Geared Down Steering Methods

[BigKLaxer]

On my Power Wheels robot project, I'm currently trying to get the automated steering control working using this motor (http://www.allelectronics.com/make-a-store/item/DCM-276/5-RPM-GEAR-MOTOR-12VDC//1.html).  Since there was no coupler for the motor, I drilled and filed out a rudimentary one with some flat aluminum.  However, at 2 inches from the motor, it still does not have enough torque to move the steering bar pictured below.  While I do plan on eventually upgrading to a window motor with more torque, at the moment I'm looking for a quicker solution to get the car in working order so I can better test some sensors and code.


(Since the picture has been taken I've drilled a hole through the center of the bottom bar)

So my question is, what are some simple methods of gearing this motor down slightly and getting the pseudo-linear motion required to turn the steering bar.  Currently I'm considering something along the lines of a lever with a pivot point near the front with a short distance to the bar, and a longer lever arm in the back with a wide travel distance, somehow hooked up by wire or string to the motor.

Any additional ideas or help would be greatly appreciated, thanks!

[heinz357]

You could use an aluminium Vee pulley, of a small diameter, say around 20/25mm, mounted directly onto the output shaft, wind kite line/wire fishing leader/etc around it five/six times, pull tight and attach to both ends of the steering tie rod! 

 Mount tension springs to the ends of the cables, to fix them to the tie rod, and you have a gearbox saver, in case of the unexpected!

...hope this helps...

[Soeren]

Hi,

So my question is, what are some simple methods of gearing this motor down slightly and getting the pseudo-linear motion required to turn the steering bar.  Currently I'm considering something along the lines of a lever with a pivot point near the front with a short distance to the bar, and a longer lever arm in the back with a wide travel distance, somehow hooked up by wire or string to the motor.

Rack and pinion is the most obvious choice, but a simpler method is to use a rod with two 90° bends at the lower end and mount it so it's free to turn. The short end should go into the hole you made. This will give the largest change around the middle of the travel and less as you gets towards the extremes.

Any additional ideas or help would be greatly appreciated, thanks!

If you want to make an Ackermann steering, the two rods connecting the wheels to the steering bar should be made to point towards the midpoint of all 4 wheels, for a smooth steering.
They seem parallel to me and that won't give the right steering profile.

[BigKLaxer]

You could use an aluminium Vee pulley, of a small diameter, say around 20/25mm, mounted directly onto the output shaft, wind kite line/wire fishing leader/etc around it five/six times, pull tight and attach to both ends of the steering tie rod!

That's a great idea, thanks!

If you want to make an Ackermann steering, the two rods connecting the wheels to the steering bar should be made to point towards the midpoint of all 4 wheels, for a smooth steering.
They seem parallel to me and that won't give the right steering profile.

I hope to upgrade to differential steering as soon as I manage to find another set of Power Wheels motors and wheels, so Ackermann is a bit more mechanically complicated than need be for a temporary system.  Especially since I'm not very mechanically inclined, haha.

However, after talking to one of my MechE friends, it seems like a lot of the necessary torque is because the stability crossbars I made also cause a great amount of friction on the front two poles.  However, after talking and planning, it seems like a better balance between torque and stability would be to switch to a backwards tricycle design.  However, I'm still having some trouble with the steering module.  For starters, I feel as if it would be easier to switch to differential steering with a caster trailing behind, but from what I can tell from casters, it seems like it'd put up a fair bit of resistance, especially outdoors where I plan on driving the car.  My other option would be to add a rotating wheel in the back that could act to turn the robot.  Does anybody have any good examples of tricycle robot implementations?