Electric equivalent to the Cox TD .020

[steve watkin]

I'm going to build myself an electric version of an old 1960 single channel model that was originally powered by a Cox TD.020 (the powerful front induction one not the reed valve PeeWee) called Stubby. There is a view of it's little brother here. The layout is the same on both models.

The model is a reasonably conventional high wing cabin model of 32" span. There is just one thing odd, and that is that the engine was mounted above the wing on a little pylon restricting the prop diameter to a max of about 4.5". Any suggestions as to a suitable motor/batt combination that will emulate the Cox and won't over power it?

[PatMc]

Hi Steve, the TD .020 was rated as .055hp at 23000rpm using a 3 blade 3 1/8" prop. (A copy of the AM test report is in Martin Hepperle's web site) This power equates to about 41W.

I flew a Graupner Lupo successfully indoors at 1/4 throttle using one of these on 2s lipos with a 7" prop. I think the Stubby is smaller than the Lupo so IMO a 4.5" prop & 3s lipo probably would give about the right power. An alternative might be this motor which is about the same weight & KV.

 

A 450mAH 3s would probably be big enough but for the extra duration etc my choice would be this 800mAH 3s with a 10a ESC

 

HTH

Pat.

Edited By PatMc on 11/02/2012 23:02:13

[steve watkin]

Thanks Pat,

 

I'll most likely go down the route of the CF2805 as it's cheap!!

I do have a CF2812 which was given to me but i think that will be too much in both weight and power. Am I right?

What would happen if I ran it on a 4.5" prop and a 2 cell LiPo, not enough thrust?

Seems it would run at about 12000rpm with out a prop, so what could I expect with a 4 x 3 of similar?

Just playing with ideas !!

 

SW

[PatMc]

Hi Steve, I think the 2812 uses the same fixing as the 2805 so you could try it first in the knowledge that it would only need a couple of turns of an alan key & the wiring to change over.

 

For comparison, the nearest small motor I have with a similar KV is an old plain bell type that I've measured at 1400KV. It turned a small Gunther plastic (ex Twinstar) at 10700rpm, 8.3v (7nimhs) 4.8A, 40W & the same prop at 12700rpm, 9.8v (8 nimhs) 6.6A, 65W.

 

Based on those figures I think you'd be well under 40W using 2s with a 1650KV motor & 4.5" prop. OTOH you have nothing to lose by trying it & as said you can easily change motors &/or go up to 3s.

 

Cheers

Pat.