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Author Topic: Electric Twins - any disadvantage to separate esc/battery setups?  (Read 952 times)

Offline Brent Williams

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It seems that most e-twins are designed around using large capacity, centrally located main battery/timer instead of two individual batteries/timers/esc's.  Paul Walker posted recently about his search for smaller esc's.   Paul's comments piqued my interest and raised a few questions in my mind regarding a shared big battery/timer vs two totally separate smaller esc/battery/timer systems.   https://stunthanger.com/smf/gettin-all-amp'ed-up!/esc-for-smaller-motor/ https://stunthanger.com/smf/open-forum/ringmaster-p-pdf-files/msg501750/#msg501750

From Paul's thread, he demonstrated that his Park 480 equipped Flite Streak can fly a full pattern using around 800mah.  Paul didn't list the line length or weight of the test plane, but one could assume that it was at least 25-30oz ready to fly.  Pat Johnston has reported flying his similarly sized 28oz rtf Shark 402 on a Park 480 sized motor(Arrowind 2810) using about 900-1100 mah from a 1550 battery.   This is a pretty light combo, motor/esc/battery/prop at around 10oz or slighly less, complete.

These questions come as I have been curious about the power arrangement for an electric twin.  650"+sq.  or so.  A minimalist, carbon tube fuselage design, probably in the mid-high 50 oz range, based around an Impact wing/tail and numbers.  I wonder if a twin equipped with two 1130kv Cobra 2808's (2.85oz each), two Talon 25 esc's and two 4s/1350-1550mah 4s batteries would have enough oomph and mAh capacity to cleanly fly a 55-60oz, 650-680" flapped twin stunter on 65-68ft+ .018" lines?   This is allowing for 20oz +/- for 2 complete, but separate power packages. 

For comparison, I do know Gordan Delaney's Pathfinder Two (now owned by Howard Rush) runs two OS FP15's (phasers set on kill) to very good affect.  On his huge Gemini twin, two 2 OS-35-s engines, 10" props, powered that plane with much authority and contest cred.  And his previous classic, Too Much twin used two fox 35's.  Those planes are huge! 900-1000sq.in or something.   A 650" plane is small in comparison... 

Given the 400"/28oz Streak/Shark model, would the efficiency of 650sq.in twin at double that 28oz weight (56+oz) and two power packages be enough for serious stunt?  Bob Hunt has commented that his next twin effort will likely be employing motors smaller than the 1100kv Power 10's he previously used, hence my question about the 1130kv 2808 Cobra.  Any thoughts or observations would be interesting.

So to summarize my questions: 
- Pros/Cons of  two independent power systems vs central battery/timer.
- 2808 Cobra / Park 480 sized motors on an Impact sized twin.
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Offline Tim Wescott

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Re: Electric Twins - any disadvantage to separate esc/battery setups?
« Reply #1 on: July 20, 2019, 06:31:11 PM »
I think the biggest reason for one battery is so that you can shove it way up in the nose for balance, and you only have to deal with one battery.  I think that's the way I'd go if it were me.

As for timers, I think that unless I were using KR timers I'd want to run one timer and two ESCs -- that way the motors will cut out at the same time.

Having said that -- if you're a devoted KR timer user then unless Keith makes a master/slave version then you're stuck with two timers.  I know at least one person who wanted to do an electric twin, but whose brain kept exploding whenever I suggested just using a 'Y' cable from the timer to the ESCs -- if you're one of them, then use two systems.

As for two 480's on a 56 ounce model -- it sounds workable, I guess.  Horizon says the Park 480 is good for 275 watts, the "11 watts/ounce peak" rule of thumb says that a 28-ounce airplane (or half a 56 ounce airplane) wants to pull 308W peak.  But on the other hand, the "look at what the manufacturer recommends for 3D flight" says 25-35 ounces.  So you may be overloading the motor -- or Horizon may be rating it conservatively.  Try it, fly it, and be ready to switch to a Power 10.

