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heliwaz
02-01-2012, 04:39 PM
Hi
Im looking at the square wave output on my scope & your right its much better than the Hyperion one (Way Less slew rate & noise). From that square wave how would i work out my Motor RPM? What would the formula be?

heliwaz
02-01-2012, 07:42 PM
Ok i was on the right track but i needed a reference.

I build a tachometer to read the head speed & it was at 2400RPM approximately.
There are two ways of working it out but either are just as accurate. Without knowing how the YGE samples the & produces its output it maybe best to use the divide by 2 option below.

The total pulse length of the YGE on the output was 868us at 2400RPM
The Low period was 432.7us
Align 115 main Gear
Align 12 tooth pinion

Divide 2 option
Take the pole count of the motor & divide by 2
Mine was 6 so that equals 3

Mrev = TotalLength * (MotorPoles/2)
Mrev = 868us * 6/2 = 2.604ms

Motor RPM = 1/(Mrev/60)
Motor RPM = 1/(2.604ms/60) = 23041.4RPM

HeadSpeed = Motor RPM/Gear Ratio or (main gear/pinion)
HeadSpeed = 23041.4/(115/12) = 2404.32RPM


You can use the low period if you like but just don't divide the poles.
The Vbar also agrees with me but If its all wrong please feel free to call me stupid haha.

Now on to making the head speed logger :)

Steve Evans
05-08-2012, 05:57 PM
Did you make a logger?

Steve

heliwaz
05-09-2012, 12:17 AM
Funny you should mention it as i have started looking at it again. I have created the PC software & the PCB with the logger on it. Im able to log values Temp,RPM & graph them on the PC but im working on cleaning them up for better operation.
The PCB is a bit of a prototype that i made up. I may make a better PCB if i have time. Its just finding time to do the whole thing.

Have you made one Steve?

Steve Evans
05-09-2012, 02:57 AM
Neat! I like to see folks doing stuff like this. :lol:

Yes, see HERE (http://www.helifreak.com/showthread.php?t=395290). It's based on an mbed eval card with a Cortex-M3 LPC1768 processor. It logs all S.Bus channels (actually using DG1 linked to my hold switch to arm it), battery voltage, BEC output, headspeed, and ESC PWM signal. It has 4Gbytes of storage (in the form of a uSD card which I access via SPI), and a backup battery for the RTC so it can time stamp logs. I have a mini USB connector on the side of the heli to retrieve logs.

Data is currently sampled at S.Bus frame rate (130Hz) and 4G gives enough storage for many flights at about a Mbyte per minute.

Steve

heliwaz
05-09-2012, 07:20 AM
That looks like a powerful module/processor on board. I had thought about also logging current & pitch but maybe later. Good job creating it. Its a fair bit more advanced than mine. At a Megabyte a minute that's definitely on call for USB. Im not logging that much data. Do you use C++ to program it, what is the programming software?