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Topic: DC Motor driver - shortening outputs when not using (Read 145 times) previous topic - next topic

jacko91

Hello,
I am wondering if there are any dc motor drivers around which shorten the outputs together if the motor driver is not used. All the ones I tested from pololu seem not to have this feature. It is only possible while driving to increase brake torque. But isn't it useful to shorten the motor wires when not in use, so that the braking torque is higher?
Is there a work around like a circuit I can built on the output side of the driver?

Thanks

jremington

#1
Nov 14, 2018, 04:02 pm Last Edit: Nov 14, 2018, 04:03 pm by jremington
What do you mean by "not used"?

jacko91

So when the motor is not driven. I want to make a positioning system. But when the motor is not driving, I wanted to increase the resistance against any big movements due to loads on the shaft.

MarkT

What sort of loads?  Active position may be needed
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

jremington

#4
Nov 14, 2018, 09:20 pm Last Edit: Nov 14, 2018, 09:22 pm by jremington
Most motor drivers feature a "brake" function, which more or less effectively shorts the motor terminals.

Post a link to your motor driver. If you don't have one, Pololu has the best selection.

jacko91

Most motor drivers feature a "brake" function, which more or less effectively shorts the motor terminals.

Post a link to your motor driver. If you don't have one, Pololu has the best selection.
I am using the vnh5019 https://www.pololu.com/product/1451 and a TB9051FTG https://www.pololu.com/product/2997. Both have a brake function, but it is only working when the motor is moving. But not when the motor is at rest. I dont understand the reason behind this. But it seems its is the way a lot of drivers work.
So I just want to understand why. And if there is a work around this, like a circuit which shortens both leads whenever the motor is not used.

Thanks

jremington

#6
Nov 14, 2018, 10:09 pm Last Edit: Nov 14, 2018, 10:50 pm by jremington
Short circuiting the motor terminals acts as a brake only when the motor shaft is spinning and  is most effective when the shaft is rapidly spinning.

A spinning motor acts as a generator, and when short circuited, the energy is dissipated as heat in the motor windings.

To implement a "hold position" function, a shaft position encoder of some sort is required.

MarkT

I am using the vnh5019 https://www.pololu.com/product/1451 and a TB9051FTG https://www.pololu.com/product/2997. Both have a brake function, but it is only working when the motor is moving. But not when the motor is at rest. I dont understand the reason behind this. But it seems its is the way a lot of drivers work.
So I just want to understand why. And if there is a work around this, like a circuit which shortens both leads whenever the motor is not used.

Thanks
Electromagnetic braking cannot hold position, it can only resist movement, its like viscous friction, not
static friction.

As I said active positioning may be what you want, ie full PID loop position control.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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