As for an "Impact-sized" twin -- Paul tells me that my Atlantis is pretty much an Impact, and it weighs 64 ounces and has a wing area of somewhere around 690-700 square inches (it's different every time I measure...).  That's more like 360 watts per motor, which is sounding like a lot more than Horizon advertises -- but still within their 25-35 ounce limit.  If it were me and I had the money I think I'd go with a 480, but be ready to buy a pair of Power 10s.  If it were me and I didn't have the money I think I'd just buy the Power 10s -- unless you or Paul try it first and find out that the Park 480's work just great.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Brent Williams

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Re: Electric Twins - any disadvantage to separate esc/battery setups?
« Reply #2 on: July 20, 2019, 07:33:24 PM »
Thanks for the info Tim.  I have a handful of Hubin FM9 timers on hand that I would probably use.  I have access to a sheeted impact foam wing and if I just ran 1/4" balsa flat tips it would end up around 59".  Stock or slightly reduced flap chord percentage sizing is another interesting question given all the extra prop blast coming over the wing.

With the general precision of Hubin timers and Castle esc's, I would guess that rpm and cutoff would be very/exactly similar with independent systems vs the more common shared arrangement.  Given, that one can push both start buttons at the same time.
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Offline Tim Wescott

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Re: Electric Twins - any disadvantage to separate esc/battery setups?
« Reply #3 on: July 20, 2019, 08:05:00 PM »
If you're using a Hubin timer, just use one with a 'Y' cable.  Any hobby shop will sell you one.  Clip the power lead (red, in the middle) to one of the ESCs.  The ESCs won't know or care that you're using one timer.  Embed a tube in the LE of the wing that's big enough to pass the connector -- phenolic/paper tube would be perfect, but you'd probably need to buy 1000 feet of it.  A sheet of paper wrapped around a pencil and glued with Elmers should work just fine.

Just feed the cable through the tube to the nacelles, and have at.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Howard Rush

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Re: Electric Twins - any disadvantage to separate esc/battery setups?
« Reply #4 on: July 21, 2019, 06:47:02 AM »
Paul suggested something I hadn’t thought of:  just use two timers. They don’t weigh anything, flipping two switches is no big deal, and you get independent speed adjustment.

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Offline Dennis Adamisin

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Re: Electric Twins - any disadvantage to separate esc/battery setups?
« Reply #5 on: July 21, 2019, 07:59:59 AM »
I built  a Pathfinder Twin a few years ago based on Brodak ARF as a follow-on & companion to the PF ARF single.  The twin used a single battery & timer, & Phoenix ESC's with data logger.  Some observations:


* A single battery & single timer each require a Y-Harness.  For the timer a modified servo harness will do, but for the battery you need heavy gauge wire - and it is dead weight.  However using two batteries is not automatically viable because batteries sizes come in steps; two adequately sized batteries could exceed the weight of one properly sized battery combined with its split wiring harness.

* For a single timer you need to disable the one (or both) of the POWER wires, leaving the signal wire intact.   Two timers is pretty easy, two timers slaved to a single remote start switch is probably doable!

* Data logs showed remarkably tight RPM control BUT the dynamic response to loading of each motor was different.  Discussion with Castle indicated that they believed that was caused by using a single battery & long/split battery harness.  No dual battery tests were ever conducted so that remains a conjecture.

* The Castle "Set RPM" mode is the best (indeed, the ONLY) means of assuring that both motors are running the same RPM.  Set RPM will also neutralize the effect of the small motor-to-motor variation in kV. If a different RPM setting is needed on each side Set RPM COULD do that but it would be a bit tenuous.  If you are NOT using Set RPM then you will be consigned to at a different RPM from side to side - not as intimidating as it sounds.  If you are using opposite rotation props on each side it is very likely that each prop is at least a little different and may REQUIRE slightly different RPM settings anyway.  I would ONLY use injection molded props (APC's) as any other type would be all but guaranteed to have variation.  If you want to use to two RH rotation props (as I did for two flights),  good luck, and wear your track shoes.

* The PF twin used two Arrowind 2810's.  The companion PF single uses a single Arrowind 2820 - so the total working iron & copper in play is the same. 

* Total prop disc area for the twin (two 9 x 4.5 APCs) is 127 sq in, prop disc area for the the single (12 x 4.5EP APC, clipped down from 13") is 113 sq in.

* Twin weighs 4 oz more than the single and uses more battery (exact numbers logged away somewhere!)

* Ahhh, but does it perform? YES, both do.  Feeling is that the twin still has some un-tapped potential - actually, both probably do!


I would advise chatting with Rick Huff, who has successfully campaigned a PF twin for several years now, and Bob Hunt, who went through several experimental itterations in developing his twin.  I believe they are also using set-ups different than what I described above.



Denny Adamisin
Fort Wayne, IN

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