Brushless motor for small prop (6-7" ish)

[LukeZ]

Ok, this is your basic run of the mill "what outrunner would be good for me" question. I'm posting in this forum because what I've read so far leads me to believe I might be building my own. But I'll also take suggestions for motors that already exist, if they fit the bill.

I recently bought a Cox Cessna Skylane - yes, they haven't made these in 15 years. It was a model I really enjoyed as a kid, and I recently saw one on eBay, brand new in box. I couldn't resist.

The original took the standard Cox .049 wheezer for power. As I recall from my childhood, it was pretty underpowered.

The fuselage is actually made of plastic, believe it or not. It isn't lightweight. Airframe without motor or radio gear comes in at 12 oz. Motor, lipo, servos, Rx, ESC I expect will add another handful of ounces. Let's be safe and say 18 to 20 ounces all up. Wingspan is 36 inches, roughly 250 squares.

Ok, enough about the plane - except to also add, that for this guy to taxi, the prop really can't be bigger than 7 inches in diameter. 6 inches would be better. If a suitable 3-blade could be found, that would work also, and actually be scale as well. I know I can get old Cox propellors but I'm not sure they were really designed to be efficient with today's electric brushless motors.

Right, so to my actual question - can anyone recommend a brushless motor setup that would provide adequate thrust (12 ounces at least) on a small propellor?

Looking in the sticky threads, I noticed a link to the GoBrushless database. There's really nothing in there for props in the 6 inch range. For 7 inches,
these are some interesting results (http://www.gobrushless.com/testing/motor_test_results.php?prop_dia=7&prop_pitch=3.5&prop_thrust=14&prop_current=16&submit=Query&email=&password=).

But I see they aren't your standard GB starter kit. Looks like 12 tooth, 25 mm stators. GB carries these stators but then I don't really see that they have all the other parts that would be needed to complete that motor. Yes, they have a 25 mm can, but not a shaft for it, and I'm not clear that their bearings would work with it either.

I'm a complete newbie when it comes to brushless - I've never built my own before. But I'm sure I can pick it up, and I'm willing to try. Sorry for the long post then - if anyone has any suggestions, hints, tips, or pointers, I'm all ears.


Luke

[olmod]

could you give us a voltage preference ? 2sp or 3sp?
results like this can be achieved use a 20mm gb stator motor.
gws hd 6030 16500 rpm 10.5v @8.5amps = 14.91oz.

[LukeZ]

I can't say I have a preference for the battery - I was going to try to see which motor would work best and then choose the battery that ran it best. Perhaps this is backwards?

I'd say 2S in general, just because it is lighter, but even that is not so crucial. I can just go down in capacity with 3S if weight becomes an issue.

Can you give me more info on the 20mm motor you mentioned? Number of stator teeth, winds, etc?


Luke

[olmod]

This was with a custom made drum made from a loudspeaker centre pole (best iron) GB 20mm stator 9 tooth
12 5x5x1n50 14tx.5mmxY
No load 25000rpm @11v @1.2amps=2272kv

GWShd 7035 10000rpm 7.2v @4amps=207g=7.3oz

APCe7x5 7900~8000rpm 7.2v @7.25amps=290+g=10+oz.

3SP 11v
GWShd7035 13200rpm@10.6v@7.5amps=394.85g=13.94oz.

gws hd 7035 13000rpm 10v @10amps =13oz thrust.

gws hd 6030 16500 rpm 10.5v @8.5amps = 14.91oz.
this motor was tested a long time back and i havent rebuilt one and retested on my current test gear so I cant guarrantee dead accuracy but i dont think it would be more than 10% out.

[john8750]

Luke--
Check out Tower Hobbys in the GWS section for brushless motors. They make two motors that should suit you. The small one weighs about 1 oz, cost 12 something, should turn small props on 2 LI's. The ESC is 22 something and will handle the motor fine, 15 amps.
Tower has 6/3 3 blade props also. Allerc has GWS also.
Let us know about your progress.

John Smith

[MorrisM]

Luke,
Check this thread on the Komodo motors. For your purpose the 11 turn looks good.
http://www.rcgroups.com/forums/showthread.php?t=594190
For battery you could run it on a minimum 700mA 3s 15C lipo.

Morris

[LukeZ]

Wow guys, thanks for the great advice. Morris, that Komodo looks like just the ticket - I think that's what I'm going to try. But the GWS motor is so cheap I'll probably get it too, and see how it compares. I'm sure I can find something to use it in.

