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View Full Version : First "big" electric conversion - looking for advice


buzzbomber
08-12-2005, 03:10 AM
Hi all,

This forum is shaping up nicely; lots of traffic. So, what better place to seek advice on my next project? I've been itching to do a .25 to .40 glow conversion for some time now, but I've kept putting it off. H-L's recent AXI sale was just the ticket to spur me into gear. So, I picked up an AXI 2826/10, and I was given an Eflite 40 amp ESC. The jury's still out on the ESC, I'm getting negative feedback on the capabilities of the unit, but I don't have a reciept, so I'm stuck with it for now. In any case, I plan to run a separate BEC so that in the even of ESC failure I will still have servo control; good practice, right? I am thinking of using 12 nimh cells to control costs, probably GP2000 or GP2200 to keep weight to a minimum, and something like a 13x8 APC prop. If I can get a capable 3S lithium for $100 or less, I might consider that route also. So, there's the power system -- 375 to 450 watts+/-; now for my biggest problem.

I haven't decided on an airframe yet. I'm not looking for a real barn-burner or 3-D performance, but I do want something that can climb out steeply, has decent vertical for stall turns and the like and can loop and roll from level flight without losing altitude.

So far, I have picked the following candidates, which all appear to be in the ballpark in terms of weight and performance:

GP .20 size Clipwing Taylorcraft kit
GP .40 size RV-4 kit
Sig Rascal .40 arf
Sig Something Extra kit/arf
Sig Four Star 40 kit/arf
Goldberg Tiger 2

If anyone has any insight on which of these planes might be better suited to e-conversion, esp. to the particular power system I have, or has any other suggestions, I'd be happy to hear them.

Mike Parsons
08-12-2005, 04:20 AM
Hmmmm....Rv4 :) I think the Taylorcraft, RV or Rascal would be good matches (I am bias towards those three anyway :) ). What is the weight? THe Rascal will come in at 5.5 or 6 pounds if I recall, but should be ridiculously light on that setup.

-Mike

ENUT
08-12-2005, 05:05 AM
I have done the Sig Something extra.Makes a nice plane.But your power may need to be more.Same go's the 40star 40.475 may fly it but you will not have that much reserve.Have fun,
ENUT

Matt Kirsch
08-12-2005, 01:46 PM
There's a whole thread on a 4 Star 40 flying on a 3S LiPoly, same as a 10-cell NiMH pack... Granted it's a kit and has been lightened, but 12 cells should fly the ARF fairly well.

Of all the planes, the T-Craft would end up with the best power to weight ratio.

buzzbomber
08-12-2005, 03:55 PM
FWIW, the motor, mount, prop, esc, and ubec come in at 11 oz. 12 GP2000s weigh 15oz and a TP3s2p 4200 weighs 10oz. So, using the figures from the great electric motor test, about 400 watts on a 13x10 for 21oz weight on the 3S(approximated from data for 10 round cells) or 480 watts on a 13x8 for 26-28 oz weight on the 12 cell nimh pack. I've been pretty happy with smaller stuff at 60-80 watts/lb, so I think that 75-100 watts/lb should make me happy on a plane this size, maybe I'm off here?

I made my preliminary airframe selections based on AUW from glow specs(3.75-5.5lbs) and wing area(500-650) and loading(16-22oz/sf) figures. The lightest airframe with the best p/w ratio, as Matt Kirsch noted, will definitely be the T-Craft, and the Rascal would be the heaviest, according to published specs but this is mitigated somewhat by the light wing loading and big wing area, probably still resulting in a floater.

I did see the thread on the Four Star and posted to it, but I didn't wish to totally hijack it since I'm not set on that airframe yet. There was definitely some good info there.

ENUT, what's the power setup and AUW on your SE, if you don't mind sharing? I really like the plane because of its clean lines, the way its little brother flies, and the 2-piece wing(I sold my pickup and my new car has pretty limited storage area). However, if it's gonna be a complete dog on my motor and battery choices, I'd rather not waste my time and just choose something else. The RV-4 is pretty similar in terms of performance expectations, as well.

Thanks everybody for your input!

ragbag
08-12-2005, 10:07 PM
We are starting the Sig Kadet LT 25.

