An electric Scale 2548 Twin?

Lou Melancon · Post by **Lou Melancon** » Sun Sep 25, 2005 11:06 pm

I am thinking about building a 2548 Twin Engine fighter for 2006. Twins can have 60" span and must weigh 4 lbs. Glow twins usually take two people to start and launch and it is always thrilling to try and get the engines running right.

I think electric might be a good way to go.

I spoke to Ed Kettler and the engine/prop requirements for electrics have a little latitude because no one is sure where to set them.

After a conversation with DrewJett about the ideas, he suggested trying to find a motor/prop/battery combination that yields similar performance to an SSC Glow engine.

Here are my thoughts so far:
<ul><li>Use 11.1 volt, 3 cell lipo packs (2) </li>
<li>Use two speed controllers, one per motor, limit and/or sync rpms if required with the Governor mode of the speed controller </li>
<li>Use brushless motors. I don't want to use gearboxes, so I'm leaning towards outrunners. </li>
<li>Find a motor combination that will turn an 8 or 9 inch diameter prop (pitch to be determined through testing), that generates 35-40 ounces of thrust per motor</li></ul>
Looking for any suggestions as to motors to evaluate. Thinking AXI or Himax brands now. Any and all ideas welcomed.

Lee Liddle · Post by **Lee Liddle** » Mon Sep 26, 2005 2:01 am

Lou, I`m not sure why, but I`ve heard that with brushless motors, you have to use one ESC per motor. With brushed you can use just one for two motors. Scott Stockwell has done a bunch of testimg on electrics for 2548. I know that he has worked on twins also. You should contact him. He is an RCCA member and has posted on the web site. Good luck with your project.

The Snake · Post by **The Snake** » Mon Sep 26, 2005 10:25 am

There are many motors out there that will turn an 8x3 with out gearing. I have use Mega, Hacker, CD ROM Himax and mant outrunners motors too.
A bird of that size may require bigger packs, like a two 3c 3p or 4p packs!! Good luck also Lou!!

Bender · Post by **Bender** » Mon Sep 26, 2005 1:46 pm

Lou, I am building Pe-2 camcorder-carrier for scale 2548. Now it fly with glow plug, but after tests it is obvious: electric engine much more attractive for such purposes. Movie taken during engine-cut gliding looks much more nice. So 100% sure soon we will have electric Pe-2 with scale 2548 parameters.

Visit FSA flying field (Laurel, MD) October 01, 2005 to fly in front of scale RC-Combat-camcorder-carrier. We need more streamers to cut.

RCCA #635

wrnstockwel · Post by **wrnstockwel** » Tue Oct 04, 2005 5:06 pm

Hi Lou,
Ed and I both built ME-110s at 60". The first build, the weight was within 1 oz and I was using Nmih batteries. After much experimenting and more to go to refine it I am going to stick with brushed speed 600 motors and an inexpensive GD600 gear box, using a 12 tooth pinion. Stay away from APC electric props and use standard master airscrew G3 props. Why am I staying away from brushless and direct drive?
1) Crash or land hard with a direct drive motor and your going to bend your motor shaft. Do you have to ask how I know?
2) Brushless, although very long lasting and very powerfull for their size, are expensive. If I did go brushless, which I have considered for a single, I would still put it behind a gearbox. Two reasons. Number one to protect it from having the shaft bent. Number two, it is more efficient to run an electric through a gearbox and use a larger prop.
Lipos are a must to keep the weight down to the minimum, I am going back to using 11x6 or 11x7 props on the gearboxes might end up dropping to a 10x8, run a single speed controller from Medusa that will NOT require a UBEC (cheaper) and inexpensive speed 600 motors, wired in series. You really only need to draw about 24 amps per motor with the 3 cell lipos. Getting into the 450-500 watt range will be plenty, then just play with the gear ratio and prop pitch to get the speed where you want. You will need at least 4000maH to make 5 minutes, more would be better. Try 2x3s2p of 2000s or larger (6s2p). Dymond has decent prices for there 3s 2000s, youll just need 4 for each flight.

Scott

Lou Melancon · Post by **Lou Melancon** » Tue Oct 04, 2005 5:48 pm

Scott that is some really good data. Need to read it through several times then test some setups with moto-calc to see what works.

Gawd I want to avoid gearboxes!

slam · Post by **slam** » Tue Oct 04, 2005 8:20 pm

drew and i had a long ride back from the jax event to talk about electrics in current combat classes.

a year ago i said it couldn't be done, that specific electric classes had to be formed. it think i was wrong.

i am considering ssc electric for the next event. but some of the same issues pertain to scale twins.

i also would like to avoid gearboxes. one issue that scott mentions is shaft bending. one thing that i think has to be done when considering electrics is to throw out alot of glow tendancies.

in designing an ssc plane i will not have to build up the motormount like i do for ic. in fact i want to build a breakaway....or more accurately a break inward motor mount system. with impact i want it to break into the fuse, hopefully protecting the motor.

vibration will be a nonfactor so the motor mounting system on a twin would be realativly easy. you could almost glue a nacell to the wing and expect it to hold up to the thrust.

as far as two brushless motors on one speed controller...drew has done it with two cd motors. don't know if that means it can be done with larger motors.

as i have said before. we need to address electrics in our combat community or we will miss an opportunity.

slam

wrnstockwel · Post by **wrnstockwel** » Wed Oct 05, 2005 12:05 am

Can someone tell me how to post pictures?
I use a Hayes AL-25 motor mount, cut a groove about 1 inch from the front for a tie strap and drill a hole about 1/4-3/16" back from the front to wrap around the back side of the gearbox.

As far as gearboxes are concerned, take a look at the GD600, the gears are 48 pitch, so you can buy pinions at your LHS that are used on RC onroad cars. I will be running some tests at the end of the week. I am about 50% complete with the EAM Bomber 17 assembly instructions, when those are done I can devote myself 80% to final testing. Then I will gladly share the information.

The key is to build light on the twins, Ed went to fiberglass rods from the full spar on the wing and eliminated the C-channel aluminum in the fuse and the weight dropped to the minimum 64 (aprox) from the original 80 oz of the first build.

When you cut your wings, leave some extra at the front of the shucks for making your nacelles. If you can afford oversize foam, do that to. Simply cut out the shape, glue a small firewall to screw the mount into and your done.

What Twins are you thinking of doing?

I have all sorts of motocalc data for the Nmih batteries, I just need to plug in the numbers for the latest set of motors I found and add the Lipos instead. I will make that available also.

Scott

Ed Kettler · Post by **Ed Kettler** » Wed Oct 05, 2005 3:07 am

Scott,

First you have to post the photos to a web site. Roy can hook you up with the RCCA photo gallery. Once the photos are on line, use the 4th button from the right (yellow with mountains) to insert the image tags. Then paste in the URL for the photo between the tags.

Ed

Which_way_is_up · Post by **Which_way_is_up** » Wed Oct 05, 2005 8:21 am

Scott, back in Feb. I set you up with a photo album on www.rccagallery.com. I'll re-email you the instructions for using it.

wrnstockwel · Post by **wrnstockwel** » Wed Oct 12, 2005 2:39 am

Thanks Roy, lets see how this goes.

Here are the Motocalc results I promised, take a look and you can tweek from these if you would like.

This is the Hayes AL19 mount. It has been discontinued but the AL25 works just as well.

The zip ties are located through drilled holes.

I broke the mount in the first round at Paris, simply put some epoxy in the crack and popped it back into place between rounds, still using the mount.

You can check out the gallery for the larger pics, if your really interested.

Scott