Siemens Schukert DIII - Electric Power - DJ?

13 April 2007, 03:14 AM

Thanks to both of you for the insiightt. Madman, you are saying that you haven't had problems with ESCs, as long as they are sized correctly? I also had no idea about the longevity of Li-Po batteries. I think this longevity is unknown to the public. Something else I see as a bug-a-boo, is trying to determine system sizes for the application. Madman, you have experience to help you; however, someone starting out in electrics will have a difficult time! As a glow guy, I think in terms of a particular sized displacement to power a specific sized aircraft. The measuring system used to discribe electrics is not intuitive, unless I am missing something.

Again, thanks!

Madman · 13 April 2007, 04:11 PM

I had one problem with a speed control. However, I had overloaded it a week earlier and I think that may have been what caused the later issue. I have had servos go bad though. All my speed controls are high quality Astro flight. I have a couple of brushless controls but have only just done a little bench testing, no flight time yet. They are all Castle Creations.

Originally Li were given shelf lives even if not used. Yes, they have only a few years in service so who knows yet. All the laptop recalls lately don't bode well, however, remember there are vastly more laptops out there than RC batteries (many orders of magnitude). The power tool industry is jumping on the Li bandwagon and appears to be the engine of development for batteries suitable for our appliaction.

A long time ago in a land far far away there was a kindly electric guy named Astro Bob. He smartly named all his motors based on their performance with comparable glow motors. There were 020s, 035s, 05s, 15s, 25s, 40s, 60s and 90s (along with a few other intermediate sizes). As he continued to develope these motors they ended up performing better than most of their namesakes. Then one day he added gearboxes and they increased the flexibility of the motors but totally blew the comparisons away. Don't mean to be condensending, just even the best intentions in this regards have been blown away.

For example I power a 1/5 scale D.VIII with an Astro 25 geared about 3.3:1. It swings a 16x12 on 15 NiCad cells. I figure it is roughly comparable to a 90 four stroke except I have less RPMs (many) on a larger prop. I don't have the comparable thrust either but my thrust and pitch speed really match the application well. I fly at just above 1/2 throttle. Any higher or lower power the plane just climbs or looses altitude. It doesn't go any faster. The big draggy plane is at Vne. So to me this is an ideal match with no wasted power. I would like a little more climb authority and plan on installing a slightly heavier but more efficeient brushed motor which should give me comparable flight performance but with a 20" prop better climbs.

With the literal explosion in electrics the choices are truely bewildering. Add gearboxes in a wide variety of ratios and I have a tough time working up power systems. Used to be we talked in number of cells (NiCads). A 20 cell plane was roughly equal to a 40. 7 cells gave the power of a 10 to 15. Back then we were talking brushed motors and high end motors ran on 25A continuous and short bursts of 40A tops. All out limited motor run competition motors could survive 60A for very short (10 sec) bursts (ask me why they were called bursts).

Now days good quality brushless motors routinely run at 50A, high power systems up to 80A and bleeding edge competition planes are reaching (maybe exceeding) 200A. Our electric heated house has 200A service! A good rule of thumb is motor weight. The heavier the motor the more power (heat) it can handle. Of course this is a relative term and all motors are not the same.

Everyone in electrics wishes the manufacturers would come up with a common identification system which means something to us users. The best advice I can give is get a copy of one of the motor simulator programs like motocalc. With it you can compare systems with reasonably close results to reality. Otherwise asking others for recomended packages, seeing what others are using in the same or similar planes is you best route until you get a feel for it. I am more than willing to help get you looking in the right direction but please note my prejudices. I will try to give lower cost greater bang for the buck older brushed systems unless you indicate this is not your interest. I will also advise towards quality, not the mosty expensive but not cheap crap either. I do not fly small planes and prefer 40 sized and above. I have a niche interest in 1/5 th scale WWI to between the wars planes as well as jets.

No you are not missing anything. The manufacturers are.

Stephen

Martin Irvine · 13 April 2007, 07:52 PM

Don, Stephen has given you lots to digest. His point about geared Astro brushed 60s and 90s is well put, but as he noted, only available second hand. You can find them fairly regularly on Ebay and Ezonemag.com

A number of thoughts:

The SSDIII was originally designed as a gas plane and I would guess is heavy as electric planes go. Can you lighten up the construction? Figure on 60-65W/lb. So, 15lb needs 900-1000W.

A large slow-ish flying biplane isn't going to benefit from a high current motor - you're not going to be on and off the throttle like a 3D plane. You need CONSTANT current capacity, so a 30-40A motor is plenty.

