Salvaging a DC motor for a childs go cart?

[Gerard]

Hi All

I'm looking to build an electric go cart for my nearly 7 year old, who is very keen on such a toy.

I was wondering if some of you might have some insight into what kind of appliance / machine I might pull off the side of the road to scavenge a suitable DC motor (the council cleanup is happening in my area this weekend)?

I'd be looking at something that might get a cart up to a slow jogging pace with a 30 kg child in it.

A quick web search suggested car starter motors might be the go (though I don't expect there'll be any abandoned cars for the council clean up :)

On a related topic, if I wanted to control the motors speed I'd guess I'd hook some kind of potentiometer up to a TRIAC of some sort (my electronics knowledge is kind of limited)?

Thanks

Gerard

[Angus Deveson]

Council cleanups are still a thing? They stopped doing those in my area ages ago in favour for 'on call' services... :(

You really want a DC system and there's not much in the normal household that will haul a 7yr kid around, there are 'kiddy carts' which have a cordless drill size motor in them but would be slow and lame at best. If you can find some old discarded 'razor' electric scooters they'd be a good source for one of these all in one units. 

Personally I'd go with one of these chained to a few super cheap auto trolley wheels and a bank of SLA batteries.

For speed control you need something beefy that can take the voltage - e vehicle controllers are notoriously rubbish but you might get by with this one if you go with the 100W razor motors.

Another, better option is to use a robotics speed controller and a 'servo tester' to control it - ie this and this. Also an in line radio controlled 'kill switch' would be good to have to prevent any runaway kids...!

[Gerard]

Hi Angus

The price is right on the motor from Oatley Electronics you linked to.

I suspect I'll hunt about the council cleanup and then decide to buy something like you suggested.

The radio controlled kill switch will also be a feature :)

Thanks

Gerard

[Aaron Power]

Each year my Cub Scout pack joins in with the District Billy Cart Derby. There are very strict rules on what is allowed for the Cubs’ billy carts, but us leaders sometimes “bend” the rules. A few years back I built an electric powered billy cart using one of the 24V motors from Oatley, chain driven to some hand trolley wheels and a motorised scooter speed controller.

 

It was great fun driving my billy cart around the (flat) marshalling area with all the kids yelling “That’s not fair” and “You’re cheating”. It also won the leader race J

 

It was able to drive around a 90kg guy, and the billy cart itself was fairly substantial – all up, cart and I would have tipped the scales at close to 120kg. However it was really only able to drive on relatively flat or down hill terrain. When I pointed it up the main hill, it stalled and the speed controller started getting hot. Still it served its purpose of stirring up the Cubs.

 

Have fun with building it!

 

Regards,

Aaron

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[Peter McC]

Hi

On Thursday, July 11, 2013 12:01:59 PM UTC+10, Gerard wrote:

On a related topic, if I wanted to control the motors speed I'd guess I'd hook some kind of potentiometer up to a TRIAC of some sort (my electronics knowledge is kind of limited)?

If you're using a DC Motor a TRIAC controller won't work - you'll need a proper DC Motor controller. TRIACs are only good for AC.

Peter

[Max Nippard]

There is a  jaycar DC motor speed controller kit at the space.
12-24v 40amp from memory.

[ada]

On Friday, July 12, 2013 8:23:29 PM UTC+10, Max wrote:

There is a  jaycar DC motor speed controller kit at the space.
12-24v 40amp from memory.

It was salvaged for parts due to being rubbish design.

 

[ada]

On Thursday, July 11, 2013 12:01:59 PM UTC+10, Gerard wrote:

I was wondering if some of you might have some insight into what kind of appliance / machine I might pull off the side of the road to scavenge a suitable DC motor (the council cleanup is happening in my area this weekend)?

I'd be looking at something that might get a cart up to a slow jogging pace with a 30 kg child in it.

I was meaning to show this to tim, but this thread is apropos:

http://www.etotheipiplusone.net/?p=2730

Some thoughts:  

a slow jogging pace for an adult is in the order of 3m/s.   

On level ground, you should be able to maintain that with negligible power on a not-too-inefficient device (eg you can easily go 8m/s with in the order of 200W human power input on a bicycle).

I'll have to see how fast one of those 100W motors drives a 90kg adult.

[Madox]

I glanced through the link, is there any handicap for the driver's weight?  Or I need to jockey or a baby to drive it? :P

Mmmm baby...

[Gerard]

I read all of the 'How to build you everything' instructable and and found it quite illuminating. Thanks for posting that.

I'm looking at the following from Oatley:

http://secure.oatleyelectronics.com//product_info.php?cPath=53&products_id=192&osCsid=sf209ips7c9929fbm33k69coh6

The fact that it is already geared and has a bike chain sized sprocket means I ought to be able to simply chain it to a sprocket on the back axle.

I'm guessing the full 250 watt may in fact be overkill for the child but imagine that I can set up the speed controller to limit the maximum power (perhaps reducing the limit as the boy gets bigger and less prone to collisions :)

And I still think Angus' remote kill switch will be a must.

As well as a brake, but I expect I can use a bicycle disk brake or something similar.

Gerard