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Old Nov 18, 2002, 11:40 PM
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Brushless power system for a WindDancer?

I would appreciate any suggestions for a cost effective brushless power system for the flapped polyhedral version of the WindDancer. This is the 2-meter electric sailplane recently introduced by Polecat Aero. I am new to electrics so I do not know how to spec out a system for this plane.

Polecat Aero's flapped polyhedral prototype came in at 22 oz with a Graupner 6V S400, a 4:1 gearbox, an 11x8 prop, and an 8 cell pack (I do not know if it was 500 or 600). Garland Hanson, its builder, reported this system provided "a screaming 60 second climb" where "the last few climbs were quite steep . . . when I turned off the motor I was looking almost straight up".

And Dr. Mark Drela, who provided the wing airfoils and planform for the WindDancer, mentioned in another thread that a 2:1 gearbox (or slightly higher) on a 6V S400 with 7 cells may also be a good set-up for this system.

But I would prefer a brushless motor, principally for trouble-free operation (i.e. minimal set-up and maintenance) and improved efficiency (longer battery life and/or less weight for the same power). I will rarely compete with this plane, if at all, so contest rules are a secondary consideration.

The mere fact that I am considering a brushless motor says that cost is not a driving consideration, nonetheless I am interested in a cost effective solution.

Any suggestions for a motor, prop, and ESC would be greatly appreciated!

Sincerely,

Michael
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Old Nov 19, 2002, 12:27 PM
MKH
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Ohio
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I've been thinking about this, too. In order to gain efficiency, therefore some power, but keep it as light as the speed 400 setups, I'd look into a geared hacker B20, either 15L or 18L on 8-10 small cells like the 1100 Hecell nimhs, and a folding prop that draws about 15 amps max. The geared Astro 020 would also do nicely, but a little heavier. For really light weight, a Mega 16/15/7 direct drive on 8xHecells and a 9x5 or 9x6 prop should do well and eliminate the gearbox while keeping the power strong with the big prop. In any of these, I'd recommend the Phoenix 25 esc, just because Castle Creations esc's are my favorite. Look at www.megamotorsusa.com or www.hackerbrushless.com or www.astroflight.com for some good info. Search the ezone for threads using keywords like 'B20-15L' '16/15/7' etc, to find threads that discuss these systems. You might also ask the moderator to move this over to sailplanes, if you dont get the help you need in this forum. Good luck however you go!
Marcus
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Old Nov 20, 2002, 12:48 AM
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How about a model motors AXI mini AC Extreme?
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Old Nov 20, 2002, 01:02 PM
MKH
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Quote:
Originally posted by FlyVA
How about a model motors AXI mini AC Extreme?
I think these are considerably wider in diameter than a 400, and the WindDancer has a narrow nose, but I could be wrong.
Marcus
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Old Nov 20, 2002, 01:31 PM
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Escondido, ca, usa
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Have you considered using the new brushless motors from Hobby Lobby that are the size of a 280 but have the power of a 480?

Terry Throop
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Old Nov 20, 2002, 07:03 PM
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Being new to electrics, I am still coming to grips with the jargon, the wealth of products that are available, and the peformance/quality/cost tradeoffs when comparing the various products one to another. Beyond that, I am still trying to conquer the fundamental design principles and application considerations underlying equipment selection. Not to mention how these principles can be applied to the WindDancer.

This is a rather long winded way of saying that I have not considered much of anything at this point. In particular, I have not looked at the Hobby Lobby motors.

My initial reaction is that these may save some weight (just under an ounce) and possibly reduce the drive current (by a little more than an amp) for about the same delivered power. But since Hobby Lobby used different props (8.5x6 vs 9X5) and slightly different gearboxes when generating performance data for these motors and a Graupner S400, I have no confidence that the WindDancer's performance would be the same for each system.

Which leads me to my purpose in starting this thread. I am hoping to narrow the field of products from which to choose and to develop an understanding of the tradeoffs between them. Some insight into the performance requirements of the WindDancer and the ability of a given system to meet those requirements would also be greatly appreciated. I would also hope that others who might be considering the WindDancer will benefit from anysuggestions and follow up discussion.

This is not to say that I expect to be provided a solution. I appreciate as little or as much help as anyone is kind enough to offer. But I still have a lot of homework to complete before I will fully understand and can intelligently comment on your suggestions.

I truly appreciate everyone's help!