Axi 2826-10, Jeti 40, MAS 11x7 prop, Polyquest 3S2P4400, putting out 4#2oz thrust at 7800 rpm.
I think you did right on your choice of motors. Of course the sale help me to decide.
George
Gainesvill Fl

jbart
08-13-2005, 04:04 AM
For a couple of years doing electrics, I'm too, doing some electrocutions, I have in mind a traditional pattern plane for.25 glow, but there's not to many to fit my taste, then I'm working in an oldie, the New Era III, no kits available, but RCM has the plans (#601) has a ws of 45" 400 sq in area AUW around 50 oz, a couple of months ago I submited an inquire to a conversion service from Hobby Lobby and Justin Smith recommended me the same set-up you got, axi 2826 with a 12x10E and a Jeti 45Amp, 3S2P 4200 mAh Lipos.
Please keep us posted with your project, I'm going to need a lot of advice...

altgeld1
08-13-2005, 09:45 PM
will that work on a graupner taxi cup II

Mike Parsons
08-14-2005, 12:11 AM
altgeld1,
The AXI 2826-12 is actually what HL recommends for the TaxiCup. I think it will do just fine :)

jbart
08-14-2005, 06:41 AM
Hi Max, I love the Axi out-runners, I have been reading lately some discussions about the convenience of using in-runners (geared?) instead, it seems to be in a certain range of weigh and speed, but it's not clear for me yet, any comments?:confused:

GeraldRosebery
08-14-2005, 01:42 PM
I am sceptical that you can put 400+ watts to the prop with that set up. 12 cells = 14.4 volts nominal x 2000 mah cells = 20 amps max = 288 watts. NiMH cells really can't be trusted to put out more than 10C no matter what they claim. NiCd's can, but not NiMh's. If you want to fly a 4 lb airframe you need 400 watts (100 watts per lb is about right in my experience.). Those are great motors so I suggest you consider using 4s2P LiPo's say 3000 mah 12 C = 36 amps x 14.8V = 444 watts. They can be had from Dymond for about $85

"DYMOND Lipoly hd 3000 12C 14.8 V 346g 140x43x24 mm PC board for easy soldering and parallel packing. Ideal power pack to use for big power airplanes. $85.00"

Mike Parsons
08-14-2005, 02:06 PM
I cant agree about not pushing the NIMH cells past 10C. I push my GP3300's to 60 amps all the time and they are over two years old and still going strong. The hotliner guys push them to over 90-100 amps in bursts with no problems.

-Mike

fdix
08-14-2005, 02:34 PM
Gerald,
selected and pushed GP2200 cells can deliver 150amps for 30sec without problems. These cells are widely used in F5B. GP2000 can deliver 100A pushed and selected.

For AXI outrunners have a look at this

http://www.bnhof.de/~ho1645/d_bl_axi.pdf

it's a table containig thrust tests. ;)

GeraldRosebery
08-14-2005, 05:02 PM
He can do it if he wants, but he is not going to be happy. This is a not a hotliner he wants to build but a daily flyer. Why overun battery packs like that in that application. What's the goal, to see just how hot you can get them? Go LiPo. They are getting much more affordable and are are much better suited to the conversion application he wants to do.

buzzbomber
08-14-2005, 06:33 PM
Here's what I'm thinking:

As far as nimhs at rates >10C, I've had no problems doing it in the past, so why would it be a problem now? I've got a pack of GP1100s that I run in a pylon airframe drawing 19 amps at peak power tested on power analyzer, and they're perfectly happy, going strong with about 50 cycles so far. I imagine the inflight cruise draw is somewhere around 13 amps, so we're still above 10C there, and no ill effects so far. Flights are usually 5-7 minutes of mixed throttle flying. I'd be running the GP2200s at about 20 C(42amps) for take off and anything requiring vertical, otherwise they'd be pulling something more like 12-14C(25-30amps). The GP3300s would be less pushed for power, but again, they'd weigh more, thus requiring more power to stay aloft. The GP cells are waaay better than the first nimhs I dealt with, which did NOT live up to their claims. And nicads are out of the question; as stupid as it may sound, I have a moral objection to buying any more batteries that will wind up as toxic waste when I'm done with them, when there are more eco-friendly choices available. LI batteries are nice and all, but still, I do have a limited budget here, and for example, those dymond cells don't seem to hold voltage that well under their max. rated load, if they're the 1500 cells I've seen graphed. I think I'd need to run those cells 3P(4500maH) to avoid risking an expensive in-flight fire--then the cost goes up. The Kokam 3200s would be okay, as would the TP4200 2P packs, but they're priced out of my league, roughly double what I can get a GP2200 pack of equivalent voltage for. If I can only afford 1 lipo, I'm out of commision for at least several weeks, whereas if I spend that same dough on 2 round cell packs of roughly equivalent total capacity, I get the same amount of flying time, and I have a backup pack as well. Perhaps when I have more disposable income, I can ignore cost factors in favor of ultimate performance, but for the time being, I have to compromise. Plus, it's looking like I need a different ESC, so there goes more of my hard-earned money that I can't spend on a battery.

