Doug Ireland Posted April 4, 2008 Share Posted April 4, 2008 Hi Guys,I bought a JP Micro Tacho some time ago but have never used it and over time I've lost the instructions that came with it. I seem to remember that the displayed value (2, 3 or 4 blades) had to be multiplied or divided by a number to give you the correct RPM. does anyone know what this number is?Cheers,Doug. Quote Link to comment Share on other sites More sharing options...
JT Posted April 4, 2008 Share Posted April 4, 2008 I believe you just add a zero to the end. Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 4, 2008 Author Share Posted April 4, 2008 Thanks JT Quote Link to comment Share on other sites More sharing options...
Former Member Posted April 4, 2008 Share Posted April 4, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 4, 2008 Share Posted April 4, 2008 My optical tacho ( set to 2 blade ) reads 30 in fluorescent light. I never use it in anything other than natural daylight Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 5, 2008 Author Share Posted April 5, 2008 Just tried it in the kitchen, reads 300 on 2 blade, 200 on 3 blade and 150 on 4 blade. Think I need to find something running at a known speed. Quote Link to comment Share on other sites More sharing options...
Mike Rolls Posted April 5, 2008 Share Posted April 5, 2008 DougJust add a zero. Electric light is 50 cycles per secon, 3000 per minute. It is govong a reading 'per minute' but reduced by a factor of ten (why?)Mike Quote Link to comment Share on other sites More sharing options...
JT Posted April 9, 2008 Share Posted April 9, 2008 That's the way theey are - mine's the same. Does anyone need more accuracy than the nearest 10 rpm? Quote Link to comment Share on other sites More sharing options...
Former Member Posted April 9, 2008 Share Posted April 9, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 9, 2008 Share Posted April 9, 2008 nah not me mate - I am unable to measure the RPM on my EDFs at all !! I have an eagle tree data logger on back order which will enable this function and many others besides Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 10, 2008 Author Share Posted April 10, 2008 Timbo,After reading your excellent articles in the mag this past couple of months, do you really need to be able to read the RPM of a ducted fan? I'd I've thought knowing what the unit draws power wise would be enough? You made it clear enough how the combinations of kV/prop size and other stuff works that even a "dyed-in-the-wood" meth-head like me would sit up and take notice!Well done and am looking forward to your next contribution!Doug. Quote Link to comment Share on other sites More sharing options...
Former Member Posted April 10, 2008 Share Posted April 10, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 10, 2008 Share Posted April 10, 2008 Hi Doug...and thanks for the comments, glad you found it interesting and understandable - still think it sounded a bit complicated m'self for beginners - but there ya go - worlds worst critic of m'self I am. The watts per pound rule and others such as "double and zero" ( ask me about that one later ) works pretty well for conventional tractor and pusher prop jobs, but if you take a look at the stuff I posted on fan testing that I did( it is quite interesting -honest ) - you can see that pure wattage does'nt really tell the story when testing EDF.Whereas it is accepted that different makes of propellors do indeed vary in their efficiency, EDF rotors vary a lot.You will see from the test rig I made, that static thrust with a midifan rotor was much higher ( over 25% ) for LESS watts than on a different rotor. Accepting that flight figures will be different, and different efflux tube diameters will vary thrust versus speed, it did nonetheless show the merit of other measurements as well as pure Amps / power.Check it out - its got videos too ! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 10, 2008 Share Posted April 10, 2008 Hi Eric, - yes I tried that already, but my fairly old ( 25 years ? ) optical tach could not cope with anything above 20000 RPM, and this fan unit is way past that. I have an eagle tree data logger on order, and this will measure RPM via the ESC "signals" and also many other parameters such as radio supply voltage levels reached in flight, temperature, altitude etc etc. Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 11, 2008 Author Share Posted April 11, 2008 Timbo,Regarding ESC "signals", a lot of people don't realise that modern Brushless motors are in fact three-phase Induction Motors. The signals you are looking at are the Pulse Width Modulation outputs from what is essentially a three phase inverter! I work on simillar systems that can drive up to a 2 mega watt motor! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 11, 2008 Share Posted April 11, 2008 Hi Doug....that would need a very big ESC! and an even bigger modelI take it these are the motive power for the fluid pumps ? Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 11, 2008 Author Share Posted April 11, 2008 Yes, and can move up to 100,000 barrels per day! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 11, 2008 Share Posted April 11, 2008 sounds a bit like my car when I am in "spirited mood " Quote Link to comment Share on other sites More sharing options...
Former Member Posted April 11, 2008 Share Posted April 11, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
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