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Motor mods to old Ripmax P-51 mustang ARF

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Tim Hickey18/10/2018 10:25:31
59 forum posts
1 photos

Hi people, bit of advice required please.

Pic below shows installation of a BM600 inrunner in the old Ripmax p-51 mustang ARF. I got the motor as a direct replacement for an old brushless speed 600 used back in the day. Its a new in box kit I found recently. I believe these were discontinued in about 2012 so difficult to get hold of.

Where the cables come out of the motor prevents the motor from moving far enough forward to clear the front of the cowl. (prop adapter has been removed). Even if I move the clam mount further forward on the beams and put the prop adapter as far forward as I dare it's still not enough.

I am thinking of replacing the motor with a 35/36 1500kv outrunner on a back plate that can be adjusted (via standoffs)

Can anybody please advise the best way to go about this modification or in an ideal world options to keep the inrunner.

Thanks in advance.



Engine Doctor18/10/2018 11:36:07
2629 forum posts
40 photos

Whats the KV of the 600 inrunner ? might need a gearbox as the old 600 brushed needed one unless a very small prop was used. The gearbox will extend the prop forward . Your suggestion for the out runner seems a better idea and probably cheaper than a gearbox. You may need a lower KV motor to drive a suitable prop for the Mustang

Tim Hickey18/10/2018 11:54:43
59 forum posts
1 photos

Thanks for the reply Engine Doctor.

The motor shown is an Overlander BM600 V3 1500Kv rated at 450w, 60A ESC, 3-5s Lipo.

Info sheet recommends between 8x6 to 9x4 prop (larger prop -lower lipo cells)

The outrunner I have available is an Overlander T3536/05 1500Kv rated at 408w, 30A ESC, 2-4s Lipo.

Info sheet recommends between 8x4 to 10x6 prop (larger prop -lower lipo cells)

I aim to use a 4s 2800mAh lipo or a 3s 2200 as I have these available.

I would imagine both of the above setups are well overpowered for the size model but can use throttle control.

Mowerman18/10/2018 12:31:40
1563 forum posts
105 photos

You may be able to make a new motor clamp which would mount further forward on the beams and would need cutting away to clear the cables ? Are there any mounting holes on the motor rear face? if so these could also be used.

Edited By Mowerman on 18/10/2018 12:34:24

Tim Hickey18/10/2018 13:28:30
59 forum posts
1 photos

Hi Mowerman,

The BM600 in the picture does not have any mounting holes on the rear only on the front.

I don't have the workshop equipment needed to make a new metal 'clam' clamp for the motor, I wish I did.

I think the better option may be what Engine Doctor suggested and go with a new back plate for the outrunner.

Still open for other ideas. Thanks chaps.

Nigel R18/10/2018 14:05:30
4199 forum posts
703 photos

Seems the nose is somewhat fixed to that beam mount setup.

Maybe one of these being sold on Ebay would work?

BackinBlack18/10/2018 14:47:42
138 forum posts
2 photos

Not enough information from the photo, but why can't you turn the motor through 180 degrees so the cables exit at the bottom?

Romeo Whisky18/10/2018 15:20:27
738 forum posts
205 photos

Mine is nearly 12 years old now and still flies well. I installed a Mega 22/20/3e 1500Kv Inrunner (fits perfectly) and 10x5 APC prop.

These motors are not cheap but beautifully smooth and powerful.

Tim Hickey18/10/2018 15:55:51
59 forum posts
1 photos

Thanks for all the comments gents.


I will have a look at the motor you suggest.


What do measure the distance to be between the front bulkhead and the front of the cowl

and to the front 'flat' face of the motor?

I think the distance of 85mm from bulkhead to front face of motor as stated in the manual is a bit on the short side.

If I can get a similar setup to yours (after checking price of motor) that would be great.

Thanks again.

Tim Hickey18/10/2018 16:32:25
59 forum posts
1 photos


Just had a look online and found this motor, link below...


Not sure if they are selling a 1200Kv or 1800Kv motor but have emailed them to ask.

What you reckon? Cables come out the rear of the motor and is a bit longer the BM600 I have installed.

This means the motor can move quite a way forward or back to suit.

Nigel R18/10/2018 16:41:59
4199 forum posts
703 photos

The Mega inrunners are really nice bits of kit. Is anyone distributing them in the UK now Puffin changed hands?

Romeo Whisky19/10/2018 10:08:12
738 forum posts
205 photos

I see Robotbirds are stocking the excellent Mega motors (they're still pricey though), but 4-Max stock an "equivalent" 1500Kv inrunner for only about £30, which should be an easy fit as there doesn't appear to be anything protruding from the can side to prevent it being positioned exactly where you need it to be. Better clamp it tight though!

Tim Hickey19/10/2018 10:24:02
59 forum posts
1 photos

Hi Romeo

Thanks for the info re 4-max

I have had an email reply from 4-max. The only 36mm diameter inrunner they do now is an 1105Kv version that they recommend only using a 3s lipo on a 10x5 prop. Will look into though. What are your thought on that one?

Having spent ages looking for a suitable inrunner I have now, in case I can't get one, CAD drawn a

mount made up from ply to suit an inrunner. This can be positioned exactly to fit the cowl and secured to the existing beams. Would also be cheaper than buying another inrunner.

