If you’re still applying force on the pedal (even to keep balance), isn’t that going to translate to the wheel going around circles? You might apply less force or more force to adjust balance during the pedal stroke, but that still translates to overall power output.
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I had a further think about this…if you have different crank lengths, and it is easier to balance with certain lengths at certain speeds, that should translate to a difference in power output, because you are not adjusting your pedaling pressure during the pedaling circle. All of the power output is intended to drive the cranks around in circles, rather than correct balance. So a harder to balance crank length should be less efficient than a easier to balance crank length, and that will translate to power output.
Which is exactly the sort of data you are interested in, because you are asking the question: ‘what is the optimum crank length to generate the most power over a sustained period on a particular unicycle wheel size/gear.’
Most experienced riders pedal very smoothly on the road, so I can’t see the power data being particularly choppy. Going from seated to standing is what bicyclists do all the time.
In terms of body english- that’s not useful in the scheme of things as it doesn’t drive you forwards. If you were on a bike with a power meter and flapping your arms around, vs holding it on the handlebar, you might be expending power in flapping your arms, but that is not the power measurement we’re interested in. We want to know power output from legs driving the pedals around in circles.
I believe a bike power meter would be sensitive enough to measure choppy or changing pedalling in unicyclists. SRM’s are used in most sporting institutes in Australia to run the cycling tests for elite cyclist and those guys can go from 0 to massive power output in split second. They also use SRM’s on MTB’s and this would probably have elements of uneven pedalling also.
I believe the cranks would be good enough to measure unicyclists power outputs however I am unsure of how the power meter would respond to unicycling where a reasonable amount of backwards force is applied to the pedal in braking situations.
Power = force x distance / time if I am correct. I assume power on a bicycle is measured as the cranks are rotated (forwards?) as they would assume that all braking is done with an actual brake.
I also assume that power meters dont work while pedalling backwards as bikes never do it so why would they bother reading it. I guess for a road unicyclist that doesnt really matter as you dont ride backwards either.
However in unicycling as you slow the pedals to brake the unicycle you would be decreasing the power that would be measured through the crank as less force would be applied to the front pedal and less “distance” would be travelled by thecranks. This means it wouldn’t accurately reflect work done (I think?) as you would be using force to slow the crank but the backwards braking force is unlikely to be measured in a power meter.
I am just throwing this out there. I am not 100% sure on the mechanics of how a power meter works. However I would love to have a working one on a unicycle to measure power output during unicycle hockey.
Ken lives in Wellington, New Zealand. Everyone that went to Unicon XV is nodding.
I agree with Harper on this; the question is how much energy is used. I imagine it varies, not only with crank length but also wheel size. And I assume we’re sticking with level ground for all of this? I know on my geared 36" there are occasional moments where a lot of extra energy is expended for balance, but then a much lesser amount when cruising along.
If riding a closed circuit with a very predictable riding surface this balancing energy would be minimized, but it would be interesting to measure how much it is.
The other form of energy expenditure, though it may be a component of the above, is what you expend making speed changes. Back in my heavy Track riding days, I remember feeling the hard strain of bringing the wheel back under me if I’d gotten too far forward, or the opposite – if the wheel got too far forward and slowed me down. There’s probably less of that in (flat) Road riding, but it’s another variable.
Pretty sure if someone has practiced enough to learn to ride a unicycle they can overcome the tiny issue of a pedal being upside down when mounting.
Just ride with it upside down for a few rotations as you flip each over in turn. Yes they will not be perfectly balanced however if someone can learn to produce the exact amount of force to do 3 crank flips in one jump and land at the right time on the cranks as they are spinning around I am fairly certain that somone can work out the required amount of force to flip a pedal with their foot and then replace their foot on it at the correct time.
It is almost certainly physically possible to freemount a unicycle with Look pedals. The point is that there are a ton of clipless pedals which would be way easier to use on a unicycle, and work just as well. The Crank Brothers Mallet, for example.
A big difference in mounting on clipless pedals on a uni is that you have to start pedaling immediately, and you can’t easily coast to readjust your foot. And pushing down to clip in also throws you off balance. If you don’t get your foot in the right position to clip in when you mount, it’s quite challenging to get it fixed. Not impossible, but you really want to have a pedal you don’t have to mess with.
As for power gauges, Justin’s latest powered uni has integrated power sensing. He can probably pull some interesting data off there.
There are two power meter options that would work on unicycles pretty easily which haven’t been mentioned.
First, for more accurate results there is the Stages Power Meter. This would have to be installed in one of the cranks, and so it could get expensive to compare a variety of lengths.
Second, fairly precise, but not as accurate, the Powertap Powercal heart rate/power strap. This uses heart rate data to determine power output using changes in heart rate. The feedback is a little laggy, and the accuracy is within 15%, but for an individual the precision is high. So as long as you are using the data to compare your results agains your own earlier Powercal data it works well. It won’t work to compare your wattage to anyone else though. Still this could be used regardless of crank length. It would give good comparative data to see if there is an optimum crank length. I have one of these that I used for a couple of years, but it’s b en sitting in a box for awhile now. I no longer use the Powertap GPS head that uses Ant+. I would like to pick up a Bluetooth version that I could use with my phone.
Both of these solutions would work with any pedal, and the Powercal would work with any crank.
