Ok guys, I'm looking to get a propulsion system for my Emile Bertin (light cruiser -- built for big gun) build ASAP... Problem is, I really don't know what I want or need. I really wanted to go with a reduction gear box of some type, and either a pair of 280 or 370 motors. I would like the gear box to have the option of changing the reduction by changing gears. From what I've read, I think I would like to be able to tune the reduction between 2:1 and 3:1 or something similar. So the problem is that both the 280 and 370 motors have 2MM output shafts, and my prop shafts will be 1/8". Does anyone make a gear box that will work for this?? Looks like the BC box is 1/8" input and output, and it seems like twin 400 or 550 motors is way overkill. If no one makes a ready made gear box, I could possibly make my own, but where is a good source for gears?? I can find a few here and there, but not too easily for the 2MM shafts, and not in enough variety to get the gear reduction ratio I'm looking for.
http://www.sdp-si.com Order their catalogs. It's a set of books that include lots of engineering information. Even if you never buy a thing from them, it's a great reference set. Best part is, they'll send them to you free! JM
I used a 280 with 5:1 gear reduction in my small merchant, with a 1.25" prop, 4 blades at 20 degrees pitch. The ship took off like a rocket, easily exceeding 30 knots. Put two of those in your Emile Bertin, with 45 degree props, and you're going to move. Fast. Furthermore, the gearbox has a larger output shaft, that is so close to 1/8" that you can use simple fuel line as your universal joint. http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXVY65&P=0 For motors themselves, I would suggest the Graupner 280s. The Electrifly 280s get hot, unless you put a heat sink on.
I had considered -- well, almost decided on, the single motor, twin output gear box. However, I really like the idea of having the redundancy of twin motors, in case of one prop jamming, or a motor or coupler failure. At least it would have a better chance of making it back to port. That and the fact that the 550s are kind of big for the small cruiser. I had looked at the S280 gear boxes. They do offer a few different ratios. I thought that all of the ones they offer were too much reduction -- but it sounds like it may be more feasable than I first thought. When you use fuel tubing for a coupler, what kind of clamps, if any, are used to hold them in place?? Where is a good place to get the Graupner motors?? I was going to use the Electrifys, since I have to order some stuff from Tower, but since you've mentioned it, I would like too look at the Graupners instead.
I run with dogbones and I machined one set of brass ones with smaller holes when I had smaller motors. I have never used the tube.
The Graupner website offers good graupner 280s. If I remember correctly, they offer two 280-size motors, one as a spare part, and the other as a standard motor. They only list the statistics for the standard motor, so that's the one I would go with. If you wish to use the electriflys, it's a good idea to also get a heat sink for them. I am using a GWS aluminum heat sink on mine, with one minor modification made necessary by the capacitors pre-soldered on the electifly 280s. When I use fuel tubing as a coupler, I don't use any sort of clamp. The friction fit is very strong, although it does start to slip shortly before the motor completely stalls out. If I really needed to, I could put a small zip tie on really tight, and trim off the excess, but that hasn't been necessary.
