One of my fellow club members is in the process of building a C-130. Serious scale model. I cant remember all the dimensions but its giant scale to say the least. He was initially going to power it with four os 25 nitro engines. Making this long story short he has decided to go electric. I have my share of the foam single engine planes. I have seen the multi engine foam planes as well. But I am far from an expert. So, this is what were needing. Four electric motors and were limited to a 11 inch prop. What set up would you go with for this? Two motors per esc? What size motors would you use? Any advice welcome.
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RE: Need help from the electric guru's!
Have him post with the engineering details.Originally posted by Ben
I can see one issue. If using brushless motors you/he will need an ESC for each motor. -
RE: Need help from the electric guru's!
We need to know the weight of the plane. Konrad is correct, you must have one ESC per motor. It sounds like four E-flite 25's might work, but the weight of the plane must be considered. Good luck with the project. Let us know how it go's. DocComment
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RE: Need help from the electric guru's!
I know its 100 inch wingspan and its about 72 inches in length. I hate to guess the weight but for arguments sake lets say 30 pounds. That's probably a wee bit on the heavy side, but there is no such thing as over powering. So, going on that data, how would you configure the esc/battery arrangement? Are we talking two batteries?Originally posted by doctormikeComment
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RE: Need help from the electric guru's!
At 30lb assuming a sport sort of performance of 75 watt per pound will result in you needing motors that can produce about 550 watts per motor On 3 cells this would be about 50 amps per motor or 200 amps total.
On 4 cells (14.8v) this would drop to about 37 amp per motor or about 150 amps total.
The for 4 cells the Eflight 32 would do this so would the Hacker A30XL-12 or the Hyperion ZS3025-10 These are 700 to 770 KV motors and should turn 11 inch 4 bladed props just fine. If going with 2 bladed props you might want a higher KV motor maybe 900 to 1000Kv.
This is all SWAG as I don't have a wing area number (this is much more important than wing span). I also like to set my pitch speed at about 2.5 to 3 times the stall speed. So I'd need this wing area to get a rough idea as to the stall speed.
30 lb looks like the model would need to have a lot of plywood to get that heavy. If building for electric one can take out a lot of structure as motors are a lot easier on structure than the old slimmer engines.
Now if it was my ship I'd look at a 6 cell set up using this ESC, This is also a good ESC for 4 cells.
http://www.motionrc.com/ztw-mantis-45a-esc-with-5a-sbec/
P.S.
A good valve motor in a 4 cell set up might be the FMS 3648-770
http://www.motionrc.com/rochobby-3648-770kv-motor/Comment
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RE: Need help from the electric guru's!
Here is a quick and dirty method (simple) I use to find stall speed. This come from the great scale modeler Keith Shaw. It is accurate to with in 10% of actual stall speed for models that are clean (no flaps) and have a Clark Y type airfoil. It is great for finding what you should aim at when selecting your pitch speed.
This is an approximation by Keith Shaw:
Stall speed = 3.7 * square root of the wing loading
Units for speed are in mph
Units for wing loading are in oz/sqft
I hope this helps.
KonradComment
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RE: Need help from the electric guru's!
Thanks!Originally posted by KonradComment
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RE: Need help from the electric guru's!
I knew the 30 pound weight was high. I talked to him today and he said 18 maybe haha. Anyway so lets say 20 poounds. Anyway my next newb question on this. How do you configure the batteries and how do you get this set up into one receiver/throttle?Comment
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RE: Need help from the electric guru's!
Still need the wing area. What charger does he have? That might drive the choice in batteries and voltage. I'd like to use a 6000 mAh maybe 8000 mAh 25 plus C rated 6 cell battery pack. Hook all the ESC with Y connectors to the RX. If you want differential throttling then mix the rudder to two engine ports (channels), just like a glow set up. At 20 lbs the "15 size" motors are look very practical.Originally posted by Ben
I'd wire the motor in parallel off of one battery. Less chance of a hook up errors. I'd also use a separate BEC for the radio. If I couldn't find a cell with a high enough amp rating I'd split the engines symmetrically across the center line over two batteriesComment
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RE: Need help from the electric guru's!
Wing area and weight are essential. Total dimension for batteries is an important consideration as well. You don't want to use a motor/prop setup only to find that you don't have the space to CG the model with the required batteries.Live Q&A every Tuesday and Friday at 9pm EST on my Twitch Livestream
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RE: Need help from the electric guru's!
With a C130 I doubt that battery space will be an issue. In fact the fuselage will look a lot like the BAE 146 in my avatar, AKA the beer cooler. :DOriginally posted by Alpha.MotionRCComment
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RE: Need help from the electric guru's!
I thought it was an ASM C-130 arf to be honest. But its not. Its a fiberglass fuse. The wingspan is the same though, but the wings are actually sheeted foam. Go figure. I do not know the chord of the wings so I cant figure wing area, but Tuck already had because he knew that four .25 os motors would pull it. I just never thought to ask him what the wing area was. Anyway were just a little lost on doing electric setups especially a four engine set up. He thought about a battery in each Nacelle. I thought that would be a pain in the ass and maybe even more expensive with four 3s batteries. I keep thinking one 6s might do it or a couple 4s if that's possible? With a couple batteries maybe power the two inboard motors with one battery and the two outboard motors with the other, then the control sufaces power off a traditional flight pack. Opinions?Comment
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RE: Need help from the electric guru's!
From my earlier post.
"I'd wire the motor in parallel off of one battery. Less chance of a hook up errors. I'd also use a separate BEC for the radio. If I couldn't find a cell with a high enough amp rating I'd split the engines symmetrically across the center line over two batteries"
This would be batteries in the fuselage. (Why have all that weight out on the wings?)
I don't like BEC on the ESC board as I don't want the heat from the power (motor) side to limit the BEC's ability to shed heat. I like separate BECs like the Castle Creation 10 amp BEC.
http://www.motionrc.com/castle-creations-10a-bec/
I haven't used a radio flight battery in 20 years!
If the guy is starting out with a clean sheet of paper I'd recommend 6 cells, 22.2v nominal set up. A 4 cell set up, 14.8V nominal is also very viable.
Saying that 4 OS 25's will haul it around isn't saying anything. We need the wing area and true target weight. As this is a kit the designer should have made some mention of the wing area.
Why can't the builder post to this forum?
All the best,
KonradComment
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RE: Need help from the electric guru's!
Lol he doesn't have internet by choice. He goes to the LHS and makes all his purchases and orders. He is old school to say the least. I have got him tinkering with electric retracts though, but just tinkering haha. Yeah 6 cell is what I was thinking and the set up like you described as well. The fuse is the place to put the batteries, there is plenty of room.Originally posted by KonradComment
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RE: Need help from the electric guru's!
Electrics motors might not be the best power plants for him. As a lot of firmware and software upgrades are web based. As he sounds like a bit of a luddite, steam engines might be more suitable for him. :rolleyes:
https://en.wikipedia.org/wiki/Luddite
long live Steampunk,
Konrad
https://en.wikipedia.org/wiki/SteampunkComment
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