elogger V3 supply voltage?

[npomeroy]

I'm confused: Where does the supply voltage come from - the ESC/BATT connection? (Another thread said on 6S the regulator overheated and there should be supply via the BEC e.g. just black and red wires from a spare RX slot). The Brushless motor RPM sensor instructions say the supply shoud be less than 5.6 V. If I take a connection from my BEC it will be 6.0v (but I could put a diode or 2 in series to cut it back). Where is the documentation on this - I can't see anywhere that states what voltage the system operates on.

Nelson P

[alexf1852]

It plugs in between the lipo and esc on my Protos. So it gets its power from the lipo.

[npomeroy]

I think I've figured it. With the (6s) pack going through the heavy connectors the little pins have just under 5v on them so there is an internal regulator.
I'm using his partly to check my headspeed on a Compass Atom 500 (showed 2400 rpm) and also as a research test tool to compare current draw with headspeed. I'm advised to use higher headspeeds for stability reasons but when I did some rough measurements using an ammeter on a tethered TRex450 I got lower current draw with low rpm/high pitch than with hi rpm/low pitch which is opposite to what many say.
I MIGHT also get to compare servo current draw with 450 on flybar vs fbl.

Nelson P

[ahahn]

Originally Posted by npomeroy

I think I've figured it. With the (6s) pack going through the heavy connectors the little pins have just under 5v on them so there is an internal regulator.
I'm using his partly to check my headspeed on a Compass Atom 500 (showed 2400 rpm) and also as a research test tool to compare current draw with headspeed. I'm advised to use higher headspeeds for stability reasons but when I did some rough measurements using an ammeter on a tethered TRex450 I got lower current draw with low rpm/high pitch than with hi rpm/low pitch which is opposite to what many say.
I MIGHT also get to compare servo current draw with 450 on flybar vs fbl.

Nelson P

I think what you see is a true statement. I've used PropCalc to see what was more efficient to produce the same thrust, a high pitched low rpm prop or a low pitch - high rpm prop. At the time I was trying to conserve power in a control line aerobatis setup.

The same diameter and width prop model was used in both calculations. And like you found, the high pitch-low rpm was more efficient--in other words, used less power to produce the same amount of thrust.

There is a lot of misinformation floating around, and believe me, there isn't really much anyone can do about it!

[npomeroy]

Originally Posted by ahahn

...And like you found, the high pitch-low rpm was more efficient--in other words, used less power to produce the same amount of thrust.

I think the point people argue from is that electric motors draw less current at hi rpm/ lo mechanical resistance than vice versa. That's why smaller pinions can allow the motor to spin faster for the same prop speed and reduce amps. But it would only hold true at optimum pitch: If you spin a rotor at an insane rate with a low pitch I imagine the parasitic drag would become large.

I might say that so far with my 8-tooth pinion on my Compass Atom 500 it always hovers at about 2350 - 2500 rpm and about 16 amps, even with widely varying pitch and throttle curves. Turning on governer mode didn't enable me to increase the head speed but did increase the current draw slightly.

Nelson P

[ahahn]

Originally Posted by npomeroy

I think the point people argue from is that electric motors draw less current at hi rpm/ lo mechanical resistance than vice versa. That's why smaller pinions can allow the motor to spin faster for the same prop speed and reduce amps. But it would only hold true at optimum pitch: If you spin a rotor at an insane rate with a low pitch I imagine the parasitic drag would become large.

I might say that so far with my 8-tooth pinion on my Compass Atom 500 it always hovers at about 2350 - 2500 rpm and about 16 amps, even with widely varying pitch and throttle curves. Turning on governer mode didn't enable me to increase the head speed but did increase the current draw slightly.

Nelson P

People always make a lot of arguments!

If you want to see how a motor performs, download DriveCalc (it is free).

A generic observation is that for a given input voltage, a motor is most efficient running at about 80% of the no-load rpm. Higher than that value, you are dominated by iron losses. Lower than that by resistance losses.

So to explore, you can put in various head gearings, and play with input voltages, and see how the overall power in/power out varies. Of course you need some idea how your gear box efficiency varies with rpm.

Now after you know that, you need to understand how the efficiency of the rotor varies as a function of rpm and pitch. For that, you can download Prop Calc and put in a typical rotor, which isn't that hard for most constant chord symmetric blades (simpler than some of the strange propeller profiles out there!).

Or you can just go and fly, try both. There are advantages to both type setups.

The high pitch/low rpm is more efficient (note this is independent of how you setup your motor rpm and gearing), so you can get longer flights.

The low pitch/high rpm is less efficient, when producing the same thrust as the other. However this option has more stored energy in the rotor, so if you pop the pitch up, you can generate a lot of thrust in a hurry! I think that is the major reason a lot of guys fly that way. They really don't care if it is less efficient!