Saw the trainerroad guys post this on FB:
“Just met with two brilliant young engineers at the back of the expo who have a prototype for a new, $500 power meter that is going to be a game-changer. Unlike anything we’ve seen before, this device will simply plug right into the center of the spindle on the bottom bracket. The new technology is impressive to say the least. We’ll have a more detailed write-up on the blog soon!”
More info: http://www.ashtoninstruments.com/
This would be awesome, if it is fully rebuildable I will use for MTB.
spindle meters measure only one leg.
Could they be creating a Left/right version?
Could they be creating a Left/right version?
Not if it only lives in the spindle. Your right leg doesn’t twist the spindle.
Now I am having trouble envisioning this.
This is a bottom bracket power meter? Correct?
Now I am having trouble visioning this.
This is a bottom bracket power meter? Correct?
yes.
push with your left leg, crank arm twists spindle, which is connected to the drive side, which pulls on chain.
push with your right leg, arm just directly pulls on chain.
so within the system the right crank arm will not create measurable torque through the spindle?
so within the system the right crank arm will not create measurable torque through the spindle?
Nope. Ergomo did something similar a thousand years ago. left leg power only.
Jack,
Curious…if the power is measured further from the leg (where the force is applied), example - instead of the crank (stages) it on the bottom bracket would that be closer to average power between the legs?
Not something I would have intuitively thought. Though after thinking about it a little more it makes sense that this would be the case.
Nope…Left leg power only. Left crank arm is connected to the spindle, spindle is connected to the right crank arm, which is connected to the spider that is connected to the chainrings. It is measuring it one step closer to the chainrings than a stages…but no power should be created or lost in the intersection between the left crank arm and the spindle. As jack noted earlier Ergomo did this a long time ago. Overall this is not any better or worse than a stages…just different. And the details will make it or break it. As dcrainmaker pointed out somewhere, they are planning on launching in 2016 and there is a lot poised to happen in that time frame, both in and out of their control.
Jack,
Curious…if the power is measured further from the leg (where the force is applied), example - instead of the crank (stages) it on the bottom bracket would that be closer to average power between the legs?
Nope, either way you get left only.
Not until you hit the spider do you get both legs.
Something you could try to do with any 1 leg power meter, is have hardware on board that has high resolution rotation speed data, which might let you estimate if the other leg is a certain % higher or lower in power, based on how the rotation speed changes during the power phase of each leg, and adjust your total power with that.
I’m know I’m a picky asshole about power meters, but I think that approach could be pretty good and sensible if it led to a cheaper meter.
Something you could try to do with any 1 leg power meter, is have hardware on board that has high resolution rotation speed data, which might let you estimate if the other leg is a certain % higher or lower in power, based on how the rotation speed changes during the power phase of each leg, and adjust your total power with that.
I’m know I’m a picky asshole about power meters, but I think that approach could be pretty good and sensible if it led to a cheaper meter.
I suggested exactly that to Ergomo about a decade ago. It should work as long as you’re pedaling constantly; the question would be how to deal with half-strokes, backpedaling, etc.
EDIT: If you think about it, such an approach would sort of be a hybrid between an iBike (right leg) and what they call a direct-force power meter (left leg).
Thanks for catching the typo! Fixed!
I suggested exactly that to Ergomo about a decade ago. It should work as long as you’re pedaling constantly; the question would be how to deal with half-strokes, backpedaling, etc.
You could probably identify outlier cases like that and just go back to normal doubling for those moments.
Something you could try to do with any 1 leg power meter, is have hardware on board that has high resolution rotation speed data, which might let you estimate if the other leg is a certain % higher or lower in power, based on how the rotation speed changes during the power phase of each leg, and adjust your total power with that.
Let me add to that comment on “high resolution rotation”: We all typically assume that a bottom bracket power meter will measure torsion in the bottom bracket spindle, thus estimating left-leg power only, because standing on the right pedal doesn’t twist the spindle.
But - standing on the right pedal does bend the spindle. And I’m wondering if you could instrument the spindle appropriately to measure the bending. If so, and if you had enough angular resolution, you could separate left-leg bending from right-leg bending, and potentially not only measure left-leg power but right-leg power as well.
All that just to say: I wouldn’t be too surprised if someone comes out with a bottom bracket power meter that isn’t one-legged. Impressed? Yes. Surprised? No.
I had this thought too, I think it would end up working terribly, but you could certainly TRY to do this!
But - standing on the right pedal does bend the spindle. And I’m wondering if you could instrument the spindle appropriately to measure the bending. If so, and if you had enough angular resolution, you could separate left-leg bending from right-leg bending, and potentially not only measure left-leg power but right-leg power as well.
All that just to say: I wouldn’t be too surprised if someone comes out with a bottom bracket power meter that isn’t one-legged. Impressed? Yes. Surprised? No.
Thanks for catching the typo! Fixed!
What typo? 
Something you could try to do with any 1 leg power meter, is have hardware on board that has high resolution rotation speed data, which might let you estimate if the other leg is a certain % higher or lower in power, based on how the rotation speed changes during the power phase of each leg, and adjust your total power with that.
Let me add to that comment on “high resolution rotation”: We all typically assume that a bottom bracket power meter will measure torsion in the bottom bracket spindle, thus estimating left-leg power only, because standing on the right pedal doesn’t twist the spindle.
But - standing on the right pedal does bend the spindle. And I’m wondering if you could instrument the spindle appropriately to measure the bending. If so, and if you had enough angular resolution, you could separate left-leg bending from right-leg bending, and potentially not only measure left-leg power but right-leg power as well.
All that just to say: I wouldn’t be too surprised if someone comes out with a bottom bracket power meter that isn’t one-legged. Impressed? Yes. Surprised? No.
The problem is that not all the bending you would measure would correspond to actual power. Just imagine the bending caused by standing on the pedal at the bottom of the stroke, that bending does not correspond to any power.
The Garmin Vector has a similar issue, but since they also track the velocity of pedal with accelerometers, so they essentially only use the deflection in the direction of the velocity vector. Using bending of the crank spindle would need a different method, since its’ only real degree of freedom is rotation. I do not know how you can differentiate between bending that is resulting in power and bending that does not.
hmm, I’m sure the BBC will have issues with them using the Stig
.