voltage, the back EMF from motor rotation, and the resistance of the motors, will set the operating point.

How would I go on calculating those? Thank you
 
It may depend on how you power the motors, assuming a fixed DC voltage.

Operate the motor as a generator to find the back EMF volts / RPM. That will be similar to the specified unloaded RPM at specified voltage in the data sheet.
That allows you to compute the back EMF from the RPM.

Measuring the winding resistance, Rs in ohms, while turning the motor slowly by hand so you can eliminate any commutator bumps.

For a specified operating RPM, compute the back EMF and subtract it from the applied terminal voltage V.
The current in amps will be; ( V - back EMF ) / Rs.
The current will generate the torque.

You can stall the motor with a fixed torque arm, then adjust and measure the current to identify the scale factor.
 

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