I’ve a project in concept stage where we want to log the angle a rowing oar makes with the boat as it is rowed. Id rather avoid a mechanical solution using an optical encoder due to waterproofing issues.
I was thinking of using a quadrature hall effect sensor with a ring magnet attached either to the oar or the rollick and the sensor to the rollick or the oar (so one part is at least fixed relative to the boat axis).
Has anyone had experience with these sensors and can advise on any problems or pitfalls, obtaining sensors etc. Some real world experience on maximum distances, maximum offset angles etc would be appreciated.
I can foresee some issues of maintaining the sensor/magnet alignment however I’ve been advised the rollick is pretty well clamped to the oar. Also the up/down movement of the oar might be an issue, but could be solved with some clever mechanical design.
I guess you have sen the Technique system from Precision Sport? (http://www.precisionsport.co.uk/) Couldn’t see immediately from the site what kind of sensor they use, but it looks like a miniature rotary encoder.
I’m not sure I see how you could use a HE sensor for what you want unless you are building a rotary encoder with it. A lot depends on degree of accuracy you are shooting for. If you just want to know the cadence, that’s easy but I suspect you want actual angle in real-time.
I’d look at the oarlock (or what ever they call it in the sport) and see if there is a way to have it press against a rotary encoder. Look at how mechanical (i.e. ancient) mice work with their encoder.
There might be some optical method that uses a multifaceted mirror to reflect IR onto several phototransistors that could be used in a quadrature fashion. The more facets in the mirror, the more accuracy.
rgbphil:
Id rather avoid a mechanical solution using an optical encoder due to waterproofing issues.
Could you paint the encoder 'disk' on the oar and then just point your opto sensor at that and count pulses? Could do an incremental encoder that way, without the need to really waterproof the mechanicals (beyond making sure your encoder 'disk' is waterproof.
We’ve got a number of issues using the oarlock…basically to do with the expense of cabling, fiddly external arms like the precisionsport system and setup time for the user.
Also oarlocks have about 10 degrees (worst case) of error. That is the oar can be at one angle and the oarlock at another. The oarlocks can be hard locked to the oar…but that’s another user setup issue and restricts roll on the return (as the rower feathers the blade).
We’re already putting electronics in the oar itself…hence we’d prefer to incorporate electronics in the oar, and passive references (eg optical disks, reflectors or magnets) outside.
Ideally we need a sensor or sensors in the oar that detect only passive references outside the oar that can handle oars moving up and down (pitch up on the return, and down during the phase) some back and forth slip for unskilled rowers and rolling the oar.