Cheers. Tim

Romeo Whisky19/10/2018 11:18:41
738 forum posts
205 photos

Hi Tim,

I think the 4-Max one should be fine. It's a bit lower Kv than the Mega, but I fly mine on half throttle all the time (which is much more scale-like anyway), so you should still have plently of power. The 5mm prop shaft on this motor will also be much better on a belly-lander than the 3.2mm on the one you've currently got in there.

Personally I wouldn't dream of putting an outrunner in mine - it's so clearly asking for an inrunner and I love the smoothness of them. (I've got one in my Overlander Tucano too - also originally designed for canned brushed 600). Of course I've got lots of outrunners in other models which were designed for them but still love the smoothness of inrunners.

The model flies beautifully on 3200 3S and can handle wind quite well. I usually launch mine off a dolly, but it is easy to hand launch too (though easier with a helper to hand launch it).

Ensure the ESC brake is off and it sets itself up into a nice glide angle for landing when you cut the throttle on finals. You don't want a heavy landing on that underbelly mock airscoop (although mine is still pristine after 12 years) so let it glide down softly. Whichever way you go, I hope you enjoy it.

Regards, RW

PS.  You can see mine flying on our Club Website:  both in the Galleries and also if you click the navigation titles at the foot of each web-page the photos change.

Edited By Romeo Whisky on 19/10/2018 11:21:57

leccyflyer19/10/2018 11:38:23
1632 forum posts
339 photos

I've just assembled an Ebay find of a Ripmax P-51 having loved the two Ripmax Spitfires that we've flown for years and admiring how well my clubmate Derek's; P-51 performs.

The version that I got had a completely different motor mount set up, much closer to the Balsacraft system and the Ripmax Spitfire, ideal for an inrunner, with no clamps or anything like that, just a litefply box, making up a CNC space frame with a front mount for the motor. I thought that one of my much loved Mega 22/30-3s would slot right in, but it wouldn;t fit. Inexplicably, no amount of coaxing and rotating could get the Mega in there. but I could just squeeze an AXI 2820/10 in there and so fitted that instead.

Come the first chance for a maiden flight this last weekend and on running the AXI up to full throttle for the first time the vibration was horrendous and despite reinforcing the bond between the front motor mount and the sides of the motor box there is still flex in the liteply mount. I had reinforced the mount before starting, with carbon tows, as these mounts did have a reputation for self destruction when they first came out.

Thanks for the illustrations. I might be able to fabricate such a mount to allow me to modify the existing fittings and put my preferred inrunner in there - I love my 2820/10 motors but the Spitfire flies so well on the 22/30-3 with the smaller prop, being a boon for belly landing

leccyflyer19/10/2018 12:05:33
1632 forum posts
339 photos

Here's the mount on my Ripmax P-51 - don;t know whether than makes it an earlier or later model.


Nigel R19/10/2018 13:11:33
4199 forum posts
703 photos

I would have thought the 4max inrunner would be find. As for the different kv, just a case of choosing a different prop to suit it.

Actually come to think of it, the 1100kv would be about right for a 4S setup.

Tim Hickey19/10/2018 14:02:25
59 forum posts
1 photos

Hi Nigel,

I have just emailed 4-max the details of the plane, weight, prop size, 4s Lipo etc. so will see what they come up with.

If the 1100Kv/4s/8 to 9" prop combination works then I may well go with that.

That motor has a longer case than I have at the moment so may well work if the cables come out the end of the can.

I have a fall back as an alternative of modding the front end to take an outrunner...last resort through.


Amazed at how different 'the same' kit can be. An old kit but still looks amazing and very happy how easily it went together. I ran thin CA glue all round the joints, just to make sure.

Get this motor sorted out and looking forward to some good flying time with this model.

Nigel R19/10/2018 14:58:56
4199 forum posts
703 photos

Tim, for what it is worth, I have two 36mm diameter Mega 22/30 motors, one 910kv and one 1250kv.

Both used on 4S.

The 910kv has an apc 10x5 fitted and shows about 450W on fresh charge.

The 1250kv has a 6x6 (cut down MA 8x6!) and shows 550W on fresh charge.

Somewhere about in the middle - 8x6? - might be about right for you?

leccyflyer10/11/2018 16:31:55
1632 forum posts
339 photos

Soooo, successful maiden on the Ripmax Mustang a couple of weeks ago, only marred by a slightly scruffy landing which broke the prop. Oh well, no shorttage of props, simple fix before the next flying session.

Came to replace the prop today to find the motor felt a wee bit loose, so took off the cowl to find that the space frame liteply motor mount was virtually destroyed, the front plate was delaminated, the top frame cracked and delaminated in two places and one of the side frames popped out. I suppose I could have cobbled it together, but, even after reinforcement with some carbon tows and epoxy it was still not rigid.

Anyway, long story short I've cut it back to where it isn't flimsy and cut a further proper rigid ply firewall to which a decent aluminium tube space frame motor mount can be bolted. The quality of the liteply frame has to be seen to be believed, it's delaminated in three places from nothing more than a slight knock.

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