small engine dynamometer

I've been crawling the net for a small-engine dynamometer for a while,
but thought someone in here might have a lead, or a hint of one.
I want either a water-brake or preferably a eddy-current dyno, rated to
a *maximum* 37kW / 50hp. This is probably way more than enough. I want
to test anything between model aircraft engines to small bike engines.
Something like a go-kart engine dyno, or smaller would do - something
you could rig up on a bench.
New ones go for around £3000, but there's no way I can afford that!
Probably up to £1000 is more like it, and would have to include a
controller, load cell, and other attendant equipment.
Any ideas gratefully received.
Reply to
Biz
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It would only do the lower end of that range, but how about the load from an exercise bike ? Cheap ones are air-resistance, but better ones are eddy-current.
-adrian
Reply to
Adrian Godwin
Hmm - that would be good. I've seen another home-spun job using a hoover motor. As far as I could tell, they'd fiddled it so it could motor the engine up to speed, then changed to loading by controlling rotor and stator voltage and current. Power was dumped in a series of resistors. It could only absorb 750W / 1hp, but the principle was there.
Reply to
Biz
American one here,might be worth a follow up.
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Alla
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Reply to
Allan Waterfall
One of the issues you will need to address is input speed, some model aircraft engines spin at very high RPM, but large electric motors normally run at 1400 or 2800 rpm.
dumping heat can be a problem... but a kettle element uses 3 kW, and if it's kept in a water tank will just need steam venting and fresh water to run continuously .
What would a dyno just for model aircraft engines need to cope with ( max power, max torque, RPM range ) ??
Reply to
Jonathan Barnes
If you fancy making it yourself there was a series in Strictly IC magazine. Back issues are still available from and you can find the dyno if you search for "Kirk" on their special projects page.
HTH,
David
Reply to
mangled_us
I built an inertia dyno for testing motorbikes - look on
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you want a brake dyno, there should be a link on there on building a water brake using a water pump - similar to the Hennan and Froude DPX series. Before I built mine, I had one that used a hydraulic gear pump Geoff
Reply to
Geoff M
As a matter of interest, it occurred to me that it should be possible to make a dyno just by mounting the engine on a beam and measuring the strain in the beam with an electronic strain gauge. If you can also measure the rpm with a tacho then the power is just a constant times the prodct of the two.
This would seem to have the advantage that calibration would be easier since no "known hp" input device is needed - it's easy to calibrate torque on a beam mount just by adding weights, does anyone know if this has been tried and, if it works, what the problems are ?
Cheers,
David
Reply to
mangled_us
Yes, I've thought of this. I guess I'm looking at between 10 and 20k rpm for really small engines; 1-10cc, say. Possibly I could gear it though.
That's a good idea. I was thinking of rigging up the motor to an air compressor - then you'd have air on tap for tools! Might as well put the energy to some use! But then you'd have engine-motor-aircompressor. Perhaps you could simply have engine-aircompressor... How you'd measure the torque in that configuration I'm not sure.
Max torque and at what speed I'm not sure. I think it'd be good - if I'm going to invest in a facility - to be able to go up to 50hp=37kW. Max speed as above.
Reply to
Biz
That's way cool! They think they want to sell it for $1500, which would suit my budget.
Reply to
Biz
Well you'd need some sort of resisting, spinning device on the end of the beam - like a propeller, disc brake, or the stator of a generator. The first two of these possibly you could use a strain gauge, but then I imagine you'd need to brush-contact the voltage to and signal from the gauge. With an eddy current dyno you measure the torque by fixing a load cell to an arm of known length on the stator.
Reply to
Biz
I seem to remember, a long time ago during my teens, I worked with a company refurbishing electric motors. Not my department, but I think they tested them using a generator of some sort, with the output connected to 2 large electrodes dipped into a conducting medium, (water with something added ?),and moved nearer together or further apart for differing loads. I suppose you could measure the electrical power produced and extrapolate from that. If this was indeed true, I would imagine it could be quite cheap to make a similar device.
Best regards
Tom.
Nunce excretia in extractum est.
Reply to
Tom Jacobs
Shift up by a factor of 10. Kart engines of 100cc regularly do up t 20k revs.
This weekend I maxed at 16200 and spent 2% of my time over 15k an that's with watercooling and simple carb. Power output is 20-25hp an that's an 'economy' class. The power band is between 11k and 14k
My guess is that you will have problems getting accurate readings fo both a 10cc motor and a 100cc tuned to the state that the conro starts to creep.
Regards Robi
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