It sure is nice that prices are coming down on these brushless setups. I think for a while I was only looking at Hobby Lobby and I thought I'd never get into brushless. I just couldn't justify spending over a hundred bucks on a motor/esc. I guess prices haven't really been going down over at HL - just that I've discovered these other companies.

I'll definitely keep you posted on how this turns out.


Luke

[Turbo442]

Luke,

Have you looked around at Tammies Hobbies in Beaverton, OR? They have a great selection of motors and batteries.

[LukeZ]

Turbo, I have, and I'm glad to see they've even started selling some DIY brushless kits - though I don't get the impression they've ever built one themselves. When I've been in there and talked to them, unless I know what I want to begin with, they haven't seemed to be able to help me much on the brushless stuff. They always recommend something that costs an arm and a leg and will give me vertical performance, which I don't need. If you start asking questions about specific applications, they admit they don't know.

They're good folks and I like the shop. I spend way too much money there. But I think they're still catching up to the electric revolution in some ways. That's why I always go to the experts at RCGroups first. ;)


Luke

[Dr Kiwi]

Obviously I liked the Komodos, but here is yet another option: Westport: see here:
http://www.rcgroups.com/forums/showthread.php?t=596405

[LukeZ]

My Komodo arrived today. This is a beautiful motor. Smaller than I had imagined. I have some props and an ESC on the way - can't wait to do some testing. Will post my results when I get them.


Luke

[Ron van Sommeren]

Luke, be sure to check out the sticky 'cd-rom tricks' thread in this subforum. May save you from frying your controller during your first test run.

Vriendelijke groeten ;) Ron

[LukeZ]

Ron, looking at that thread, I presume you mean the recommendation to use a current-limited power supply in the case of a short. I don't have one of those. How about I just use an inline fuse? ;)


Luke

[Ron van Sommeren]

Actually, I meant all the tips and trics, since you'll be carving your own motor.

Vriendelijke groeten ;) Ron

[LukeZ]

Right - I will read the whole thread. For now I'm going to try the Komodo, so no work involved there. But you're correct, I do want to build my own at some point. Your tips and tricks thread will come in very handy. Thanks for setting it up.

Luke

[ScubaSteve]

Luke,

Read the Brushless 101 article @ http:/www.gobrushless.com/kb if you want a really good down and dirty walkthru on DIY brushless. Applies to all kits, scratch-builts, etc... regardless of mfr.

[LukeZ]

Had some time to do a bit of testing with the Komodo tonight. It's a sweet little motor, and as others have noted, very quiet.

It's shown in the pictures with a Master Airscrew 6x3 3-blade, which looks the coolest by far, but is not very efficient. Doesn't put out much thrust and is kind of heavy as it was designed for slimers.

Best results were with a GWS 7x3.5 on 3 cells - I think I can get away with a 7 inch prop and still have adequate ground clearance. I haven't completed the steerable nosewheel yet so I'm not entirely certain what height I'll have, but I'll just make sure it can handle 7 inches. This plane will only be able to taxi on cement anyways...

I'm using a cheap GWS 15A ESC. Seems to work fine. Results on the 7x3.5 were:
10.4 volts
9.73 amps
101 watts
~15 oz thrust

I'd like to measure RPM as well but for the life of me I can't get my Emeter to read anything other than 3600 from the lights in the room. The only time I've gotten it working is when I've been outside in sunlight. It is extremely sensitive to indoor lighting. I've tried using a flashlight but then I really need to have a couple more hands...

I'll post some pictures of the aircraft when I get the motor mounted.


Luke

[BeavrdamElectric]

I'd like to measure RPM as well but for the life of me I can't get my Emeter to read anything other than 3600 from the lights in the room. The only time I've gotten it working is when I've been outside in sunlight. It is extremely sensitive to indoor lighting. I've tried using a flashlight but then I really need to have a couple more hands...

Luke
That's a common problem with tachs, artificial lighting blinks at 60 cycles per second (2 blinks per cycle). You have to work by flashlight or more often, daylight.

Good Luck!

[MorrisM]

Luke,
You motor mount looks like it may have the motor positioned too low. The length from the pivot to the scale contact should be the same as the length from the pivot to the centerline of the motor.

If the motor is too low, it will cause thrust reading to be low.

Morris

[Dr Kiwi]

Luke,
You motor mount looks like it may have the motor positioned too low. The length from the pivot to the scale contact should be the same as the length from the pivot to the centerline of the motor.

If the motor is too low, it will cause thrust reading to be low.

