Wireless Work and Resonance Solved

Work continued this week with the pair of RFU220 wireless transceivers. The software for AMOS and the PC are now working pretty seamlessly, so everything that could be done before with a WiFi or cell link can now be done with this serial wireless link. I also soldered up an extra pair of communication lines to the PC transceiver which lets me poll it for additional data, like for example the strength of the wireless connection. That should be useful as a troubleshooting tool when the boat becomes unresponsive and starts floating out to sea. 😉 To allow the link to work with an Android or iPhone device I think I would probably need to add some sort of a Bluetooth low energy dongle, to allow the phone to communicate with the serial transceiver.

Some long awaited spare propellers arrived today, so I replaced the warped and broken one with a new version; here is a comparison of old vs. new:

To evaluate whether or not there was any difference in thrust between the two propellers, I used my kayak straps to suspend AMOS from a beam in the garage, and measured the horizontal deflection distance at full throttle. There was no noticeable difference in thrust between the two, at full speed they both gave AMOS a horizontal deflection of ~ 1 inch. Based on the weight of AMOS (36 lbs) and the suspension distance (~ 4 ft) this translated into a pretty small thrust; no more than a pound. One added benefit of the new propeller though was that it ran much smoother, and there was no noticeable resonance at any speed whatsoever. So at least I was able to remove those lines of code that disallowed any speeds between 3 and 6. The lesson learned from this thrust test is that AMOS needs to go on a diet and slim down (i.e. become lighter and more hydrodynamic) if it actually hopes to use an air propeller for real navigation.

Right now I am soldering together some current sensing capability to the transceiver module on AMOS. I am basically just using the two ends of the ground return cable on the +12 V supply as a sort of shunt resistor and amplifying the voltage between the two ends with a surface mount op-amp that I had from an old project. The eventual goal is to add some software and enough smarts to be able to gauge how much battery power is left or how long it will take to charge given the amount of available sunlight.