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?)

 

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One problem with a wiper motor is that just about all of them are built for chassis ground systems. I'm not sure I want that for Yard Gnome.

I found this nice 24VDC geared motor on eBay:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=300372429085&rvr_id=&crlp=1_263602_263622&UA=%3F*I8&GUID=dcc93eaa1280a0aad5b1e4a1ff81d84b&itemid=300372429085&ff4=263602_263622

Horse Power Cont.

1.5 W

Length of Motor Body(excluding spindle) (BL)

50.2mm

Gear ration

1:200

Full Length of Spindle (SL1)

14.0mm

Voltage & Current

24 V DC

Length of Spindle (SL2)
12.0mm

RPM

30

Length of Spindle Flat(SL3)
10.0mm

Reversibility

Reversible

Diameter of Spindle (SD)

4.0mm

Length of Motor (including spindle)

64.2 mm

Height of Spindle (no a flat ) (SH)

3.5mm

Diameter of Motor (D)

25.0 mm

Center Distance of Mount Hole(H)
16.8mm

Torque

41 LB-Inch

It'll only cost me $20 including shipping. Think that'll handle the job? I'll still need an h-bridge to drive it, and a servo controller (purchased or hacked from an old servo) to control it.

 

Regards,

 

Andrew

 

For the same price I can also get the same motor at a different gear ratio that delivers 60 rpm and about half the torque.

I did a quick check and one "high torque" hobby servo has a 6V speed of .18 seconds/ 60 degrees. This translates to 64.8 rpm, so I think a motor that turns about 30-60 rpm is in the right speed range for the steering servo. I just need to decide if I want more like 40 lb-in of torque at lower speed or if 20 lb-in is enough and get more speed.

Yard Gnome only goes about 5 mph, so maybe the lower speed steering will be OK and I won't have to worry about an underpowered steering under heavy load.

Hi, I looked up that article in servo magazine, it was April 2008, the article has a lot of information you could use in your project.

the author used a BS2 stamp as a controller, for steering he used 2-sm ball bearings/length threaded rod/2-switches/2-hall effect switches/3-magnets/2-relays/1-motor w/2 gears (from battery drill). I don't know if its legal to post the article on this site, maybe I could email it or something.

Thanks. I was able to find a copy of the article online. The approach is very different than the one I am trying. I will keep this article handy for future reference. If my idea doesn't work out, it will be the very near future...

I dabbled in "robotics" off and on over the years, when i had the time & life wasn't getting in the way. I recently started to be more serious about it, when i get the chance I'll post a couple of projects i'm working on myself. Good luck with yours.