RC Mobility Scooter / Go-cart / Truck...

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Minifig666

Senior Member
Hi Guys,
As always, I have grand plans but not all the knowage to complete them. So my question today is... How powerful would a motor need to be to move a wooden go-cart (with a person on it) around?
It is to be 2 wheel drive, with both an onboard arcade joystick to controll the movment when it is being used as a 'car' probably an X-Bee remote controll for use as a truck, and of course has a PICAXE brain.
Where would be a good place to get these motors? And what sort of price should I be expecting for them?
Thanks in advance. :)
 
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papaof2

Senior Member
The simplest answer is to use something designed to move a person around on wheels. The most readily available units are motor + gearbox from an electric wheelchair. Used units are around $130US http://cgi.ebay.com/ELECTRIC-WHEELCHAIR-MOTORS_W0QQitemZ290411458730QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item439ddf30aa

If there is a shop near you that does wheelchair repair (usually near orthopedic/spinal clinics), you might find a good deal there.

Smaller motors (PowerWheels ride-on toys for kids) don't have the power or the gear strength for moving most adults - a pair of the motor/gearbox units has a maximum load of 120 lb. Four of these might work, but the mechanical mounting may be awkward.

John
 
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Rickharris

Senior Member
Stand by to go into shock!

As always a lot depends.

e.g.

how fast do you want to go.
On level ground?

What sort of range / battery life do you expect.

inside / outside (inside perhaps could use a trailing mains lead (I don't even want to go into the safety aspects!)

Our school racing car which could do 30 or 40 MPH for 2 hours on 2 car batteries used a 250 watt wheelchair motor obtained from FANUC. They cost just short of £200!!!

You may get an old disused mobility scooter but they tend to be pricey £100+ unless not working then not a lot of good for your project.

If slow speed is OK - you may get some mileage out of a lorry 24volt windscreen wiper motor from a scrap yard - even that may be surprisingly expensive.

BUT be prepared for a LOT of engineering to get it all working. Months in fact.
 
premelec

premelec

Senior Member
If you don't need to go very far very fast a couple of DC electric drill units driving bicycle sprockets and chain to wheels [reduction gearing] could get you started... on that long path to success!
 
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Minifig666

Senior Member
Thats convenient, one of my dads drills just broke. We checked it and it was just the gearbox that was broke. Only problem is its 18V so its going to be awkward to power.
 
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vttom

Senior Member
Or how about salvaging a motor from an old treadmill? If you're going to use something a la rack-and-pinion steering, then you only need 1 motor + a differential gearbox. If you want to use "tank turning", then you'll want 2 motors (that how most motorized wheelchairs work because you get zero-radius turns that way).
 
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Minifig666

Senior Member
I think I may go the 'tank turning' way, steering may be a bit awkward to engineer. A couple of trolley wheels at the front is much easier than trying to motorise a rack and pinion system.
 
premelec

premelec

Senior Member
Note Minifig666 you DO need the gear box on the drill to do initial motor speed reduction - you won't get much torque from just the drill motor...
 
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Minifig666

Senior Member
Yeah but if I use a big enough gear reduction (my dad is conveniently also a cyclist) with bike gears then it should be ok... I think.
 
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tjetson

Senior Member
This seems like a really interesting idea (using drills). I hope that when everything works, you're able to post your finished ideas over on the finished projects board.
 
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Andrew Cowan

Senior Member
I'm not so sure. An ungeared 18v DeWalt drill motor has a very high rpm - 22,000. The output of the gearbox in the drill (in low gear) gives you 650rpm - if anything, a bit too fast to go straight to the wheels.

If the gearbox is dead, you'll need to get a 33:1 reduction using spokets and chains - that would need something like a 10 tooth sprocket and a 330 tooth sprocket. Not feasible/possible.

With multi-stage gearing this can be done, but it's pretty complex as Rick says.

A
 
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Wrenow

Senior Member
Minifig666 said:
I think I may go the 'tank turning' way, steering may be a bit awkward to engineer. A couple of trolley wheels at the front is much easier than trying to motorise a rack and pinion system.
Click to expand...
Why worry about motorizing a rack and pinion? Just use the good old fashioned lever system. You can operate it with a linear servo (though they are not inexpensive) one source is http://servocity.com/html/heavy_duty_linear_servo__25__l.html

Or a regular heavy duty industrial servo where the ball-joint in an old fashioned steering wheel box would be.

