Maximum Motor Power

13 years 11 months ago #13685921 by hemantdandekar
<P style="MARGIN: 0px">Can i limit the maximum speed in position mode ?
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<P style="MARGIN: 0px">Is it safe enough to control a 1.5KW dc motor using RoboteQ 2850HE from a 24V battery through one channel and a 1KW PMDC from the other channel?

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13 years 11 months ago #13686067 by cosma
Replied by cosma on topic Re:Maximum Motor Power
<P style="MARGIN: 0px">In position mode, the controller tries to reach the destination as fast as possible. The speed cannot be limited in the current version of the firmware.
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<P style="MARGIN: 0px">1500W is 62A at 24V, 1000W is 42A. Both values are within the controller's capabilities. Heat generated and dissipation will also be a matter of how long the motors are running at full power and the ambient temperature. You should conduct real life tests to verify that there is adequate cooling and that the controller stays within acceptable temperature. ~50oC case temperature would be a good value not to exceed, even though the controller will operate at higher temperature.
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13 years 10 months ago #13807273 by hemantdandekar

Thanks for reply.

One more doubt that we are facing is regarding "E-STOP". When E-STOP is triggered while the vehicle is moving on inclined is it that the controller will hold the vehicle in position or the controller simply puts off the MOSFET bridge? Because real time demands that the vehicle should not move any further when E-STOP is triggered but if the MOSFET bridge is turned off then the controller will not generate any holding torque. Is there any other alternative way of holding the vehicle in position at any desired emergency situation?

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13 years 10 months ago #13812197 by cosma
Replied by cosma on topic Re:Maximum Motor Power
When estop is triggerred, two of the bridges turn full on, shorting the motors. Beware, however, that this is done instantly (without decceleration) and is therefore mechanically quite brutal.

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13 years 10 months ago #13829747 by hemantdandekar
<P style="MARGIN: 0px">We have tested the E-STOP for low power motors and found the motor stopped immediately with jerk. But the problem starts here in E-Stopped situation(E-STOP switch triggered) the vehicle wheel can be made to rotate with little force applied to it with hand. Thus if in case the vehicle happens to be on slope and E_STOP is triggered there exist possibility that the vehicle would roll off. This in fact should not happen.
<P style="MARGIN: 0px">What is the remedy?

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13 years 10 months ago #13830656 by cosma
Replied by cosma on topic Re:Maximum Motor Power
<P style="MARGIN: 0px">The fact that the robot stopped right away with a jerk shows that the motors got shorted as expected.
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<P style="MARGIN: 0px">The braking occurs because the motor acts like a generator and, by shorting it, the generated power is turned to heat.
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<P style="MARGIN: 0px">The braking effect stops when the motor is no longer spinning and this is why you can rotate the motor slowly. If you try to rotate the motor faster, you would feel the braking effect to grow with speed.
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<P style="MARGIN: 0px">The bottom line is that you cannot rely on this effect to keep the robot locked in a fixed position while on a slope, for example. The only way to do this is with some kind of mechanical brake.

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