Sincerely,

Michael
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Old Nov 20, 2002, 07:15 PM
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Welcome to the EZone !!!

Well for starters, how about a Mega 16-15-x motor. It is a drop in replacement for S400 and can run on the 2/3 A nimh cells easily.

It can draw more amperage than a S400, but can be geared or proped to suit your needs. You can also get the KV of your choice to do the same thing.

To learn more of our "jargon" here, check out the AQ link up top. It will explian many things.

Then download motocalc (same URL and free for 30 days) and play with motors, gearing and cells.

Of course then, you may have no need for us
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Old Nov 20, 2002, 07:41 PM
MKH
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We've all been there, where you are now, so don't despair. You could always start with the recommended Speed 400 setup, which could be bought with motor/gearbox/esc/battery right from one supplier, for a reasonable price. I've flown 2 meter sailplanes on geared 400's before, and they did fine, and were heavier than the WindDancer. If you're sure you want to go brushless from the start, try contacting some of the vendors that advertise on the ezone, tell them you want a small brushless setup for a lightweight sailplane, that is speed 400 size and weight, and can use the same batteries. Most of them should be able to recommend something. Some of the vendors, like Kirk at New Creations RC, will even solder up the whole package for plug 'n play simplicity. As for trade-offs, the small brushless motors can be pushed much harder than a speed 400, i.e. more power, but this will require bigger batteries to handle the amps, and this increases your weight. That's the real challenge, increasing power at the same weight. If I were buying it today, I'd look at 8x1100 Hecell Nimh batteries (same size, weight, performance as 600AEs but bigger capacity) and either a Hacker B20-15L geared motor, or a Mega 16/15/7 direct drive motor, with a 9" folding prop for both. I have seen both of these setups fly, and they perform very well, and would no doubt lift the WindDancer with ease. At 20-28 ounces, and a super efficient wing planform, the WindDancer won't need much power to climb well. Let us know what you find, once you start researching.
Marcus
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Old Nov 21, 2002, 12:23 AM
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Thank you for all the responses!

I have already begun following up on several of the suggestions. In addition to reading the FAQ (which will take a several days and numerous re-readings to fully appreciate much of what is there), I talked with Sean Plummer at Aero-Model about a Hacker based solution.

Sean suggested a B20-12L Hacker brushless motor with a 4:1 gear box with a Hacker Master 30-3P controller running on 7 or 8 cells. He also mentioned that a Hacker Master 18-3P controller would work and be less weight, but the 30-3P would allow the motor to be driven at its maximum curent which was something over 20 amps. Although not important in this application, the headroom for motor current could be useful in another model.

Sean reiterated much of what I have read in the archives about Hacker's Master series of controllers being optimized for Hacker motors. Any additional thoughts on or other brushless controllers would be welcome though.

I read what Hobby Lobby has posted on their web site, but I still need to follow up with them by telephone. I will also talk with Mega tomorrow and look into Astro.

So it looks as if I should have several systems to compare within a week or so. I then expect to begin comparing them, hopefully using performance prediction software. Is Motocalc the preferred tool or should I be looking at other choices?

When I do get to comparing the various systems, do they factor in controller performance? Everything that has been said about Hacker's Master line of optimized controllers leads me to wonder if controller considerations are being taken into account.

Prediction software lets me compare performance, and cost is easy enough to get. That only leaves quality and features to be considered. Over time, I should develop a feel for the features that I need and the quality to expect from various manufacturers. I plan to research previous threads discussing quality, but anything anyone would care to add here will be greatly appreciated.

Thanks again for your comments! Please keep them coming as I have much to learn.

Sincerely,

Michael
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Old Nov 21, 2002, 01:09 AM
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Hey Michael! I think I've seen a wind dancer before, it's a bit like the bubble dancer in style if I remember right. Anyway, I've seen one at a speed 400 "F5J" contest (just stock 6v motors). The climbs were just fine once the pilot had the planes CG set correctly. I saw efficient climbs, but I actually didn't see it scream up to altitude too fast... So, the brushless motors you're looking at will definitely get it up to altitude in a jiffy. The speed 400's put out about 50-75 watts power at full throttle. for that size of a plane I recomend something significantly more powerful than a speed 400. The Mega motors, Hacker, and Aveox motors are great choices if you really want the screaming climbs. Aim for about 180-300 of power if you really want a difference. (Roughly 1/4 to less than 1/2 hp) Brushless motors are great.
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