Does the powerpod work with a bionic runner

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Arnoldus
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Joined: Sun Jun 24, 2018 2:04 am

Does the powerpod work with a bionic runner

Post by Arnoldus »

Hi,

I have been looking for a power meter for my bionic runner for while without luck.

I have garmin speed and cadence sensors installed and is supports freeweeling.

You can see it in action here: https://www.youtube.com/watch?v=K4t4PPpFTZk

Will the powerpod work with a bionic runner?

Thanks Jan
Velocomp
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Re: Does the powerpod work with a bionic runner

Post by Velocomp »

The good news is...I think so! We've successfully used our technology with products similar to this (eliptigo).

Basically, you'd set up PowerPod on the handlebars of the bionic runner, put a speed sensor on the wheel, then set the correct wheel circumference in Isaac.

The bad news is...I can't check anything in detail. Their website run4.com is not working. Maybe this is why:

https://www.cpsc.gov/Recalls/2016/runni ... s-bicycles
John Hamann
Arnoldus
Posts: 10
Joined: Sun Jun 24, 2018 2:04 am

Re: Does the powerpod work with a bionic runner

Post by Arnoldus »

Thanks for the response. Run4 unfortunally when broke in january due to being ripped of by a chinese vendor. That why their website is down. The problem in the link you provided has been fixed. The bionic runner is a lot like the elliptiGo so if this work the bionic runner should be fine.
Arnoldus
Posts: 10
Joined: Sun Jun 24, 2018 2:04 am

Re: Does the powerpod work with a bionic runner

Post by Arnoldus »

Hello again,

I have now bought the PowerPod for my Bionic runner (ElliptiGo lookalike).

During setup I could not select my tyres (20x1.35 schwalbe marathon plus) so I selected the 20x1.75.

For the ride position I choose Hoods, but I am standing all the time when using the bionic runner.

I choose the best calibration and did the calibration ride in some rather windy conditions. Afterward I took it for a 29 km ride. The average effect were 134W and 109W which seems very low (had expected an average over 200W if the effort should be comparable with running). My running FTP is 274W and I had hoped that effect between bike and running were a bit more comparable.

I have attached the two rides - Do you have some suggestions for a better calibration?
iBike_07_02_2018_1248_5_km_CalRide.ibr
(55.46 KiB) Downloaded 217 times
iBike_07_02_2018_1337_29_km.ibr
(264.25 KiB) Downloaded 216 times
PS - During the calibration and the 29km ride the firmware were 6.24. It is now updated to 6.40

Thanks Jan
Velocomp
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Re: Does the powerpod work with a bionic runner

Post by Velocomp »

There are several points to be made:

1) You need a much higher CdA for standing; basically, your entire body is facing the wind. A higher CdA will increase your watts. I used the number 0.5 for CdA; this provides consistent watts results when you're descending.

2) Other than CdA your PP is well-calibrated. I have attached a corrected ride file and profile for you to use.

3) Bicycling watts is a well defined concept, both in physics and in measurement devices. Power is defined as Force x speed = watts. The force and speed measured is, specifically, what moves your bike down the road. The concept of "running watts" is bogus. What is running speed? How fast you move down the road, or how fast your body bobs up and down? Is it both, neither, or something else? How do you measure the applied or opposing forces your body produces while running? If it's applied forces: where is the strain gauge placed on your body? What is it measuring? Is it the frictional forces of moving your legs front to back? What about the forces required to move your body up and down? And each time you move your legs, you accelerate your body; that requires energy, too. Where and how is that acceleration measured? The point is: there are no sensors in existence that can measure your running forces. Therefore, there is no accurate way to measure running power.

4) "Running power" is a term that some sleazy marketer invented (Stryd?), to give a recognizable meaning to to whatever it is they are really measuring (probably heart rate and its related parameters). This is a total guess on my part, but one thing that COULD be done is to put a runner on a treadmill, measure oxygen usage (which would be a proxy for energy spent for exercising), compare that energy expended to heart rate readings, and infer energy usage from heart rate changes and oxygen expended. Since power is energy expended per unit of time, a power number could be calculated. But the key word is: INFERRED. Such a power measurement is indirect.

5) Another fine point, but important to consider, is that a running power measurement, such as the one suggested in 4), measures how much energy the body uses to convert its fuel (fat, sugars, etc.) into the movement of the body down the road. Cycling power measurements do NOT include the conversion of body fuel into energy; cycling power is ONLY the energy required to move the bike/rider down the road. Think of it this way: when you're on a bike, at a stop sign, your cycling power is zero. But your body is still burning energy.

