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Poppy the Frenchy01/10/2016 18:46:02
23 forum posts

Hi everyone, I've been flying 32 years and finally moving over to electric. I am trying to convert a vic smeed tomboy at around 75oz and a keilkraft scorpion at around 1lb1oz. I've seen formulars etc on line but fine them conflicting and confusing, one thing I do know is that I need a 100w for the scorpion that will use a 9" prop and the tomboy needing an 70w with an 7"/8" prop, that's as far as I've got and don't the kv needed speed controller and battery, any help is very welcome.


Fun Flyer01/10/2016 19:05:35
342 forum posts
59 photos

My, very personal, calculation would be that both should fly with a 13A ESC, a 1300 - 1600Kv Motor and a 6" to 8" prop, but I'm open to correction. I've successfully flown a Cherub converted to electric with a 1000Kv motor and a 10 x 4.7 prop.

kc01/10/2016 19:37:40
6736 forum posts
174 photos

You might find that looking at the BRC website gives you a better idea of what motor prop & Lipo to use. for example this motor    or this one - note carefully the different props when used on 2s lipo and then 3S. Very different output due to increased voltage. BRC alone seem to give such detail of props etc. Look up some of their other motors too.

I assume you missed out the decimal point and the Tomboy does not weigh 75ounces.  You might look at the comments here about the Outerzone plan which gives details of one persons motor and lipo for the 36 inch version.

Edited By kc on 01/10/2016 19:47:06

John Privett01/10/2016 20:56:49
6095 forum posts
243 photos
Posted by Buffymadforrc on 01/10/2016 18:46:02:

... a vic smeed tomboy at around 75oz ...

I do hope that's a typo! A Tomboy should probably come out at around 15ozs!

DCW01/10/2016 22:21:13
100 forum posts
66 photos

Hi all.

Try this website..


The information they provide for each motor etc. I have found to be very accurate.

Hope this helps


Geoff S01/10/2016 22:28:10
3836 forum posts
49 photos

You know I glossed over the 75 ozs without noticing that it's more than my Ballerina weighs

Actually I think 100 watts will be well over the top for both models (assuming 15 not 75 ozs). The oft quoted 100 watts/lb is for aerobatic flight and I don't think either model could be considered aerobatic. My aforesaid Ballerina flies quite aerobatically on 90 watts/lb so I would think around 75/80 watts would be more than adequate for vintage style flying.

The main problem will likely be getting CoG far enough forward so consider how you can get the battery right up front. You may even need to use one much bigger than you need but better battery weight than lead.


PatMc01/10/2016 23:18:07
4482 forum posts
548 photos

I'd go even lower than Geoff with the power/weight. My Veron Deacon was originaly nicely powered at 46W/Lb using a 9.6v nimh battery now overpowered on 3s lipo at 70W/Lb. Flew at part throttle with the nimh now flies at lower throttle setting with the lipo. Also flew an APS Frankenstien (weighing 36 oz) on nihms and a geared brushed 480 motor at under 40W/Lb.
Both models were/are capable of loops & rolls on these power levels.

This Youtube video from the Frankenstien made 6 years ago demonstrates that the original power was adequate. Camera is pointing to one side to avoid the prop, excuse the low res quality.

Poppy the Frenchy02/10/2016 15:51:48
23 forum posts

Many thanks for you help guys, the Tomboy weight was a typo, I'm going to spend the rest of this afternoon deciding and buying online, but not sure on manufacturer now, I know are meant to be poor and I only like the best, but what are the best.

Thank you fun flyer, KC, John, DCW, Geoff and PatMc, your help is very much appreciated.

Poppy the Frenchy02/10/2016 15:58:12
23 forum posts

KC, I've just checked out the brc site and it's brilliant for a dullard like myself, found it to fit my needs, spot on and thank you agin everyone.

Poppy the Frenchy02/10/2016 16:11:45
23 forum posts

The tomboys I have are actually 11oz and 8.5oz, sorry for the confusion

kc02/10/2016 16:37:16
6736 forum posts
174 photos

One thing about the BRC site- The data they provide is great but once they no longer stock that motor the data disappears! ( obvious really, they used to print prop size etc on the actual motor and send out a data sheet but when I bought a motor it from their other company - Robotbirds - it came without data and no printed prop size on motor ) So download the page for the motor you buy and save it - preferably print it out. same applies to Hobbyking etc, etc.

Poppy the Frenchy02/10/2016 16:44:51
23 forum posts

Cheers KC, wildo

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