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Author Topic: Disengaging a motor from the wheel  (Read 1483 times)

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Offline baalexanderTopic starter

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Disengaging a motor from the wheel
« on: November 06, 2009, 05:24:09 PM »
Planning out my first robot. I have a computer science background, but am trying out a field where the inputs aren't always keyboard entries and the output isn't always a screen. It feels liberating so far.

The robot I'm planning will follow a person, but also be human pull-able (think like a tilted movers dolly). I don't want the motors to be engaged to the wheels when the user is pulling because that seems like a damaging action to the motors and adds extra resistance to the user.

Do you know what I should be searching for to find a way to disengage the motors? I'm not sure if this is like an extra clutch type system, or can be built into the gear head, or if some motors can go into free spin. If you need more information, please let me know!


Offline SmAsH

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Re: Disengaging a motor from the wheel
« Reply #1 on: November 06, 2009, 05:45:37 PM »
There are quite a few ways of doing this, it just depends on which you want :)
Although spinning a dc motor while its not moving doesnt really damage it at all, its how a generator works...
The one i am thinking about involves physically detaching the gear from the wheel gear, then re-attaching when the motors need to drive.
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Offline Razor Concepts

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Re: Disengaging a motor from the wheel
« Reply #2 on: November 07, 2009, 08:25:24 AM »
I would just leave the motors attached and use it to recharge the bot's batteries  ;D

Offline SmAsH

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Re: Disengaging a motor from the wheel
« Reply #3 on: November 07, 2009, 04:13:39 PM »
Yeah, i had that exact idea while i was writing my previous post...
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Offline baalexanderTopic starter

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Re: Disengaging a motor from the wheel
« Reply #4 on: November 09, 2009, 04:43:13 PM »
Thanks for the replies!

From my basic understanding, turning the motor via the wheels will generate voltage, which goes to the wires. If I go with the simplest approach and do not disengage the wheel from the motor when being pulled, is it right to assume I'll need a stronger diode to keep the back-emf from hurting the rest of the circuit (and possibly a bigger resistor for LEDs or whatever down the line of the motor)?

Using the motor as a generator looks like an awesome idea. Probably too much for my first iteration, but definitely something for the future. I couldn't figure out how to switch from motor to generator at the circuit level. Maybe like a transistor switch so if a high enough voltage from the motor, send to a battery charging control? Are y'all aware of any projects that have done something similar?

Offline SmAsH

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Re: Disengaging a motor from the wheel
« Reply #5 on: November 09, 2009, 05:19:40 PM »
Quote
From my basic understanding, turning the motor via the wheels will generate voltage, which goes to the wires. If I go with the simplest approach and do not disengage the wheel from the motor when being pulled, is it right to assume I'll need a stronger diode to keep the back-emf from hurting the rest of the circuit (and possibly a bigger resistor for LEDs or whatever down the line of the motor)?
Well, if you have a diode on the circuit then the motor wont be able to turn in the other direction...
Do you only want the motors to turn in one direction? If you have a motor controller you wont need diodes.

Quote
Using the motor as a generator looks like an awesome idea. Probably too much for my first iteration, but definitely something for the future. I couldn't figure out how to switch from motor to generator at the circuit level. Maybe like a transistor switch so if a high enough voltage from the motor, send to a battery charging control? Are y'all aware of any projects that have done something similar?
well, you could have a switch that takes the motors leads from the controller to the battery, quite simple...
The only problem with measuring the voltage on the motor leads is that there will be voltage when the motor is being run from the battery...
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Offline Soeren

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Re: Disengaging a motor from the wheel
« Reply #6 on: November 10, 2009, 06:42:41 AM »
Hi,

The only problem with measuring the voltage on the motor leads is that there will be voltage when the motor is being run from the battery...
Just measure sign and magnitude of the current instead.

Releasing the wheels:
 decouple an electromagnetic clutch.
 use a centrifugal clutch (which only couples when the motor reach a certain speed).
 manually remove a single spur gear mounted for the purpose.
 mount the wheels with some kind of locking system that can be released to let them spin freely on their axle.
 etc.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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