Esc power safety switch?

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ShowMaster
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Re: Esc power safety switch?

Post by ShowMaster »

Brent suggested I add a 1k in series with the receiver throttle ppm out. Have the switch short the esc ppm input to ground on the other side of the 1K. This gives the receiver 1k to drive when the esc input is at ground (-).
I think I'm able to solder the resistor between the first 1/2 set of the dpdt slide switch and be able to short out the resistor when the switch is on. When the switch is off it'll ground the esc input side of the resistor and remove the short across the resistor.
I'll draw it up after I test it. I found I had some old small receiver dpdt slide switch assemblies with a fuselage mounting plate and screws.
I'm trying to use parts many have already from their into days.



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Re: Esc power safety switch?

Post by jhsa »

Don't forget that with only the switch you won't be protected next time you power the plane on if you forget to disarm the esc ( flick the switch) after flight. In fact that could be even more dangerous as you might think you are protected but you aren't.
For 100% protection against fools and non fools, you'd want it to work like it does on our radios when T-cut is programmed. The Esc starts always disarmed at power on even if you forgot to disarm it the previous flight. That can be achieved with a small mcro controller that is smaller than your switch :D

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ShowMaster
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Re: Esc power safety switch?

Post by ShowMaster »

I'm all for trying a micro controller, but most can't build or program the circuit. If it's $5 many would buy it but $10 and they wouldn't I think. Electric flyers seem to favor HK prices.
Maybe a good project for the forum and could be sold on eBay?
If you can design it, I'll build a few to try.
I would think the Heli or quad flyers would like an onboard motor failsafe.


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ShowMaster
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Re: Esc power safety switch?

Post by ShowMaster »

Quick and dirty drawing of what Brent added to my idea.
No drawing app for my iPod touch. If it works I'll do a better one on the computer.
ImageUploadedByTapatalk1398437986.889655.jpg

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Bill
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Re: Esc power safety switch?

Post by Bill »

When the switch is on passing the signal to the ESC the resistor does nothing, when the switch is off grounding the signal, the resistor just loads the output of the RX for no purpose. The best place for the resistor in this set up is between the switch and the ground so it prevents floating, but it's not really required at all.
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Re: Esc power safety switch?

Post by ShowMaster »

I added it at a request. I should see what my scope shows with it loading the RX ch output or not.
My original idea was to just float the esc input but grounding it was suggested.
What I have found out is I MUST wait 3 seconds or more after switching the switch to the off/ground the esc input. If the esc doesn't have that time or more to time out and go into the motor off condition, it can stRt up again when switched on.


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Re: Esc power safety switch?

Post by SkyNorth »

[quote="jhsa"]Don't forget that with only the switch you won't be protected next time you power the plane on if you forget to disarm the esc ( flick the switch) after flight. In fact that could be even more dangerous as you might think you are protected but you aren't.
For 100% protection against fools and non fools, you'd want it to work like it does on our radios when T-cut is programmed. The Esc starts always disarmed at power on even if you forgot to disarm it the previous flight. That can be achieved with a small mcro controller that is smaller than your switch :D

João

So how do you know the Micro is working...??? I guess you will have time to think about on the way to the Hospital. :mrgreen:
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Re: Esc power safety switch?

Post by jhsa »

I think I don't understand what you mean Brent..
When the micro is powered on, it would connect the signal to ground via a transistor and a resistor, the same as in your schematic. Motor wouldn't run.. the person would have to press the button long to arm the ESC before flight. After landing just have to power the model off. next time he turns the model on, the ESC will start disarmed again..

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Re: Esc power safety switch?

Post by gohsthb »

I think he meant, should the micro circuit fail, then what happens. The circuit would simply need to be configured such that if it fails, the esc is disarmed.
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Re: Esc power safety switch?

Post by gohsthb »

On the micro idea I think it could be really simple. Using the pin change interrupt the delay through would be minimal. And with a watchdog timer if the program did for some reason stop, then the controller would reset, and disarm the esc. This probably needs an LDO regulator, so the Rx could operate on whatever voltage 4.8V or 6V. And a couple of inline resistors between the esc and Rx. I would also add an LED, so there is a visual indication of the status. LED on the ESC is armed, or something like that.
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Re: Esc power safety switch?