A worm gear would be a compact way to reduce the speed for the wheels.

If you are looking for cheap - you might consider windshield wiper motors for the wheels. Tank-steer will require stouter motors, methinks, than wheel-steer (the motors have to overcome each other and friction on turns).

Cheers,

Wreno
 
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Minifig666

Senior Member
Just messin with the drill, I dissembled it hooked it to my ATX and set off the short protection! I tried it again with an unprotected one and not paying attention to polarity it worked on all the speed, torque, and direction settings! I then burnt myself on the controller! Ow... but noticed that I'd messed up the polarity so I reversed it and it stopped working on all of the settings, the gearbox simply made a grinding noise. Can anyone workout why this is?
Also what does anyone think would be the best way to interface a PICAXE with said controller?
 
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Rickharris

Senior Member
This is just my humble opinion but your barking up the wrong tree the drill motor will not do what you want - i.e. move a cart + person at 30MPH -- see my instructable on bulding an electric racing car http://www.instructables.com/id/Building-an-electric-racing-car/- It took 250 watts to move anything like a heavy vehicle to carry a person at 30 mph.

Our racing car was built of aluminium and weighed about 70 pounds without batteries + motor. + the driver a young puply weighing perhaps 8 or 9 stone (114 to 128 pounds) This is not a trivial task and the motor controller interface is the least of your problems at this stage.

If you MUST do tank steering then i would go to relays because a 250 watt motor may pull upto and over 70 amps - the value of our safety breaker - and they blow.

Mechanic steering and a single motor makes both cost and practical sense. There are posts bout converting a windscreen motor to a servo with picaxe control.

you need to do a LOT of thinking and planning before you expend time and effort and money on this project. Our budget in our final racing year was about £1500 to build a new car from scratch.
 
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pyrogaz

Member
I can't find any mention of a target speed, if you want it to reach "exciting" speeds of maybe 25mph upwards then the challenge is significantly different from say a load carrier around the garden at speeds of just a few mph.

For instance if only low speeds are required worm gears are ideal as they give very low gear ratios and remove the need for brakes, in this case tank steering would also be perfectly feasible and power requirements may well be less than 100W per side.

For higher speeds you need to appreciate that a single gear design has a very narrow operating window in terms of speed unless you introduce some form of current limiting to prevent your motor becoming a smoke generator. That's why it's very important to get the gearing right, you probably need to be looking at a reduction ratio of anywhere from 4:1 to 10:1 depending on motor, wheel diameter, weight, etc, these sorts of ratios are virtually impossible with cycle sprockets.


A quick search on Ebay reveals numerous suppliers of electric scooter parts, £25 upwards for a 24v motor, £30 for speed controller but quality is likely to be variable at best! You can also find suitable sprockets on there to give realistic gearing.
 
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Minifig666

Senior Member
Yeah, frankly I was looking more on the load carrier end of things and, unless I could get more speed easily, nothing more than about 10 MPH (mi/h as my science teacher says). Of course at the age of 14 the speed would be nice but not necessary... The cheapest 70A relays digikey have where £175-ish so that's the H-Bridge out the window. (Two 40As from Maplin may do the trick for £5).

I'm about to set on with a scale model with DC 'toy' motors (it will probably end up going faster than the real thing using those cheap things) after I've finished this blinking homework. (Does anyone know what happened at the great debate of 1920? LOL) As tjetson suggested I will upload that as a project too. LEGO time! Yay!
 
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Minifig666

Senior Member
Thanks for these links, will definitely have too look into this. Unfortunately our scrap yard has long gone ='[, so it looks like a trip to Gisborough.
 
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dazarooney

New Member
Minifig666 said:
Hi Guys,
As always, I have grand plans but not all the knowage to complete them. So my question today is... How powerful would a motor need to be to move a wooden go-cart (with a person on it) around?
It is to be 2 wheel drive, with both an onboard arcade joystick to controll the movment when it is being used as a 'car' probably an X-Bee remote controll for use as a truck, and of course has a PICAXE brain.
Where would be a good place to get these motors? And what sort of price should I be expecting for them?
Thanks in advance. :)
Click to expand...
Did you manage to do this in the end, I'd be interested to know?
 
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