Power Meters and Unicycling

General
1

I’m wondering if anyone has installed a power meter on their unicycle yet?

The data would be even more interesting on a unicycle than a bike, because we use variable crank lengths, and only one or two fixed gears. You’d be able to calculate optimum crank length and cadence based on power output for a particular rider, rather than speed (which would be affected by wind resistance).

There are also ways of calculating the drag co-efficient based on power measurements, which would be cheaper and more readily available than going to a wind tunnel for testing.

There is at least one model out (Garmin Vector), which is mounted on the pedal and should be compatible with a unicycle. The only concerning thing is that in an event of any unplanned dismount, it’s a pretty expensive device which will come in contact with the ground first.

Has anyone tried this?

2 Likes
2

Oof. At $1,500 I’ll let someone else test it first. Sure would be interesting though. No other power meter would really work in a uni though…

3

It’s cheap compared to when power meters first came out. I remember them costing four or five times that. It’s about the same price as a Schlumpf hub, and one of mine lasted only a couple thousand kms.

I’m a bit concerned about using it on a unicycle though- you’re more likely to damage the system than on a bike.

Another option might be to mount it on a fixed gear bike, with different crank lengths, if the intention is to measure the efficiency of different crank lengths in relation to ones power output.

It would be interesting information because I think that is something that is missing from not just unicycle, but also bicycle science. Bicycle crank lengths vary mainly from 165-180mm, yet there is much more than 9% difference between the leg lengths of the shortest and tallest cyclists.

It’s less obvious on a bike because the gears compensate to an extent, but pretty evident on a unicycle. For instance, I’m comfortable spinning much shorter crank lengths that most people, but I have short legs even accounting for my height.

4

I agree that it would be interesting to see power output data based on crank length. I’ve looked into getting power data while unicycling, but it’s still out of my price range.

There is power meter setup by Brim Brothers (http://www.brimbrothers.com) that puts the power meter on your shoes (via the cleats & an electronics pod which interconnect through a wire). Unfortunately, no definitive word on pricing or availability. Here’s a good write-up on the whole system: http://www.dcrainmaker.com/2011/09/hands-on-with-brim-brothers-zone-cleat.html

There’s also a review of the Polar/Look Keo Power pedals that touches on crashes: http://www.dcrainmaker.com/2011/09/everything-you-ever-wanted-to-know_19.html

Carl

5

You want to use Look clipless pedals on a unicycle? Not only attaching yourself, but with pedals which have no secure platform at all when not clipped in, aren’t that easy to clip as they don’t sit flat, and require a protruding cleat on the bottom of your shoe which makes standing on one foot a lot harder. Rather you than me.

Compared to the downsides with that, I really don’t see what the big issue is with comparing performance by speed. Is it really that hard to find a location with low wind for comparisons? In any case, such comparative testing of crank lengths is to some extent a bit futile, given how much difference training makes to how well you perform with a given crank length - almost impossible to separate how well trained you are for a crank length and how fit you are on any given day. Back to back testing of two different lengths on the same day would only even be any use if you were sure you were just as well trained with each crank length - and how exactly do you tell that?

6

I use Look Keos on my Litespeed (they’re the best roadie pedals ever), but the purpose of this thread is to talk power meters in general.

If the intention is to try different crank lengths to figure out optimum power output, it could easily be mounted on a fixed gear bike with different crank lengths (probably drilled out).

And it can’t be that difficult to built a platform to attach a look cleat onto, which clips into the pedal.

7

You have a Litespeed unicycle? :astonished:

It could, but then in that case you could just as easily use a power-tap hub which is somewhat cheaper.

One which is going to sit with the platform up for you to put your foot on? That would be kind of difficult.

8

I don’t think that would translate to use on a unicycle. I assume that this system uses some kind of strain gauge for a time dependent force measurement and folds it in with a fast clock to calculate time integrated power output. On a bicycle, none of that power goes into maintaining fore-aft balance. On a unicycle, a lot of that power goes into maintaining balance. Were the power expended to maintain balance linear with respect to crank length, what you propose would be valid. However (and this may only be my belief system) the relationship between crank length and ease of riding is anything but linear. For short cranks such a system would measure substantially larger power input.

9

A powertap hub isn’t going to fit on a unicycle if you wanted to do further measurements.

I’m not sure what you mean in your second part. Why can’t you have a flat clip in platform on the pedal? You’d want to lock out the float if you can, and I don’t think it would sit that much higher because the shoes sit quite close to the axle on the Keos.

I disagree with the statement ‘a lot of power goes into maintaining balance’. I think a little bit of power is used to adjust your balance, but someone cranking in high gear, say, on a Schlumpf 36" must expend most of their power driving the cranks around in circles.

Even with ultra-short cranks- you’re trying to spin it as fast as you can but balance is only a small component in the power output IMHO.

If you think about a stationary unicycle, and measured the power output required to adjust balance in a stillstand- I don’t think it would require that much power at all. And the amount of pressure on the pedals required to do a stillstand is much greater than required to keep your balance on a moving unicycle.

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This is what I recommend that you try. Set up your fixed gear bike to 36 gear inches to simulate an ungeared Coker and 54 gear inches to simulate a geared Coker. Use the same cranks as on the Coker. For a standard 42 chain ring, a 21 rear cog is required with a 27" wheel to make the approximately 54 gear inches. To make the 36 gear inches a 31 or 32 rear cog is required. That’s big and maybe impossible to find. You may need a smaller chain ring.

