Good Judgment comes from experience.  Experience comes from bad judgments!

OK, I am not ready to claim "expert" status, however on my journey to "goo roo" I have made, uh, some "experience enhancing discoveries" on how NOT to e-fly!  As an engineer I am not satisfied in knowing "how" I want to learn as much as I can about the "why" our various e-setups work the way they do.  Unfortunately some hardware got sacrificed along the way.  Hope that I could share these, as well as encourage others to fess-up, so we might all learn a smidgen more.

MOTOR SIZES
Jack Sheeks Classic "Swinger" swept wing design is prone to build nose heavy, as I discovered when I build mine.  Indeed, I cannot comprehend how Jack managed to get his to balance with the muffled Enya 35 he used.  Because my bird also finished a little heavier than I wanted, I tried nose-lighteners rather than adding tailweight.  I downsized the battery, pushed it as far aft as I could and still could not hit the balance point I needed.  Next step was to downsize the motor - from the Rimfire 35-36 (3.6oz) to a 35-30 (about 2.5oz) It worked too - sorta.  I was flying along, happy as a clam cuz the bird was really showing its potential - up to the 4-leaf clover.  I did the first loop then I heard a screetchy sound followed by a free wheeling propellor that was not producing any thrust.  Did not actually SEE a puff of smoke, but the CSI revealed what could best be described as a smoked out motor!

This year I tried again, this time with a Turnigy 28-36 motor.  We have been having good luck with the "oversquare" motors - those that are longer than their diameter.  Again the specs looked good, so we gave it a try.  Again the Swinger was flying well, but it was obvious that the motor was really laboring to get the job done.  No smoke this time, but the afterrun temperature was in the 150 degree range vs 105 max observed for the other motors that day.  Concluded that this was not a good idea.  Later on I also determined that the smaller motor used around 300 mah MORE battery than the larger motor.  High current draws are a sure sign of overworked motor!  I finally put the 35-36 back in it and added a slug of lead to the tail.  The Swinger is now flying better than ever, and the motor is up to the task.  However it still uses about 15% more power than the new Mythbuster.  The new bird is lighter with more efficient aerodynamics, ironicallly the small motors would have stood a better chance with the new bird. Except....

I started flying the Mythbuster with a Rimfire 35-36 motor and a 10x5 prop, quickly moved on to the 11x5.5.  Motor temperatures were good, power was great.  While trimming I decided to add a subfin, and wanted to counteract that with a slightly heavier motor.  Thus I replaced the Rimfire 35-36 with the 1 oz heavier Turnigy SK 35-42.  Was happy everything worked per plan, but discovered that the slightly larger motor at the same RPM using the same prop was using roughly 100+ mah less battery power. My "conclusion" (with the small motor experience in hand) is that the larger motor is working less hard - and using less power as a result.

As a result of these two experiences, I am going to be a little more willing to use slightly larger rather than slightly smaller motors in the future.


CHEEP ESC's
Hard to remember that far back but roughly 1 year ago the Phoenix ESC still did not have a CL governor and would NOT let you use the prop brake with the Heli governor.  While researching alternatives my Nephew found the Turnigy Sentry ESC WOULD allow you to use both features - plus it cost 1/3 the price of a Phoenix 45 - SUCH A DEAL! In my misguided exhurberance I bought FIVE Turnigy 40A ESC's to prepare for the coming ECL wars. Sure enough you COULD set the governor and prop brake, setting the speed was as simple as turning the pot on the Will Hubin timer - this ECL stuff is easy... EXCEPT the Turnigy did not hold RPM over the course of the flight - it kept falling off.  I attributed this to the ESC overheating, and tried adding a heat sink to compensate, seem to be a little better but not nearly enough.  I put all the Turnigy's in a box and set them aside.

Will Hubin did some bench tests and discovered the REAL problem, when he reported his results you may have heard a dull thud as I slapped myself in the noggin.  The Turnigy was incapable of adjusting for the loss in battery voltage as the battery wore down (duuuuh!)  His bench tests showed that a throttle-up compensating timer held promise by gently adding throttle to compensate for the loss in battery voltage over the course of the flight.

