Unintentional starting of flight motors

[Shaunie]

Sitting and thinking as you do, I had an idea.....

I have seen lots of reports of unintended flight motor start-ups. I have an idea for a simple fix.

Take a standard receiver power switch harness, open it up, desolder the red wires(or positive feed, I'm a Futaba man at heart) from the switch and join them together insulating as appropriate. Now cut the signal wire (white) and run that through the switch. If placed between the ESC and the receiver the radio will be powered whenever the flight battery is connected, but importantly the control signal to the ESC can be turned off thus preventing the motor from running. The ESC will beep if so equipped to show no signal is being received and that the motor is safe. If the charge connector has a signal wire (or is modified so it does) you could plug in your programming card to set up your ESC.

Not tried this yet but I intend to real soon.

Let me know your thoughts.

Shaun.

[PatMc]

I can't remember coming across unintended start up of flight motors.

If the throttle is in the power on position when the flight power is connected the esc usually enters program mode.

 

But if you did want to use a switch on the esc signal wire I don't see how a standard Rx switch harness would be useful. Surely they always come without any signal wire

 

Edited By PatMc on 27/10/2011 23:20:55

[Martin Harris - Moderator]

 

It seems simpler to just create a switchable mix - here's an extract of something I put together for our club newsletter:

The principle is a throttle to throttle mix of -100% and offset to zero to neutralise any throttle input.

Not having any real experience of them, I can't advise any specifics on Spektrum/JR systems but hopefully they will be capable of similar functions and perhaps one of their expert users will be able to add some advice?

I've knocked up a step by step guide... specific to the FF9 but most Futaba sets will be very similar – hopefully reference to the manual will clarify things on other sets.

1. Enter programming mode and select advanced mode:

2. Select a free programmable mix (use the rotary dial for most selections and move down the menus with the cursor keys):

3. Set as follows:
Use the select (up) (cursor) key until you see the screen as below and set:
Mix “OFF or ON” (depends on the selected switch position i.e. not INHibited)
MAS(ter channel) THRO(ttle)
SL(a)V(e channel) THRO(ttle)
SW(itch - choose whichever switch you prefer to use)
POSI(tion – choose your normal “neutral” position as we want the mix to be active – in this case it is a 3 position switch and I only want the throttle to be active when switched fully backwards i.e. down – a 2 position switch would just show “Up”

4. Use the cursor to continue down from the bottom of the screen....
and you'll see the next screen.

Set the RATE to -100 with the throttle stick at the bottom, move it to the top and do the same with the throttle set to fully open (selected item will move to the “up arrow”.  

 

OFFSET will normally be at 50 % so you will need to highlight it and move the throttle stick to closed, then press the rotary dial down until it changes to 0%

5. Now come out of programming mode and test carefully – with any luck you'll now have an added margin of safety which you can use while fixing hatches, carrying the model out to the flight line etc. It isn't totally foolproof – e.g. you might have left the switch operated from the last flight - so remain cautious at all times and treat it as live but it might just save a trip to casualty so I think it's a worthwhile exercise.

 

Edited By Martin Harris on 27/10/2011 23:37:31

[Seamus O'Leprosy]

I think I did something similar on my Cularis where I have a switch which neutralises the motor and turns the throttle stick
into crow mode below 50%
Mind you the programming nearly had me reaching for the bottle.

[Steve W-O]

My TX has a throttle cut switch (like many others ),which I programme to set the throttle to zero, and when I turn the transmitter on, it checks all the switch positions, ad won't start transmitting if they are not in the correct position. To make doubly sure, it won't start transmitting unless the throttle is at zero either.

 

Don't think much more is needed

[Martin Harris - Moderator]

How does that protect against catching the throttle accidentally though? You often have to fit hatches, carry the model to the flight line etc. after connecting the flight battery giving plenty of opportunities for the prop to nibble someone.

 

With the programmed motor switch method, the first time the motor needs to be capable of turning is after I've placed it on the ground to taxi or am ready for a hand launch.

 

Having extolled its virtues though, I still always regard the motor as live.

 

The only potential downside is accidentally operating it in flight - like I did once with an EP glider which I just managed to creep back over our local trees after the motor failed to start - only got my head in gear after the final turn, flicked the switch and carried on like I'd meant to do it!

Edited By Martin Harris on 28/10/2011 12:15:47

[Steve W-O]

Posted by Martin Harris on 28/10/2011 11:52:40:

How does that protect against catching the throttle accidentally though? You often hav.............................................................

