stunthanger.com
Electric Stunt => Gettin all AMP'ed up! => Topic started by: frank williams on March 27, 2012, 09:20:15 AM
-
I learned something last weekend. The wingover is a very stressful manuever. The two spikes in current that you see in the logged data are to be respected. These are typically the largest current draw in the pattern.
I had my Ice 50 set to sensitive (60A). I thought that this would be fine for most flights, and it was. It should easily cover a prop strike. But I decided to try one more prop the other day. A large 13x6 3b was made from JXF pushers. The motor was a Scorpion SII-3026-710 and had been working fine for the other props I had thrown at it.
But ..... a nice sharp pullup into the wingover, apparently is such a load on the system (even with piped systems this corner has caused problems) that the ESC decided to protect me from the surge of current needed to fly. The motor shut off and the plane arced over and hit about 10 feet from the center of the circle.
I think from now on I'll select the insensitive mode for current limiting. or should it be disabled? This is the case of the transistor blowing to protect the fuse.
-
First off, sorry for the loss,, that always bites!
as an alternative to adjusting the current limiting, you can ( should) always check the current load with a new prop, a three blade prop is a LOT more load than a two blade.
There are amp meters you can plug inline, this would allow you to see the static current load on the prop. from my experience, the static load is a bunch higher than the in flight load so you will see variations with load more profoundly. I would be hard pressed to beleive that the static amp draw would be less than the wingover load. I have always used the static load to make sure my ESC is not being overloaded...
Its also possible the extra load caused the motor can and magnets bounced off the stator with the g loading, not sure how your motor is mounted, but its worth looking at,,
-
solution for such cases is slow down instead of cut off ... it saved many eirplanes so far
-
Frank, Maybe going to the 75 amp version of the ESC and leaving it in the sensitive mode would be worth considering.
-
Igor,
Are you saying that one should ease into the wingover pullups for this very reason? Have you seen this before?
Mark,
I thought the same thing about static loads, .... the three blade I know was a stretch for that motor ..... the motor was supported at both ends ...... I keep coming back to the fact that piped planes had a tendency to flame out at the same spot ..... don't think we ever solved that one.
Crist,
Yes I think now's the time to move up to the 75 or even the 100.
-
Even a motor that's well supported on the ends of the shaft might see the magnets twisting into the armature on tight turns; that would cause much higher drag than the static load of the prop.
As a designer, I hate things like snap-action current limits in systems like this. It is very difficult to do it right, and when you don't get it perfect the cost (as you've just found out) is high. Making an accurate current detector is hard enough in a nice well-lit lab at shirt-sleeve temperatures and still air; keeping things accurate when your motor load is all over the place and the environment is totally uncontrolled is a nightmare.
Which is really just a long-form way of saying that Mark is right: you should check current on the ground, and you should make sure that the static load is well within the current limit (I'd say that if you're over 80% of the current limit, you should hesitate to fly).
I dimly recall Igor talking about slowing down before: I think he's using a controller that allows him to set a "do not exceed" current that smoothly throttles the thing back on overcurrent, rather than just switching it off. Other than weight and cost, there's certainly nothing preventing an ESC designer from doing so. Hopefully he'll clarify.
-
Igor,
Are you saying that one should ease into the wingover pullups for this very reason? Have you seen this before?
I think Igor is saying there is a mode that in the event of an excess load slows down the motor for a moment instead of killing it. There is a guy in our club that has the esc setup that way, it keeps his system from frying in the event of a prop strike but it gives at least partial power if overloaded in flight to prevent disaster.
-
Sorry, yes I mean exactly that slow and gradual slowing instead of immediate cut off. I saw it several times in case that flyer used uncharged battery. It happened to me also as result of overheating. I use Jeti SPin and when it slows down I can still react and take model to safe position.
I personaly use voltage cut off set to 3,2V it is usually enough to cut off motor in case of crash. However I do not like cut off in case that motor hits the grass, I do not make prop nut very tight, so in such case the firction does not break prop and do not stop the motor, it happened to me on world championship in hungary, motor did strong squeek and after take off I sucessfully finished flight.
-
This is a great discussion. Thanks, guys.
-
Thanks Igor,
I understand what you are saying now.
The plane was just a practice ship, but I think I've learned something real important here.
