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Author Topic: Rack and Pinion Help  (Read 2744 times)

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Offline VariousTopic starter

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Rack and Pinion Help
« on: July 05, 2007, 03:29:00 PM »
I am working on the steering system for my robot, I would just like some guidance on how to go about creating a rack and pinion type steering system.  The reason i chose this type of steering is because i only have one drive motor turning the wheels with a differential. I am working from an electric scooter frame, below are some pictures.










You can see a motor in some of the pics that i plan on using to turn the wheels.  How would i center the steering after turning?  Should i fabricate my own rack and pinion?  Is there a better way to do it?  Thanks for your advice.

Robot N00b Mike
« Last Edit: July 05, 2007, 03:32:08 PM by Various »

Offline sdk32285

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Re: Rack and Pinion Help
« Reply #1 on: July 05, 2007, 08:05:46 PM »
You can order a rack and its pinion (spur gear, etc..) from McMaster.com.To center it you can use sting pots, magnetic hall sensors, etc... to detect the center point.
Are you using a geared differential, if so how do you use the rack/pinion since you use the three or four spur gears with two axles to create the differencing effect.
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Offline VariousTopic starter

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Re: Rack and Pinion Help
« Reply #2 on: July 05, 2007, 08:09:27 PM »
If you look at the last of the photos, you can see the black motor attached to the silver looking thing connected to the axel.  Thats the back of the bot, the front is where the wheels need to be steered.

Offline Ro-Bot-X

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Re: Rack and Pinion Help
« Reply #3 on: July 06, 2007, 03:25:10 AM »
I would use 2 springs to center the steering bar. I would apply an PWM signal to gradualy turn the motor until the torque will get stronger than the springs pulling force and the bar will steer to one side or the other. To hold it at an angle, just send the motor a specific PWM signal that will equal the torque force with the springs pulling force at the desired angle (the motor will be stalled). To center, just remove the signal and the springs will auto center it. Use switches to detect the end of travel.

The only thing is that the motor might get hot if it is stalled for long times. You can build a radiator on the motor to disipate the heat.
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Offline VariousTopic starter

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Re: Rack and Pinion Help
« Reply #4 on: July 06, 2007, 10:55:29 AM »
Thanks for your ideas Ro-bot-x
Some questions!
Is that to be used in conjunction with a rack and pinion set up?
Is heat the only negative effect of stalling the motor?
Thanks

Offline Ro-Bot-X

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Re: Rack and Pinion Help
« Reply #5 on: July 09, 2007, 01:56:27 PM »
I don't think you need rack and pinion. As I saw in your pictures you have a bar connected at the ends to the wheels and in the center to a pivot. Connect to this pivot a sprocket and a chain to a motor and you're done.
Check out the uBotino robot controller!

Offline VariousTopic starter

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Re: Rack and Pinion Help
« Reply #6 on: July 09, 2007, 08:21:18 PM »
simple and genius thanks for your ingenuity.
:)
Mike

Offline Soeren

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Re: Rack and Pinion Help
« Reply #7 on: July 13, 2007, 08:59:43 AM »
Hi,

Take a look at this page: http://en.wikipedia.org/wiki/Ackermann_steering_geometry

The yellow bar in the illo is the rack, that you move with the (not shown) pinion.

But... Do you need Ackermann steering ?  How fast are you gonna go ?
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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