In sum, I have no reason to believe there should be any correlation between cycling power and running power. Cycling power is a well defined, accurately measured number. Running power has no definition in physics and no direct method of measurement.
Attachments
arnoldus.ibp
(411 Bytes) Downloaded 212 times
arnoldus_07_02_2018_1337_29_km.ibr
(282.44 KiB) Downloaded 193 times
John Hamann
Arnoldus
Posts: 10
Joined: Sun Jun 24, 2018 2:04 am

Re: Does the powerpod work with a bionic runner

Post by Arnoldus »

Hi,

Thanks for the quick response. The bionic runner isn´t very effective which means that the speed will be lower for the same effort (eg. HR). Shouldn't the same effort result in the same watt on the powerpod for two different bikes? If yes then one thing is the extra wind resistance, but I also think the different pedalling system and the small wheels cost a lot extra. Would it be the fric parameter that should be adjusted to adress a more ineffective bike?

Thanks Jan
Velocomp
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Re: Does the powerpod work with a bionic runner

Post by Velocomp »

There is a lot going on here:

1) As stated in the previous post, a cycling power meter measures the amount of work (energy) required to move the bike down the road. A power meter does NOT measure how efficiently your body burns its energy to move the bike.

2) I agree that HR is a proxy for the body's actual work.

3) Yes, two road bikes will produce similar heart rates. But a bionic runner is not a road bike. What its HR/power factors are, I do not know.

4) An experiment you might want to try is putting your PP on a road bike, then do a ride with it. Take your road bike out on the same course, and pedal at a speed sufficient to get your HR up to the level of your bionic runner. At the end of the ride, you can compare average watts from your road bike and your bionic trainer ride file, then adjust the profile coefficients of your bionic trainer to get total power similar to your road bike.
John Hamann
Arnoldus
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Joined: Sun Jun 24, 2018 2:04 am

Re: Does the powerpod work with a bionic runner

Post by Arnoldus »

Thanks for the answer. I will try that. Which parameters would you suggest I change to get similar watt from the two rides?
Velocomp
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Re: Does the powerpod work with a bionic runner

Post by Velocomp »

Post your ride files and I will help. Obviously it will be a combination of CdA and Crr.

Make sure you set up PP "normally" for your road bike!
John Hamann
Arnoldus
Posts: 10
Joined: Sun Jun 24, 2018 2:04 am

Re: Does the powerpod work with a bionic runner

Post by Arnoldus »

Hi John,

I was thinking that a bionic runner and a road bike won’t be comparable. E.g. due to the higher weight the power to climb hills will be higher on a bionic runner than on a road bike.

It is not important to me that the watts is completly correct, but than the watts vs. effort is good. So an idea could be to make a ride with a stable effort (eg. stable HR) with head/tail winds and some hills. With a good calibrated power pod I would expect the watts to be fairly constant during the ride.

So if I afterwards try to adjust the parameters for the ride so the result the watts are fairly constant with an average power of eg. apx. 200 watts I would think that could be usable.

What do you think of this approach and do you have any descriptions of the parameters so I could play with these when calibrating the powerpod?

Thanks Jan
Velocomp
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Re: Does the powerpod work with a bionic runner

Post by Velocomp »

As long as you put in the weight of your bionic runner correctly, you'll be OK. With a heavier bike you'll climb more slowly. Watts will remain the same.

I think the thing to do now is to calibrate your PP for your road bike, go do a known course, then repeat the same course with your bionic. Try to hold the same level of HR for both rides. Post both ride files
John Hamann
Arnoldus
Posts: 10
Joined: Sun Jun 24, 2018 2:04 am

Re: Does the powerpod work with a bionic runner

Post by Arnoldus »

Hi John,

I are probably right. I have an old road bike at my summer house and summer vacation is one week away. I will then do the test and upload the two rides.

I did an out and back ride today while trying to keep my HR constant. I have uploaded the ride. The out and back ride with constant HR starts apx. after 4 km and last until 19km. The rest is warmup/cooldown. When I look at the ride there is a large variation of the power during the ride. I have set the weight of me and the bike correct, but it seems like gravitation affects the power more than is should.

Does the CdA means how much area I and the bike covers from the front? If this is case then I would think the value should be more like 0,6 (175cm x 0,34cm) for me alone. Maybe a bit more with helmet and bike wheel.
iBike_07_09_2018_0805_21_km.ibr
(180.99 KiB) Downloaded 205 times
Thanks Jan
Velocomp
Velocomp CEO
Posts: 7793
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Re: Does the powerpod work with a bionic runner

Post by Velocomp »

Your ride file looks fine. Power variation is very normal.

I agree you should probably use a CdA of 0.6 for your bionic trainer.
John Hamann
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