Paddlewheel speed log by humberto_mb

Last crawled date: 4 years, 1 month ago

INTRODUCTION
This is a design of a simple paddlewheel based speed log. The working procedure of the speed log is similar to those commercially available for boats ands yachts, but at a smaller scale. The incoming flow of water makes the impeller rotate. Each of the impeller paddles contains a small magnet. A simple electronics board counts each time a magnet passes the top most part. The velocity of the vessel over the water is proportional to the count (in reality it is not proportional, but for the intended use is perfectly fine to assume proportionality).
The intended use of this design is two-fold: for the one hand showing how these systems work; for the other hand, allowing the use of a simple and inexpensive speed log for small DIY crafts.
Although the use of a small size GPS could do much the same with more accuracy, I have developed this for use in a small size low-cost ROV (Remotely Operated Vehicle) for underwater exploration. There, there is no GPS at all.
The code and schematics for the Arduino based electronics are freely available in my GitHub account:
https://github.com/humbertomb/arduSpeedLog
MATERIALS
1 x Upper part case, for the electronics (printed, PLA)
2 x Lower part case, for the impeller (printed, PLA)
1 x Impeller (printed, PLA)
4 x Small circular magnets (5 mm diameter, 0.1 mm thickness)
1 x M3 bolt 15 mm
1 x M3 locknut
2 x M3 washers
BUILDING
I printed all the parts with a XYZ Davinci Jr, low infill (10%). Very solid and accurate.
The three parts for the case have been printed using white though PLA (although regular PLA could have been enough, I just run out of it). The impeller has been printed using orange translucent PLA.
I started printing the impeller. I re-drilled the axle hole with a 3mm drill. Then glued in place the magnets (on top of each paddle) and the washers (on the axle hole) using cyanoacrylate. Then I printed the two lower part halves and the upper part. Then I glued the three together using cyanoacrylate.
Last I fitted the impeller inside and pulled the bolt trough the axle hole and firmed it using the locknut. Do not tighten too much the locknut, otherwise the impeller will not spin freely.