Morris

For the flashlight, I made a stand for it from a defunct desk lamp - in operation the flashlight is further away! (but for a temporary fix just sit the flashlight on a box in front of the prop).

Morris, you are right on the motor alignment. This is what I got with the 7x3.5:
10.9v, 9.85A, 107W, 14640rpm, 48.5mph, 558g, 19.65oz, 5.22g/W

[LukeZ]

Whoops! You guys are absolutely right on the test stand setup. I need to rotate my motor mount 90 degrees. Although the setup sure looks nice, it was actually the first time I've used it. :o

Here's another question for you experienced guys - I'm kind of new to brushless motors in general. I'm having a real pain of a time fitting my GWS props to these things. APCs are fine, because they have those little adapter thingys to fit the prop onto just about any size shaft. But the GWS props which we mostly use for the smaller stuff have that incredibly small shaft hole, and not very much material to work with. I've tried reaming them with a drill bit but invariably I get off-center, especially at larger hole sizes (a lot of these collets have a prop shaft close to 1/4 inch!). I'm not sure if prop-reamers are easier to use without off-centering, but the ones I've looked at are all too big anyways - I think they were designed for gas engine props.

It would be nice to find some 3mm or so collet adapters that had a somewhat narrow shaft - they could fit on the thick shafts of the motor but have a narrower shaft for the prop. The less I have to ream on the prop the better.

Any tips or hints in this area?


Luke

[LukeZ]

Dr. Kiwi, that's a good idea on the flashlight, I'm going to have to make something similar.

Luke

[Dr Kiwi]

Whoops! You guys are absolutely right on the test stand setup. I need to rotate my motor mount 90 degrees. Although the setup sure looks nice, it was actually the first time I've used it. :o

Here's another question for you experienced guys - I'm kind of new to brushless motors in general. I'm having a real pain of a time fitting my GWS props to these things. APCs are fine, because they have those little adapter thingys to fit the prop onto just about any size shaft. But the GWS props which we mostly use for the smaller stuff have that incredibly small shaft hole, and not very much material to work with. I've tried reaming them with a drill bit but invariably I get off-center, especially at larger hole sizes (a lot of these collets have a prop shaft close to 1/4 inch!). I'm not sure if prop-reamers are easier to use without off-centering, but the ones I've looked at are all too big anyways - I think they were designed for gas engine props.

It would be nice to find some 3mm or so collet adapters that had a somewhat narrow shaft - they could fit on the thick shafts of the motor but have a narrower shaft for the prop. The less I have to ream on the prop the better.

Any tips or hints in this area?


Luke

Unfortunately you won't find a 3mm collet or set screw adapter which requires less than a 5mm hub bore (as you say, some need 6mm or more). I drill my prop hubs using incremental drill bit sizes.

[LukeZ]

Unfortunately you won't find a 3mm collet or set screw adapter which requires less than a 5mm hub bore (as you say, some need 6mm or more). I drill my prop hubs using incremental drill bit sizes.Ok, that's good to know. At least I can stop my search for such a creature.

I've been using the incremental approach as well but with a hand-drill it's still not very accurate. I do have a drill press, but since I live in a small apartment it's stored away in the closet. Getting it out is a task of monumental proportions that always involves a month at the chiropracter's to rectify. :rolleyes: Guess I need to just buckle down and haul that thing out, all to drill a 5mm hole in a small piece of plastic. I'm going to stock up on some props and do a big batch all at once. ;)


Luke

[manuel v]

Luke.

put a washer and 1/8 well collar front prop. glue the washer and collar.

o put collar back. and front. in front glue.

Manuel V.

[tann200]

Well, I have an aero-nuts 1806 motor for 19$ that spins EP5030 prop decently. Havent had it on any model yet, but it runs nicely and doesnt get hot. Can anyone suggest me how to mount this motor in a profile foamy, when i dont have a spare gws gearbox stick mount lying around?
http://www.aero-nuts.com/product_info.php?cPath=30_46&products_id=368

[bz1mcr]

Well, I have an aero-nuts 1806 motor for 19$ that spins EP5030 prop decently. Havent had it on any model yet, but it runs nicely and doesnt get hot. Can anyone suggest me how to mount this motor in a profile foamy, when i dont have a spare gws gearbox stick mount lying around?
http://www.aero-nuts.com/product_info.php?cPath=30_46&products_id=368

The 1806 motor has an 8 mm bearing tube. So after you remove the firewall mount you can use any of the STRONG motor mounts (http://www.strongrcmotors.com/Mounts.htm). To connect to a 5X8 or 10x10 GWS stick use the SM5 or SM10 mounts shown below. Mounts are $4.50 and US shipping is $2 per order.