The battery is a bit crunched on one end ..... it held its charge and didn't catch fire or anything ...not leaking anything..... do I dare try to use it again?
-
Thanks Igor,
I understand what you are saying now.
The plane was just a practice ship, but I think I've learned something real important here.
The battery is a bit crunched on one end ..... it held its charge and didn't catch fire or anything ...not leaking anything..... do I dare try to use it again?
NO!!! said simply - more due to Murphy than anything else - as sure as there's Sh*t in a cat - it will burn up or something when IN your plane..
-
Aw, Wynn, I would rather Frank use one of those little cameras and capture the whole episode for our enjoyment.
-
For what it is worth, I have been using a battery that is crunched on one end for a couple of years with no problem --- but that is my battery and not yours. I use it on a junker practice plane because I do NOT have full confidence in the battery and I would not cry if I lost the model. I might cry if it took out my Castle creations ESC!!! HB~>
-
It sounds like the low voltage cutoff rather than hitting the over current limit of ESC. I don't believe you can pull 60A during the reverse wing over. Data log should tell you what happened.
Two things might help: 1. Lower the cutoff voltage just like Igor mentioned. 2. Adding more decoupling caps at the ESC power side.
Regards,
Sean
-
Schuang
I think you may have hit on it - 3VDC per cell and maybe more Caps in the primary line. Castle sells a board with four additional capacitors and very easy installation. Could be worth a try. The capacitors are for reducing ripple voltage and Castle recommends less than 10% ripple volts of the total battery so for a 4S, 1.48VDC and for a 5S, 1.85VDC. I have normally seen .4-.7VDC on my logger but if it could hold the ESC input voltage for a milli second? It seems a majority of the stoppages are on the way up the wingover. This is also the most power demanding maneuver on the ESC other than start-up.
Norm
-
Norm
Do you mean the two capicitors that are on the ESC are for stabilizing the input side to the ESC?
-
You can buy the proper Capacitors from www.digikey.com/ (http://www.digikey.com/)
Part # P12411-ND @ .51 cents each (dirt cheap)!!!
Just remember that these are electrolytic capacitors and you need to match polarity when you solder them in to the battery leads on the ESC.
-
Well ....... nevermind ........ maybe its something else
I just looked closer at the output data ...... and I see that the throttle command went down to 1ms about one second before everything else shut down .....
Note that I did two wingovers and it was the second one that caused the problem ....
Could it be that the timer start/stop button is at fault here? Its just a momentary switch contact I think.
Hummmm
-
Well ....... nevermind ........ maybe its something else
I just looked closer at the output data ...... and I see that the throttle command went down to 1ms about one second before everything else shut down .....
Note that I did two wingovers and it was the second one that caused the problem ....
Could it be that the timer start/stop button is at fault here? Its just a momentary switch contact I think.
Hummmm
Humm.. Timer shuts down exactly at 70 seconds. Are you sure the timer was not tweaked prior to the flight?
I learned the hard way myself BTW...
Regards,
Sean
-
This is also the most power demanding maneuver on the ESC other than start-up.
Yes Yes ;D ... I had already high current cut offs, and it was ALWAYS on start
-
1. Lower the cutoff voltage just like Igor mentioned.
No, I mean just opposite, I mean to REPLACE high current cut off by setting low voltage cut off to 3.2 or 3.3V ... that is what we found with beginners in gym.
-
Well ....... nevermind ........ maybe its something else
I just looked closer at the output data ...... and I see that the throttle command went down to 1ms about one second before everything else shut down .....
Note that I did two wingovers and it was the second one that caused the problem ....
Could it be that the timer start/stop button is at fault here? Its just a momentary switch contact I think.
Hummmm
hmmm ... this certainly does not look like over current cut off ... it it was me, then I really forgot that I set 1 min test flight :- )))))) ... check timer flight time
-
I'm certian that the flight time value was not changed. It was a full flight.
The even second increment probably is from the data logging quantization due to being set to 1 set data rate.
Could the little spring in the timer push button get weak and allow contact to be made during a hard manuever? Why is it always the wingover? Could the throttle data value being a second early just be an artifact of the data logging quantization and it all really is from the same time?
Hummmm?
-
Hummm is right!!!
