I'd like to pose a question. Given the same motor, esc, prop, plane, timer, what affect will result on going from a 3 to a 4 cell lipo pack on current draw and on mah taken out of the battery for a flight?

bob branch

So basically I could reprop, reprogram the esc by going to the govener mode and programing power setting in accord with the power needed by the plane for the maneuvers ie a lower setting than 100% that the plane is currently flying and not quite having the guts for overhead maneuvers in bigger wind and these things could reduce the battery draw?

bob branch

Hi Bob,
Well yes ... but this presupposes that you are going to prop and set the RPM in the right neighborhood. How comfortable are you with e-power in the first place? Upping the voltage 25% can have a dramatic effect (way more than 25%) on the current draw, depending upon a whole pile of factors including the motor specs.
Let me suggest this: gather the 3 important specs for your motor (Kv in RPM/V, Ri in milli-ohms, and Io or the no load current) and go to the Aveox website. Under UAV propulsion (hey that's us!) find the virtual testbench.

Now let's make some assumptions: Let's say you have a ~ 4 A-H battery. That means to fly comfortably, but with as much power as practical, for ~ 6 minutes you will prop to 30 A. That drains about 3/4 of the battery capacity. Put your motor constants in, and you will have to guess at the number of nickel cells that equate to 4 lithium. Depending on the current, it will work out to about 14 cells. The Aveox virtual testbench accepts fractions of cells (e.g. 14.7 cells). We all seem to fly within a few percent of 55MPH, so work out a prop diameter and pitch that draws 30A and flies at 55 MPH at the correct motor voltage (about 14.4 for 4S) .  Feel free to use oddball pitches like 4.35 and non-ieven inch diameters. Note the diameter, RPM, and pitch.

Now add 10 or 20% in pitch, to get the prop you will really use. (find the next standard pitch up, or two) Then take that % increase in pitch and take the same percentage off the RPM the simulator showed, and set the Governor to that RPM. That will keep 55 MPH. The average current draw should be very close to 30A. With the higher pitch put into the sim, it will show the maximum current BUMP you could possibly get from the ESC in a vertical climb. You may not get that much because the ESC will only do what it has to to maintain RPM, but you can see how much "headroom" is available for grunting through high drag and climbs.

The governor is not the same as throttling back: your controller came in normal throttle mode, and you will have to change it to heli-governor mode.

I hope I helped, but yell if I just made a mess.

Dean Pappas

Dean

Ok, I have to go there and play with the program some to see what comes up. One question though, how do you account for different prop charactaristics at the same size and pitch. For instance the difference between a Zinger wood sport prop with its narrow thin blade and a zinger pro wood prop with its much larger blade?  Or does this program just really get you to the point you have to go fly and see if the prop is taking the load out of the battery you expect?

Bob

Bob,
I would recommend the EagleTree Data recorder which would tell you what is actually going on during the flight. What matters to the plane (ignoring weight etc.) is thrust. I believe that there are a lot of props that can supply similar thrust, but what may vary a lot is the power draw from the battery. Since in electric, we can't be as energy wasteful as we can in a glow engine because that battery weighs so much and high current flows probably will shorten in life (=$ !).

So what I am saying is that working on the right prop is probably the best investment you can make! I would see if you can find some good electric props. They are a lot thinner than the glow versions since the electric power is so much smoother than that 1 kick per cycle (or 2 if you are four-stroking). I believe the thinner prop (I mean in cross-section, not necessarily blade width) will cut down the  battery  load.

On your Smoothie it probably is important to be conscious of the total weight. About the only thing you have to play with is battery weight at this stage --and maybe not even that. We are limited by the batteries we can buy--not like in glow where you can build your own tank to the exact size you want. However minimizing the current draw may give you longer life from those batteries.

Dean

What do we input in the Aevox computer for motor resistance for the AXI 28/26/10 and controler resistance for the Poenix 45?

Bob