Edited By Martin Harris on 28/10/2011 12:15:47

 

 

Which post did your question refer to?

[Martin Harris - Moderator]

The previous one. As I'm reading it, your switch simply prevents the rf output until the throttle is set to closed - once that's happened, the throttle is active as soon as the flight battery is connected, allowing the potential for a knocked stick to cause injury or damage.

[Pete B]

This is another mechanical option to protect yourself from the dangers of wandering about with a live and armed model.. Insert a safety arming socket on the positive side of the battery to ESC circuit . The first pic shows the socket flush to the surface:

 

 

The second pic (sorry, different model!) shows the Deans socket epoxied in place with the positive lead between the battery and ESC.

 

 

Make up a Deans plug (or whatever type suits you) with a simple loop beween terminals. Insert battery in the pits, carry the model out to the flightline, insert plug and there you go!

 

Pete

 

[Steve W-O]

Posted by Martin Harris on 28/10/2011 12:45:16:
The previous one. As I'm reading it, your switch simply prevents the rf output until the throttle is set to closed - once that's happened, the throttle is active as soon as the flight battery is connected, allowing the potential for a knocked stick to cause injury or damage.

 

 

 

No,my post says to make doubly sure the throttle has to be at zero before t TX transmits.

 

By doubly, I meant two. The switch shuts the throttle down whenever it is active (I set mine to be away from me to kill the throttle)

 

 

 

If the kill switch is not in the safe position when you turn the transmitter on, it won't transmit.

If the throttle is not zero when you turn the transmitter on, it won't transmit.

 

Once the transmitter is transmitting, the throttle won't work until you switch the kill switch off.

 

 

Hope that makes sense now,sorry if it was not clear

[Tony Bennett]

surely if you run a seperate rx battery and put a switch in that feed, the motor won't fire up until the rx is turned on.

[Martin Harris - Moderator]

That's made it much clearer to me - sounds like a fine arrangement!

[Steve W-O]

Posted by Martin Harris on 28/10/2011 13:31:17:
That's made it much clearer to me - sounds like a fine arrangement!

 

 

I like it, can put the plane down, check the controls, check the rates, check flaps, gyro if there is one, then finally enable the throttle and test, it all fits into a nice routine.

 

I will have tested the engine in the pits whilst restrained and then disabled the throttle, and checked it is disabled. I like routines,and all my planes are set up in a similar way.

[PatMc]

Posted by Tony B on 28/10/2011 13:19:16:
surely if you run a seperate rx battery and put a switch in that feed, the motor won't fire up until the rx is turned on.

The majority (probably) don't have a separate rx battery.

[Martin Harris - Moderator]

Posted by Steve W-O on 28/10/2011 13:46:13:

Posted by Martin Harris on 28/10/2011 13:31:17:
That's made it much clearer to me - sounds like a fine arrangement!

 

 

I like it, can put the plane down, check the controls, check the rates, check flaps, gyro if there is one, then finally enable the throttle and test, it all fits into a nice routine.

 

I will have tested the engine in the pits whilst restrained and then disabled the throttle, and checked it is disabled. I like routines,and all my planes are set up in a similar way.

 

Sounds like a similar result to my mix but I think the majority of throttle cut switches only add a percentage to the movement at the bottom end of the throttle movement (designed for IC engines) In order to give that functionality on the transmitters I'm familiar with you need to arrange a mix to neutralise any stick input.

 

Anyway, however you get there, there's no argument that a means of isolating the motor run until you actually need it is very desirable.

[Chris Bott - Moderator]

On a Spektrum DX8, the throttle cut switch (whichever switch you assign) sets the throttle to a fixed position.

I set mine to 31% because that is exactly the same as when the throttle stick is right at the bottom.

This way, whichever way the switch is when you plug in, the ESC arms at the same position and there aren't any surprises when you switch from cut to normal.

[Steve W-O]

Posted by Martin Harris on 28/10/2011 14:01:29:

Posted by Steve W-O on 28/10/2011 13:46:13:

Posted by Martin Harris on 28/10/2011 13:31:17:
That's made it much clearer to me - sounds like a fine arrangement!

 

 

I like it, can put the plane down, check the controls, check the rates, check flaps, gyro if there is one, then finally enable the throttle and test, it all fits into a nice routine.

 

I will have tested the engine in the pits whilst restrained and then disabled the throttle, and checked it is disabled. I like routines,and all my planes are set up in a similar way.

 

Sounds like a similar result to my mix but I think the majority of throttle cut switches only add a percentage to the movement at the bottom end of the throttle movement (designed for IC engines) In order to give that functionality on the transmitters I'm familiar with you need to arrange a mix to neutralise any stick input.

