Originally Posted by SteveC68

Bingo,

Voltage cut-off changed to low and it runs like a champ. 6500RPM.

No load info.

3S 1750mah 20C
RPM: 7869
V: 12.34
Amps: 0.9
KV=637

You went from 4s to 3s? If not (typo?), that 4s is dipping way down low. I assume you're using a UBEC with 4s, right?

Kev

I swapped batteries. I now have a 4S, 3000mah, 40C Flightmax battery. This battery isn't sagging at all. The problem is that now the motor stalls again at full throttle. I've tried low and medium timing and it still stalls. Should I try high timing? These are the readings I get just before the motor stops.

GWS 1280HD
RPM: 6266
Volts: 15.23
Amps: 15.2
Watts: 229

I'll try the GWS1170HD next.

Originally Posted by Truglodite

You went from 4s to 3s? If not (typo?), that 4s is dipping way down low. I assume you're using a UBEC with 4s, right?

Kev

Yeah for the no load test I used a 3S battery. The first test was with an old 4S 2500mah 20C battery that I thought would hold up, but it's sagging pretty badly. See the new battery numbers above. Using this ESC:

http://www.hobbycity.com/hobbycity/s...idProduct=2165

GWS1170HD
RPM: 7836
Volts: 15.73
Amps: 15.8
Watts: 246

With this prop the motor makes it to full throttle no problem.

Drive Calc calls that 1439 grams (about 50oz) @ roughly 75% efficiency. That's holding the same efficiency mine did at about 2/3 that power level.

Looking good!


Dave

I was curious as to what the thrust might be. I did find this:

http://www.rcgroups.com/forums/showp...78&postcount=8

from Bruce Abbott and when I put in the RPM it came out extremely close to the number that drive calc gives for thrust. I'm planning on putting this into a UAV airframe that I'm designing out of Dow protection board. It has an 8 foot wingspan with a spruce spar. The plan was to pack it full of batteries to see what kind of duration I can achieve. I have another Turnigy motor on the way that I will do some testing on to see which one is better.

http://www.hobbycity.com/hobbyking/s...idProduct=8484

I had the DT750 on hand so I was curious as to what it could do. Any idea how much the efficiency would change if I could have done 22awg instead of 23?

Originally Posted by SteveC68

Any idea how much the efficiency would change if I could have done 22awg instead of 23?

Usually good for 3-5% (more usually 3) to add a gauge. Power level goes up a bit too.


Dave

Originally Posted by SteveC68

Yeah for the no load test I used a 3S battery. The first test was with an old 4S 2500mah 20C battery that I thought would hold up, but it's sagging pretty badly. See the new battery numbers above. Using this ESC:

http://www.hobbycity.com/hobbycity/s...idProduct=2165

That esc is good to 6cells, but it has a linear BEC, which is good only up to 3cell. So to use it with 4-6cells you need to isolate the BEC and use a UBEC or a separate battery. You're sorta lucky you haven't fried the BEC yet if you aren't using a UBEC or a separate rx pack. Regardless, that's more than likely why you're having problems.

Lots of people learn the hard way about going over 3cells with an esc equipped with a linear BEC, so pause on the 4cell testing until you understand what I'm talking about. Here's a diagram of how a UBEC is installed:

http://www.castlecreations.com/produ...ec_wiring.html

If you have a 4cell NiCD or NiMH pack, then you can use that instead. To do that, use the same wiring diagram, but leave out the connections to the battery plug. Wire the NiXX pack in to the RX ensuring the red and black wires go where they are supposed to go. Of course, when you're flying a plane (except for 1/4scale stuff), it's usually better to use a UBEC cause it's much lighter than a NiXX pack.

Kev

If there are no servos hooked in, the BEC doesn't much matter at this point does it? (Though certainly it's an issue on the "plane").


Dave

You wouldn't think so, but I wouldn't take that chance myself. I bet if he sticks an isolated power source on the RX, it'll test fine. Besides, the idea is to use that setup in a plane, so like taxes, pay now or pay later.

Kev

I can retest today with a Turnigy Plush 80amp just to see if that is the problem. I don't think it is however.

Confirmed that with a Turnigy Plush 80amp ESC the motor still stalls at full throttle with the GWS 1280HD on 4S.

I could try a HobbyKing SS 100amp ESC with a Dimension Engineering ParkBEC, but it's installed in a plane and would be sort of a hassle to pull out.

It was just a guess, but it sounds like I guessed wrong. I have a plush 80 coming in next week, which I ordered so I could test 4s safely. I wouldn't go to the trouble of making the ss100 available if you have a plush 80 on the side.

Kev

I can test my 37 turn half parallel on 4s if you want me to. The mystery 40A they sell on HC for $23 is almost excatly like my Reaper 40A, with a switching BEC and all the programming goodies. It is a great, functional, and inexpensive ESC, the best for the money IMO, especially if you are going 4-6S.

Sweet Mike! Thanks for that bit of "top secret" info. There is no note of a switching BEC on HK's mystery 40 esc page, it's $11 cheaper than a Plush 60 (Turnigy's entry level for a switching BEC), and it weighs half as much as a plush 60; perfect for a 40A 4-6cell setup.

Thanks,
Kev

So I finally got my Plush 80 hooked up, and my 10T parallel 20awg has been sitting on the stand waiting for it. I went right for the home run with the 1280hd, and it lost sync at about 2/3 throttle... screeeeech! So I fell back to an 11x7e and same deal, screeching halt at about 2/3 throttle. In both cases Eagle tree showed a peak of about 25A and 8000RPM when sync loss occurred. This was with low timing, and tried medium with the same results.

After soaking in the humiliation, I dropped right down to a conservative 10x5e, and finally got somewhere. Here are the numbers:

DT750-10Tx2-21awg-Y
no load
11936RPM/15.33V/1.797A -> 779Kv
(29m, 19.4C)
APC 10x5e
9465RPM/14.32V/16.75A/44.7oz/83.7%

How about that Io!!! The 10x5e also looks very nice, but it would seem there's room for a lot more than 240W (just 39W heat). Needless to say, that screeching was very frustrating, and why it was losing sync is a mystery to me. Any ideas? It did have a slightly wobbly shaft, maybe it was shaking too much? Maybe there's a prop with slightly more bite than the 10x5 that won't lose sync, but I feel like I need to put it away for a while.

Kev