DIY Dynomometer


A Dynomometer measures actual horsepower and torque output at the wheels of a vehicle. Aside from racing, it’s long been the way to test out engine modifications. [Steve] built his own. It uses a Basic stamp for data acquistion, and a custom machined drum for the physical interface.

Comments

  1. mike says:

    I built one in welding shop in high school for use in the small engines class, but it wasn’t microcontroller’ed or anything. I forget which all parts I used, but they were old 80′s buick parts. I think like a power steering pump or something, but that doesn’t seem right.

  2. Yuffie says:

    I foresee spelling nitpicking.

  3. Gyro John says:

    Lots of fun and very impressive. Thanks very much, Steve, for the free education.

    I just have one concern with this thing: all the stored energy in a 1050 lb. flywheel (on a trailer) which will be rotating at 2800 rpm when the bike reaches 150mph.

    Obviously the machinist balanced the drum adequately, or we would see the trailer bouncing all over the place in the videos, but imagine the mayhem if one bearing failed catastrophically at high speed and the drum tore loose and went for a run through the neighbourhood.

    Also I saw brake lights coming on during decelleration, and imagined my brakes heating up and wearing out as I strove to slow that spinning flywheel. Seems to me that’s a much bigger job than a bike’s rear brake was ever designed for.

    Thoughts?

  4. xerxesdaphat says:

    @gyro john:

    I’m a motorcyclist, and one who rebuilds his own engines. The sort of bearings you’d be using for the drum would be pretty heavy duty. The wheel bearings I put in my motorcycle cost about $5-10 each, are used regularly in 300kph motorcycles, and are neglected and exposed to rain, moisture, dust, big temperature differences and massive physical shocks. Imagine the carnage if a wheel bearing failed; you’d be alright in a car, but on a motorcycle you’d be killed straight away. Very, very rarely do you ever hear about wheel bearings failing, and that’s usually due to major neglect or some mechanic cocking up. I don’t think we have to worry about `high speed bearing failure’ in this.

    When he puts the brake on, that’s to gently slow the flywheel so the engine doesn’t take the strain of the engine braking. As for it being more than it’s designed for, I would refute that again. Brakes on bike like that are designed to be used up to and well beyond the traction limits of the tyre (which aren’t that much lower on the track compared to this drum) again and again, corner after corner, for races that go on for multiple hours. I’m not sure what you’re worried about happening; the worst case scenario is usually when so much heat is produced that the brake fluid bubbles, causing the hydraulic fluid to become compressible, so the brakes stop working. Otherwise known as brake fade. I’ve had discs (and drum brakes) glowing red hot. The calipers aren’t going to tear off the mountings or anything.

    I know personal computers and electronic systems (of the sort Hackaday readers are familiar with) are usually mass-produced shit that has a design failure expectancy, but designing things like bearings and brake calipers, especially in connection with motorcycles, are generally engineered to a higher standard, as at the end of the day it comes down to spending months in hospital if it all comes to pieces.

  5. TJHooker says:

    For a fraction of the cost of the drum itself you can buy a small engine dyno that will do up to 15LRPM.

  6. sly says:

    the only problem with using an engine dyno is that you have to take stuff apart each time you want to test. using a chassis dyno (one that measures at the wheels like this one) only requires that you get the wheels in contact with the drum and lock the rest of the vehicle in place. there are no parts to take off to hook the dyno up to.

  7. Dirk says:

    plus an engine dyno doesn’t help you determine power losses in your transmission and belts/chain etc.

  8. Doug says:

    For a chassis dyno to be able to detirmine power losses in the drive train, you first have to know the engine output. An engine dyno and a chassis dyno go hand in hand, if you are building a total vehicle package. An engine builder needs only the engine dyno. The vehicle builder only needs the chassis dyno if they purchase the engine from a trusted engine builder. Someday I’d like to build a prony brake to measure the torque of small engines and motors. A hydraulic pump as in a PS pump could be used for the “brake” portion. Thanks for switching on the light bulb Mike. Designing a simple brake wasn’t a problem, but cooling it was presenting one. Running hydraulic oil through a cooler and a large reservoir isn’t. There also may be a way to have the pump do double duty by measuring the torque, but that hasn’t hit me yet

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