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Motor Swap

Old 10-22-2012, 01:17 AM
  #1  
matiac
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Default Motor Swap

Airfield/FMS 750MM P47 with a 20A ESC, and a KV1550 brushless motor, directly swap it for the KV1300 brushless motor, as it has facilities for a 2 blade prop, and from what I've read, it's a real bear to swap shafts, and I'm not sure of a direct replacement for the 7x6 3 blade prop. It's been said the 1550 will fry with the 8x6.5 2 blade prop even if you DID swap shafts, that the 1300 has stock. Both motors use the 20A ESC, so I GUESS that would remain the same, and the battery could be upgraded to a 3cell, as long as it doesn't go over 850maH at 20c, right now the stock battery's a 1000maH 2cell at 15c. Right now I'm wondering if it would be advantageous to switch to a 2 blade, as this planes BURNIN' UP 3 blade props?
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Old 10-22-2012, 02:33 AM
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I'm a bit confused as to why you would need to swap shafts in order to change to a different prop size. Also, what do you mean by "burnin' up 3 blade props"? I've had motors burn up, but never props.
Anyway, a prop with 2 blades is more efficient than a prop with 3 blades. I would recommend two blades over 3 blades any day.
You should really invest in a watt meter. It will take the guess work out of choosing what prop to use.
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Old 10-22-2012, 03:14 AM
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Its an expression for "going through" props, these 3 blade FMS props are basically made of "spit-and-tissue", and counting the 2 today, in a relatively short time it's been through 6 (!) props, and at 3 bucks a pop, my God, I could've bought the KV1300 by now, can't understand why they put that kind of prop on what's supposed to be a belly landing parkflier if the pilot so chooses, and to change to a 2 blade, you have to at least swap out the shaft because the FMS setup for a 2 blade is a longer shaft, takes a different spinner assembly than the 3 blade prop, and it would just be easier to get the motor that runs the best (stock) with the 2 blade prop from FMS, but you're right, I DO need a wattmeter...
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Old 10-22-2012, 05:44 AM
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Try a 2 blade 7x5 or 6 prop on your stock motor. No need to swap the motor.
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Old 10-22-2012, 06:40 AM
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For anyone who considers swapping a shaft or needs a new replacement .... check out RCTimers site ... they have shafts of different diameters and lengths to suit most we use ... plus the C clips and bearings.

But as Pm says - no need to change motor.

And yes ... a 2 blade is much better for what you want to do - ie belly land.

At how much a prop ? $3 !! I buy a bag of them for that ... even APC style will give 2 for less than that ...

OK - onto load a prop puts on a motor ....... generally if you change from a 3 to a 2 blade - you can go UP 1 on pitch OR diameter ..

So you are using a 7x6 3 blader ... I would expect for 2 blader that a 8x6 would be OK on same set-up ... or drop a touch to a 8x5. BUT if you want to up to a 3S LiPo - then drop back to the 7x6, or a 7x5 ... as you will likely overload the motor if spec'd for 7x6 3 blader on 2S
I would not say a 2 blade is better in performance than a 3 ... it all depends on brand and construction. But a good 2 blade 7x6 will outperform a poor 7x6 3 blader.

Nigel
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Old 10-22-2012, 03:36 PM
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I gotta wonder if there's a direct replacement for the retainer on the motor shaft, because I don't believe FMS makes one for this particular motor, or at least I haven't seen one, and all the 2 blade rigs in their "800 Series" have a completely different setup from the 3 blade planes, hence either doing the shaft swap (which I've read is more trouble than it's worth), or just swapping the motor for the 2 blade setup...this is getting rather confusing...
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Old 10-22-2012, 04:10 PM
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Shaft swapping is usually not that hard ... once you identify whether it has C clip, grub screw lock, etc.

Shafts from RC Timer and simnilar can be screw threaded or plain for props ...

For plain shafts - you buy a shaft adaptor of correct size and use that ... you can get in collet or grub screw format - I prefer the collet style. I replace the dome nut with a plain nut and that allows me to fit a spinner.

You can get spinners that have the adaptor .. centre screw .. back plate all included as a matching set to fit the shaft. My Ultimate has a beautiful polished alloy spinner fitted of this type.

Once you have adaptor of correct size ... you fit prop of your choice ...

Any chance we can see a photo of your motor front end and shaft / prop fitting ?

Nigel
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Old 10-22-2012, 04:17 PM
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Here's a review comment on one Sellers site :

"Great little plane. Get rid of the stock prop go with a two bladed 8x4 prop, 3s 1100mah, 30c battery, and watch this plane cut through the air like a razor blade! Also easy to hand launch."

Sounds like a straight swap prop .... and seeing the numerous photos there - it has a 'chromed nut' centre spinner ... I'm a little confused why you think the prop needs a shaft change ?