If you had the stuff to do it, wouldn’t mounting a standard crank based power meter onto a giraffe work? It would solve peoples worries about clipping in, though I’m not sure it would satisfy Harper’s complaints.
My response was about mounting a look pedal that had a platform attachment that made it simiar to a regular pedal.
The person seemed to think that having to mount a pedal with a platform in it would make the entire process of mounting impossible because the pedal may be upside down. having one of those platform attachments upside down when mounting then flipping them up one at a time with your foot would be very doable.
The Stages Power Meter appears to be a crank which you install which has the power meter inbuilt. First issue is finding one of the ones they sell that is compatible with a unicycle hub, the Qaxle from Quax may work with shimano.
However the length of bike cranks is fairly useless for unicycling as the smallest is about 165mm. If I want to see power outputs during hockey and I ride with 100s or 125s the pedals with a platform attachment to make them into a regular pedal is more useful I think. I have seen other power meters that a company will install in your cranks. I just worry that once my cranks go so does $800. Cranks go a lot quicker in unicycling.
PowerCal will not give accurate or reliable power data as it’s based on HR.
It appears it isn’t reliable for one person across multiple sessions let alone comparing between people.
Also I would like this to be scientifically accurate if possible so will have to steer clear of the PowerCal band.
Do you know if there are any power meters that use this pedal? If so it could be great. If not then you would need to stick with whatever pedal is on the pedal power meter. Currently all pedal power meters require a platform extension on top of them as they are all clipless (and unlikely to ever change to non clipless as no recreational cyclist would want to put a power meter on their bike :D)
That is interesting about the Powercal. I should look into it more because that doesn’t match the results of any of the other testing that I had read.
As for the Stages meter, they used to do custom installs into any crank you sent them. This is why I brought it up. I haven’t looked into it in awhile, so they may not be doing that anymore.
The problem is heart rate data cannot be used to work out power due to heart rate not directly measuring force x distance / time. Even as a proxy it is iffy because though your heart rate is related to effort as fitness increases your heart rate at a given workload decreases.
When unfit at 200W you may have a heart rate of 185, 2 months later at 200W you may have a HR of 150 due to improved fitness. At that later date a HR of 185 may represent 320W. This means comparisons between workouts is not possible.
This also shows why it can’t be compared between people. A Tour de France cyclist will probably be hitting 450W at 190BPM while most of us will be hitting 300W at the same HR. I am not sure how they calibrate it in the first place to try and determine what Power you are hitting at max as that is fairly difficult.
You are right about the stages meter building it into your crank, I am not sure if they still do but I have seen a few other companies that do that also
I’m not surprised Powercal has been found to be inaccurate - I’m kind of surprised it’s even considered a realistic way of getting accurate measurements. Because one of the places I’d expect to get benefits from a power meter is on a bike when doing time trials - if you base your efforts on heart rate for one of those then you’ll tend to start off too hard and then fall away as the HR lags the effort. Graphs I’ve seen for people using power meters and riding at constant power show the heart rate ramping up over time. The Powercal would be pretty useless in that situation.
Are you using the power meter to gauge how much power you can produce at different levels of exertion/fitness, and as a training aid? In that case, backward pressure could be considered, but it is only significant when going downhill, and even then, not important for what you are measuring power output for.
I race in the standard class, so of more importance to me is finding the highest power output based on wheel size, crank length and cadence. I want to know what crank length will give me the best sustainable power output, at a comfortable cadence, for that particular crank length.
Because the wheel size is fixed, the thing that affects my power is the cadence and the amount of force I can exert on the pedal.
Backpressure doesn’t matter, because what I’m interested in is forward motion on the flat/climbs, where there is little or no backpressure.
If you are looking at finding the optimal crank length, then it may be possible to do this on a regular bicycle with hub/wheel based power system, setting up the bicycle with different crank lengths, but you have to correlate this with the amount of resistance you expect from different unicycle wheel sizes/weights.
Actually no. I’ve been experimenting the old fashioned way…using a timed cycle route and a ride diary to make notes about how it ‘feels’.
The other trouble is that takes no account of the effect crank length has on the amount of energy you use to stay upright. I appreciate you’re a lot better than me, so it’s not as significant a factor, but are you good enough that it’s not a factor at all?
Seems a sensible approach given how tricky measuring real power is on a unicycle. Are you also using a heart rate monitor to measure actual effort? ISTM that if your aim is to maximise speed then measuring speed against heart rate should provide you with all the information you need and is actually more useful than measuring power.
1st pic: 4 strain gauges on KH 137/165mm cranks.
2nd pic: is a power meter I made for my bike. I used 4 strain gauges, an instrumentation amplifier, and an Arduino 101. 170mm square taper cranks.
3rd pic: was before I soldered everything together and was testing with a breadboard.
4th pic: I set cadence to be 60rpm, red line is torque, orange is calculated power with a moving average.
Here is a video of it working, with 5 second averaging.
The KH cranks are destined for a trike, but in the future I’d also want to try making power meters for unicycles. I get about 800 samples per 5 seconds, which should be plenty to analyze forward/backward forces that are very short in duration.
It currently ‘works’, but there is a lot that I want to change/try. Current problems include reliability and power; it disconnects and sometimes require me to press the reset button while riding. Also, the averaging time can’t be adjusted unless I connect it to my computer.
Future goals: averaging time adjustment, reliability, size, battery life, right and left crank power, displaying/logging reverse torque/power and cadence.
