World Models Spit 80" Conversion ??'s
 

Hello all:

I've purchased a World Models 80" Spitfire and intend to convert to electric. I've been looking at the Actro 40-5 and 40-6 motors. Any thoughts of pros/cons of one over the other (I know that the 5 has higher rpm/v and higher amp draw). I'm looking at an 18 or 19 inch prop max due to ground clearance issues. I'll probably be going with a 10s?p pack.

I recently read Greg Covey's post about problems with overheating the Jeti 77 controller on his big aerobatic conversion. Is the '77 the way to go or should I look elsewhere for a controller?

The weight of this plane out of the box (less servos, batteries, etc) is slightly under 9 lbs (very light for the size of the kit). I figure I have a 4 to 5 pound weight budget for motor and batteries. This plane is very similar to the old Dynaflite kit. The recommended wet power is an OS160 two stroke.

Other than knocking over a bank to get the money for the LiPos, any suggestions or thoughts from the gurus out there?

Thanks,

Larry
Ankeny, IA

RE: World Models Spit 80" Conversion ??'s
 

If you read further in Greg's post, you'll see that his system was drawing over 80 Amps at full throttle. That's why he had the thermal shutdown problem. Even at partial throttle, the pulses going between the motor and ESC will still be at 80 Amps, and the ESC will still heat up.

As long as you run the ESC within its specified limits, you will be okay. Greg was running a 20+lb airplane with enough power for wild aerobatics, and possibly 3D. I believe the figure was 3000+ Watts at 80 Amps. You'll be powering a heavy-metal warbird with an all-up weight of around 15-16 pounds. For that, you'll need around 1500-1600 Watts. On a 10S LiPoly, that's only about 45 Amps.

The Actro 40-5 will buy you one of the following over the 40-6:
1. It will spin the same prop at a higher RPM, and draw more Amps.
2. It will spin a smaller prop at a higher RPM, drawing the same Amps.

Unfortunately, I don't know of any application tables for these motors, or any testing data. Hobby Lobby's pretty vague in their specifications on the motor too. I know that either motor will easily do what you want as far as Watts go, but if the 40-6 does it with a 21" prop, for example, you'd be better off with the 40-5. Even the 40-5 might not be "hot" enough to turn a prop within your diameter limits.

RE: World Models Spit 80" Conversion ??'s
 

Larry,

I would recommend the lower wind 40-5 motor over the 40-6 motor because it will handle more current if you need it.

Hobby Lobby is looking into higher power controllers that provide capability beyond the Jeti 77-amp Opto. (Hint: Remember that Jeti makes the Hacker Master controller series)

I would not recommend using the Jeti 77-amp ESC on this application with a 10s Lithium power supply. Instead, I would use the Hacker Master 90-O-Acro or wait to see what Hobby Lobby offers soon.

As for Lithium cells, the new Kokam 3.2AH (20C) cell will be hard to beat and the packs will be the safest on the market.

Good luck!

RE: World Models Spit 80" Conversion ??'s
 

Greg,

You thinking maybe the voltage is a little too much for the ESC? I never considered that, just figured 80 Amps through a 77 Amp ESC was the problem... Now that I think about it, the Jeti 77 is only rated to 30 cells, and by my count, a 10S LiPoly is the equivalent of 34 cells. (3S + 3S + 2S + 2S = 10 + 10 + 7 + 7 = 34 cells) You might be able to get away with 9S, but not 10S.

That's a real bummer, because these big outrunners have some real promise in 50cc gasser applications. I mean, your 1/3 scale Edge is meant for an 80cc gasser, isn't it? On a 15lb 25%-29% ship, it should easily give 3D performance without pushing the motor nearly as hard.

I don't know where they are on it, but Castle Creations was supposedly going to come out with a Phoenix ESC rated for more than 30 cells last time I asked Shawn Palmer about one. Modelmotors is also supposed to be coming out with a TMM8032, 80 Amps, 32 cells.

RE: World Models Spit 80" Conversion ??'s
 

The AXI 5330 18 or 24 wind might be what you want. Scroll down this site.

http://motor.hepf.at/axi/ Click on Messdaten und Prop-Auslegung for performance figures

Also the AXI site has some info, but not as many prop/rpm details

www.modelmotors.cz/index.php?id=en

Gordon

RE: World Models Spit 80" Conversion ??'s
 

Matt,

Yes, it's the power (IxE) that is the final determinent. The Jeti 77-amp ESC can easily handle 80amps at a lower voltage without cutting off.

Gordon,

I agree that the AXI 53xx series will work here as well but you'll still have a problem with the ESC selection.

RE: World Models Spit 80" Conversion ??'s
 

Yep, the exact motor used isn't important, as long as it has the capacity to transfer the power from the battery to the prop in a reasonably efficient manner.

I wonder if at less than 80 Amps, such as 60 perhaps, the Jeti 77 might be able to hold up okay.

RE: World Models Spit 80" Conversion ??'s
 

Matt and Greg (and others too!)-

Thanks for your input and advice - I really appreciate it.

Anyone have any idea of the number of parallel cells needed for the Kokam 3200's Greg references? I take it the 90 controller is safe at 10s LiPo from Greg's comment.

I picked the Spit because it had the lowest wingloading of any of the ARF 80" warbirds out on the market. I figured that gave me the most room in the weight budget (by comparison it has pretty much the same sq inches as my Byron Corsair at half the weight). I really want "warbird" kind of performance out of it. While standoff scale, the planform is pretty correct. Good quality materials and construction overall, nervous about ARF retracts, but they seem to be "better than your average (ARF) bear" quality - time will tell.

I've had the kit a couple of months, when I start this winter, I'll post some pics.

Thanks,

Larry

RE: World Models Spit 80" Conversion ??'s
 

Larry

You want about 6000mAh atleast, to get enought flight time, and a low enough avarage discharge of the cells. if you like full throttle flying a lot a C50XL or AXI 53XX can not handle the 3kW, then you need a larger motor and larger pack.

if you use the throttle properly the "3kW burst" motors would work fine on a 10s2p pack

RE: World Models Spit 80" Conversion ??'s
 

Larry,

I agree with Henke. Kokam USA has just started making three versions of the 3.2AH cell where the welded cells in parallel are treated like a single "cell" for balancing. The three versions are 3.2AH, 6.4AH, and 9.6AH. Each cell has a continuous current rating of 64, 128, and 192 amps, respectively.

The "cells" will be available soon in unitized packs from 1 to 6 in series that contain a seperate charge connector with taps to each cell. Also, appropriate cell balancing chargers and modules will be available soon.

The idea is to break your 10s configuration into several smaller packs. My choice is to use a 6s and 4s combination that will allow for my exisiting Astro Flight chargers to work as well as provide a 4s supply to my FMA Power Force regulator. Additionally, the common 4s and 6s packs can be used on many other applications.

Matt,

Recall that we were flying the Edge 540 at only 1/2 throttle for the entire flight so figure about a 50amp draw. Granted, the cooling was not optimal but why push the ESC when you you just risk a cut-off in flight on a very expensive plane. Perhaps a 50amp current on a 10s voltage with proper cooling would work if you only needed that level for bursts.

For a slightly better ESC, the Hacker Master Controller 77-amp version uses 60v FETs instead of 45v FETs and uses a thicker 12# wire. It's about $50 more than the Jeti 77-amp ESC but will handle more power...closer to the 77amp rating on a 10s voltage.