Anyway, with the short cranks and these gearing schemes I predict that the fixed gear bike will be a breeze to ride…and it will be very slow, like a unicycle. The reason it will be so easy to ride is that (1.) it will be geared exceptionally low for a bicycle and (2.) no energy will be wasted maintaining balance.

I may be wrong. Maybe your balance is that much better than mine. But I think that it’s not.

There is no power output that would be measured by an accurate system during a stillstand. There is pressure applied to the pedals but no appreciable motion. Your muscles will be expending energy and therefore developing power. You’ll get tired doing it as a result. A rotational power measuring instrument, however, will register nothing.

11

But if you’re going to measure stuff on a uni, why even mention the fixed gear bike? I presumed that was a way round the issues with using Look pedals on a uni.

You have Look pedals? You know how they don’t sit flat for you to clip into - they hang at an angle so you have to push with your toe to spin them up to clip in. Well if you add a platform to them you’re going to make the balance even worse - they’ll hang with the platform almost upside down. How do you plan to get the platform to sit the right way up to put your foot on when mounting?

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I mentioned it because it is a way of measuring the effect of crank length on power output.

I’m not measuring power output when mounting, I’m measuring power output when pedaling. You foot is already on the platform. Where it hangs when you are mounting is totally irrelevant.

13

How do you get your foot onto the platform when mounting then?

14

I don’t adjust my pedals completely level before I freemount, they can be at 90 degrees, 45 degrees, 180 degrees, 55 degrees, whatever. Who cares?

Even if you landed on the pedal upside down it doesn’t take much effort to flick it the other way.

15

Neither do I, but that’s with a double sided pedal which easily spins into position to provide me with one or other side to pedal on (I don’t care which).

Really? Have you actually tried that with a pedal which is weighted to hang upside down whilst riding a uni, or are you just speculating? Have you also tried mounting onto the back of a Look pedal?

16

I’m not sure why you’re so hung up on the idea of free mounting a Look pedal. It’s big enough to ride upside down if you wanted to.

This thread is about power meters. If you can’t figure out how to mount a Look pedal the right way up, hold onto something and manually place your foot on each pedal with it held right-side-up by an assistant :roll_eyes:

17

For someone who’s ridden as much as you, Ken, I think balance correction has become an unconscious reaction. You’re likely doing it more than you’re aware.

Here’s the rub… when working out the maths, how are you going to determine the correction factor that cancels out this “small component”? Can you even figure out the order of magnitude of that “small”? Is it 10%, 1%, 0.1%?

I suppose there could be some way of determining this correction factor by doing several trials with several different crank lengths, and using some sort of linear algebra to solve for the unknown. What do you say, Harper? I might be totally wrong here… it’s happened once before.

18

I’m skeptical that a cleat based system would work very well even on a bicycle, and it would have even more challenges measuring unicycle power.

Power is force times velocity, which means that the system needs to know not just the downward pressure on the pedals, but also the speed your pedals are moving, and what part of that downward pressure is oriented at right angles to your crank arm (downward pressure when the pedal is at the bottom of the stroke doesn’t produce any power, for example).

So it needs to know your crank length, which is easy enough to program in, though the writeup makes it sound like you can just blithely go from bike to bike without changing anything, which is nonsense.

And it needs to know your cadence, to get the pedal speed. You can make an estimate by looking at a few cycles and taking an average, but there’s going to be some error, a few percent at least.

The killer part is that you have to know exactly what angle your pedal force makes with the crank, and you can’t get that from averaging a few cycles worth of data. You would need to know that you are at, say, precisely the 4 o’clock position on the pedal stroke at this particular instant, and that your foot is likely to make an angle of x degrees with the pedal given the way a cyclist typically pedals…

That all seems hard enough on a bike that even ten percent error seems like a pretty ambitious goal. Now add in the fact that unicyclists apply force a lot less evenly than road bikers do, as they vary their pedaling to keep upright. Throw in all the body english we use, and how much more we move from saddle to semi standing to standing to saddle, at least offroad. Throw in the fact that we are actually backpedaling pretty often on uneven or downhill terrain.

Crank mounted systems, hub mounted systems, even chain based systems can bypass all this stuff, but not pedal based. I can’t see it working.

19

If I had an extra 1500$ lying around I’m sure I’d rather spend it on another geared hub than on a power meter.

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Intuitively speaking (because no one has experimented yet), I think it would be very little compared to the power needed to drive the pedals forward. Maybe 1%. Certainly not 10%. If you’re cranking out 300W, are you really going to be using 30W to hold your balance? Seems excessive. It might be higher at very low speeds as you don’t have the benefit of angular momentum keeping your unicycle upright, but ultra-low speed data isn’t going to be very useful to someone racing a unicycle anyway.

If you use a bicycle with fixed gears and variable crank lengths to measure the effect of crank length on power output, then the balance adjustment isn’t a factor.
If you use a unicycle with different crank lengths, then the additional ‘balance component’ is only the ‘difference-in-power’ needed to balance a short cranked unicycle vs a long cranked unicycle, which introduces an error in power measurements between different crank lengths, but again unlikely to be hugely significant.