 

Anyway, however you get there, there's no argument that a means of isolating the motor run until you actually need it is very desirable.

 

 

You are correct, all I do is add a mix to the throttle channel, so that when I push the throttle cut switch forward, it replaces what ever the stick position was with zero throttle.

 

You can use anything as an input to a mix, and in fact you can use the same switch in more than one mix, for instance I use the gear switch to activate the flaps and at the same time the gear switch activates a mix that progressively feeds in down elevator as I open the throttle when the flaps are down. I can then mix again so that the down elevator is also dependent on how far down the flaps are down.

 

My zero throttle is on -100 position wise, full throttle is +100.

 

[Peter Beeney]

Is it worth trying to consider exactly how an electric motor can inadvertently start? At the top, one way might be the occasion if the speed controller were to go short circuit, and thus apply the full voltage to the motor. In the case of a brushed motor, because the commutation is mechanical, and automatic, then the motor would run up to full speed with no way of controlling it, other than disconnecting the supply. In the case of the brushless motor, because the commutation is done on the speed controller, this relying on transient voltages being returned from the motor to switch the transistors on and off, and if those transistors were short circuit it would be impossible to switch them on and off. So the motor would not be able to run. A large current might flow, however, this being proportional to the resistance, and this might be affected by the quality of the components, the better the quality, the lower the resistance. A really good motor and speed controller will have as low as a resistance as possible.
So, whilst things might get a little hot under the collar during a short, I don’t think the brushless motor can actually run without the full cooperation of the speed controller.

Also it’s very difficult to envisage a fault on the ESC that will allow the motor to run without the controlling signal from the rx. If the control signal is not present the motor can’t start and run, again, what sort of sort of short circuit can mimic this exactly, allowing the motor to run with no control?

I think the one condition that happens with electric planes is that the throttle stick is accidentally opened and the motor starts without warning. So for the last twenty years my tx has had a switch configured to disable the throttle stick until it’s switched off. I call it Throttle Lock, it takes but two seconds to assign it, and a few more to calibrate the ‘off’ setting, in the case of electric motors, fully off, with regard to i/c engines you simply need to adjust it to the reliable tick-over point. just a few key-clicks. One of the many (I think!) advantages of a computer driven transmitter.

And as Terry B says, the separate switched rx battery is also another ideal way of preventing the motor from starting. I’ve always thought this anyway, and other than small foamy models, any electric models that I owned would have a separate switched receiver battery pack. This is from a personal safety point of view, from a number of different angles, I’ve no idea if it’s ever saved the motor from inadvertently starting, that’s never happened to me, but it has saved a hot-liner, a Simprop Diamond, from certain uncontrolled total destruction on two occasions.

Perhaps one of the little problems with electric planes is that they can operate apparently satisfactorily under many conditions, it’s only when things change slightly that the unexpected happens.

PB

[Stephen Grigg]

I have the scars to prove an unintended electric start fortunately without long term damage but a good way to learn a lesson.Even so I also had a drama after this.I changed from Spectrum to Futaba.On Spectrum each model has its own unique channel when bound,so if a model is not selected correctly it cannot be flown on another models channel/.I put my Fun Cub down and selected a GWS Texan.>As I started to increase throttle I heard and saw Mt Fun cub tear off up the field at the same time as the Texan because on the Futaba even though I had correct model selection it appears to use a commomn channel for all models and I stupidly hadnt for some reason diconnected the Fun Cub.Fortunately I had put it in some long grass away from everyone but another lesson learnt.I now tend to check my model is swiched off befor putting the RX down.I did see our resident club critic try to change hit RX to reverse on the elevator on an older Rx with the little switches in the back and he inadvertantly switched the throttle at the same time taking out a foamy Wot wing and tearing the U/c and motor off the Fun Cub oops.

[Chris Bott - Moderator]

Yep I've witnessed someone who found his motor was stopped with the stick at the top and flat out with it at the bottom, so what did he do? He left it all switched on, with the stick at the top, and reversed the throttle channel before any of could shout noooooo!

[Ben B]

I use the -100% mix method with my flying wing with the "kill switch" allocated to a right hand toggle switch. This means I can launch it using my left hand with the throttle on full and the kill switch "on", and then shortly after launching flick the kill switch to get the motor going whilst obviously using the right stick (mode 2) to control any wayward wobbling. It also makes me much happier when I go to collect the model post landing knowing that after flicking the kill switch the engine is safe and I'm not going suddenly fine 850w of activity a few inches away from my fingers..

