Open Letter to Thunder Tiger, Align, Hirobo and others...

[WillJames]

Electrical or mechanical, a safety interlock is needed on bigger e-Helis. It's the right thing to do because it is the safe thing to do.


If you had the equivalent of a hot start on a big E-Heli, it would strip the main gear or break something or smoke the ESC instantly and not start the mains spinning. I don't know of even a mid sized E-Heli that would not strip a main gear or belt or break with instant full power applied to a stationary head.

[DebianDog]

Electrical or mechanical, a safety interlock is needed on bigger e-Helis. It's the right thing to do because it is the safe thing to do.


If you had the equivalent of a hot start on a big E-Heli, it would strip the main gear or break something or smoke the ESC instantly and not start the mains spinning. I don't know of even a mid sized E-Heli that would not strip a main gear or belt or break with instant full power applied to a stationary head.

Exactly! Inertia and Mass. I forgot about the bad connection I had with a voltage drop a few months back. I lost the main gear on my T-Rex 600 trying to hunt down the problem. TWICE! To top it off the blades were already swinging!

The pinion will shear the teeth of that gear in less than a second. I know because it happened so quick. When I went over to pick up the helicopter I wondered WTH all the white stuff was all over the frame and canopy. From my perspective it was a power drop and a bad auto.

[AlanMcSwain]

Will, DDawg...

Are you asserting that the mains of larger e-helis are specifically designed by each manufacturer to shear at a precisely calculated pre-determined load??

If that were true, there would be very specific admonitions in the instruction manuals not to fit any alternate, modified or aftermarket main or pinion gears to the heli.

Sorry guys, not buying that argument.

[DebianDog]

Buy a big heli, override the soft start on the ESC, and start the heli at 100% throttle. I guarantee it will not spool up.

You are talking about instantly adding 3-6 HP to and non moving object attached with plastic gears. It is the same reason you can not do bail out autos without a VERY specific radio setup on certain ESC's. Because... if the pack delivers the HP/Amps... the gear is gone!

Don't you have a Razor or something you can test with? :twisted:

[AlanMcSwain]

Buy a big heli, override the soft start on the ESC, and start the heli at 100% throttle. I guarantee it will not spool up.



It **will** impart some motion to the blades until the gear fails. How much that is, is unknown at this time, and I agree that some real world testing is likely in order. But even an enabled soft start may have enough speed and power to hurt someone who is not prepared to anticipate a hot start possibility.

From this thread, it does seem that most of us approach powering up the ESC with caution. That is because we know there is alot of power that has the potential to be unleashed quickly and we are in close proximity to the source.

So, lets frame this very interesting debate in another way...

If by magic tommorow, you could choose between two e-helicopters that had basically the same price, features and all up weight, but one of them featured a cam-lever motormount plate like I have described as a safety feature, would you buy it and use it?

And DDawg, no, for some reason I have never owned an X-Cell of any model. I could never get past those damned butt-ugly FRP canopies!!!

[DebianDog]

Sure if it was not a PITA to use I would not care about some additional safety.

Do you have a big electric or are you just thinking about getting one?

Have you tracked someone down or ever even heard of anyone that had a current generation ESC hot start on them?

[LITHIUMSTATIC]

I respect everyones opinon on the topic and yes their are many variables. My mind has not waverd as to how I feel. Things can happen and they do. It's just that when 99.9% say it can't happen at all without a shadow of a doubt that's just beyond me . :dontknow

I for one will protect myself. It only weighs 1oz and cost me $55 bucks. My saftey is worth that much..... at least to me it is.

[AlanMcSwain]

DDawg...

Yes, I am throwing together an e-550 right now.

I have been whacked by the little ones and I sure as hell don't want to get whacked by a big one!! :WOW :WOW

Alan

[Pinecone]

It may not impart enough energy to start the head moving. You can shear something so quickly that the piece doesn't move.

Years ago when I was shooting a lot, I made some swinging targets out of 3/8" steel plate. At the range we had great fun shooting at them with pistols hearing the clang and watching them swing (lead bullets, sufficent distance and the were pivoted from the top so any ricochets went into the ground). So I tried a rifle. Hmm, nothing, must have missed. Shot it about 5 times without any result. When I went up to the targets I found 5 perfect holes. The high velocity rilfe rounds penetrated without mparting any visible motion to the plate.

As for liability, if the manufacturer puts a warning in the manual, they are pretty much protected. Thus all the stupid warnings in manuals, and some good ones.

But considering how many people here have flown MANY times, along with not ever hearing of a story of this happening, makes it very unlikley. You are more likey to be hit by lightning. Actually you are more likley to be hit by lightning than to win a big lottery jackpot. :)

Also with electric you don't have as much stuff around during the start up to drag or drop on teh Tx to change settings.

I use a set procedure to make my start up safe. No, I will not protect against a run away ESC, but again, have we ever had that happen? And the main power switch is nice, but it also an fail (either way) or you can forget to turn it off after the last flight. You could set up a relay setup with a start button that auto drops the relay when you disconnect the battery after each flight.