Post by jhsa »

Are you thinking of reading the PWM from the RX and then generating the PWM for the ESC? That's a good idea.. you could also implement a kind of sticky throttle cut. On start up send let's say 1ms pulse. that will keep the ESC at idle/off. then a long press on the button to arm it but only if the incoming rx signal is around 1ms. then the attiny would pass the RX signal through. If thr is not at idle, the tiny will continue to send 1ms, not arming. Does it sound good?

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Re: Esc power safety switch?

Post by gohsthb »

I was thinking of not reading, and then sending the pulse. Simply matching the level of the input to the output. More of a pass through. Probably could have it read the incoming pulse before allowing it to be armed though. Trying to read a pulse and then send a pulse could introduce to much error and delay I think.

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Re: Esc power safety switch?

Post by jhsa »

too much for the tiny85?? If you could implement the sticky thr cut the way you described, then is not necessary to send any PWM. you would use the tiny to just ground the signal through a resistor, right? then just having a pin reading the pulse an checking for the 1ms pulse..

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Re: Esc power safety switch?

Post by gohsthb »

It takes at least 2ms to read the pulse. Takes micro seconds match the voltage level. The micro doesn't need to know the pulse just whether to pass it through or not.

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Re: Esc power safety switch?

Post by jhsa »

I mean to make it sticky you would need to read the pulse and check it is around 1ms.. to make sure the thr is at idle..

EDIT: oops, wrote the same as my previous post.. :( must be cos it's well over bed time :)

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Re: Esc power safety switch?

Post by gohsthb »

I think you have it. To arm you would need to hold the button for 2 to 3 seconds. As well as have the pwm signal from the rx be near 1ms.

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Re: Esc power safety switch?

Post by jhsa »

That would be great... and safe..
Anyway, off to bed now. After 4 am here :(
Ahh, maybe another 2 or 3 seconds press to disarm it, in case the person is working on tbe model. No need to power off then ;)

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Re: Esc power safety switch?

Post by SkyNorth »

From a reliability point :
I'll stand by my circuit ....3 transistors (2 are in SCR) will be more reliable than your Micro (thousands of transistors) and software which must execute.
The Armed status is shown on the LED , On power up the PPM signal line is held low....Unless the SCR is triggered , the PPM line
will stay low. Once the SCR is triggered the Current flowing through it lights the LED...and turning off the transistor shorting out the PPM line.
The Arming time can easily be increased by a resistor / capacitor. To disarm Short the SCR or cycle the power.

I do under stand you want to use a micro , but a simple ESD event (spark) could destroy the micro ...and you cant guarantee that it will not pass
the PPM signal when it has failed. Yes you can hook up a LED to the micro , but its status indication cannot be trusted.
The micro could also be effected by the noise of the Motor lines...and could dis -arm it self in flight.

Another thing is the ESC could be damaged , and could show strange/un predictable operation.

Any How..... we all have our opinions ... after 30 years of designing Electro muscle simulators and portable X-ray units , I know a little about NOT damaging people .... simple is better some times..

The best place for this function would be IN the ESC , Some of the OLD Brush type ESC , had a ARM button and LED indicator attached to them.

But all of these "Safety's" are still secondary to common sense ... like stay away from the Props , or remove them or unplug one of the motor leads, if your screwing around near the front of the plane ...

-Brent
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Re: Esc power safety switch?

Post by jhsa »

If we can't trust on a micro controller for a safe throttle cut, then we can't trust our own radios ;) :D
They are everywhere.. tx, rx, esc, servos, etc.. And we fly with all of them.. Maybe control line is safer? :)
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Re: Esc power safety switch?

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Until the wires break! :)

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Re: Esc power safety switch?

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SkyNorth wrote:How about something like this?
ESC_Safe.JPG
-Brent
What's a part number for the scr? I can try the circuit and see what happens.
The esc manufactures and in the USA, the AMA, should address this option. It could be an extra pin header on the esc for the optional arm switch and maybe a led.
Use it or not, but it's there!
Maybe castle creations will respond to an email to add it to their line of esc's?
A start!
The accidents seem to affect all ages. New flyers that have no clue or safety mentoring. Senior flyers that CRS ( can't remember "stuff". Finally just stupid flyers that should be flying paper air planes but would probably get a paper cut doing it!
Mine seat belts, it'll save those that use it.