Nigel
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Old 10-22-2012, 04:47 PM
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With the 3 blade setup, if you look at the shaft, where the spinner goes onto the shaft has a semi-rectangular "knob" (for lack of a better term) the spinner assembly fits onto to prevent slippage of the prop. The 2 blade setup (stock) is completely different, the shaft is longer on the 2 blade, most likely because of the nose cone on the spinner (?) (P40, P51, BF109), where the others (emulating a radial) have a shorter shaft. And asking Nitroplanes tech support (sic) about a direct swap is a bit like pulling teeth, also the planes (in the same series) that have the 2 blade prop have a higher output motor than the 3 blade variants, and that's what confuses ME is all the conflicting information about doing that sort of thing. By the way, the bell on the KV1550 is held on by a circlip. Is that 109 you have an FMS?
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Old 10-22-2012, 05:02 PM
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No my 109 is a Lanyu and currently in 5 bits !! awaiting a fuselage rebuild.

Can you dissasemble the prop / motor / adaptor combo so we can see it ?

Second - short shafts are no problem if you add a collet prop adaptor - unless the motor is so far back behind cowl ... it really has to be a long way back !

My short RC Timer motor and shaft that would be ideal for that size model - it was in my Lanyu replacing a Brushed motor / gearbox combo .. shaft is about 3/4" long in front of motor .. once adaptor is on that increases to about 2" ... with prop sitting at about 1 1/4" from motor front. (All figures there are from memory but will not be too far wrong).

Nigel
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Old 10-22-2012, 05:19 PM
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I can, but currently all cameras in the house await batteries, which will be remedied tomorrow when I get paid. Thing is, it wouldn't even be an issue if these 3 blade props weren't so damned delicate, but they see the ground coming, and they break! Was looking at the Art Tech 650MM P40...another belly landing parkflier with ANOTHER 3 blade prop that will probably break too. Nice lookin' plane though. And this one I have is PLENTY fast for me. Compared to the U.M.s we have, it's SCARY fast...it becomes a little speck quickly.
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Old 10-22-2012, 05:28 PM
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Originally Posted by matiac View Post
I can, but currently all cameras in the house await batteries, which will be remedied tomorrow when I get paid. Thing is, it wouldn't even be an issue if these 3 blade props weren't so damned delicate, but they see the ground coming, and they break! Was looking at the Art Tech 650MM P40...another belly landing parkflier with ANOTHER 3 blade prop that will probably break too. Nice lookin' plane though. And this one I have is PLENTY fast for me. Compared to the U.M.s we have, it's SCARY fast...it becomes a little speck quickly.
No-one in their right mind (sorry - not trying to be rude), belly lands a model like that with a 3 blade prop and expects to keep prop in one piece !!

Years ago I had a SLEC variable pitch Multi-Prop ... wonderful piece of kit ........ each blade was separate and slotted into a keyed back-plate. You then rotated one blade which in turn rotated the other 2 to same pitch. You then tightened the front plate and spinner up ... I used them on my Spitfire, FW190 for show flying .. but as soon as I was back at club field flying - it was back to 2 blade normal props. My bank account couldn't afford the continuous replacement of blades ...

Nigel
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Old 10-22-2012, 05:46 PM
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That's what I'm saying, why would they do that? I would just keep the wheels on it, but no pavement to take-off/land from, and even with the ridiculous rake these gear struts have, the plane SUCKS in grass, nose-overs when landing are a common occurance, and that's why a lot of guys are just belly-landing them, but then the prop issue rears it's head, it'd be great if FMS made a direct spinner assembly replacement for a 2 bladed prop...there ARE people who have used washers and a lock-nut to use a 2 blade...could just do that...
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Old 10-23-2012, 01:35 AM
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?
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Old 10-23-2012, 01:37 AM
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OK, used my crappy webcam to take this rather grainy picture, but I think you'll be able to see the shaft:

and here's the backside of the spinner hub:
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Old 10-23-2012, 02:53 AM
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OK ... oinly thing missing now is the distance of motor front to cowl front edge ...

As I understand now - you would like to keep the fancy centre style of the prop - as it's part of the P47 style ?

The shafft of the motor as I see in your picture is a plain short shaft ... no problem for a collet shaft adaptor ... all you need to do is obtain the right size for shaft diameter ... probably either a 3mm or 3.17mm ...

Here's the sort of adaptor I mean :

http://www.hobbyking.com/hobbycity/s..._Type_3MM.html

Look through that page on HK ... Ebay has loads ... plus HS of course.

I accept that you will lose that fancy prop boss centre - but I feel you had already accepted that to go to 2 blade prop anyway. The props you buy ... I like APC / APC style ... will have shaft rings to fit the prop boss to centre onto adaptor shaft.

I really cannot see any problem unless theres something I'm missing ?

Nigel
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