[Seamus O'Leprosy]

Posted by Martin Harris on 28/10/2011 11:52:40:

How does that protect against catching the throttle accidentally though? You often have to fit hatches, carry the model to the flight line etc. after connecting the flight battery giving plenty of opportunities for the prop to nibble someone.

 

With the programmed motor switch method, the first time the motor needs to be capable of turning is after I've placed it on the ground to taxi or am ready for a hand launch.

 

Having extolled its virtues though, I still always regard the motor as live.

 

The only potential downside is accidentally operating it in flight - like I did once with an EP glider which I just managed to creep back over our local trees after the motor failed to start - only got my head in gear after the final turn, flicked the switch and carried on like I'd meant to do it!

Edited By Martin Harris on 28/10/2011 12:15:47

When you use this switch "trottle Cut" warning flashes on the transmitter screen and you only arm it after your ready to launch.

Its part of my pre flight safety routine.

[Shaunie]

Didn't realise I would cause such a lively debate!

Just checked and it does seem most receiver power switch harnesses are only two core now, sure they used to be 3 core, must be my memory ore something. Just splice a switch into an extension lead.

My idea was merely to put some hardware in place to force the ESC into standby while testing gear, in the pits etc. and switch it on when ready to fly. I'm converting from nitro power where they take a concious effort before they become a hazard, whereas electric will start the moment you open the throttle, it takes a different mindset.

Clever mixes etc. are a good idea and with my two planes on my DX7 I will blatantly nick that one. However they can only work once setup is completed. A switch in the ESC signal will work whatever, but still allows everything else to be live and tested. It may not be for everyone it was just intended to be an idea which may help somebody out.

Shaun

[fly boy3]

Hi all, as a 20 years + ic man, dipping my toe into this leccy stuff, I am quite worried now ! Cheers

[Peter Beeney]

Shaun,

Yes, I would certainly agree with you, where a brushless motor is concerned the motor can only run under the influence of the throttle signal and if that’s missing I think it’s most unlikely that the motor will ever move. What I contemplated doing once upon a time, but never did, and in the interest of KISS, (Keeping It Strictly Simple), was just simply cutting into the signal wire from the ESC and extending it to a SPST switch; as you say, you can put an extension lead in, but that’s only more clutter. Customize and reduce everything to a minimum. But I don’t own and fly any small electric models, so it’s never been a top priority. However, it's still a fact that the flight pack has to be connected first and so a small de luxe optional extra might be the addition of a flashing led when the switch is in it’s on position. These days it’s very easy to cobble up a small lightweight circuit, it might just help to make the situation a little bit more ‘failsafe’; it might be a trifle embarrassing if you had such a switch, it became inadvertently knocked on, and you still had an unwanted motor run! Just a thought, and you might not consider it at all necessary. When Lipos first appeared I tried them as a standard receiver supply and I had a flashing led indicator to help to prevent the regulator discharging the pack. It actually saved the day once, when I accidentally left it switched on.

As I said previously, with regard to anything other than a small chuck-up I’m easily persuaded to install a separate rx battery supply anyway. Now I can indulge in the luxury of checking the model out, at leisure, in the certain knowledge that the flight pack is not connected. I’m sure that most pilots these days that are serious about flying have transmitters with model memories and will have already sorted out the correct tx/throttle/motor operation first, on the bench, with the prop off. So the correct throttle operation when the flight battery is connected is never going to be an issue.
There are other potential advantages to this configuration, too.

There is a little story about one inadvertent motor starting incident, slightly bizarre in fact. We are a small club, so we all generally have our ‘own’ 35 MHz frequencies; but there are no rules that we can’t use any frequencies, if that happens we just need to be fully aware.
Pilot A, an elderly gentleman has a small plastic powered glider. Pilot B has a second hand i/c model, complete, that he wishes to test fly. It so happens it’s on the same frequencies as A, so they talk to each other and A places his tx by the tombstones so that he won’t switch on until he gets the nod. However, he busies himself putting his model together on his model stand and suddenly the motor starts, the prop cutting the back of his hand, sufficiently enough that he takes himself off to A&E, but he soon returned, it was superficial and they’d fixed it with sticking plaster. It soon became obvious that this had been caused by B opening the the throttle to take off with the i/c model! With hindsight it was obvious, of course, but understandably nobody had really given it any thought until then, least of all pilot A.

As you subtlety point out in your OP, you can never be too careful where electric models are concerned!

PB