Comments on: Laser spoke power meter

By: Ron George

Ron George — Mon, 02 Jul 2012 03:50:02 +0000

The interesting thing with these power meters is the development time. I’m always entertained by new concepts, but until a reliable, mass producable product comes to market that has the accuracy required of a powermeter, I’ll simply be….entertained.

By: Gennady

Gennady — Fri, 01 Jun 2012 11:26:07 +0000

We have some great news to share! I’m happy to announce that Laser Spoke ltd has applied for an Invest Northern Ireland grant (£50K) to run research and development on this project.

We have reviewed carefully our budget taking into account this serious government support and success of our IndieGoGo campaign. We are able now to introduce new prices for our perks for the period of this campaign.

We want to invite even more people to our project. Please share this great news with your friends, cycling clubs and welcome.

By: art

art — Fri, 25 May 2012 18:49:19 +0000

Stiffness of the wheel in any direction is not dependent on spoke tension unless they’re so loose they’re going slack. Even if you expand the rim thermally, you still have the same torque-rotation relationship between the hub and the rim. Elastic deflection of the tire doesn’t matter either, since it’s in series with the rim. You will get negative power under braking, but presumably this thing has a cadence sensor and knows when you’re not pedaling.

Dish deflection is linearly independent of power, so unless you’re bending the wheel so far that the laser misses the prism it’s not an issue.

There will be a bit of a sneeze if the wheel hits a bump when the prism is at the bottom. Adding a beam splitter and a second prism at 180deg would take care of this and the aforementioned balancing issues.

The only real problem I see with this is dirt fouling.

By: James Thomas

James Thomas — Fri, 25 May 2012 17:10:15 +0000

They definitely do have some issues to deal with. Something as simple as dirt or grime on the prisms could possibly throw it off as well. It is interesting though, so I am looking forward to following the project as it develops.

By: Mike

Mike — Fri, 25 May 2012 16:29:09 +0000

I can’t imagine this would ever be accurate without constant calibration. The device depends on even spoke tension and a consistent amount of torsional deflection from the tire. You’re also going to get goofy thermal expansion effects from both ambient temperature changes and heating the rim from braking. Dish deflection in a sprint will also give bad readings, and you’re also going to see weird readings every time you go over a bump. More power to the designers if they can engineer all of this out, but I’m not optimistic.

By: Bubba Nicholson

Bubba Nicholson — Fri, 25 May 2012 12:22:46 +0000

A similar laser-based rather than a magnet-based speedometer would increase appeal, albeit slightly–perhaps as slightly as the speed improvement.

By: Mohsen

Mohsen — Thu, 24 May 2012 21:07:41 +0000

I think that instead of asking riders to adjust stiffness of the wheels for calibration, it is better to calibrate the device by applying a known force(e.g. 10kgF) to the pedal and measuring the deflection of the rim to that force and calibrate the device based on the proportion of sample force/deflection.

By: Stu Cox

Stu Cox — Thu, 24 May 2012 19:25:38 +0000

Should have gone to Kickstarter!

By: Mzungu

Mzungu — Thu, 24 May 2012 18:57:49 +0000

oh, yeah. not sure if I like an un-balance wheel this may create either. had globs of those anti-flat sealant on my bikes once, and the unbalance feel of the wheel on the bike stand just drive me nuts. not that I can feel it on my mountain bike on a trail, but some thing about it don’t feel right. Measuring the strain on the pedal/Crank/BB to derive power output is still the way to go.

By: Willem

Willem — Thu, 24 May 2012 18:54:39 +0000

….But if instead you ride at 30mph but with the smoothest stroke, the deflection would be nearly zero….

not zero: power required for 30mph = torque * rpm = Constant * deflection * rpm.

if you mash the pedals, the torque may vary, but on average still is equal to above and > 0.