Recommendations for steering

Community General Discussions
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1

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.

YG_Parts_011.jpg

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?)

 

2

I’m thinking DIY servo -

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.

3

1/4 scale

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

4

Wow! I had discounted

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!

5

Leave some room for error,

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

6

also, if you can’t get

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.

7

Thanks for all the

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.

8

Like this.

Like this.

Or this.

9

How to make your own servo…

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

https://www.robotshop.com/letsmakerobots/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.

10

which motor should i use

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!!

11

One problem with a wiper

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

 

12

Unfortunately, this item is

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

13

For the same price I can

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.

14

recomendations for steering

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.

15

Thanks. I was able to find a

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…

16

Glad I could help

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.