Also most ESCs I have will not start in other than Idle. If you power them up off idle, they don't do anything until you move the stick to idle.

Start Checklist:

Flight Mode - Normal
Stick - Full Down
Tx - On
Correct Model - Confirm
Throttle Hold - On (have to do this after turn on or Tx beeps)
Tx - Set down in safe location

Battery - Connect (with a quick glance at the Tx to make sure the switches are correct)

Tx - Pick up
Walk away a safe distance

Fly

It is a risk assessment. Is there a risk? How bad are the consequences? How likely it is to happen?

In this case, there is a risk, the consequences range from minor to bad (depending on size and how much head speed is generated in the short time), but the likelihood is low. Overall, I have other things to worry about. We all accept greater risks every day. Heck, you drove to the flying field. :) You charged your lipos (indoors?). You walked into the bathroom.

[LITHIUMSTATIC]

You walked into the bathroom.

Oh my!!! I forgot about that one. Now is truly living on the edge.

:lolol :lolol :lolol :lolol

[AlanMcSwain]

It is a risk assessment. Is there a risk? How bad are the consequences? How likely it is to happen?

In this case, there is a risk, the consequences range from minor to bad (depending on size and how much head speed is generated in the short time), but the likelihood is low. Overall, I have other things to worry about. We all accept greater risks every day. Heck, you drove to the flying field. You charged your lipos (indoors?). You walked into the bathroom.


Well said Pinecone. Life is all about risk assessment. Everyones' comfort zone for risk is different. The older I get, the more I value the avoidance of limb damage, digit loss and brain damage. Lipo fires is also a risk that I am not comfortable with which is why I'm setting up my e-550 for A123 cells.

What got me thinking about this problem was setting up my TT e-325. Those of you who have one know that it has a novel two point motor mount that pivots to set the pinion to main gear lash. Since it is so easy to swing and lock the pinion away from the main gear, I was able to do all the setup with the blades on and the motor plugged in. With the pinion dis-engaged, I had zero apprehension about working with a new esc and a new 14mz radio. Basically I knew that nothing bad or unexpected could happen with the motor pinion physically disengaged from the main gear. I started to think about how nice it would be to have this same level of comfort powering up the heli for flight on a routine basis.

For those of you who are having trouble visualizing what I'm talking in terms of how a safety motor mount would look like, I've taken a few moments to make a sketch for a mount that would work on the TT e-550/620. This is, by no means the only way to design such a safety feature so please feel free to post ideas for improvements.

Features:
Simple two second engage/release cam lever action.
Positive retraction upon cam lever release using captured spring action.
Gear lash setting does not vary because slide plate is forced against stop rail.

[LITHIUMSTATIC]

I think that would be great on a Mini-Titan! It would require being machines on a CNC type devise. It would need strong springs to keep the lever lock in place during flight.

I was adjusting my buddies transmitter on his Mini-Titan and it for no reason decided to spool on him. He already had his hand light on the skid but had to quikly grap it. I hit throttle hold and it would no repond at all. We had to carefully unplug it while it was spooled up. Sucked big time! :badair:

[Jermo]

1. I think it's good that you are thinking safety.
2. We need data on if this has ever happened when it wasn't pilot error.

I'm new so I'm probably not a vast repository of mis-hap data, however, I also have extensive electronics background and education. The only recourse I see that would effectively render the model safe but not require high precision would be a belt with an idler pully. Messing with gear backlash is just asking for trouble IMHO because it's hard enough to get it right when you are going to lock it down. Too tight and current draw goes up (parts run hot..etc), too loose and you eat a maingear.

If this isn't a widespread problem then I'm not sure the added weight/effort is the answer. No matter what you do there will be times the modeler is exposed to a potentially dangerous situation.

At the end of the day the most effective safety device we have is our brains. When we fail to pay attention things happen. No manufacturer will ever be able to overcome that.

[LITHIUMSTATIC]

Very true!

It would require very exact tolerances for the pinion backlash to NOT change once engaged. That would be a large feat in itself.

[Probedude]

Messing with gear backlash is just asking for trouble IMHO because it's hard enough to get it right when you are going to lock it down.

Problem is with a belt and idler you have to deal with slippage with increasing power, tighten the belt too tight to eliminate slippage and you have the same problem as tight gears. Eliminate slippage and high tension with a toothed belt, and now your idler setup is harder to effect since you now have to loosen the belt enough and have it disengage the timing pulley.

Alan's dwg is nice - moveable platform that can only be set in 1 of 2 positions - engaged and disengaged. The motor pinion clearance is then set with motor mount slots with the plate in the 'engaged' position. Elegant!

[elwitten]

when i spool up.

-first turn on transmitter and check if its correct model.
-check al switches (throthle hold is active and idle 0)and throttle al the way down.
-plug in battery (i always put a blade against my leg as i crouch to connect battery.) im guessing that this way it doesn't have any momentum if it spools up by accident.

i fly a trex 450.

[spork]

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[AlanMcSwain]

Great comments Rick. Much appreciated.

