Successfully rewired the strain gauges this time with thin plastic insulated wire. Not the way to connect strain gauges as its far too thick and could pull them off but at least the chance of a short onto the crank is less. This time instead of applying Araldite directly to the gauges I’ve used a layer of wax first as a seal. On top to provide protection a layer of Araldite with foil on top. I felt that resin was too rigid and liable to crack allowing water to seep in. When I removed the resin it peeled away easily leaving the gauges in place fortunately.
Once I got rid of the dodgy connection to the Arduino it has settled down nicely during recent test rides. The zero force value at the end of a resent ride had remained the same as at the start. I can leave it running and there is almost no drift at all. I do get a slight variation in the value from day to day but its only equivalent to a kg or two of force. The Arduino’s startup code measures this value each time and stores it for use in the calculations so no affect on the forces measured unless it drifts during the ride.
To give an idea of the amazing sensitivity of the strain gauges this graphs shows the difference between the crank being at 90o and 270o. And I was worried I had a lot of noise but its not that bad.
![[Image: jlZc4z.png]](http://imageshack.com/a/img923/7411/jlZc4z.png)
Next is to get the NRF24L01 modules to communicate with each other and provide the power meter to auto shifter connection. It seems that wireless communication is challenging me again. Another challenge would be connecting to an ANT+ device, Arduino code is available that suggests can provide a link.
After that is taking the project to the exciting and new territory in the world of cycling, mapping optimum cadence against power output. BioShift have made a start but there system will always be limited by the ratio steps of derailleur gears. They talk about a sophisticated algorithm that can tell your fatigue level and calculate FTP *on-the-fly*. That’s what l want to start to learning about.
Once I got rid of the dodgy connection to the Arduino it has settled down nicely during recent test rides. The zero force value at the end of a resent ride had remained the same as at the start. I can leave it running and there is almost no drift at all. I do get a slight variation in the value from day to day but its only equivalent to a kg or two of force. The Arduino’s startup code measures this value each time and stores it for use in the calculations so no affect on the forces measured unless it drifts during the ride.
To give an idea of the amazing sensitivity of the strain gauges this graphs shows the difference between the crank being at 90o and 270o. And I was worried I had a lot of noise but its not that bad.
Next is to get the NRF24L01 modules to communicate with each other and provide the power meter to auto shifter connection. It seems that wireless communication is challenging me again. Another challenge would be connecting to an ANT+ device, Arduino code is available that suggests can provide a link.
After that is taking the project to the exciting and new territory in the world of cycling, mapping optimum cadence against power output. BioShift have made a start but there system will always be limited by the ratio steps of derailleur gears. They talk about a sophisticated algorithm that can tell your fatigue level and calculate FTP *on-the-fly*. That’s what l want to start to learning about.
- Oran