View Full Version : Driving a wheel

10-26-2009, 10:07 AM
I am currently building an auto-mower for my lawn. I bought some of these 10" wheels from HF.

I also bought some 135 watt DC motors from here ...

I guess the weight of the mower with batteries will be about 60 lbs at most.
I plan to have a left and right power wheel in the front with one swivel wheel in the back being pulled by the front power wheels.

So, any suggestions on how to attach a shaft and drive the wheels. I was thinking of directly coupling the motors to the wheel, not sure how the motors would take that. I also thought about a drive chain or pulley system.

The motors have a 3M pulley already glued on. I can get a belt but not a matching pulley so that probably won't work.
Any suggestions welcome. Also if anybody knows a parts suppliers that be good too.


10-26-2009, 10:23 AM
those motors are 3000 rpm and will require a massive downgearing to be useful, so direct coupleing is out.
Basicly your gonna have to do some math to figure out what RPM's you wish your wheels to go, and figure out what gearing turns that to 3000rpms at the motor

Insure a good deal of the weight is over the power wheels, or it may get stuck on rough lawns. (I have a self propelled lawnmower that has about half the weight on the smaller front wheels and it sometimes gets stuck and needs a little push)

I hope you have a good guidance system, a swivel tail wheel is not likey to stay very straight and the mower will likey drift side to side with every little bump if you just supply power equaly to the wheels, or spin them at the same RPM (Wheels WILL slip)

http://www.mcmaster.com/ these guys are likey who you can find your parts from.. but they are expensive.. -_-; they have everything, just expensive...

I think a chain would rust rather quick after getting choked full of wet grass and left. Of course I doubt grass does wonderful things for pullys either... but an autotensioner could compensate for debrie in the pully.

Roy Andrews
10-26-2009, 11:10 AM
i think i would put the castering wheel in the front and possibly go with 2. you want to run the motors near max speed and that would be close to 90 mph with direct drive. i would go with bike chain drive and get a couple junk 10 speeds to get chain wheels from. the rim bolts together so just make a hub with that bolt pattern to hold your chain wheels. have you thought about radio control with the two motors steering would be easy. mount a camera on the front and sit in the house and mow away. then you could go to steppers and write a program and mow from work. you could even teach it to plug back in. i can see this in the future gangs of robotic lawn mowers going out at night and mowing the whole neighborhood. i have to stop now, my mind has ran away and i have to catch it.

10-26-2009, 11:20 AM
Yes, I thought about the bike chain. That would probably be the easiest. In another life I was a programmer so software and electronics are easier for me. Right now I have microprocessor talking to this radio module.

I was thinking about a home grown GPS system for my back yard :)

I also have a decent design for an H-Bridge I am going to use with PWM to drive the motors and attach some kind of optical or physical encoder to the wheels or motor for speed control.

I am relativly new to machining but I have a decent lathe and mill to fabricate parts for the drive system if needed.

Thanks for the suggestions.

Pete F
10-26-2009, 11:58 AM
Please post progress on this. I found my way here through an interest in building small robots (although I am still a rank amateur) and this sounds like an interesting project, and quite similar to my long-term goal for my current project, sans grass cutting. I'm looking to create a small robot that can repeatedly navigate a smooth floor environment, and sense obstacles. I want to try out some ideas I have on adaptive navigation and shortest path calculation in a real world, changing environment.

Plus, I just like to see them drive around. :D


Pete F
10-26-2009, 12:12 PM
Please post progress on this.

Um, I suppose if I'm asking for progress updates, I should at least provide some of my own.

I've prototyped the circuits for a simple motor driver connected to an IR object detector, according to advice and instructions from http://www.amazon.com/Intermediate-Robot-Building-David-Cook/dp/1590593731/ref=sr_1_1?ie=UTF8&s=books&qid=1256573114&sr=8-1, and am ready to move on to constructing the chassis. However, I want to practice my machining skills with a couple of other projects first, so the robot is on hold.

Once I get the simple object avoidance working, I plan to install an arduino board and try out some more advanced logic.


10-26-2009, 12:17 PM
If the motors/battery have sufficient torque to start the fully-laden mower then you should be able to get away without gearing and just use feedback to control the speed.

10-26-2009, 12:31 PM
The batteries have plenty of juice. 12V 20Ah deep discharge.

EVX-12200 is designed specially for electric vehicles, such as electric golf cart, electric wheelchair, mower, dust collector etc. It has high cycling life, high efficiency and long service life.


10-26-2009, 12:39 PM
Why not get the drive system of a junked or used engine-driven self-propelled mower? That engine runs about the same speed as you motor, and all the parts are are configured for the harsh environment they'll be working in.


10-26-2009, 03:54 PM
I've used the wheels you have listed on 120lb robots. by removing the bearings and filling the holes with an aluminum bushing dto addapt to a shaft. Use a 5/8" shaft and you can reuse the bearings to support the shaft.

we use this motor http://andymark.biz/am-0255.html concected to a 12.75:1 http://andymark.biz/am-0145.html gear box that then drives the wheel through about a 2:1 roller chain.

More than fast enough for a mower and good tourqe. You'll may even want it slower.

Look at photos @ Hawkeyeindutries.us and more detailed pictures @ projectneo.net

10-26-2009, 07:37 PM
concected to a 12.75:1 http://andymark.biz/am-0145.html gear box that then drives the wheel through about a 2:1 roller chain.

I like the gear box idea. Anybody know of any plans or apps that would help me make a gear box from scratch ? After all I do have a mill and a lathe :)

Actually that website has about all you would need to make your own gear box.

10-26-2009, 09:20 PM
You will definitely need a speed reduction of some kind. Those motors are going to be overloaded if they can't turn at least 2000 rpm under load, with the rated voltage of 24 volts. If you plan to use 24v, then figure out what the wheel speed is going to be, then calculate the ratio needed. You'll probably be able to get up to about 10 to 1 with a single pair of gears, but that's pushing it for commonly available spur gears. You might have to use three gears in a gear train, and you'll probably be able to get up to about 20 to 1. Going to a worm gear you'll be lucky to get down to about 20 to 1. The worm gear set won't freewheel like spur gears can, so you need to make a choice based on whether you'd ever need to push the thing if no power was available, like if the battery died for example.

I wish they'd publish specs for motors under rated load, which would suggest what rpm they would be turning if operating at rated power. In other words, at what rpm are they working in an efficient way for their maximum continuous power output. That's the rpm you need to put into the equation to determine what step-down ratio you need. I've suggested 2000 rpm for that motor which is rated at 3000 rpm, probably unloaded, with 24v input.

10-26-2009, 09:45 PM
Actually I was thinking about buyinng some of these gears
http://www.grizzly.com/products/G4000/parts/5 (16T)
http://www.grizzly.com/products/G4000/parts/2 (127T)
That would give me an 8 to 1 ratio.

or I could piece something together from these guys

This is the manufacturers website for the motor.
http://en.unitemotor.com/ProductView_34.html Looks like rated speed is 2800 RPM.

The motor was for one of those kids two wheel electric razors.

10-27-2009, 10:16 AM
If you have a lathe, a really easy DIY choice is a belt drive system as making V pullys on a lathe is really easy and fast. making your own gears without a CNC while doable, is a tedious process.
For your drives you might want to find some smaller then standard belts however.

10-27-2009, 01:06 PM
Yes, I would really like to get a 3MM HTD Belt and 6 or 8 inch pulley. I found fifty websites that sell them but nobody post prices :confused: Seems strange to me. The motor came from a scooter and it already has the pulley. That would really make it simple for me. I am not sure how to calculate speed with a belt and pulley system though ? I'll keep looking on the net.