Quad-Motor Electric Kart Gets A Little Too Thrilling

[Peter Holderith] has been on a mission to unlock the full potential of a DIY quad-motor electric go-kart as a platform. This isn’t his first rodeo, either. His earlier vehicle designs were great educational fun, but were limited to about a kilowatt of power. His current platform is in theory capable of about twenty. The last big change he made was adding considerably more battery power, so that the under-used motors could stretch their legs a little, figuratively speaking.

How did that go? [Peter] puts it like this: “the result of [that] extra power, combined with other design flaws, is terror.” Don’t worry, no one’s been hurt or anything, but the kart did break in a few ways that highlighted some problems.

The keyed stainless steel bracket didn’t stay keyed for long.

One purpose of incremental prototyping is to bring problems to the surface, and it certainly did that. A number of design decisions that were fine on smaller karts showed themselves to be inadequate once the motors had more power.

For one thing, the increased torque meant the motors twisted themselves free from their mountings. The throttle revealed itself to be twitchy with a poor response, and steering didn’t feel very good. The steering got heavier as speed increased, but it also wanted to jerk all over the place. These are profoundly unwelcome feelings when driving a small and powerful vehicle that lurches into motion as soon as the accelerator is pressed.

Overall, one could say the experience populated the proverbial to-do list quite well. The earlier incarnation of [Peter]’s kart was a thrilling ride, but the challenge of maintaining adequate control over a moving platform serves as a reminder that design decisions that do the job under one circumstance might need revisiting in others.

37 thoughts on “Quad-Motor Electric Kart Gets A Little Too Thrilling

  1. As it turns out, you can’t just ghetto-slap together some CNC’d parts (sponsored project!) and expect them to work at anything beyond walking speed. Maybe next time study some fundamentals of mechanical engineering and car kinematics instead of going “head first” as in O’Reilly books.

    1. Yup, building a Kart chassis out of 4080, giving it no appreciable steering geometry other than straight and having no suspension or flex built in to the chassis, using horrible thin tyres etc. is pretty much a recipe for problems.

      I would like to see the idea extended to a well designed chassis with adjustable everything though, could be a lot of fun. (and I’m sure someone will have done it)

      1. It is possible to build a good or perhaps even great Kart chassis in your shed or garage, heck I’ve seen it done by someone with an angle grinder, MIG welder, a tube bender and a pile of tubing, but that pile of CNC’d parts aint it and the builder seems intent on injuring themselves because they really don’t seem to understand or know how to design for the forces involved (though the concept is fun and has potential if it’s given a decent chassis)

        FWIW, I’ve never *personally* owned or raced a Kart (though I have driven a few for fun and testing).

        But I have been the mechanic for a company owned Kart race team.

        1. > because they really don’t seem to understand or know how to design for the forces involved

          Yeah, thats why he build this project. To understand such things. That’s why he typically changes only one part per dev cycle, to understand what it does. It’s learning project in progress. After several cycles he will probably make a good one.

          1. i agree with the mentality but one change per iteration limits you to “hill climbing”, which is a great approach to optimize a design but has the liability that you can only find the peak of the hill that you’re on. there’s a reason people keep using the word “CNC” in these disparaging comments — he’s on the wrong hill. i think it’s fine to build an awful toy but the problem is, it gets to be not fun.

            for myself, i took one look at how those front wheels are mounted and said exactly what everyone else here is saying — this is an extremely unserious approach to automotive engineering. the hill he’s on is centered on “CNC metal fabrication makes infinitely strong pieces where you can disregard flex and stress” and it’ll be very hard to get off that hill.

            we’ve all been novices going down an unproductive path but this adds the novel dimension of doing it with a very expensive tool. so we’re feeling a little jealousy at the same time as wondering how could anyone who has so much money at their disposal possibly ever learn anything? he’ll get bored of failing at this and move onto failing to use a different expensive tool.

            i don’t have any idea if that’s an accurate description of the actual person at the heart of this project but it’s the image that’s conjured by the write up and photos and i think it makes us sad. it’s like pondering whether the next generation will ever really learn how to program, now that there’s no incentive to learn the fundamentals on a shallow device. our own childhood is so far away and kids these days aren’t learning anything. it’s the mirror that upsets us.