Armed with this, I installed a Turnigy in my new Brodak Stinger OTS and fitted it up with one of Will's FM-0c throttle-up timers.  Successfully flew this at Brodak's, where the combination kept the lap times within a .1 second range - plenty good enough for the OTS pattern - or the CLPA pattern.

I am NOT going to suggest that the low-buck Turnigy ESC is an alternative to the Phoenix, however for OTS, sport models and probably even simple CLPA, I  think the combination is workable.  I know I have no plans on changing the Stinger, and have equipped Dad's new Zilch with the same system!

Dennis,
I think it is true, that up to a certain point, a larger motor will be more efficient than its smaller cousin (like a Scorpion 3020 vs a 3014 at nominally the same kV). Basically the reason is that you can get a lower motor resistance with the larger motor.

Like I said, this works up to some point. That point is where the motor resistive losses are smaller than magnetic losses (like hysteresis and eddy currents). So if you run the two motors unloaded, the larger motor will have a higher no-load current that the smaller motor. Somewhere between that no-load point and the ~80% of the no-load rpm is where the cross over occurs (the large motor becoming more efficient). You can see that in some of the motor calculators out there.

It is a soft crossover probably and as long as you aren't really abusing the motors, you can choose the one you want based on other considerations (like weight, physical size, or even cost).

Only comment about the lower cost ESC is I wonder what governor means if it isn't monitoring the rpm of the motor (as long as the desired rpm is reachable at the lower voltages). One thing that has been good of late is that the Phoenix ESC cost has dropped considerably from last year. At that time the Phoenix 45 was always over $100 and I bought the Phoenix 35 because I could find it on sale in the $60-$70 range. The Phoenix 45 that I just bought was $80. That's a pretty good deal I think.

Hmmmm, more food for thought, could be I am missreading the larger versus smaller motor results.  Also, the smaller motor is a 1200 kV, the larger a 1000 kV, I really need something coloser to a 800kV to be in the "zone".  The differences in resistance plus the PWM dance probably all contribute to different current usage.  I guess to close the loop I would have to run the smaller motor in its 1000 kV flavor for comparisons sake.

I have only messed with the Phoenix, Turnigy, and the E-Flite ESC's.  All say they have Heli-governors, but only the Phoenix asks for a target RPM to try to achieve and lock into.  I speculate that in the case of the Turnigy & E-Flite the governor works over a short term load disturbances.  If we are running say 10,000 RPM in level flight then pull the nose up, the governor mode PROBABLY only does its best to maintain that 10K -  and the opposite for when the nose turns down.  I do not have enough experience with the set-up to comment about the effectiveness of the Turnigy governor.

Prop brake works though..

This sounds to me that you are running out of battery capacity, the battery cannot hold voltage under load, or you are using a starting RPM that is to high (ex. 90% throttle rather than 80%). Although the Z-Tron timers offer voltage compensation, I have never used it when running in governor mode.

Mike 

Mike & Mark:
This is low load conditions - as simple as hooking up the freshly peaked battery, powering up to desired flight RPM (in this case about 66% of max RPMas calculated AND confirmed with tach) and then watching the RPM slope down for the next 5:30 minutes at the rate the battery voltage falls.  End of flight revealed 1500-1600 mah out of 4000 used.  Meanwhile the bird next door with same motor and battery only with the Phx-45 was using 2300-2600mah to deliver constant speed start to finish.

The Turnigy (and lateley the E-Flite) ESC just keep delivering (fixed throttle) 66% of the voltage available.  I think that is the nature of the beast with lesser ESC's

(that make sense?)

Mark, Mike,
If I understood Dennis, it isn't the "head room", because he said Will Hubin could linearly advance the throttle and it would keep up the rpm. If it were a "head-room" problem, advancing the throttle wouldn't do any good.

Exactly!

Hi Dennis,
   That makes sense. It is running like a standard fixed wing aircraft setting. Put the transmitter stick (pulse width) at a given power setting and the RPM slowly falls with the voltage. It sounds like there is no governor??? Might be a sales pitch

Mike

Ah yes, the old over-promise & under-deliver strategy!    Oh well at least it plays MUSIC! 

I don't need my ESC for that, I'm self supporting.....
 
Up to last year (I'm having a sabattical from flying in 2009) I've been using 3 different ESCs.