buzzbomber
08-15-2005, 07:04 PM
Sorry for the battery discourse in post #15, I just get annoyed by the way proven technology gets dismissed in favor of the "flavor of the month" sometimes. So, I've re-thought a bit, and here's where I'm at:
This project has to have my wife's blessing since what's mine is half hers:rolleyes: and I don't like the idea of sneaking expensive goodies past her since we're not exactly rich. The total budget for this conversion project is not to exceed $500 and she has to approve the airframe. I've spent $75+/- on the motor and mount, it looks like I'll need to spend another $75(net cost after returning current ESC) to get a more suitable ESC and external BEC, I figure $100 should cover radio flight pack, and I'm budgeting $100 for the kit and $50 for covering and hardware or $150 for an ARF.

Basically, I have $100 left to spend on batteries(maybe $150 if I can sell some of my current inventory). My wife was with me at the field the only time I burned up a Lipo and saw $50 puff up and die in about 30 seconds(the kicker is that the battery was well within discharge specs):eek: and so she's not crazy about me spending $150 on a single battery that may suffer the same fate. For that reason, if I am to consider Lipo, the total cost must be equal to nimh($50-70) for a battery with a 40 to 45 amp rating or up to about $125 for a battery that is capable of 50 to 60 amps, which I won't be pushing as hard and therefore be far less likely to puff. Unfortunately, I don't know if there are any known "good quality" cells out there yet meeting this specification(I'm skeptical of those dymond cells without seeing more info). So, I may be looking at moving up to sub-C cells and increasing to 14 cells if 12 lightweight cells won't do the job. So I need to get 400-600watts(depending on airframe) for about $150(preferably for 2 sets of batteries).

As far as the airframe goes, I have narrowed it down to the following, in descending order of preference: Somethin' Extra, Four Star 40(if I can convince the wife I can modify it to NOT look like an Agwagon), and 1/6th scale Clipped Wing Cub, all from Sig. Any information about an existing electrocuted Somethin Extra would be very helpful, since that's the one I'm least convinced is capable of being powered by the system I have in mind, but would be the most convenient and likely most versatile plane of the three, and any further input on power system requirements for the other two are welcome also.:cool:

ENUT
08-17-2005, 12:03 AM
Buzzbomber I used old technoligy when I built my sig extra.A/f 40 standard gearbox with16x3000 NimH cells(well used:rolleyes: ) Props I swung 13x10,14x8,15x8 .I also added a block under the landing gear.This keeps the prop from getting too green:D .I used the plane to learn aerobatics.But 2feet off the ground and alierons on high rate is a bad combo:eek: Mine wasn't lightend at all.I think I was 6lbs R.T.F. Only thing that was a pain was setting the battery packs.I had two packs of eight.Because of the aluminum tube that ran through the middle of the plane.Everybody else will guess it wasn't any speed demon; but with a thick wing like it has it's not going to be that fast.Anyhow thats my2cents.

ENUT

allena99
08-19-2005, 10:32 PM
I've flown glow for a long time, but have always wanted to dabble in electric. I sort of favor airplanes in the .40 size, and am just a sport flyer with mild aerobatic tastes. I settled on the Hangar 9 Twist 3D for my conversion because it is strong and light and cheap. Since I don't care about it's 3D capabilities, I just set it up with gentle control movements, I do not need high power. I chose an AXI 2826/10 motor with a Jeti 40 Amp Opto speed controller. I decided to go with NiCads because I am comfortable with them, and realize that I will get short flight times. I have two Great Planes 10-cell 1900SCR NiCad packs, for a total investment in batteries of $80. The plane exceeds my expectations in every way but my choice of power was not perfect. The motor can handle more current than my speed controller can. If I use a 13x10 or a 14x7 prop, the current goes too high for the 40 Amp controller. If I stay with a 12x8, that keeps current under 40 Amps. I should have gone for a higher capacity ESC to take full advantage of the available power of the AXI 2826/10 motor. I fly at about 2/3 throttle for about 4 minutes with a little reserve left for landing. I do not like the fact that I can't make more than one landing attempt. That might be a good reason to go for higher battery capacity. I am considering trying a GP3700 NiMH pack. That might allow me to fly for 5 minutes or more, and still be able to go around a couple of times if I wish to. Lipo's just cost too much in the capacity that I would need to do this right.

