DIY hub dyno on the cheap

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BennVenn
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Re: DIY hub dyno on the cheap

Post by BennVenn »

IMG20210809111358.jpg
IMG20210809110537.jpg
Trailer hub wasn't exactly 120mm PCD but a little tap with a mallet got it seated.

The car side flange went on like a glove.

Mating them concentric was easy thanks to a tapered lip I included in the flange faces.

A little cutting and Welding and adding the sensors and I should be able to verify the design today. The only unknown now is if a 300kg actuator will brake the hub at full power. There's always a 600kg actuator I could use or add a lever to increase it. Or even use a vacuum master for help
BennVenn
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Re: DIY hub dyno on the cheap

Post by BennVenn »

The Chinese stub axles aren't the greatest. They're running slightly off-true. The slight shimmer is absorbed by the suspension so that shouldn't be too much of a problem. I'll need to locktight anything that can come undone. One more reason to use AU falcon stubs on the next revision.

The hubs and axles take the full weight of the car with no problems. The pillow block is fine with the weight too and can rotate freely.

I'm off to town to get some steel for the torque arm and we'll be ready to load test :-) 1m should translate 300 newton meters of torque to 30kgs at the cell. It's a 75kg cell which will be fine for up to 200NM at the flywheel in 5th gear - assuming a 3:1 diff and 1:1 5th gear ratio. Not sure if that's the case here but there's margin for error.

I'll strip the paint off the stub axle face incase that's contributing to the run-out.
BennVenn
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Re: DIY hub dyno on the cheap

Post by BennVenn »

IMG20210810151759.jpg
I can't get this PID control dialed in... I think the code will need fixing as this was for motor speed control, not so much increasing or decreasing braking on a motor.

I tried a pretty basic if speed is > then more brake kind of thing. There's lots of overshoot and oscillation though it did prove this rotor can hold what would be around 70HP.

Hall speed sensor... The small magnets supplied pretty much loose all magnetism once they're warm. Of the 7 on the rotor, only two are triggering the sensor once it warms up. 7 is not enough for fine speed control either. Approx 90rpm granularity.

It also occurred to me, if using axle stands and don't need the car suspended on a hub, this project becomes a whole lot simpler...

At least the actuator can brake this rotor and we're getting load cell data back. I think with more higher temp magnets and working pid code, we've got ourselves a hub dyno! And under budget :-)
Last edited by BennVenn on Tue Aug 10, 2021 4:00 pm, edited 1 time in total.
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Gareth
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Re: DIY hub dyno on the cheap

Post by Gareth »

Sweeeet :thumbup:
According to chemistry, alcohol is a solution...
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antus
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Re: DIY hub dyno on the cheap

Post by antus »

Some good progress there. It would have been great if it all worked perfect first try, but that's usually not the case. Hopefully only some minor refinement and changes are all that you need from here.
Have you read the FAQ? For lots of information and links to significant threads see here: http://pcmhacking.net/forums/viewtopic.php?f=7&t=1396
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Re: DIY hub dyno on the cheap

Post by BennVenn »

I'm wondering if I should just grab a hub with ABS sensors in it and pop that on. Seems most magnets will stop being magnets over 150deg c, harder to find ones will work up to 300deg - still well below what the rotor is capable of. Or move them off the hub and onto the aluminium flanges...
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Re: DIY hub dyno on the cheap

Post by antus »

Yeah i'd build an OEM sensor in to it, its designed to measure wheel speed in the OEM application.

But you probably could use a sensor to detect the bolts between the hubs as they fly past, though I see potential alignment problems how it is at the moment with that.
Have you read the FAQ? For lots of information and links to significant threads see here: http://pcmhacking.net/forums/viewtopic.php?f=7&t=1396
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Re: DIY hub dyno on the cheap

Post by BennVenn »

I'll see what I've got in the shed. A sensor built for the purpose sounds like the better option
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Re: DIY hub dyno on the cheap

Post by MudDuck514 »

antus wrote:Yeah i'd build an OEM sensor in to it, its designed to measure wheel speed in the OEM application.

But you probably could use a sensor to detect the bolts between the hubs as they fly past, though I see potential alignment problems how it is at the moment with that.
Hi all;

Perhaps he could use some type of optical sensor?
That would allow for a greater range of off-set to the bolt heads.

Mike
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Re: DIY hub dyno on the cheap

Post by BennVenn »

I found a Variable Reluctance sensor in the box of bits (cam tooth gear sensor etc). I'll build up a small amp and see if the arduino can detect it. If it can read the cooling fins of the rotor it'll be pretty much perfect. If not I'll get it reading the rotor bolts and change the code to work out the frequency from the period rather than pulses per time interval.

I think half the problem with the PID control was the lack of RPM resolution, with 6 magnets it'll give 100rpm precision, so asking for 1000rpm will bounce between 900 and 1100, best case.
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