First the CC Ph 45, that didn't have a combined governor/brake mode yet. It might make a come back next year...
Then the Kontronik Jazz 55, that did every thing right except kicking in the governor boost quick enough, so I ended up with egg shaped rounds. But it helped me through the WCh 2006. The weather there was kind to me as well.
Lastly the MGM  TMM4416, that finally provided me with round loops without the need for excessive corrections. The governor works flawlessly but, like all governors,tries to keep the airspeed constant. This, coupled with a motor working at the top of it's range, made the WCh 2008 into a nightmare. In strong winds, this makes you lose so much groundspeed, when climbing over 45 deg. in the vert. eights, hourglass, overheads and clover, that the line tension almost disappears.
Those who were in France can imagine the amount of 'elbow steam' I had to put in to prevent disaster....
So the next development will be dedicated to curing this.

Bruno!
Welcome back - its been too long since we heard from you! 

I think you will be pleased with the new CL Software Castle Creations has for the the Phoenix ESC's.

I have the Turnigy set-up in a Old TIme stunt model.  Some folks think it is wrong or disrespectful to use electric in OTS.  I tried to counter that opinion by demonstrating proper respect:

When I plug it in the ESC plays Auld Ang Syne... 

Dennis,
You can always point them to the 1948 Aeromodeller that has an electric control line airplane in it.  I'd say thos who think that are misinformed.

Too bad it doesn't play "Happy Days are here again!"

Hmmm, don't have the list handy but there are 15 different tunes.  I know it will play Oh Sussana, Ode to Joy, and Love is Blue.  I tried that last one but had to change; it is so sad that I was crying on my way to the handle... 

Does NOT play We are the Champions either.  Hey Bruno is there a Blue Grass version of that???

Bruno!
Welcome back - its been too long since we heard from you! 

I think you will be pleased with the new CL Software Castle Creations has for the the Phoenix ESC's.

Been working hard on establishing my new band, besides of having another part-time day job. All in all it's enough to keep me from anything else at the time.

We had the newest software in the CC Ph 45 already and it wasn't as friendly as the MGM 4416 Acro.
The governor has a steeper response, so the resolution was too twitchy. Erik re-wrote the controller software and cured that for the time being.
Because we want to control the power output to keep the line tension over 45 deg. to a pleasant value, it needs to respond linearly from 50 to 100%.
CC doesn't like that. Actually a governor that works from 0 to 100% would be ideal.
Maybe it's even better to use the non-governor mode and let the controller take responsibility for that. There's plenty of room in the controller processor. But that would take some more software and circuitry to take a usable rev pulse from the motor. We'll see.... 

If you are trying to maintain airspeed, then you need to vary throttle input based upon other sensors like airspeed or airplane attitude, and that is another kettle of fish!

That's exactly what we're working at, hence the need for a ESC that closely follows the input variations.
We don't want to maintain airspeed 100%, we also want a somewhat constant manoeuvering speed, partly a constant line tension, so we need to balance all parameters to obtain the best possible combination.

Kettle? Fish? I like my herrings dutch style, raw, fermented by salt. http://us.holland.com/e/7775/Herring.php
Let my collegue Ashleigh Elson explain: http://www.rnw.nl/english/video/my-first-taste-dutch-herring

As a statement, it is impossible I think to maintain airspeed or tension simply because modest rpm changes aren't enough to fight Mr. Newton's force. Level lap thrust is on the order of 2 lbs or so. When you point the nose up gravity now pulls about 3 lbs directly opposite the thrust. So for thrust to double (without losing airspeed) requires a pretty hefty rpm increase (I am not sure how much actually to double thrust--someone here knows).

Of course gravity opposes thrust mainly when the plane is climbing below 45 degrees. But at the top, assuming you have regained the airspeed, now you have gravity aiding the lines to apply the mv^2/r centripetal force, so even here you lose ~3 lbs of tension.

But I know what you mean. You want just enough extra grunt to give that good pulling feeling!

Alan,

We do not want to maintain a constant airspeed ever. A model flying at 55 mph airspeed in a 55 mph wind has no forward movement and thus no line tension. Bad outcome!

Far better would be to shoot for a constant ground speed. The ultimate of course is to govern the setup to produce a constant line pull regardless of where the model is on the hemisphere. We are working on this.

Kim.