jrb
08-20-2005, 02:45 AM
Here’s a few of my conversions:
http://www.rcgroups.com/gallery/showgallery.php?cat=500&ppuser=497
http://www.rcgroups.com/links/index.php?id=4485
http://www.rcgroups.com/links/index.php?id=4788
http://www.rcgroups.com/forums/showpost.php?p=1873648&postcount=4

A search on my username there will find other postings that might be of interest

E-Challenged
08-26-2005, 09:19 PM
I have a couple of old Dynaflite .40 sized Funscale kits , the P51 and P40. Theses designs are known for trainer-like flying qualities and lightweight .
I plan to use a geared Astro 25 and a brick-like 16 cell Sanyo 1950AUP pack for motivation. I expect scale like flight with easy ROG takeoffs and 8 minute flights with some simple aerobatics. I will use a 4-cell flight pack in addition to the motor pack as my esc has no BEC.I think that many kit planes designed for IC power are too heavy for electric power unless you can carve, dremel and redesign for a much lighter but still strong airframe. Another good bet would be the .40 size Sureflight foam WWII designs. I am not nuts about large electrics but had so much fun with the .40 glow powered Dynaflite Funscale P51 that I had to give it a try. This months Model Aviation (AMA) mag has an article about a .40 size trainer conversion you might find interesting.

DickCorby
09-01-2005, 11:59 PM
Depending on what you expect to do with the plane, I have posted 2 conversions that I have done over the past few months. Both were quality kits and both fly great.

The Paramount 46 for the money is the best ARF I've ever seen. It's available from Hobby People.

Matt
09-02-2005, 01:31 AM
Also consider some of the planes that are about the same size, but aren't conversions. NEsail sells a couple planes (The Accord series, Samba, Vermont Belle). I fly a Samba.

I see your points made about Li-Pos (your smoking experience and the $$$), but you can't beat the capacity and weight. I have also read about the Dymond RC cells not holding up at voltage, but I had to try them for the price. I put three of the 3S 2000mAH (6AH total) cells in my Samba for $105 and I have been very happy. I do not pull the full rated 10C of the packs. At just under a 7C pull (39A, 11.0VDC, 7650RPM, 429W 12x8 prop on a MPjet MPJet 2820-7), they work great. The 6 ampre hour capacity lets you fly. Some people like to build, I like to fly. It is great being able to fly around (with throttle management) for 15-20 minutes. Perhaps you need the 4S cells which would bring the price up.

Good luck with whatever you wind up with. I think you will like a "big" electric.

Matt

DickCorby
09-02-2005, 02:11 AM
The Sportsman Aviation Paramount 46 is the best $100 airplane I've ever seen. It has a great package of parts etc. and that would definately increase your battery budget. As to the Dymond cells, I have some of them and they have proven to be as good as the higher priced Li-Po's.

jonnyjetprop
09-02-2005, 04:35 AM
I'm happy to hear about your eTwist. I coverted one also. It first got an Astroflight 05 brushless geared running on a 3s4p pack. The motor didn't like being pushed to 40 amps on long flights. I then went to an Astroflight 40 brushless geared runnig on a 5s2p 4400 Tantic pack. Much better but still lacked the verticle hover I was looking for. It was a prop clearance problem. I just switched over to 6s and I'm a happy camper now.

John


I've flown glow for a long time, but have always wanted to dabble in electric. I sort of favor airplanes in the .40 size, and am just a sport flyer with mild aerobatic tastes. I settled on the Hangar 9 Twist 3D for my conversion because it is strong and light and cheap. Since I don't care about it's 3D capabilities, I just set it up with gentle control movements, I do not need high power. I chose an AXI 2826/10 motor with a Jeti 40 Amp Opto speed controller. I decided to go with NiCads because I am comfortable with them, and realize that I will get short flight times. I have two Great Planes 10-cell 1900SCR NiCad packs, for a total investment in batteries of $80. The plane exceeds my expectations in every way but my choice of power was not perfect. The motor can handle more current than my speed controller can. If I use a 13x10 or a 14x7 prop, the current goes too high for the 40 Amp controller. If I stay with a 12x8, that keeps current under 40 Amps. I should have gone for a higher capacity ESC to take full advantage of the available power of the AXI 2826/10 motor. I fly at about 2/3 throttle for about 4 minutes with a little reserve left for landing. I do not like the fact that I can't make more than one landing attempt. That might be a good reason to go for higher battery capacity. I am considering trying a GP3700 NiMH pack. That might allow me to fly for 5 minutes or more, and still be able to go around a couple of times if I wish to. Lipo's just cost too much in the capacity that I would need to do this right.