          2. Ignoring a century of accumulated and easily available knowledge seems an odd way to develop stuff but fair enough, each to their own.

            I just hope he doesn’t hurt himself too badly while he reinvents the wheel.

          3. His years of effort will surely save him a half hour in the library.
            After several cycles it will be as good as a Model T (not likely).

            Hope he’s not too badly injured.
            Also hope he’s injured at least a little.
            Seems like the type that needs a little pain to learn.

            We ripped on this cart last time it was posted.
            We were right.

      2. Replying to Greg A:
        Thank you for your self reflection. This is the most honest and thoughtful thing I’ve seen in the Internet in some time. Too many people jump to say what they feel without taking any time to think about why

      3. Bingo, this is “Hack” aday not exquisitely designed in an ivory tower a day. The hacked together, and poor decisions are a big part of the fun. We get to see what fails, how and why. It’s gritty and awesome. Can’t wait to see this guy’s growth.

    2. …But half the fun is in winging it, applying huge forces in the field until it breaks, then going through and reinforcing those parts and refining the design. Why would I want to go back to fundamentals textbooks for a hobby? He doesn’t need all that, he can replace the broken parts with bigger ones and arrive at the same destination

      1. That destination being injury or death?

        There are things you should not wing. This includes anything you need a driving license for on the public roads of most developed countries.

        It also includes things that have been developed for over a century to get where they are now (think: vehicle suspension and steering geometry). You don’t even need to be a mechanical engineer to read up on and understand it.

    3. That sure is a lot of words to say “I’ve never had the balls to try this myself.”

      Hindsight is 20/20 dude. It takes approximately zero skill to see mistakes AFTER they’ve been made, and less than zero skill to comment somewhere about it.

      If you’re so skilled and talented, make one yourself and show us how it’s done. You do not get to complain when we say your mistakes are obvious after you’ve discovered the mistakes.

      1. It doesn’t take much effort to look, as someone said above, at some of the 100+ years of accumulated knowledge on this sort of thing and make a few very different decisions though.

        I remember the last time this thing was featured and several blindingly obvious flaws were evident then too.

        Yes it’s fun & fine to cobble together a kart from whatever you have laying around but when you’re bolting kilowatts of power into it you need to at least pause and consider things.

  2. Personally i would have just totally locked out the steering and had it torque steer through software. As a back up in case power went down i might have added cable brakes that could be biased left or right when turning the steering wheel. Could probalbly get it to turn pretty well still with all that power.

    1. He’s still using bike/scooter wheels/tires. Meant to lean. Tiny contract patch.
      Clueless parts choice.

      Didn’t RTFB (blog). But assuming he’s in HS, this is expected.

      If he’s older, he needs to go back to Engineering school ASAP.

  3. This seems like a typical hacker / maker HOOK illustrated here: “I found or received this awesome and unique part, and now have to build something around it”. Yes, those electric powered wheels are really cool! But now you have multi-disciplinary issues building a vehicle around them. Likely the most common way to accomplish an electric kart or vehicle would be to electrify an existing ICE golf-cart, ATV, etc so the focus is minimal mechanical, and maximum electronics / controls / integration.

      1. What part of a bug would you use for this kind of project?

        Remember bugs are expensive now.
        You can buy a sand rail frame for less then the price of a VW pan.

        Also 20kW is heinously underpowered for a bug.

  4. Loves me a good go cart project! I think I’d convert the the wheels to drift wheels and make a 4WD drift cart. That would dramatically increase the fun factor and dramatically decrease the top speed.

  5. cool project, even without suspension.

    however, clicking through to their blog reveals an attempt to build suspension without welding, and even though it did fail swiftly, it does show that Peter has a decent awareness of some mechanics of vehicles.

    the series is stated to be more about “down to earth, accessible” learning material, rather than a project car with nigh-unlimited budget.

    he even compares sodium ion cells to lithium ion cells on one post, definitely worth a glance

  6. First thing I’d do is fix that seat. Then throw a Briggs & Stratton on it, Evinrude if you want to be cutting edge, and call it a day. Nah, heck just call it a day. What’s next Mrs. Landingham?

