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TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

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TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

Old 04-03-2008, 11:46 PM
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Spychalla Aircraft
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Default TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

I bought a Top Flite T-34 Mentor off RCU Classifieds and decided to pull the Saito 120 that it had out and to convert it all over to electric. I've flown a lot of little electrics for years but nothing big. It's time to mess around with something big and see how it goes. New powerplant is an E-Flite 90 powered by two parallel 9cell A123 packs. The motor controller is a Phoenix 85. The system is just under 30 volts and will have 4600 mah capacity. I think I should get 10 min. flights. Maybe 15 if I stay off the throttle. Propeller will be a 16 X 8 to start with. I started by gutting the airframe pulling out the engine, fuel tank, and some servos to get a clear front area. Batteries are extracted from Dewalt 36V packs I bought on Ebay. Interestingly they have gone up in price lately. About 6 months ago I bought 10 cells for $98 delivered. This time they were $128 delivered. They must be popular. Leo
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Old 04-03-2008, 11:52 PM
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Default RE: TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

I configured two battery packs of 9 cells each. You can get good instructions off the web on how to take the packs apart safely. I now have to solder on a ton of balancing wires.

The cowling on this plane had 1 lb. of lead in it. I plan to mount the batteries very far forward to do away with any added lead. Current weights taken on the E-Flite 90 motor are 1 lb. Battery packs are 1.5 lbs. each. Wow. 4 lbs. of power. I hope the airframe can handle it. Leo
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Old 04-03-2008, 11:59 PM
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Default RE: TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

I am really puzzled as to why the Top Flite kit has the front landing gear mounted off to the right hand side of the firewall? You can see from this firewall picture that I cut it off and plan to re-mount it in the center. It will look better and be more scale. As best I can tell from full size Mentor pictures the nose gear is in the center. So if anybody knows what's going on with that, let me know. I ordered a new fiberglass cowling from "Fiberglass Specialties". Craig said it would not ship until after the Toledo Show because they are so busy. Leo
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Old 04-04-2008, 06:34 AM
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Default RE: TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

Leo,
I just flew my 132" Wellington using the 2- 10 cell A123's for each motor with the E-flite 110 motors. Running wide open I get about 12 minutes of runtime. I really like the A123's.
Have you run the 90 yet and checked for best prop? I ended running APC 18x6w props on the 110. I did not get any better preformance with the 16x8.. I am getting about 7000-7200 from the 18x6...

http://youtube.com/watch?v=xst-WJjlONc


Ty
Old 04-08-2008, 12:31 AM
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Default RE: TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

Ty,

I ran the E-Flite 90 for the first time tonight. Just bolted to a bench. Smooth and powerful. I'm not sure how to check for best prop. How did you determine that? With a watt meter or something? I plan on running Bolly 16 X 8. I want a somewhat scale looking blade. The APC may be more efficient, but I just don't like the look of the blades.

Finished up one A123 pack tonight. Lots of soldering. Made up a 10 slot connector for balancing out of a PC board socket connector. Works fine. You can see my Astro Blinky working on the cells to balance them. It can only do 6 cells at a time, so I figure I will just move it down to pick up the other 3 cells when if finishes with the first 6, then I will move it back again. That should bring them all to the same level eventually. Not sure since I am new to this. Leo
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Old 04-08-2008, 06:27 AM
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Default RE: TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

Leo,

I just spent the weekend making up 3 more 6S packs for my FW. Since I'll need the extra weight in the nose to balance anyway I'll be running 12S2P A123. I got 2 more 36V dewalt packs for $160 shipped about two months ago, but they're out of stock now. Now I have enough packs to run 10S, 11S, and 12s and experiment around with different props.

I suggest getting a few blinkies and let them all run at the same time. I haven't measured the bleed-off current of the blinkies yet but it's not too high, and after my first charge it took about 8 to 12 hours to get the each pack balanced. I also wired up a couple 10 ohm 10 watt resistors to put across individual cells that are really high and bring them down a lot faster. Hopefully after a few cycles they should be closer in balance.

The only thing about the blinky is that it balances to the lowest cell that it's hooked to, so it might be a bit of a balancing act to get a 9 cell pack balanced with it, but it will work eventually.

But you really should have a watt meter to know that you're running the motor and ESC within their limits and know how much power you're getting to the prop.

Can't wait to hear a flight report!

Ron
Old 04-08-2008, 10:51 AM
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Default RE: TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

Leo,
Finding the best prop is the expensive part. The e-flite 110 and 160 both have a 12mm shaft so if a prop does not perform like you want it to then you waisted a prop. Yes i used a watt meter and tach to figure out the best prop. I had people and motocalc telling me the 110 would never fly the Wellington, but I new with the RPM's I was getting that it would.
I am just using 1 blinky for balance my packs. I my opinion if you fly alot in the same day or several days in a row and are really charging the A123 hard and fast. We are balancing them just to keep one cell or two from getting too high of a voltage. I don't charge hard and fast. so I will fly all weekend and then when I get home I will charge again and then balance the packs. My 10 cell packs have 2 blancing connectors each and I balance 5 at a time with one blinky.....

Ty
Old 04-08-2008, 10:53 AM
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Default RE: TF T-34 Mentor Conversion to E-Flite 90 Electric w/ A123 Cells

Has everyone noticed how much the (dewalt) A123's have gone up over the last month on Ebay? I was going to get a couple more but can't right now....

ty

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