Looking for low voltage DC motors

[Oldblock]

Hi folks,

I'm building a gardening cart for my invalid wife and am looking for something to power it.
Anyone know of an outfit that sells or services anything that uses DC motors?

Australia only please (That narrows the field a bit)

Ray

[DavidG]

Windscreen wiper motor.

[Cliff Rogers]

G'day.

Check out the 4WD shops for winches.

Also check out bosting places for the same sort of thing.

[glenn k]

wheel chair motors.

[echnidna]

Wiper motor is a good choice as they have heaps of torque.

A winch motor would work but might be overdoing it to the extent that the high current drain could need a huge battery in the cart.

As you don't need a high speed cart another alternative could be a 12 volt cordless drill wired to a car battery.

[Oldblock]

Thanks guys,

I have a couple of wiper motors, I didn't think they would have enough grunt but I'll try them out.

Winch motor might be the way to go, sure they draw a lot of current but surely this would only be when they are working hard.

Wheel chair motor is what I had in mind but haven't been able to source Oz maker.

Cordless drill. I would have thought it wouldn't have been up to continuous duty.

Anyway, you have given me food for thought and having chewed on it I can see I have a bit of experimenting to do.

Incidentally does anyone know of a forum for engineers/ model makers etc. they might have some ideas.

Ray

[BrianR]

Winch motors are series wound. They have loads of starting torque and draw huge current to get it but then they will go faster and faster if run unloaded. Very poor speed regulation and unsuitable for this job.

You'll not beat wiper motors for performance and cost but they will probably be short on torque for your application. You could use 1 per wheel but the control will be difficult. Wheel chairs use PWM drivers to get speed control and you might be better off getting a second hand one unless you're good at electronics.

[Oldblock]

Thanks BrianR,
Wiper motors - my thoughts exactly, PWM let me guess Pulse Width Modulated?
I could probably modify my application to suit wiper motors, had been toying with steerage by using a drive to each wheel and varying speed. I can see me spending more time experimenting with electronic steering control than building the drive system.

I'm a pro woodworker but rank amateur at engineering and electronics.

Thanks for comments anyway, you have helped to steer my thinking and probably the cart.

[Dan]

Hey Ray, check out the Silicon Chip Magazine back issues for some ideas (if you haven't already). PWM circuits are dealt with in their remote control section and they have done at least one project on a high current DC speed control (50A).
http://www.siliconchip.com.au/

[BrianR]

OldBlock, this is a link to a low cost pulse width modulator motor driver kit for $16USD. http://electronickits.com/kit/complete/motor/ck1400.htm
It is limited to 5A and 60V however. A few years ago I designed a closed loop servo using 12V windscreen wiper motors and remember that drew 12A if you stalled them. If you have no luck with another driver and decided to try this one then a clue would be to use truck motors rated at 24V as this will halve the current and a 5A 60 V driver starts to look possible.

[echnidna]

Is variable speed necessary in a garden cart and the associated fooling around with electronics. I would be inclined to get the cart going first and try it out before you decide whether or not it needs to hurtle around a garden at high speed. Most wiper motors are 2 speed anyway so you can get 2 speeds without electronics.

Some years ago when I was an Auto Electrician I measured the torque of a wiper motor at around 70 to 80 inch pounds. The motor had a no load speed of 70rpm. It was a common old motor so it would have been a holden, falcon or valiant wiper motor.

Theres no reason why 2 or more motors couldn't be mechanically connected with belts or chains etc to give more torque if you need it. or even fit a roller in place of the crank and just let the roller ride directly on the tyre. I suspect however that you will find 1 wiper motor will have enough grunt for the job if you use a suitable gear ratio.

[Oldblock]

BrianR & echnidna,

Thanks, good practical advice. I like the idea of wheel rim drive. It couldn't get much simpler and I am encouraged by the torque numbers.

Now where did I put those wheels?

Ray