Inrunner to Outrunner Conversion ??

[Simon.O.]

I have read and read and still am not sure

Is there a rule of thumb to convert from Inrunner to Outrunner ?

I have a few hulls that are all speced for 540S motors, they go well but I want to give an outrunner a whirl.
The 540S is 36mm dia and 50mm long. Do I look for a 36mm Ootrunner like the Typhoon, or can I go a bit smaller in dia ??

I know the Kv of many outrunners is lower but I can go up to 6S on my speedies to get me the circa 30krpm I like to run for small props. Yes I like small props and wicked rpm as it just sounds so nice.

Is a 450 heli motor similar to a 540S can.

Any useful input is appreciated.

[Fluid]

IME it is a case-by-case consideration. Not all 450 or 500 heli outrunners are the same (diameter and length), just as not all 540 inrunners are the same (S, L, XL, Fiegao, Neu). At this time I'd suggest following what others have done, or to err on the conservative side if you don't want to follow. Meaning, go for the larger outrunner format and use 6S. The smaller outrunners like the Scorpion HK3026 have similar performance to a UL-1 motor and will not hang with a Feiago XL.

I've had pretty good luck with a Scorpion HK4025/6 running on 6S. It is not the equivalent of a Neu 1527/1Y (similar Kv) in the same boat but it is a good replacement as a sport motor. The Neu gets my SprintCat into the 60s on 6S2P, the Scorpion hits near 50 on 6S1P. The latter will swing more prop too.

Considerations with outrunners:
- Keep a tidy interior, that spinning stator can grab any loose wires, etc. when the boat flips.
- Heat dissipation is required, in tight hulls motor temperature can soar. The motors may not be damaged at 250F, but you can sure get a nasty burn or melt nearby plastic hull parts. IME outrunners are better suited for monos, cats and full-bodied hydros.
- Thin motor wires and small connectors. These motors are not rated for the amps that most inrunners are with their thin wires and cheap connectors. At least replace the connectors.
- Motor wires exit the front of the motor. This can cause problems when replacing an inrunner with an outie, requiring excessive wire lengths.



.

[ozzie-crawl]

i will add my 2c on the scorpion 3026, its a nice motor i am running it on my vs1
no cooling issues as its in the wind so to speak,spins a x642 well and tho i haven't run more than a few minutes at a time temps are around 40c (100f) average amp draw is around 65 amps. i think the ul-1 would be a bit better motor imo
i did try one in my mean machine and it will spin a larger prop but not for long,i think there continues amps are a bit over rated by manufacturer.
very nice sport motor but if chasing more speed a ul-1 would be better or a feigao xl, that is just as far as the 3026 1900 kv goes as i have not tried any others.
if i could wind my own motors i would like to buy the scorpion kit and wind a slightly higher kv and see how it runs.

[bea5017]

i plan to run the 3026 1900 kv on 5s for my twin cat build, any thoughts on the speed i can potentually get outta that set up (32" skunkworks 2nd gen hull)

[ozzie-crawl]

not sure how they will go on 5s, i thought they were a 4s motor
1400/80 = 17.5 volts, they do use them on 5s in helis but there geared so not sure

[bea5017]

we will find out haha, should put me right at 35k rpm.. im tryin for around 60 mph, i think this should/could get me there with 3+ hp... should sound sick wit the twins cause a single on 4s sounds nasty..

[Simon.O.]

Here is a possible motor that appears to be popular for what I need.

Run on 3S or 4S or 5S to a 32/3 Venom prop

It is an Inrunner and has a proven history.

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5146

Now if I chose an Outrunner which would be a winner ?

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=11174&Product_Name=Turnigy_450_H2218_Brushless_outrunner_2500KV

or

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=11179&Product_Name=Turnigy_450/500_H2223_Brushless_outrunner_2900KV

Just an idea if I go with the OR motors,

I could also go this way for IR motors with a jacket or coil.

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6527&Product_Name=Turnigy_B36-56-04_2600kv_Inrunner

IR or OR is the big question for the day.

Packs as needed to get the shaft to over 30krpm and prop to be a 32/3 venom plastic as has been run by some at impressive rpms.

[m4a1usr]

I think alot of folks confuse inrunners with outrunners and their applications so there should be some clearer details about the 2 different motors construction.

Most outrunners cannot run shaft speeds of 30k plus rpm. Yes,..........you can find them but its not the norm. You see this typically in their description of applicable motor voltage. Just like inrunners, outrunners use bearings that indeed are 40-50 rpm rated. Yet you will find that rated voltage puts these guys at 25k rpm range. Thats because the magnets are glued inside a cup or bell. And its supported only on one end. So the mass wants to deform the structure as centrifugal force (RPM) increases. You dont see this to the same extent with inrunners as both sides of the output shaft are supported in a inrunner design.

I'm not talking down outrunners, but be aware of rpm limitations from motor construction as the motors are not interchangable in every application.

John