Frank,
Check your wiring very carefully!! Are the ESC and timer firmly fixed so that they cannot move and is the wiring also restrained so that it cannot move in violent maneuvers??? Is there any possibility that your arming switch and/or the battery wiring could somehow open for an instant??? Could the wiring from the timer button to the timer short under stress or movement????
Very curious!!!
-
Frank
So the motor shut down during the inverted “up line” on the second wingover.
Frank, as you know I have had two of these occurrences. The only common element of my two identical occurrences was the switch. It was not Will Hubin’s switch but a cheap one from Radio Shack. Switches of course are a high failure rate item when compared to IC's.
During the first incidence I did not have the data logging looking at the input pulse of the ICE Lite 50. The second incidence was with a Phoenix 60 (without data logging capability). I reused the same switch that was involved in the first incident as I did not suspect the switch.
BTW: For an ICE 50 you are operating very close to the line at about 48A - I know you know that but others should consider this when making ESC selections.
One other point. I no longer use a switch to start my timer. I use a 2 pin JST connector and a shorting plug to insert momentarily for start or stop.
Norm
-
Igor
Could you explain why you would set the low voltage cut-off higher... 3.2 to 3.3V?
Norm
-
Yes, Frank,
I think it's best to ignore the slopes between points and just look at the values at the sampling points.
How often are you sampling? It looks like you are set 1 second per sample.
I'm with Norm and John on this, as it looks like the input went to zero and there was still full RPM at one point.
By the way, I like the bulletproof and lightweight solution, Norm!
Regards,
Dean P.
-
Igor
Could you explain why you would set the low voltage cut-off higher... 3.2 to 3.3V?
Norm
because we have good experience with cutting off for low voltage after crash, stopped prop and its overcurrent makes voltage drop and it seems that it is safe working if set to 3.2 or 3.3V ... at least on indoors, I didnot see crash of large model which can show running motor after hitting ground, so I cannot say, but on our indorrs it works perfect ... may be because measuring battery voltage is easier and precise, while curren is measured typically on FET transistor ant it can be +/- something especially if temperature changes etc
-
I was going to say that it couldn't possibly be the switch, then I read Frank's post.
It may be the wires -- if you get a power glitch to the ESC it'll (presumably) reset. I'd put the plane on the bench, take off the prop, install batteries, turn it on, and while it's running, wiggle every wire I could get my hands on. In particular, I'd wiggle the wire from ESC to timer, and most particularly around the spot where it goes into the ESC and the connector to the timer. With the prop off the load is going to be very low, so you should be able to do a 6-minute "flight" on the bench in still air and not have any cooling issues (and if you do it'll be the ESC or battery, and you can feel them.
This won't necessarily find a loose connection (nothing will -- I hate intermittent problems), but if wiggling a wire makes it misbehave, and if wiggling the wire didn't also wiggle the timer and hence the switch, then you've found the problem.
I'd also look at the way that the switch and/or timer is mounted, to make sure that the switch itself doesn't flop around in maneuvers and get actuated accidentally.
Come to think of it, if wiggling wires doesn't make it misbehave, try rattling the whole plane with motor on and prop off -- if that makes it cut out, you know you have a mechanical problem of some sort, not a motor loading issue.
And speaking of mechanical issues -- is the prop well balanced? Does the plane stay vibration-free with it turning? If you've got high vibration that'll cause no end of problems with wires and switches and whatnot.
-
Igor
I may not be understanding completely - are you saying turn off the "current cut-off" in the ESC and only use the voltage cutoff feature but set that to 3.3v ?
Regards
Norm
-
Igor
I may not be understanding completely - are you saying turn off the "current cut-off" in the ESC and only use the voltage cutoff feature but set that to 3.3v ?
Regards
Norm
It not needs to be really "off" I mean that it should be safe enough. And in combination with current limit, it is good to use also high voltage limit. I can see what was the reason for cut off in my ESC (spin) and guy who crashed with his model and burned also motor and also ESC had setting for 2.8V ... while I am sure that 3.2V did safe cut off, and additionally it was clearly written in ESC that the reason for cut off was low voltage.
Some ESCs does not have adjustable current limit, and we found that voltage limit is safe also in those cheap ESC like this one: http://www.himodel.com/electric/HiModel_COOL_Series_11A_Brushless_Speed_Controller_6A_LBEC.html
-
OK finally got it - thanks Igor
Norm