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

15 Responses

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

    […] Herndon] is working on building an electric kart, mostly with surplus parts. He’s got some experience with electric vehicles but that […]

  2. Written by Nonya
    on July 8, 2010 at 3:04 pm
    Reply · Permalink

    you need some 90’s in that motor mount plate to keep it from flexing

    • Written by Henry
      on July 8, 2010 at 3:30 pm
      Reply · Permalink

      I considered bending the edges of the plate forward or back for rigidity- it would be almost trivial to throw it on the brake and do so- however the plate is made of 3/16 steel and is pretty stiff as it is. We didn’t see much flex when testing it. It’s definitely something I’ll consider doing down the road. Right now there are more pressing things to fix! Thanks for the constructive comment.

      • Written by Nonya
        on July 8, 2010 at 3:45 pm
        Reply · Permalink

        where do you get all these high amperage motors? i have some kd221k75 transistors and i’m looking for something to test them on.

      • Written by Nonya
        on July 8, 2010 at 3:58 pm
        Reply · Permalink

        some of that groaning in the turns is probly from lack of a diferential, one of the wheels always has to slip.

  3. Written by gzus
    on July 9, 2010 at 5:51 am
    Reply · Permalink

    do you know that swapping two of the motor wires results in the motor spinnig the opposite direciton? this means that the controller can operate in the right direction. i think rc brushless controllers have a less aggressive/power throttle curve in reverse.

    • Written by Henry
      on July 9, 2010 at 10:40 am
      Reply · Permalink

      Indeed switching the phase and sensor wires around can reverse the rotation of the motor. In this case I’m not sure if the reduced speed was only due to the controller of if the motor has a timing bias as well. This controller is designed for all sorts of sweeper machines and warehouse machines and has a bunch of options about reduced speed forward/reverse- but we have no idea how it was setup. On the night we put this together we were so fried just getting it together we definitely didn’t feel like experimenting with motor hookup variations- and now the Sevcon controller is completely dead and unresponsive… Back to square one!

  4. Written by Rob
    on August 4, 2010 at 8:25 am
    Reply · Permalink

    [I didn’t make a mark on the case before pulling it apart so I may have slightly altered the timing (the hall sensors are on the inside of the front case).]

    An incorrect position of your hall sensors after your repair could be the cause of part of the problem. I had a current sensor reversed (on a induction motor system), giving reversed feedback to the controller. This caused the controller to produce maximum negative current instead of a small positive current. Weird thing is, the motor still ran, but very noisy and with crazy currents.

    My guess is you need to change the position of the hall sensors relative to another, instead of just swapping them; so if #1 is at 0 degrees and #2 is at 60 degrees, move #2 to -60 (or 300) degrees.

    Good luck!

  5. Written by Dan Danknick
    on August 4, 2010 at 7:45 pm
    Reply · Permalink

    If you guys want me to check/document the configuration of your Sevcon controller, I’d be happy to. There is normally no fwd/rev bias in the setup for the Mars BLDC but there are some phase timing differences that Sevcon recommends when using that motor.

    BTW, great job on fixing the magnets. I sent the link of that page on to John F. who designed the motor! 🙂

    Dan Danknick
    Team Delta

  6. Written by AcuteAero » In Search Of Cheap Fast
    on August 22, 2010 at 10:48 pm
    Reply · Permalink

    […] last time’s disappointment with the performance of the “Alt-Kart” set up with Mars BLDC motor and malfunctioning (now dead) Sevcon PMAC controller it’s been on […]

    • Written by Andrew
      on February 26, 2012 at 6:22 am
      Reply · Permalink

      Dear Builder!

      I read your post: “malfunctioning (now dead) Sevcon PMAC controller”
      I’m a student and soulful EV (small motorbike) builder.
      Do you have this failed Sevcon controller now, or can you sell it possibly?


      • Written by Henry
        on February 28, 2012 at 10:14 pm
        Reply · Permalink

        I’m afraid the millipak controller is long gone, sorry. Good luck in your endeavors!

  7. Written by Electric Go-Karts « TiroKart
    on October 13, 2010 at 6:18 am
    Reply · Permalink

    […] experience, I am seriously considering making an electric racing go-kart. Mythbusters built one . This is another attempt and this is an MIT project. So it can be […]

  8. Written by Aaron
    on December 4, 2011 at 1:03 am
    Reply · Permalink

    I recently purchased the Sevcon Millipak controller and a Mars PMAC motor for my electric car. I’m having quite the spot of trouble trying to get the thing wired for one direction only. Any ideas, the diagrams are a little complex for me

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