Tuesday, November 16, 2004

Andre Kilian on electric conversion

I converted a standard Shotgun 5000 to electric as a proof of concept, asone of my objectives was to prove that I can have similar weight and performance to glow by using electric power. The only change I made to astandard off the shelf Shotgun kit was to ask Mike Hirst not to cut off thenose but to leave it the length of a standard balsa plank (I wanted to keepthe distance between the prop and the wing leading edge the same as on aglow model, and to provide space for batteries in the nose just in case I ran into CG problems.)

An Aveox motor (1200rpm/v) was bolted to the nose, and I started with 10 CP1700 cells, which I had available. On this combo the CG was no problem, anda 13X4 APC electric worked fine (it hardly flew with the same wooden prop),with the amp draw about 30A max. Only problem was that I was slightly heavier than a glow version (although the CP1700s are a 4/5 sub-C size andweight), and flight times were about 5 mins. Next move was to install 3S3PKokam 1500 packs. Performance was up (prop hangs very easily, fantasticacceleration) and flight time was about 30 mins. Only problem was cooling on the motor, which overheats when prop hanging continuously. With hindsight it was not a good idea to use the plastic Robbe mount (very easyto mount, but shields about 50% of the motor from any airflow). A standard540 motor RC car heat sink solved the problem of overheating, but I also sourced some alu tube mounts that I intend using.

The greatest performance improvement came when Mike showed me how to set up the plane. It really helps when you know how, and whichever version you build it would be worthwhile getting some expert assistance with the setup!

My conclusion was that electrics are now able to compete on an even footing with the glow versions, and I suspect that it will not be long before ourtop pilots realize the advantages of electrics and start competing using electrics.

The only problem is that the Shotgun really shows up my lack of flying skills, which I am now working at with a Shockflyer (fantastic way to improve flying skills at very low risk and costs).

For the serious competition flyer I would recommend using a Axi 28/20/12o utrunner motor(new version) or similar, and Kokam 2000 packs, which will bring the all-up weight down well below the glow versions and have better performance on a 4S pack. The cheaper option would be to use a Jeti 30/3 motor with 3S2P Kokam 1500 batteries, which would enable you to have similar weight and performance to the glow versions, and about 15-20 mins of flying time.

Regards,

Andre

1 comment:

BallisticRC said...

I agree with Andre, most older kits do not have the space for battery packs and may cause the CG problem mentioned.

Alternative and better priced motors ie MSComposit Twister motors are available that have the same performance as AXI and/or better. Most of these bigger Twister motors have a very nice metal mount, keeping the motor open to all possible cooling, these mounts are perfect for the type of 3D airplanes. In cowl mounts for scale aircraft's are also available.

Check this site for Hanger 9 90 size Mustang electric conversion.

Newer packs are also available from Kokam ie 4S1P 3200 and 5S1P 3200 packs. Now you only have to charge one or maybe 2 packs at a time. Better voltage for better punch and with these packs in parallel the possibility for large scale are endless.

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