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Author Topic: Stepper motor / Servo Suggestion  (Read 1416 times)

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Offline Mike88Topic starter

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Stepper motor / Servo Suggestion
« on: February 24, 2011, 07:44:27 PM »
Hello,

I am looking to control the position of a throttle valve on a drive by wire vehicle (using an arduino board). The requirement would be for a motor have a fast enough response time and enough torque to overcome the release spring. The motor would also need to return to the zero position (with the help of the spring) when no voltage is passed through is case of an emergency.

Three questions I have:
1) Firstly which would be best for this application a stepper or servo. I am leaning towards stepper because I believe it rotates freely with no voltage (is this correct?).

2) My major concern is how much power the stepper will take. I am looking at the one below:
http://www.sparkfun.com/products/9238
Would something like this be able to run for over 30 minutes with constant use with a small 12V lead acid battery (14Ah)?

3) Would this stepper be able to be powered directly through the arduino board (I am using an arduino Mega)?

Thanks for any replies.

Offline klims

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Re: Stepper motor / Servo Suggestion
« Reply #1 on: February 24, 2011, 08:36:28 PM »
I would think if you used a stepper you would need an encoder/resolver to ensure the stepper hasn't missed any steps. Whatever the system, it should be closed loop.

Offline Soeren

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Re: Stepper motor / Servo Suggestion
« Reply #2 on: February 24, 2011, 08:46:33 PM »
Hi,

The requirement would be for a motor have a fast enough response time and enough torque to overcome the release spring. The motor would also need to return to the zero position (with the help of the spring) when no voltage is passed through is case of an emergency.

Sounds a bit dangerous to me, unless other means of safety is involved (Like a brake made like a Dead Mans Handle).
How much force (N/kg/Lb) is needed to press the pedal down?


Three questions I have:
1) Firstly which would be best for this application a stepper or servo. I am leaning towards stepper because I believe it rotates freely with no voltage (is this correct?).

Neither.
A regular gear head DC motor with a magnetic clutch to disengage the shaft in an emergency (loss of radio signal) would be a possibility.


2) My major concern is how much power the stepper will take. I am looking at the one below:
http://www.sparkfun.com/products/9238
Would something like this be able to run for over 30 minutes with constant use with a small 12V lead acid battery (14Ah)?

It takes 0.33A so it should be able to run it for (very roughly) 32 hours.
However, this stepper does not have the power to overcome a speeder pedal.


3) Would this stepper be able to be powered directly through the arduino board (I am using an arduino Mega)?

No.
You will need a driver no matter what motor you wanna run (except for an R/C servo which has got one built-in, but which I don't think will work).
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

Offline Soeren

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Re: Stepper motor / Servo Suggestion
« Reply #3 on: February 24, 2011, 08:48:48 PM »
Hi,

Whatever the system, it should be closed loop.
Why?
I assume it's being used like an R/C car, so the eyes and ears of the operator would give the feedback needed.
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

Offline klims

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Re: Stepper motor / Servo Suggestion
« Reply #4 on: February 24, 2011, 09:07:31 PM »
Why?
I assume it's being used like an R/C car, so the eyes and ears of the operator would give the feedback needed.
My thought was that either in a drive by wire or RC situation you give position input via the foot pedal or remote. If you were to miss steps then your position input might not actually represent what is happening in the system. Lets say you input the maximum position on your joystick and for whatever reason you miss some steps you won't actually be putting out full throttle. Your calibration would then also be out for neutral position.

 


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