Author Topic: Turning the front wheels of a car  (Read 2485 times)

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Offline DaaniiTopic starter

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Turning the front wheels of a car
« on: February 20, 2010, 06:13:29 PM »
This stretches the definition of a robot a bit, but I plan to replace the steering linkage of a car with some linear actuators. Then steer each wheel independently. (This will be an off-road vehicle used only in good conditions. More for testing and development than use.)

Measuring the steering knuckle and related parts, I need about 30 centimeters of travel. Travel time will ideally be 3 seconds or less, but 5 seconds would work. I'm not sure about the required torque yet.

It's hard to find linear actuators that would work. Am I being unrealistic in planning to use them? Any other suggestions for doing electric, independent steering?

Thanks.

Offline nottoooily

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Re: Turning the front wheels of a car
« Reply #1 on: February 21, 2010, 12:28:38 AM »
I bet you can find an industrial pneumatic or hydraulic cylinder to do it.

It's still electric because you'd control it with a solenoid valve and have a sensor for feedback.


Offline DaaniiTopic starter

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Re: Turning the front wheels of a car
« Reply #2 on: February 21, 2010, 01:51:52 PM »
Thanks for the suggestion. I'll take a look at those kinds of cylinder. As you say, they are electric enough for my needs.

Offline DaaniiTopic starter

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Re: Turning the front wheels of a car
« Reply #3 on: March 11, 2010, 11:34:35 AM »
I looked into pneumatic and hydraulic cylinders. They are hard to control linearly. Looks like an electric linear actuator is the best bet. I've seen one that might work -- a Linak LA36. Hobbyists use it to control a chair in simulation games. But at just under $1,000, it's very pricey.

Offline nottoooily

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Re: Turning the front wheels of a car
« Reply #4 on: March 12, 2010, 06:35:10 AM »
Ouch, tho I'm not suprised, you're probably paying for excessive reliability.

But hey for a really low cost idea, how about just add a 2nd power steering rack for the other wheel?




Offline DaaniiTopic starter

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Re: Turning the front wheels of a car
« Reply #5 on: March 18, 2010, 01:58:22 PM »
Unfortunately, that won't work for me. I need something that will take two inputs -- a digital signal and electrical power -- and turn the wheels. No mechanical force from the driver will be available to feed into a power steering rack.

Offline waltr

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Re: Turning the front wheels of a car
« Reply #6 on: March 18, 2010, 06:59:33 PM »
Ouch, tho I'm not suprised, you're probably paying for excessive reliability.

But hey for a really low cost idea, how about just add a 2nd power steering rack for the other wheel?





And place a large servo motor on each power steering shaft. The power steering unit would be mechanical amplification so the servo would not be as expensive.

Offline Soeren

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Re: Turning the front wheels of a car
« Reply #7 on: March 18, 2010, 11:37:01 PM »
Hi,

[...] you're probably paying for excessive reliability.


[...] I plan to replace the steering linkage of a car with some linear actuators.


Excessive reliability?  ::)
I doubt that is something that can be found in a car  ;D

With Linak, you're paying (through your nose) for Danish design and reliability   ;D   ;D   ;D
Seriously, they're so darned reliable that you can buy used ones and know they are still good to go (if not damaged in any way of course).

Here's one on eBay (that probably won't fit the bill, but do a search for more - there's usually plenty.

Remember that you need much more power than what it takes to move the wheel(s), in case the wheel hits a curb or similar.

Why not keep the rack and pinion and use just one motor (with a heavy duty worm gear)?
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 DaaniiTopic starter

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Re: Turning the front wheels of a car
« Reply #8 on: January 27, 2011, 10:49:02 PM »
I'm back working on this project. After hearing some suggestions here, I've abandoned the linear actuator approach, and taken the suggestions. (Thanks to those who made them.)

Instead of linear actuators, I'm planning to use the existing steering linkage and gearbox for the left wheel. I'm going to disconnect the existing steering linkage for the right wheel. To turn the right wheel, I'll go to the junkyard and get another steering linkage and gearbox. So I'll have an independent steering linkage and gearbox for each front wheel.

I'll need two motors to turn the gearboxes. I'm trying to find motors that would work. As Soeren says, they should be heavy duty. They'll need to turn the shaft that the steering wheel turned before. If I recall correctly, that's about four revolutions lock left to lock right.

Any suggestions on motors? I would like to scavenge them from something, but I can't think of what other device might have a motor that would work. Maybe some sort of forklift?
« Last Edit: January 27, 2011, 11:20:25 PM by Daanii »

Offline Soeren

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Re: Turning the front wheels of a car
« Reply #9 on: January 28, 2011, 07:17:36 PM »
Hi,

Not too sure about the torque vs. speed possible, but wiper motors may be a possible candidate, perhaps geared down a notch or two (could be done through a chain drive or similar.
I guess you could measure how much force it would take, worst case on a high friction surface at standstill and then add some 50% or so for curb hitting stamina and such.

The gearbox on the linkage will help some by reducing the hits to a wheel getting through to the motors you add.

If you could install power steering, much less power would be needed of course.


An interesting project, don't be shy with the camera :)
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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