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scorpio condor magic 2.9m question

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Old 09-23-2015, 09:36 AM
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revnkevn
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Default scorpio condor magic 2.9m question

I Just acquired a scorpio condor magic 2.9m sailplane. This is my first sailplane and it needs a motor, esc, and battery. I fly nitro planes but this will be my first brushless plane and and the brushless motor sizes im not sure about. I would like some input on what size motor, esc, and battery i would need. I dont really need any high end components, just something that works and isnt extremely expensive. Any advice will be appreciated. Thanks
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Old 09-23-2015, 12:24 PM
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You'll need to get a handle on the final flying weight to figure this out. From there you want to run a motor, pack and prop that will provide something around 100 to 130 watts per lb of final weight of the model. This power level will provide anywhere from an 80 degree climb angle on up to straight up and fast vertical.

If you don't need or want that sort of full power climb then you can consider options that result in 80 to 100 watts per lb.

When looking at the motors pick from the options with a lower Kv value. The Kv value is sort of like the "gear ratio". Lower numbers turn big props more slowly with lots of torque. Perfect for gliders climbing at steep angles. Higher Kv values work well with smaller props and higher pitch values to give higher level flight speeds. Generally the motors come in a variety of winding counts on the same core and it's the winding count that alters the Kv value of the motors. But the Kv value is your indication. Don't worry about the actual turns count.

Each motor has a list of recomended props. I'd pick a motor, ESC and pack to use then research what that motor, or frame and turn count, is able to run well with on a sailplane.

To get a handle on what the all up weight will be take the model and plunk in the radio gear then ballast the nose to get the balance point to within the suggested range. One way or the other this is what your model will weigh with the motor and pack and set up to fly. Or at least within a couple of ounces. Weigh the whole setup and then go motor shopping.

For sport flying take the number of watts you want to run and add on a 50 to 70 watt "fudge factor" so you don't run the motor too close to the peak allowable power. For sport flying this will ensure you have a nice long life for the motor by not straining it too far. For contest flying where you want to shave the last gram buy a motor that is spec'ed right at the limit for what you need. Same with the battery pack. For contest work by a high "C" rating pack and run it close to the max. For sport flying buy a higher but maybe not top "C" rating pack and add a few extra mA-Hr's to the pack so you're not draining it at more than 70% of it's maximum value. That way it'll live for more charge cycles.

For the ESC we tend to tuck them away where cooling air can't reach them. Do NOT pack the ESC in padding. Give it as much air as practical to allow it to dissipate the heat from operation. For the same reason buy an ESC which is rated for 50% over what you expect to be running at in this model. This over rating is pretty much a standard recomendation in any event.

Obviously you'll want to figure on a folding prop to be nice to the motor's shaft. And try to avoid plowing in during landings. If you have an option pick the motor with the larger shaft size to try to get a more rugged motor.

In fact if you likely plan on buying the stuff from Hobbyking I'd suggest buying TWO motors. They are so cheap for them from HK that it's worth it just to avoid any downtime in case you bend more than just the shaft or bend something in trying to switch shafts. Having powerful motors with crazy light weight comes with a price. It's all to easy to bend the end bells on many of the brushless motors. But at the price HK charges for most of them considering them as expendable isn't much of a stretch.

Last edited by BMatthews; 09-23-2015 at 12:26 PM.
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Old 09-23-2015, 01:07 PM
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Thanks for the info, i will use it !
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