    He’s putting the putting the horse power plant before the kart. Not worthy.

  7. I’ve been wanting to do something similar, but use supercapacitors instead of batteries. Back in college we did something like it on a small scale, so I’d like to scale it up.

  8. While the implementation had problems, the idea of a motor at each of the 4 wheels is a good one. You spread the total electrical current out over 4 separate motors. This reduces the current any 1 motor gets by 4. This makes the electronics much less expensive. Also if a smart enough controller is used, it is easy to implement traction control, regenerative braking, and other fancy suspension tricks. Keep trying, you’ll get it.

    1. I agree , using a 4 wheel motorized with negative braking is the way to go. I currently am working, with a team , on designing a full race car and a lot of tech comes from f1 racing our problem is keeping it affordable for your everyday future racer , sure we all make design flaws that is a part of the build but we should also think of the builder and not fuss on his design. I believe it’s people like him that build the very future of our motorized world. . I think he is on a good track and after each design he builds he will realize what tech he is going to need to bring his build to completion and to those that nock it down well l don’t see you doing anything to even match his, Learning anything in electric builds are high tech, for advise l can give keep in mind your heat factor and everything that pushes it and collects it but funding will be the the only thing that keeps you back . Stay focused on these tips , it will be all wheel drive that will bring your build to new highlight and the negative braking will be a part of your brake system along with a.b.s tech . Look into speed controlling and your steering should really be looked at. High speed line changing can be very jerky , if you will so steering ratio will have to be a real fouse when working with 4 wheel motorized carts. Now all this is a bit much but it can not be overlook in design . I think your on a good track and the learning is the very best out of it all and in time no matter how many times you change this or get criticized about that it will be you that will have the last laugh when your up here with us racing with your kind ,

  9. I’ve been quietly observing this project unfold since the first time it was covered here, and have read the *entire comments section on every post* since. Full disclosure; I didn’t read his blog (yet) or any articles from other sources, so my perspective is limited to hackaday—but that’s entirely my focus here.

    That said, it seems to me like many have forgotten their roots and lost the spirit, or something… y’all just getting too old for this? Too many nay-sayers, doomsday-prophets, know-it-alls, and grumpy-grampas who need to lighten up a little here, cause frankly, if I was in the author’s shoes, I would probably request that hackaday stop covering my project altogether since it’s such a BUZZ-KILL.

    All the armchair experts talking like they’re standing on top of their own 20 kW AWD go-kart with custom CNC parts, or claiming the author “needs to go back to engineering school” should perhaps quote their own engineering credentials, link their own project, or at least reference some actual scientific source—anything to give their critiques some credibility. Anything less than constructive criticism adds nothing of actual value to the discussion.

    There, /rant. Thanks for reading, for those who did.

    Last words: I’m no Engineer myself (but I am an Electrical Eng. Technologist), and I can’t link any of my projects (yet), because I’d rather spend my time actually working on my own sketchmobiles than waste it documenting my errors for others to rip apart… Furthermore, I won’t even bother referencing any scientific source either, because it won’t help anyway if you can’t immediately understand why those wheels are simply UNSUITABLE for this application. But if I had such a set of wheels (with a rounded profile clearly intended for leaning) that I specifically wanted to use for a project, I personally would have chosen to do something like a 3-wheeled drift scooter (think Yvolution Y Fliker etc), an AWD skateboard, or perhaps even a pair of rollerblades… NOT a 4-wheel vehicle such as a go-kart.

  10. What alot of repliers don’t recognize is the man put more thought than they ever would into something and made it work. That is more than most can say that they have done. I know because I have built alot of things monster trucks to Go-Karts and no two are alike. He deserves more credit than discrimination.

  11. awesome, i would defo, design some suspenmsion out of bicycle rear shocks, would look rad. kind of resembles the electric go cart this excellent engineers at drotek in france did a few years ago

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