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Our tool sponsor - Teng Tools are supplying us with an laser tachometer - simply stick a white spot at the object, spin it up, and point the tachometer at it.
Were planning to bring it along to some events with us this year to give people the opportunity to measure just what their spinner does.
I think people will be surprised just how much energy (and rpm) is lost due to wind resistance alone - espcially bar spinners !
Ed
http://www.stormrobot.comhttp://www.stormrobot.com
Agreed- simple laser tachos can be found most places- stick on a nice refective spot (as ed said) but you need the rest of it to be non reflective, cos nice shiny stainles discs will confuse the thing into reading 10000000rpm. As for wind loss, and other frictional loses, it should be possible to put an exact figure on that, then you can calculate how much energy is being disipated, and so how much work your motor is doing. Obviosly more friction an wind resistence results in more current being used by the motor, which is not good for anyone. Aerofoil spinner bars anyone?
Eds spot on - I can confirm that windage between discs and brg structure of a jet engine consumes many KWs of power! (I design em at work). His laser tacho :) is just what organisers need in their Tech Check box (along with Scales, Tape Measure, Calcuulator and Charts (who thought this was going to be easy :sad:)
BE VERY CAREFUL about standing by discs and checking their speed at an event (classic situation for injury) - but it would be really usefull if we could set up controlled conditions to plot theoretical disc speed (ie, motor free revs x ratio) against measured disc speeds - and create a rule for correction factor(s) based on an assessment of windage.
Then we measure motor revs (while the disc is off for weighing) and can more acurately asses your potential disc speed :)
Kev.
well im all for trying new things with the arena, before / after events, tests can be carried out in the arena with discs, with no audience around to help further this little project.
Jonno
Featherweight spinners are being carfully monitored at rr events by myself, each one, both construction and design is looked at... its in hand dont worry about that.
Jonno
Surely the only way were going to get a simple and fair answer is by measuring the actual speed of the disc itself at events and use a set of figures matchibg weights againest rim speed.
Any attempt to provide theoretical figures based on motor specs, operating voltages etc is likely to be seriously flawed due to losses in the system or maybe even misquoted gear ratios.
A decent optical tacho isnt that expensive and it isnt exactly rocket science to produce a safe enclosure to spin up discs in for testing.
Regards
Tim Jones
You can buy a tacho intended for measuring the speed of model plane props for 25 - 30 pounds. Works well for me. I position it near the disc and stand well back - binos to read it might be a good safety measure.
Yes John thats what Ive used to measure our disc speed
A simple optical tacho (I used it for my model aircraft) ..you just stick a white stripe down your disc (or any contrasting colour)....it is VERY accurate ..I measured the rpm of of my bench circular saw by painting a line of tippex on it and it was spot on the makers rpm.
You do have to be pretty close though ( 6 inches or so)and though I felt safe measuring Chips rpm at home, I dont know safety wise whether it would be advisable at an event.
Eds laser system seems like it might be quite safe as it seems it may have a longer range (what is the max range of the laser pointer Ed?)
But as mentioned they are very accurate.
Tom
Ive Never used a laser tacho before, but I would assume that it has a LCD screen displaying rpm. This should be easily removable, and cables extended meaning range is no longer an issue.
Strap robot in a cradle
Mount tacho on floor beside
(LCD outside Arena/Test area)
Crank up the Juice + Measure RPM
Roger.
Tim Jones states Any attempt to provide theoretical figures based on motor specs, operating voltages etc is likely to be seriously flawed due to losses in the system or maybe even misquoted gear ratios
Fully agree, but some people are so good at engineering that their losses are much less than others - so we are currently assuming there is No Loss of rpm, which is unfair to the less sophisticated builder. It may come to nothing, but the experiment might help us - to help others.
Kev