6cell motors swinging props are the sure fire way to lose fingers without warning.
I have a related question. Trying to kiss and cheap, how about a deans plug external jumper added to one motor lead? Would the extra length of one lead mess up the timing?
Again, the idea is to arm the rec and servos, but not the motor being able to develop full cutting power without warning.
Larger systems, a 4mm bullet jumper setup.
My senior friend with all the arm stitches went flying Friday. More afraid of the prop now but nothing changed. No tools to remove the prop, brushless wires too short to disconnect one wire easily while we were setting up his Eagletree guardian gains on the bench.
I was able to get to the wires with my big nimble fingers so we did discount one motor lead!
Ugh!




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Re: Esc power safety switch?

Post by Flaps 30 »

ShowMaster wrote:What's a part number for the scr? I can try the circuit and see what happens
I would have thought that any low power SCR would do the job. My junk box has a variety of TO92 canned SCR's hiding in it.

Looking at the circuit the value of R4 (1K Ohm) in Skynorth's circuit seems a bit on the high side, given that most low current SCr's need a minimum of around 5mA to keep them turned on.
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Re: Esc power safety switch?

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Thanks, my parts box doesn't have any small scr's. I did find one I used as a 20A ps crowbar, nothing smaller.

Trivia...
I also may have found a few 4 leaded silicon controlled switches I used for my digitrio construction when I was "5". I must have been gifted ha ha.
I built every system rcm and world engines offered as a kit. My rcm classic and digitrio was sold to a friend that wanted to use it for his RC boat from his real boat. As luck would have it, I got my money and later his real boat sank with the equipment aboard. I've always wondered what the insurance company paid him for my gear?
SCS as used for RC in 1966.
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I built, but didn't own, and Heathkit RC gear then. I do have a working Heathkit 4 ch single stick waiting for a Frsky upgrade.
What fun, very few prop strikes, but front end overload did claim many planes on the taxiway.
That or a misplaced freq clothespin.




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Re: Esc power safety switch?

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ShowMaster wrote: What fun, very few prop strikes, but front end overload did claim many planes on the taxiway.
That or a misplaced freq clothespin.
Good old times :)
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Re: Esc power safety switch?

Post by SkyNorth »

I have found a problem with my design .... It wont work at 5V.
The 5V supply in not enough to trigger and get enough holding current flowing to latch the SCR.
Sorry about that ... :oops:
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Re: Esc power safety switch?

Post by ShowMaster »

Thanks for the update.


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Re: Esc power safety switch?

Post by Flaps 30 »

I had some time today so I used it to smash together Skynorth's circuit with a few changes incorporated. It does work with voltages down to 4.5Volts and up to (and beyond) 6 Volts.

Here is the revised circuit.
ESC_Safe Mod.JPG
The above was tested with a couple of SCR's that were lurking in the junk box. The other one tested was a C203D which is now obsolete. IMO any low current SCR will do the job. The LED is specified to be a red one rather than a white one as the voltage drop across the white LED's is greater than the red ones, and I wanted to keep the resistor (R4) value fairly high. You could lower the resistor value to around 180 Ohms if you wish to use a white LED. The addition of C1 was an afterthought and it can be treated as an option so it can be left out.

I could give you a picture of the prototype, but it is a birds nest rather than some neat finished article at the moment.
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Re: Esc power safety switch?

Post by SkyNorth »

Good to hear it worked .... On the simulator , it would not work with under 10V.
The cap is a good Idea , to stop and noise spikes from triggering the SCR.
R2 should also be reduced to 100R as 2K might be too high a resistance in the PPM signal path...
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Re: Esc power safety switch?

Post by Bill »

I can't believe what I'm seeing here talk about complications a toggle switch and a resistor (if that) will reliably do the job, and indicate if its on or off by its position, and disable the drive after flight (so no cuts on picking up the plane). Keep it simple!!
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Re: Esc power safety switch?

Post by Flaps 30 »

Bill wrote:I can't believe what I'm seeing here talk about complications a toggle switch and a resistor (if that) will reliably do the job, and indicate if its on or off by its position,
That would spoil the fun of doing this. :)

You could add another push button between the SCR gate and ground, so you could disarm the system if you so wish. For added safety a nice toggle switch (not an open slider type as they tend to be unreliable) can be wired between Q1 collector and emitter to make doubly sure that your model is safe. Sadly the toggle switch if it is a single pole one will not give you any indication (in the form of a LED) as to if the system is armed. This can be sorted of course. :)

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