Let's Make Robots!

Recommendations for steering

I'm building a yard bot. The initial blog is posted for my Yard Gnome already.

This robot will steer like a car, with one drive motor pushing two rear wheels, and a two-wheeled steering mechanism up front.

I'm looking for recommendation for how to automate steering on this thing.

Is there an affordable servo that is strong enough?

Should I build my own servo?

How about linear actuators? I've heard they are kind of slow. This bot may go up to 5 miles per hour.

Maybe I'll need a powerful stepper?

Or perhaps a simple geared motor with limit and position switches?

WWLD (What Would LMR Do?)

 

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

I'm thinking DIY servo - chunky gear motor with potentiometer feedback to ADC. Maybe a home and left/right limit switches too, to save on manual calibration.

Like this.

Or this.

Google 1/4 Scale servo. That should be all you need. You can also look for "Sail servos" they are wicked strong as well.

Wow! I had discounted servos, but there are some REALLY strong ones out there and the prices are not too bad. I'm going to make some load measurements tomorrow and see how much torque I really need.

Thanks, CtC!

Leave some room for error, servo torque ins't always true, i have ''capable of lifting 15Kg" it lifts 11... it was 10$ though...

also, if you can't get enough torque out of the servo or want to turn faster, you could use a hybrid differential drive kind of thing. I think you're saying you have two motors on the front? You could make one go slightly faster than the other.

Thanks for all the suggestions. After some more research and though, I think I'm going to try a DIY servo. The trick is, I'll use an old servo mechanically linked to the steering mechanism as my feedback. So all I need is a decent sized gear motor that I can control using the guts of an old servo.

As the motor turns the steering, the arm of the old servo will also move, and we'll have a feedback loop.

I just remembered this one going by. You know, there really is everything you need here at LMR!

http://letsmakerobots.com/node/2653

Link is for the "Giant servo kit" (of which an even stronger version is available) that will allow you to turn any gear motor and any pot into a big-ass servo! I'm thinking power window motor or winshield wiper motor --I have seen a lot of these type of motors go by around here with good results.

Unfortunately, this item is no longer available! Rats, that would have been perfect!

I am new to LMR but I remember an article in servo magazine about one of those childs cars that they can drive in the yard, the author of the article modified it to be autonomous and steered using elec motor/threaded rod/limit switchs, i'm on vacation so I can't tell you which issue it was in 2009 though. I hope this helps you,  good luck!!