Thread: Discussion E-power F3B set-ups
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Old Oct 17, 2012, 11:52 AM
Tony Fu is offline
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Roy, good advice.

We have recently done a lot of testing with skinny clean 3m F3X electric models in mind and previously converted a lot of 3m gliders to electric power mainly because manufacturerís electric versions of 3m F3X ships are just not as good for the purposes we wanted.

That is; light and not too much difference in weight to the glider version, clean so lower drag and finally ability to take a fully loaded F3B plane to height safely so approx 4kg +.

This basically led us to 1 Kw out put power trains, which of course is a very nice amount of power for sports flying a 3m F3X.

At this power level we discovered some interesting things about what works keeping the system as light as possible. You would think that a Hacker B40 or Kontronik Kira 480, basically off the shelf 28mm can geared motors, would work well. They didnít, yes whilst these motors can be pushed to 1kw in the air, they are not efficient and so need bigger batteries than you would expect. The climb is slower, so you need longer motor runs. Around 750w is good but not 1kw.

A better solution was when we ran 36mm can motors, where the efficiency is much higher at the 1kw level. (We used a Hacker B50 12s geared after a few changes). Then you are looking at 5-6s motor runs for 250m and so high C rating small capacity cells can be used. We have tested TP, 65c 1300mah 4s which with a safety margin can provide 30s at around 80a so about 5-6 climbs. Motor weighs 250g and lipos 165g so 415g in total. This is marginally lighter than a B40 geared set up with larger capacity lipos weighing 250g and motor 180g (=430g). But because of reduced efficiency you would be on the road to ever decreasing returns pushing a B40 to climb in the same way even though you might measure the same 1kw.

The problem of course that there are not many skinny F3X fuses that will accommodate a 36mm can motor. Those that do like the New Air One allow a really lightweight set up. Ours using TP1300mah weighs just 2.4kg. As you might imagine it can thermal very well at this weight.

Incidentally, we settled on 4s as the minimum lipo cells to support a UBec at reasonable currents. 3s was just too much for comfort and 5s excessive. Remember we wanted to optimise for lightness and 1kw.

Another route is to use long case 28/29 can motors and marry to a Kontronik gear box, a custom motor then. Neu motors 1115 will do and also one of the Mega 28mm cans. These are basically longer than stock B40L and Kira 480s and will handle 1kw efficiently. They are also over an ounce lighter than say a Hacker B5012s geared.

So for a skinny F3X- E glider there is a bit of difference in what 1kw can do, not all power systems deliver in the same way and also you really you need a 16-17 inch prop to make use of it in a 3m. Our results in flying look like much more power as the previous video posting shows. Itís definitely no slouch!

The results on the flat without a slope were also much better than we expected.
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