How Much Electric Kart Can You Build in a Day?

Last week I rebuilt the kart with fresh fasteners and axle bearings, plus picked up a steering wheel and some #35 sprockets. Then, once the Mars motor looked repaired and good to go onto the kart I picked up a handful of 7/8 keyed #35 sprockets from Surplus Center. The parts were forecast to arrive on Thursday- so I made plans with my friends to bring everything to Laney and try to get the kart running. I came in at two and got started- about eleven hours later the kart was driving, a half an hour later it was broken, and finally at about four in the morning we all went home.

Miles drew up the motor mount plate in CAD and cut it out of 3/16 mild on the CNC plasma table. It’s bolted right to the outer bearing frame support with slotted holes to adjust the chain tension- the stick he’s using is to help support the motor while he tightens the plate in.

Micah made up all the cables out of 6GA welding cable. We didn’t find enough lugs locally at any sort of reasonable price so we made “lugs from the ghett-o” by smashing copper tube around the wire, filling with solder then drilling. A little trick I learned from Home Power Magazine about ten years ago. I mounted the Sevcon Millipak controller, contactor and fuse, and made up the control panel, throttle, and hall sensor wiring harnesses.

See the rest–

Micah set up battery mounting using only the best pallet-wood and ratchet straps

A dead cushman carcass was ransacked for the 0-5k throttle pedal mechanism, which Micah cleverly secured using hose clamps.

Igniton and forward/reverse switches. Classy purple switch cover courtesy of Surplus Center. Of course.

(warning: there’s a little F word in the video)

So, what happened? Let’s just make a list:

All of these things were non-optimal but did not prevent driving the kart around.

Then the mishap that ended things for the night- Due to a combination of the sprocket carrier axle-clamping screws not being tight and the awful jerking cogging-torque from the screwy commutation the sprocket holder key jiggled out, then the chain derailed. Casualties- the key was smushed up pretty good, the keyway suffered a bit, and the sprocket carrier became a bit pretzel shaped. Turns out that if a chain in a system without any give in the chain-path length derails it’s going to deform the weakest part of the system. In this case the aluminum sprocket holder. At least it wasn’t the motor shaft (though I should probably check that carefully)- that would be significantly more expensive. So that’s probably one of the reasons kart suppliers sell “sprocket guards” – a bit of insurance against chain derailment. Maybe worth it.

So I will pick up a new sprocket carrier and a new key, this time I’ll get one that is the entire length of the keyway- so that there’s nowhere for it to escape to, and to fortify around the mooshed part of the keyway. Then we should be back in business, for some faster gear ratios and higher voltage…

Posted on June 20, 2010 at 11:40 pm by Henry · Permalink
In: Electric Alt-Kart

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  1. Written by Building an Electric Kart - Hack a Day
    on July 8, 2010 at 10:13 am
    Reply ·