Tony Harrison 2 Posted November 30, 2014 Share Posted November 30, 2014 I am aware of very helpful advice on this site about motors and their characteristics, but I was sure I'd seen somewhere a sort of "how to" on selecting motors for specific models and purposes. I'm building the Aquarius electric glider about which I posted in the "Traditional Builds" section and to expedite this build, I want to get a motor and other electric bits so I can build the bird around them. It will be my first motor purchase and I want to get it right... Thanks, Tony Quote Link to comment Share on other sites More sharing options...
Pete B Posted November 30, 2014 Share Posted November 30, 2014 Easier done than said until you have a few behind you to be honest, Tony I can't immediately think of an all-in-one 'how to' but the Electric Flight Database is worth a browse to give you a ball-park' idea for the type of model you're looking to power. Briefly, when I'm looking for a suitable motor for a model, my first consideration is the AUW. Depending on that, I then apply the type of aircraft and the level of performance I'm looking for. A good average for a sport flyer is about 100Watts/lb, so a 3.5lb model will need 350W for a reasonably good performance. For gliders and vintage models, you may be happy enough with 50-80W/lb. For more aerobatic performance or EDF etc, you'll be needing 150-200W/lb. Once you've established your power requirements, consider the type of model. A slow-flying bipe will typically have a larger prop and won't need a high RPM to turn it, compared to a high speed aerobatic jobbie, which will have a smaller prop turning at much higher speed. This is where the Kv number of the motor comes into play, Kv being the number of RPM per minute per volt, ie a 1000Kv motor with 11v applied will turn at 11000RPM under no-load (ignoring efficiency losses). Taking 1000kV as being a convenient mid-point, you'll find that motors with a lower Kv will tend to support larger props, whilst those with a higher Kv smaller props. There's a lot more to it, of course, with factors such as the number of LiPo cells, duration, motor and ESC amp limitations. To give you an idea of the sort of packages for a given power output, BRC Hobbies have a useful list of motor/ESC combinations listed on power output. That will give you an idea of the spec of the motors required for various tasks. In your case, take the AUW of the Aquarius, work out the power requirement at, say. 80W/lb and see what BRC suggest in their listing. WebOCalc (look under 'Software' on that page) is a very useful tool, as well. Insert all the known parameters and it should give an idea of a working setup. It's then just a matter of looking at the motor specs on the web and choosing one to suit. Pete Quote Link to comment Share on other sites More sharing options...
eflightray Posted November 30, 2014 Share Posted November 30, 2014 Doing a search I found some videos on Youtube on building an Aquarius. Galaxy Models Aquarius Build - Part 1 to 8 This one Part 7 mentions the motor used -- Quote Link to comment Share on other sites More sharing options...
Tony Harrison 2 Posted November 30, 2014 Author Share Posted November 30, 2014 Posted by Pete B - Moderator on 30/11/2014 13:01:35: Easier done than said until you have a few behind you to be honest, Tony I can't immediately think of an all-in-one 'how to' but the Electric Flight Database is worth a browse to give you a ball-park' idea for the type of model you're looking to power. Briefly, when I'm looking for a suitable motor for a model, my first consideration is the AUW. Depending on that, I then apply the type of aircraft and the level of performance I'm looking for. A good average for a sport flyer is about 100Watts/lb, so a 3.5lb model will need 350W for a reasonably good performance. For gliders and vintage models, you may be happy enough with 50-80W/lb. For more aerobatic performance or EDF etc, you'll be needing 150-200W/lb.....................r of looking at the motor specs on the web and choosing one to suit. Pete Pete, many thanks for taking the time to assemble this handy summary plus links - I appreciate it. Physics was never my strong point at school but I'm reasonably handy & practical, so will work hard at getting my head around these electronic/electrical definitions... I thought I had a reference somewhere to the AUW of this glider but can't find it - from what you say though, a motor of around 1000kv might suit. I'll be studying your info and following links too - off into my cold garage now, to sand some balsa... rgds Tony Quote Link to comment Share on other sites More sharing options...
Tony Harrison 2 Posted November 30, 2014 Author Share Posted November 30, 2014 Posted by eflightray neath on 30/11/2014 15:30:02: Doing a search I found some videos on Youtube on building an Aquarius. Galaxy Models Aquarius Build - Part 1 to 8 This one Part 7 mentions the motor used -- Ray, thanks a lot - I rarely look at Youtube so it didn't occur to me to search there. The young man's videos (I just took a quick look) will I am sure prove useful, though in #7 he doesn't give much detail about the motor. He says it's an "Overlander Thumper V2" but a quick Google produces a list of motors in that range, varying from 720kv to 2700kv. Going by Pete B's advice, perhaps one of the 2-3 models spec'd at 900 - 1100kv will do. Or maybe a motor from E-Power or Keda, brands I've seen recommended at modest prices. It's very interesting to see how someone else tackles exactly the same model one is building - especially when I've just about finished the fuselage without reference to anyone else! Hope I didn't make any major errors... rgds Tony Quote Link to comment Share on other sites More sharing options...
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