This was my goal. To get people thinking about the problem, and innovative ways to make an energized e-heli safer to be close to.

I've shared the basic idea with Jeff Fassbinder over at Ace. Hopefully this thread will catch the eyes of key individuals over at the other "Heli Houses".

[flyinfool]

My understanding is that with some of the small helies that still have brushed motors there is a real and not totally uncommon failure mode where the ESC can fail to short and allow full battery power to the motor regardless of software in the ESC.
All a brushed motor needs to run is dc power which is abundantly available from the battery. I have seen this happen more than once and yes those little buggers can bite.

All modern helies bigger than the 450 class (that I am aware of) are brushless.

With a brushless motor if the ESC should fail shorted and put battery power direct to the motor all that will happen is smoke, at the most 1/3 of a rotation of the motor to align the magnets with the powered coil.

In order for a brushless motor to run, the software in the ESC must be functioning correctly. The correctly functioning software will not allow a hot start when the battery is plugged in. A brushless motor is not a DC motor and can not run on battery power, a brushless motor is an AC motor that requires the software in the ESC to generate the AC power to the motor.
An ESC failing to a full power condition is not realistic and may not even be mathematically possible.

If you are looking for an extra level of security against your self, you can always set a flight condition and or P-mixes to require that 2 or more switches need to be moved before the throttle is enabled. All safety devices assume that the user will use them correctly.

It was mentioned that the gears can not be relied on to fail in the event of sudden full power. I don't think that there is a plastic made than can take the sudden full power of a big brushless motor. The main gear will always fail long before there is dangerous momentum built up in the rotor system. As was mentioned even bailing out of an auto can and will blow out the gears, and that is putting power to an already rotating system.

I can not come up with a realistic scenario to cause a hot start with a brush-less motor, other than operator induced and there is no possible way to stop that.

There is some danger in this hobby, It is not possible to make anything idiot proof. There will always be a better idiot.

I could be incorrect in some of my assumptions and beliefs and will listen to facts that could change my mind. So far I have seen what ifs and maybes with no evidence to back it up.

I am not against safety by any means, but I feel that in this case we are looking to try to find a problem to fit a solution.

[spork]

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[flyinfool]

But what did you do to whack yourself?
Was it due to a hot start from a faulty ESC or due to you not following proper safety practices that were already there?

It happens when it's sitting on the desk and you're going to adjust the swash programming - not thinking about it.

If you disable all of the safeties that are built in now and advance the throttle there is NOTHING that will protect you from that. Whenever I am working on the heli on the bench I ALWAYS unplug one of the motor leads. It is a safety measure that is already installed on the heli unless you have elected to solder the motor direct to the ESC. If you have chosen to eliminate a safety feature and replace it with another, Great, Go for it.

[spork]

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[flyinfool]

I think we are both making the same point.
That there is no perfect safety system to prevent anyone from ever getting hurt with a heli.

What I was trying to highlight is that you or anyone else getting whacked was not due to a malfunction of any of the equipment. It was due to improper use of the equipment.
The whole point of this thread was about an equipment failure causing the equivalent of a hot start with all of the power of the bigger helies and should there be additional safeguards in place to prevent that from happening. I don't think that with the safeties in place now that it is possible to have a big brushless heli come to full power at the point of plugging in the battery and I still have not heard of that ever happening.

I am not trying to make you or anyone else look bad, I am just stating the facts as I see them, and I am willing to change my mind if other facts are presented.

[Finless]

I wacked myself with a Trex450 as well and it hurt like a SOB.
It was not a hot start but my own mistake!

I was setting up a friends 450 on my 14MZ for buddy boxing to his 9C. This was a FM PCM system and I had not set up fail safe yet on my radio (his was set). My radio was to become the MASTER and his radio the student.
Needless to say for some dumb reason I powered down my radio with the heli still plugged in... Well by default the 14mz has 50% throttle for fail safe. The heli spun up on the table and wacked the hell out of me and busted up the blades etc before someone could get it stopped.... I was fumbling to turn the 14mz back on but a 14mz takes a long time to boot up...
Needless to say it wacked me up pretty good!

NOW the FIRST thing I do when setting up a radio is set the fail safe!!!!! It use to be the last thing I did but now it's the first!

Bob

[ghtracey]

I have to say Alan, if you have so little faith in the faceless ones that programmed your unseen code in the ESC, and you can't be sure its safe, well you shouldn't be flying. After all your chopper once in the air at full RPM is completely and totally under the control of unseen code programmed into your computer radio that could fail at any given time resulting in you losing control of your heli and killing someone. Odds on that? Slim. But hey, there's always the RF hit that causes your Rx to stop responding to your inputs, that is a very real issue, and more likely than a hotstart on an ESC. Or... how about mechanical failure in one of your collection of parts flying in loose formation? Maybe we should all change to metal ball-links so that they can't fail.

The hobby is inherently dangerous to some extent, you will never eliminate the risks. There are very real safety issues, I agree. But to be honest, I am more afraid of the guy flying next to me having a failure than his electronic equipment having one. Pilot error is still the biggest cause of accident and injury by a large margin.