So, the story so far is that I've wanted to build a fairground dodgem with some kind of petrol engine for a few years to take to Le Mans.
However, it seems dodgem shells are quite hard to come by in that in a couple of years of scouring eBay I've been unsucessful, at least for a
sensible price.
The idea was always to use a mobility scooter chassis, the front end at least, and squeeze it under the fibreglass dodgem body to create the car, but
somewhat inspired by this video I'm intending to ditch the dodgem part (for now at least) and build a petrol powered scooter. With a couple of
baguettes and a string of garlic in the front basket it should make for good Le Mans campsite transport.
Now unfortunately my father was a geography teacher, not a mechanic/engineer/anything of the sort, so I missed out on the whole 'build a
go-kart' thing when I was a kid and cut my teeth when I was 17 by taking my Fiesta apart. Somehow I think car running gear will be a bit too
big for this project, so I'm turning to the forum for some go-kart experience.
...although not that one as it's missing all it's bodywork, but the auction has a bunch of photos of the scooter chassis to give an idea
of what these things look like underneath. I assume I'll need to replace the engine back end as that aluminium housing arrangement is designed
to go 8mph under electric power and probably isn't going to like having a whole load of power shoved up it's backside.
But, first things first, I need an engine. The one in the video has a Honda CR125 engine which seems to push it along pretty well, so I guess
that's a good place to aim. However, I understand that it's water cooled which seems like a lot of unnecessary effort. Clearly whatever
engine I choose needs to be quite low profile so that it will fit under the rear bodywork. I don't mind chopping it a bit, but I really want
the finished product to look, at a quick glance, like it's a completely stock mobility scooter. So, what suggestions do the LB collective have
for an engine for it?
Next I'm worried about the back axle. I assume it's got to be a solid bar rather than a tube, and I'll need a bearing at each end
to support it, perhaps another next to the sprocket to help with the load? I guess some kind of bearing in a housing like this is the answer?
Assuming that's correct, is 25mm sufficient for a rear axle? Do I just use plain steel bar or is there something special to buy?
I assume that the axle just pushes through the centre hole in the bearing, but how do I stop left-right movement of the axle? Will I have to have
someone cut a groove into the axle (on a lathe) and have a circlip type arrangement or is there some trick to this?
How do the wheels and sprockets fix to the axle and no rotate? Is there some kind of fixing I can buy off the shelf to do this?
From looking at pictures of go karts it looks like the rear axles have a ridge in them, kind of like a woodruff key on a camshaft. Is this the key to
understanding how to put all this together?
the trike idea using a twist and go moped sounds like a great idea
or there are loads of easy to get kart bits that would make a very good base, they are very easy to work on, solid rear kart axles have 4 key slots
machined in them two for the hubs and one each for sprocket and brake carrier.
maybe try and pick up a cheap cadet kart to rob for parts
A kart will be far too wide for the scooter chassis though I'd expect. I guess I'll need to have an axle made up specially if it needs to
have slots machined in it.
Shortening a kart axle wont be a big deal, at worst you might have to add a keyway.
Kart axles are located by grub screws through the bearings that push onto the axle.
That looks good, thanks Fred.
I've been doing some reading too. Do I need to have indents machined into the axle for the grub screws to locate in or will they grip
sufficiently as they are?
Shortening the axle wouldn't be difficult if I had the right kit. I guess I'll need someone with a lathe!
One other dumb question... how do the keys stay in place? The axles I've seen pictures of have long keyways, so surely the key could slide
out?
Older (and small) karts use 25 mm axles, with a 5 or 6 mm grub screw. We used to use a drill point (just pushed through the hole in the bearing as you
fitted the axle) to put a slight recess into the axle at the point where the grub screw bottomed.
New karts that used 40 and now 50 mm axles (sometimes very thin walled) and 8 mm grubscrews were fine without a recess, the grub screw has a raised
lip on the front face that grips into the axle. Below is a pic of a modern kart with a big axle. You can see the grub screws.
The keys need to be long enough (cut from lengths of key stock) to not be able to slide out from under whatever they are locating (wheel hub, brake,
or sprocket), on older 25 mm types. A dodge is to pull a cable tie tight over the key, if it is too short.
Newer karts have keys that have locating dowels sticking out that go into holes in the axle.
Shortening the exle need not be any more complicated than just cutting it off with a chop saw, and dressing the end with an angle grinder as you test
run your creation on a stand (with the wheel off). It not like anything locates on it. Karts are designed to have an adjustable track by sliding the
hubs in or out on the axle.
When I built the bar stool I was lucky enough that I did not have to add any keyways, the existing ones in the axle I had fell to suit the new
configuration. I may have shortened it from both ends.
Cheers
Fred W B
[Edited on 19/3/12 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
Thanks again for the pointers, Fred. Reading this is certainly making my other research make more sense!
I don't want to spend a huge amount on this so the path of least cost is going to be the best. I've got a mate who has a mill and a lathe
so I wonder if he would be able to make up an axle for me for some beer tokens.
Still not sure what I should be looking for engine wise. Obviously a bike unit of some kind, somewhere around 125cc, but other than that I've
no idea.
Photo Archive
Building: Locost Fireblade BUILT - now sold :(
posted on 20/4/12 at 10:20 AM
Google a quadard or a mini quad or 49cc quad. You can pick up a broke one for peanuts on eBay, and the rear axle would be about the right size, and
they ate steel chassis do you could cut and shut it easy.