[Dr Kiwi]

Perhaps an even better mount for a foamy might be the Slo-Fly tube mount: http://slofly.com/cart/product_info.php?cPath=0_23_46_223&products_id=117&osCsid=82df075e6c734ac6cc72262d3adeecd6

I used one of these on a Simi Wing:

Cheers, Phil

[tann200]

Well i have a p51 profile with stick to mount a motor, so the first mount looks more promising, but for now i have to figure smth else, because no point to pay approximately 10$ to get a mount here:P
By the way the motor i have looks neat with tidy windings, but i havent opened it yet to check the wire gauge and winds. Looks like 0.35 or 0.4mm. Tried a 7035 prop on and it spun well with my 10a esc and 2s lipo, but the bearing assembly got slightly hot after copuple of minutes, so i guess i overpropped it a bit.

[bz1mcr]

Yes, I would say a 7-3.5 is too much for that motor with an 18 mm stator and Kv over 2000. It should be much happier on a 5-3 using 2S. The manufacturer of that motor offers 2100, 2500 and 2900 Kv windings. The 2500 motor uses triple strand .2 mm wire. The 2100 and 2900 Kv windings both use larger wire. Sounds like you have one of those.

edit: I just checked the aero-nut website and they are selling the 2100 Kv motor. So, you might be able to use a 6-3 if you have a light model and use throttle management.

[tann200]

I don't know the outcoming weight of my model yet. Its the smaller version of Gene Bonds profile p51 Mustang with ailerons and elevator. I will use that motor there with futaba 156f receiver and 2s 1020mah lipo. Servos are E-sky 8gm servos. Hope the little motor has enough power to get this thing airborne:D

[ecologito]

Had some time to do a bit of testing with the Komodo tonight. It's a sweet little motor, and as others have noted, very quiet.

It's shown in the pictures with a Master Airscrew 6x3 3-blade, which looks the coolest by far, but is not very efficient. Doesn't put out much thrust and is kind of heavy as it was designed for slimers.

Best results were with a GWS 7x3.5 on 3 cells - I think I can get away with a 7 inch prop and still have adequate ground clearance. I haven't completed the steerable nosewheel yet so I'm not entirely certain what height I'll have, but I'll just make sure it can handle 7 inches. This plane will only be able to taxi on cement anyways...

I'm using a cheap GWS 15A ESC. Seems to work fine. Results on the 7x3.5 were:
10.4 volts
9.73 amps
101 watts
~15 oz thrust

I'd like to measure RPM as well but for the life of me I can't get my Emeter to read anything other than 3600 from the lights in the room. The only time I've gotten it working is when I've been outside in sunlight. It is extremely sensitive to indoor lighting. I've tried using a flashlight but then I really need to have a couple more hands...

I'll post some pictures of the aircraft when I get the motor mounted.


Luke

Nice test stand, what kind of prop adapter did you use for the master airscrew prop? where did you get it?

[LukeZ]

Nice test stand, what kind of prop adapter did you use for the master airscrew prop? where did you get it?ecologito, the prop adapter is from Hobby Lobby - look at about the fourth section down on this page (http://www.hobby-lobby.com/gear280.htm). They're 3MM collets and the "scale" rounded prop nut is sold seperately. Looks good on a Cub. They say the prop nut is M5 but in fact it's something different, slightly smaller - about 4.8mm, and won't thread on to my other M5 collets. So if you want to use that prop nut buy the collet with it.

FWIW, I bought my test stand from BPHobbies. Check out this page (http://www.bphobbies.com/view.asp?id=A0320107). The stand kit alone costs $20 but they also sell a version for $36 that includes a kitchen scale. I already had a scale so just bought the kit. It's very easy to assemble, took me about 20 minutes.

I really like BPHobbies - I only discovered them this past summer, but have started to order from them more and more. They have a surprising amount of stuff if you browse around.


Luke

[LukeZ]

Oh yeah, I should mention - I had to drill out the Master Airscrew prop to get it to fit. Drilled it crooked, too, as always. Too bad it doesn't perform better, it would look killer on my little Cessna.


Luke

[LukeZ]

For those that helped me select my motor - thanks. Finally, here's the build thread (http://www.rcgroups.com/forums/showthread.php?t=636780) for the airplane it went into.


Luke