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Home > Forum > Triathlon Forum > Build your own Power Meter for $350 - Link to instructions

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Re: Build your own Power Meter for $350 - Link to instructions [kwakeham] [ In reply to ]
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el_slice
Jan 31, 13 21:20
Post #26 of 37 (4044 views)
I'm definitely bookmarking this page and your site. I might have my power meter by the end of the year after all!

Great work!

And also, your seat is too high.
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Re: Build your own Power Meter for $350 - Link to instructions [el_slice] [ In reply to ]
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kwakeham
Mar 19, 13 16:06
Post #27 of 37 (3916 views)
Just posted an update comparing my prototype to a new Powertap G3.

After recalibrating you'd be hard pressed to see a difference. Some other things of note, such that a Powertap only updates at 0.8hz instead of the 4.06hz it's capable of!

http://keithhack.blogspot.ca/...ersus-prototype.html
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Re: Build your own Power Meter for $350 - Link to instructions [kwakeham] [ In reply to ]
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kwakeham
Jun 11, 13 10:07
Post #28 of 37 (3686 views)
Just wanted to post back to this as a update.

I've currently been working with the new Nordic Semiconductor Arm microcontroller which has a built in ANT+ transceiver. It's a very low cost chip that has allowed me to do a major design change. The board is quit small and unobtrusive and the developer kit version is < 5ma current draw equating to 100+ hours per coin cell battery (CR2450).

Once the antenna is trimmed and tuned the board will be 27 x 32 mm sitting between the right crank arm and the chain ring. For those interested please take a look at the blog, and if anyone is a cyclist in Kitchener-Waterloo Ontario or surrounding area then feel free to drop me a line if you are interested in being part of the beta group. I'm on track for August prototypes for people to test.

http://keithhack.blogspot.ca/.../boards-ordered.html
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Re: Build your own Power Meter for $350 - Link to instructions [kwakeham] [ In reply to ]
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playmobil31
Jun 11, 13 10:13
Post #29 of 37 (3671 views)
kwakeham wrote:
Just wanted to post back to this as a update.

I've currently been working with the new Nordic Semiconductor Arm microcontroller which has a built in ANT+ transceiver. It's a very low cost chip that has allowed me to do a major design change. The board is quit small and unobtrusive and the developer kit version is < 5ma current draw equating to 100+ hours per coin cell battery (CR2450).

Once the antenna is trimmed and tuned the board will be 27 x 32 mm sitting between the right crank arm and the chain ring. For those interested please take a look at the blog, and if anyone is a cyclist in Kitchener-Waterloo Ontario or surrounding area then feel free to drop me a line if you are interested in being part of the beta group. I'm on track for August prototypes for people to test.http://keithhack.blogspot.ca/.../boards-ordered.html[/quote[/url]]

Hey Keith, Is Toronto close enough for the beta test ?
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Re: Build your own Power Meter for $350 - Link to instructions [playmobil31] [ In reply to ]
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kwakeham
Jun 11, 13 10:18
Post #30 of 37 (3659 views)
Yes Toronto is certainly close enough, I'm there usually twice a month. Pm me.

I should note, currently all prototypes are going to be based on SRAM Rival GXP. They are 172.5mm crank arm length and 53/39 Cranks. There is one SRAM S950 that I'm using to test the viability of Carbon Cranks, however initially I need to stick to aluminium.

The idea is that they will be lent to people to test with for a few weeks and if there are any problems to give me a call.

Thanks
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Re: Build your own Power Meter for $350 - Link to instructions [kwakeham] [ In reply to ]
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blitzkrieg
Jun 11, 13 10:30
Post #31 of 37 (3628 views)
I'm in Toronto as well and would love to be part of the beta testing!

I was just in the waterloo area a few weeks ago for the Victoria's duathlons, too!

Pm incoming...
Duathlete by choice?
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Re: Build your own Power Meter for $350 - Link to instructions [kwakeham] [ In reply to ]
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Dilbert
Jun 11, 13 10:36
Post #32 of 37 (3616 views)
Oh man I'd be interested in making this. My soldering skills are mil-spec. :)

Will you let us know when the PCB is done... with the printed-on 2.4 GHz antenna I assume?

The biggest challenge doing these things is making a decent PCB and putting it all in a form-factor appropriate case which will also accommodate the battery and the buttons/switches. Finding the parts and soldering them onto the PCB is the easy part.

Edit: oh yeah I may have access to 2.4 GHz service monitors (spectrum analyzer, receiver, signal generator, combined). I know we have 2 GHz units all over the shop. Probably at least one > 2 GHz somewhere.
Last edited by: Dilbert: Jun 11, 13 10:37
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Re: Build your own Power Meter for $350 - Link to instructions [Dilbert] [ In reply to ]
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kwakeham
Jun 11, 13 10:55
Post #33 of 37 (3569 views)
The next challenge is the reflowing of the components. Two of them in particular are improbable to do by hand (The nRF51422 is a QFN and the weird BGA Balun).

I'm also converting to a two part epoxy for strain gauge installation. This is normally what's used for long life transducers (All commercial power meters use this) but it requires elevated temperature setting. So there are some challenges to replicating the new design in total and new features like fully active thermal compensation is still being developed. The short is this should almost never require re-zeroing during a ride. I'm guessing, but I suspect my approach is similar to Rotor's.
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Re: Build your own Power Meter for $350 - Link to instructions [kwakeham] [ In reply to ]
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Dilbert
Jun 11, 13 10:59
Post #34 of 37 (3560 views)
Uh oh BGA. Yeah that's an issue. It can be done by hand - reflow the PCB and then use a heat gun to attach the chip carefully without damaging it thermally. But realistically BGA etc... are designed to be assembled by robots.

Keep is informed please. This is very interesting. I've not worked with such strain gauges before. I ought to get some and experiment....
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Re: Build your own Power Meter for $350 - Link to instructions [kwakeham] [ In reply to ]
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Jan de Visser
Jun 11, 13 11:15
Post #35 of 37 (3530 views)
kwakeham wrote:
and if anyone is a cyclist in Kitchener-Waterloo Ontario or surrounding area then feel free to drop me a line

Keep me on your mailinglist please. Kitchener, a block down from Waterloo in Westmount :-) I guess I can also offer my services in software dev.

My email is in my profile, I think.
Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.
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Re: Build your own Power Meter for $350 - Link to instructions [Dilbert] [ In reply to ]
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kwakeham
Jun 11, 13 17:50
Post #36 of 37 (3387 views)
Dilbert,

Seriously, one lucky guy to get that nickname on anything

Also, in terms of strain gauges I've done a lot of experiments and there will be quite a few more to ensure the quality of my design. Some posts have a lot of detail, some are more superficial. So worth a read potentially if you want to get into strain gauging. I also have some youtube videos that are on the page linked back on the first page of this thread.

Thermal compensation
http://keithhack.blogspot.ca/...and-calibration.html

Force Sensitivity to offsets (and more thermal data)
http://keithhack.blogspot.ca/...testing-results.html

My old Prototype versus Powertap
http://keithhack.blogspot.ca/...ersus-prototype.html

While I wait to get my boards I'm designing the enclosure to be rapid prototyped via 3d printers. This is all consuming at this point.
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Re: Build your own Power Meter for $350 - Link to instructions [kwakeham] [ In reply to ]
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kwakeham
Aug 22, 13 3:50
Post #37 of 37 (3171 views)
I just updated my blog last night with my latest prototype tested outside with some video. It's located here

http://keithhack.blogspot.ca/...sting-video-and.html

I also provided the fit file and a link to the garmin connect site. I need to get the housing finished to secure the battery.
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