The Astros are great as they will turn large props at reasonable currents. My 60 with a 2.71 ratio gearbox will spin a 24 X 15 at just over 3000 rpm for 30A on 10 Lipos. That converts to a pitch speed of about 44mph.

There are a several battery options other than NiCads and NiMh, although the SSDIII is a short nosed plane so can probably use the nose weight! In addition to Lipos, you could consider E-Molis, a metal cased 2600 Lipo that is pretty crash resistant(!), good for about 30A and 3.5oz. a cell. Another cell is the new A123, a metal cased 70g 2300 cell that needs a different charger, (Astro has one now). Both these cells seem to have good longevity. Oh, yes, NiMh tend to be a bit "tender" and not as durable as NiCads

If you go with Lipos, use the 2/3 rule for long(er) life. Never use currents above 2/3 what the manufacturer claims, and never use more than 2/3 their capacity. Lipos are still a young technology and we are working out the parameters!

Keep us up to date on the progress - this is a spectacular project.

Martin

14 April 2007, 09:53 AM

Madman, I was involved in electrics for a couple of summers back in the early 80s, when transitioning from sailplanes to power. At that time I thought it was a technology which needed more developement. Once I got through a couple trainers and started building scale, I no longer considered electric power. I am interested now. However, I like you, like .40 sized and up and also like 1/5th scale WW1. If you guys don't mind I'd like to tag along on this thread!

Mark

Madman · 17 April 2007, 04:09 PM

Quote:

Originally Posted by Mode One

Madman, I was involved in electrics for a couple of summers back in the early 80s, when transitioning from sailplanes to power. At that time I thought it was a technology which needed more developement. Once I got through a couple trainers and started building scale, I no longer considered electric power. I am interested now. However, I like you, like .40 sized and up and also like 1/5th scale WW1. If you guys don't mind I'd like to tag along on this thread!

Mark

I started in electrics about '92, a couple of years after getting into flying. I was interested in electrics from the start but didn't know where to start and had no one to advise. Soon after getting into electrics I found out about our local (Southern Ontario) infromation group the Electric Model Flyers of Southern Ontario (EMFSO). If I had this contact from the start I may never have gone into glow. As it is I have flown almost no glow for the past 15 years, only just started again with a couple of YS 45 for a specific appliaction.

In '92 the technology was very mature WRT high end brushless motors of power comparable to glow up to .60 size. Gearboxes were just becomming common but brushless was still years away.

Martin is my guru for electric scale and especially WWI. As shown above he is up on current developments in batteries which is an area I have not worried about. So little time, two kids and other aspects to pursue.

I would suggest if you want to pursue info on WWI electris and 1/5 in particular start a new thread with a specific application as the topic.

Stephen

17 April 2007, 07:41 PM

Quote:

Originally Posted by Madman

(SNIP)
I would suggest if you want to pursue info on WWI electris and 1/5 in particular start a new thread with a specific application as the topic.

Stephen

Stephen, this doesn't sound like you want me to "Tag along!" Am I not welcome here?

Madman · 18 April 2007, 02:32 AM

Quote:

Originally Posted by Mode One

Stephen, this doesn't sound like you want me to "Tag along!" Am I not welcome here?

Sorry! Didn't mean that at all. Haven't heard from Don, so don't know if he is digesting all this, examining options or pursuing his choice (or just out of town). Also, based on the 'flying models is a dying forum' discussion I thought starting a new and specific thread, on a different topic, was how we were being asked to pursue this type of branching. Sorry no offence meant.

Stephen

DJ · 18 April 2007, 11:54 AM

There really isn't many areas on this design where it would be safe to take any weight out. as a rule, I design pretty light. i would get an inrunner and gear it. Don't use the Briso as a baseline motor as that had enough power to pull the plane vertical.

DJ

Martin Irvine · 18 April 2007, 01:46 PM

Hi Don:
Any idea as to what the empty airframe weighs?

Martin

18 April 2007, 03:58 PM

Quote:

Originally Posted by Madman

Sorry! Didn't mean that at all. Haven't heard from Don, so don't know if he is digesting all this, examining options or pursuing his choice (or just out of town). Also, based on the 'flying models is a dying forum' discussion I thought starting a new and specific thread, on a different topic, was how we were being asked to pursue this type of branching. Sorry no offence meant.

Stephen

I don't know enough to start a thread on electrics and feel following along is a good way to learn. Also, I have started plenty of threads here and contributed to many more!