Alan,

We do not want to maintain a constant airspeed ever. A model flying at 55 mph airspeed in a 55 mph wind has no forward movement and thus no line tension. Bad outcome!

Far better would be to shoot for a constant ground speed. The ultimate of course is to govern the setup to produce a constant line pull regardless of where the model is on the hemisphere. We are working on this.

Kim.

Hmmm, sounds like a sensing device that measures speed relative to the ground and throttles to suit.  NIRVANA!  Sounds like you would need some kind of position sensing, possibly with some kind of transponder(s) on the ground around the circle... 

Alan,

We do not want to maintain a constant airspeed ever. A model flying at 55 mph airspeed in a 55 mph wind has no forward movement and thus no line tension. Bad outcome!

Far better would be to shoot for a constant ground speed. The ultimate of course is to govern the setup to produce a constant line pull regardless of where the model is on the hemisphere. We are working on this.

Kim.

Kim,

Well if you are going to fly in 55mph winds, I    !!!

Just one comment about the topic of line tension---or more specifically the pursuit of it.

It may seem a little heretical here in the Electric Forum, but I always get a little uneasy when we begin to get too "techie". By this I mean coming up with onboard sensors that feedback to the motor (I certainly don't mind measuring this stuff, which I have done). Of course one can also apply these techniques to glow engines (as long as you are willing to put up with a throttle and a servo). However all this begins to evolve into an all out technical arms race, which I am not sure is really good for control line stunt in general.

Up to this point, an onboard governor sort of replicates a pipe on a glow engine (or any technique which tends to limit the running rpm range of the motor). A feedback system based on motor power draw also tends to emulate a 4-2-4 run. But something monitoring the line tension seems maybe farther than we may really want to go.

Just my 2 cents!

Eventually, dear friends, what is needed instead of on-board intelligence is a bit of real-time human brain power at the trottle? The rule, not without intent, leaves room for a hand held power lever. At least as long as the change of power functions via the lines. After all, the instant and and repeatable response of electric motors, and their ability to apply brake, lends itself to manual throttle/brake control.

Perhaps a proof-of-concept experiment could be done using a simple 2.5 Gzh  R/C car system with its trigger type throttle?

rgds Peter Germann
 

Actually folks lets circle back a little.  If I read back several of these posts, it sounds like it would be impossible to fly a tethered aircraft through a precision aerobatic schedule, IC or electric.  Of course that is not the case, and even the famous Fox 4-2-4 only trades one set of good behaviors (power-up) for bad behavior (wind-up in the wind)

I am inclined to agree with Igor's comments.  There are limits on BOTH sides of the PROPELLOR equation.  Too little propellor is bad, but too much propellor is a bad idea too because it can become a hinderance to penetrating wind and bad air.

The ability to fly in the wind requires the ability to penetrate the wind (higher speed, lower drag) with the ability to avoid wind-up (prop-braking, low inertia).  I especially beileve the propellor braking ability we have with electrics makes it possible for us to design low drag and light weight airframes to fully exploit that advantage.  Note that this is heresy to IC flyers (even pipe flyers?) who often opt for heavy, high drag and FAST to try to exploit what their power systems do best.  Also note that (as Igor pointed out) folks using their big power IC systems can be at a severe disadvantage when weather deteriorates.

That is why I am so DARNED excited about dedicated electric CLPA designs!  My "formula" for the new bird was low drag/high effiecincy combined with light weight.  The concept proved itself recently at the Brodak meet when my 42 oz bird was able to complete a pattern immediately after a flyer with a Piped RoJett 72 in a 65 oz bird was not able to complete his vertical 8. 

That is why I am so DARNED excited about dedicated electric CLPA designs!

Me too !!!

There is no reason to limit oneself to dealing with prop/motor behaviour. Once you accept that you can have a processor on board you can look at wiggling and deploying all manner of aerodynamic surfaces. If you have not ventured into indoor R/C aerobatics you should at least have a good look. People need to stop thinking of a control line model as a monolithic structure the gods forbid you to change and start playing "what if" a whole lot more. ( I know they will be appalled at what I am thinking of doing) Forgive me Father for I have had impure thoughts and know not what I do.


Alan: I think they have already flown Old Timer at the Nats this year. Maybe you could sign up early for next year.      



Kim.