Jollyroger
09-05-2005, 05:59 PM
How about another plane suggestion just to stir up the pot. Take a look at the Adrian Page Super Cub. An Axi 2814/12 should have plenty of power to fly it. It is an all laser cut kit and turns out looking great! There is a build thread on RC Groups .com that is quite long with lots of pics . Good luck on whichever you decide jolllyroger

buzzbomber
09-11-2005, 02:15 AM
Hi all.

I've been offline for a week, having just returned home from a rendevous with my wife's Scottish family. 'Twas a good week to spend in the Orlando, FL area because the kids are all back in school and the weather was just marginal enough to scare off the other tourists but not bad enough to stop us from fulfilling our itinerary. By the way, if you're ever in the area, make the trip to Polk City for Kermit Weeks' Fantasy of flight museum--most excellent for airplane lovers. But, I digress. Yesterday, the weather was sorta blech, so I made a side trip to Graves R/C, after reading Carlos'(Guapoman2000) posts about the place. After spending an hour or so looking around in amazement, all I can say is "Thank God this place is 1,000 miles from home, or I'd be very broke!" :eek: I have never before had the pleasure of visiting such a well stocked shop, especially one where the staff knows the difference between a toothbrush and a brushed motor. To make a long story short, I walked out with a Sig 1/6th scale Cub kit, full-wing version. I figured it's easier to start with a full wing and later decide to clip it than it is to add wing that isn't there to start with. So, the airframe is chosen. Now, I just need to figure out what batteries to use and find time to get working on it.

DickCorby
09-11-2005, 02:53 AM
If It is the 40 size, I recommend the following package. This has flown 40 size planes for me with great success.

AXI 2826/10
CAstle Creations 60 AMp ESC
4S-2P (5000-6000) MAH Li-Poly pack

If it is the 60 size, go up to the 4120 so you can spin a larger prop. Batteries should work well with either motor. Current draw should be in the 40-45 AMP range if you prop it right. giving a good margin for both the battery and motor.

I'm using Dymond Motorsports batteries with great success, and reduced battery cost.

buzzbomber
09-11-2005, 05:52 PM
Hi, Dick.

It's the 71" wing model, the old die-cut stick built kit dating back to the 70s. Sig recommends a .19-.35 two stroke, so in today's power-hungriness I guess most would use a .40. On this one, the 4120 on 4S would be serious overkill, and I imagine the 2826/10 could easily get by on 3S for scale flight--4S would be gravy, but then again I could be wrong.

DickCorby
09-11-2005, 11:04 PM
With Li-Pos I always like to go with the max MAH I can get to get the longer flight times. In this case you seem to be absolutely right - the 2826 should get the performance you want, and with 4S and 5000-6000 MAH packs you may have to make a special landing for the pilot to re-enlist.

E-Challenged
09-12-2005, 12:39 AM
" I walked out with a Sig 1/6th scale Cub kit, full-wing version. I figured it's easier to start with a full wing and later decide to clip it than it is to add wing that isn't there to start with. So, the airframe is chosen. Now, I just need to figure out what batteries to use and find time to get working on it.[/quote]

Sig used to sell a "clip wing" kit so you could switch wings from scale to aerobatic flying. Maybe they still sell them. I have the clip wing kit and plans, intend to finish my cub that's been 1/2 finished for 25 years. When I bought the kit it cost $33. I plan to use an old geared Astro 15 and maybe a 10-12 cell NiMh pack to power it.

buzzbomber
09-12-2005, 01:03 AM
Thanks for the tip! I just checked that out on Sig's web page, and sure enough, the wing kits are available separately. The clipped wing kit is $39, and the full wing kit is$40. So, that settles it. I'll build this with a full wing and when I get that done and in the air, I'll order up the clip wing kit and build that to go with it.