Siamese Electric Motors

I’ve been meaning to post something about these for a while. Jim builds motors for EV hobbiests on the side – one of his cooler creations is the siamese electric motor. Some others have used belt drives to combine motors, but Jim actually builds the motors into a single unit. He built this set of 8 inch twins for the White Zombie drag racer.

I pumped Jim for more details, but he’s not done tweaking his next set of siamese motors. So, why is this even a hack? It’s a nice piece of machine work, but it gets interesting if you consider some stock specs. Most EV cars get 9″ motors – these are rated at 19hp or so. They take some monster hardware just to drive – high amperage, high voltage. Running a pair of 8hp motors can produce similar power with significant cost savings – everything gets cheaper. To generalize, you need a $1500 motor and $1000 controller just to get in the game. Not to mention that rebuildable forklift motors can be had for a song.

19 thoughts on “Siamese Electric Motors

  1. See how compelling this work is?
    People are already clamoring for more details! :D

    Darkcobra, I would wager that you could e-mail jim for specifics if you’re looking to get started right away.

    I’m sure the details would be interesting to read about even if there aren’t any pics! (hint hint) ;)

    A few years back I built a wheeled ROV and barely scratched the surface with EV drive systems.
    It’s nice that the equipment (controllers, etc), while still expensive, have more availability nowadays.

  2. It is about time to have a open-source EV controller…One that can be built for 1, 10, 100 or 1000 amps, just adding more mosfets. Not that Zilla isn’t a great controller. But not everyone has money to buy one of that, nor access to one (I’m Brazilian and have no ways of buying one overseas)

  3. I’ve known about the osmc for a while since I’ve build battlebots. But they need a super osmc like Tabajara said for 1000 Amp EV controller. You’re already spending several thousand for a ADC motor, batteries, and charger, the controller needs to be affordable and fixable. I can’t wait to build a EV someday, maybe a 12 second car like white zombie.

  4. #2 – Will O’Brien: Thanks! Hope your recovery is quick, I’ve got a cold too and it’s a nasty one. That is a clever cost-reduction technique. Perhaps it offers some redundancy as well – if one motor goes bad, you won’t be racing, but you could at least drive back to the shop. EVs are out of my ability/budget right now, but this could be used for robotics and R/C too.

    Others: I’d agree the OSMC would be the best starting point. With google’s cache of “why mosfets fail in sstc duty” as a laundry list of things to check if (when) it blows up. :)

    The controller in the Tesla Roadster is quite talented. There is *one* controller for both driving the motor and charging. The switching transistors (and heatsinks, fans, etc.) used to drive the motor are reused and reconfigured on-the-fly into the heart of a regulated, step-up/step-down switching power supply to charge the battery from almost any power source. Apparently it even eliminates the need for an inductor as normally seen in a switching power supply, by using the motor windings! That’s an improvement in cost, component count, weight, and versatility. If anyone can figure that one out, at either robot or EV scale, that would be a truly moby hack.

  5. this looks a lot like the brushless motors model airplane guys are building from old CDROM drives, stacking armatures in a single can and custom winding the armatures.

    Tho with brushless your controller is in charge of timing which allows adjustable output and greater efficiency where this dual motor DC unit has to be physically configured to time correctly.

    Not bad if you have a machine shop handy and sponsors, electric vehicles used to have the curse “it’s the battery, stupid” as the performance limiter. Now things are becoming ” its the controller, stupid!”. Finding a way to properly manage a minimum of 2 kilowatts safely and reliably and affordably is the new challenge.

    that, and of course, having enough electricity to charge your batteries, which Kalifornia has shown it’s unable to do reliably at even current demand over the last decade-much less in the future.

  6. ummm, ya cool for dragging were you almost anticipate blowing something up on every outing… bad bad bad idea for everyone else.

    I’ve done it with a few motors [small 1hp ones up to 12hp suckers]… never felt safe with the results.

  7. didnt even look that close at the pictures, opposing shaft outputs! have you ever tried to get a matched set of perfectly neutrally timed motors. have you ever tried to neutrally time motors yourself. If they hold up, I’d say he did some impressive work.

  8. not to rag on you or anything, will, but this is *hack*aday (italicized, bolded, underlined, size 120 font). if we wanted to see ev’s we’d go to an ev site. i was going to say this earlier but decided to wait until another post. this is the next post. so i am saying it now.

  9. andrew: it’s been said before, and will be said again: if you don’t like the content, wait 24 hours. after a very ev-oriented hack I’m sure tomorrow’s will be something different. ezombie makes a good point: salvaged hardware + ingenuity + new purpose + photos of the process = hack.

    if, like me, you wanted to see more pictures of the motor build process but couldn’t find them, go to

  10. just in time for impatient andrew I will be unveiling my latest uber_hack. It’s a computer interface device modelled after a typewriter. Get ripley’s on the phone!

    also ready to re-test the automatic cat petter after updating the firmware. still need a new cat though ;).

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