I do a lot of cycling. I purchased a new high end all composite bicycle last year even though I have been very happy with my old aluminum bikes. I was trying to keep an open mind but that meant keeping an open wallet. Even the crank arms on this bike are composite but they may have aluminum spines. I just replaced the crank set and my claim is that the composite crank arms started to flex on me after one year of use. The dealer and his mechanic thought I was out of my mind. I instrumented the crank with a strain gauge setup and I was able to measure some flex. I estimate/claim that I got about 2-4 mm flex in my composite crank arms. The setup was not perfect but it was a start. Now I have a new crank arm set that I would like to monitor over the next year.
I would like to instrument my crank arms with a wireless strain gauge (each) setup and ship data off to my Droid-1 phone or an otherwise home built data logger that I can carry with me on my rides. Eventually I would like to instrument the major structural elements of the frame with some strain gauges as well. I use a power meter which is installed in the rear hub and it communicates to the head unit via ANT/2.4GHZ. In the long run it is my wish to “hack” the power hub data and record it on my device to see power vs. strain. I have never worked nor designed a wireless system and I am looking for some advice and/or opinions. For some reason xbee came to mind.
GoldenEmbed I believe"collects all ANT+ messages sent on an SD Card". Which is good. I want to build one or similar, but time and money limiting me and I’m already working on another ANT+ based project.
So what I would do is build up the GoldenEmbed device which solves the capturing problem. Also the GPS’d version could be good.
But what you what will need you to build an “ANT+ sensor”.
The “Transceiver nRF24AP1 with Trace Antenna” used for the logger can also be used as a transmitter, so you’d need two of these. One for the general purpose logger and one for this sensor.
You’ll need a microcontroller to talk to the nRF24AP1 board, a tiny Ardunino would fit the bill. Plus you can use the analog inputs directly after the wheatstone bridge and instrumentation amplifier chips.
Most strain gauges are simply affixed with “cyanoacrylate”… superglue by it’s non-technical name. It’s easy and fast. Sounds like you’ve already done some affixing though. I’ve been warned by the technicians and prof’s at my university that this is not a good long term strategy as it can creep and break. Sounds like a possibility on a bike outside in varied temps. And some strain setups ARE temp sensitive. I think Omega.com has a cheat sheet I use. Load cells are made up using a different adhesive compound that I believe requires chemical cleaning of the area it’s affixed.
The other cheaper way is Ardunio or similar as a logger. The gauges, wheatstone, and instrumentation amplifiers tie in directly to it and you have one nRF24AP1, which is 4 channel, to log speed/cadence, power, and heart rate. Whats even better - most combined speed/cad sensors only use one channel, leaving you a spare in case you want to do secondary instrumentation and make an ANT+ load sensor.