Tuesday, August 13, 2013

Accuity V4.1–95% Complete!


It’s coded. It’s been running for about 70+ hours of testing and programming and forgetting to disconnect it on a CR2450 and still has life. It’s been extensively calibrated on the bike (this is necessary for removing bending from the left leg sensor). All parts (crank included) is less than $200 dollars. However skilled labour required is very high in terms of both skill and time. No, I won’t be selling these for $200 – my time is very valuable – but I still think a dent can be made in the $1500 mark. Powertap is forging the way.

To do:

  1. Move the Reed Switch closer to the Quarq Magnet location
    • My Madone has a different magnet taped on. The Nice Quarq ring magnet is on the old GT GTR Series 4.
  2. Put on Chain rings
    • RIGHT! I knew I forgot something.
  3. Test on Trainer
    • But I’m so out of shape.
  4. Test on Road
    • See above…? I’m really out of shape lately.
  5. Finish Enclosure design
    • Don’t ride in the rain until then!
  6. Torque effectiveness and Pedal Smoothness
    • Easy to calculate, but need to spend more time modifying the nRF51422 ANT+ library to support it.

It’s taken a while, but it’s doing well. It has 16 – 18 bits noise free. I’m using only 16 bits of the 24 the ADC is as it’s just about 100% noise free. It’s about 15 and 24 counts per N-M. Essentially this relates to < <1% error BUT keep in mind there is some sensitivity to pedal offset. It’ll likely come in at the competitions 1.5% – 2% quoted marks.

Okay, so maybe not 95%. I am very close. I am off schedule though, but honestly not by much:


I really didn’t include a prototype stage! Major oversight. However, if I build another 4 in a few days I’m 100% on schedule. No, I don’t expect this to happen. I need another month. So mid September for beta group I suspect.

What can it do?

It’s a powermeter so:

  • Measure Left and Right legs torque individually
  • Measure Cadence
  • Calculate Power
  • Transmit power data on the most common wireless powermeter standard - ANT+
  • Calculates L/R power balance
  • Costs a lot less than the competitors, but a lot of build time (Mixed feelings!)

Here are some pictures

Calibrating the non-drive side. The 5k on the right is to keep the rope stretched and the cranks level. 15kg “calibration weights” measured on calibrated scales at work which are good for 0.1g.


Debugging: Programmer talks to Accuity. Arduino receives the serial output. The .NETMF Fez Panda talks to another ADS1248 that’s also measuring one of the sensors to ensure Accuity is reading right. The Gripper is connected to a test strain gauge beam to ensure the Fez Panda ADS1248 is working.


Accuity up close. Personal. And poorly soldered!.


Serial Terminal and ANT+ Display Simulator.


So long for now


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