Is it possible to shut down an electric system on demand after it has been started?  I thought of this while reading the arming switch rules proposal thread.  An IC motor with a full tank can be stopped by holding the nose straight down and starving it of fuel.  Does the typical electric set up have this capability, or once a full flight timer sequence has started, will it run for the duration?  Obviously unplugging the battery will do the trick but may not be a practical choice depending on the design and/or set up. 

Thanks.

Thank you, Crist.  I figured that would be the answer.

With the KR timer you move the on/off switch to the off position and it shuts down the motor.
Andy

As far as I know, all modern, brushless esc's are designed to not function at all unless the pulse width presented to them by the controller (timer in our case) is within normal parameters. If the pulse is too short, the motor will not start. If the pulse is too long, the motor will not start. If no pulse is present, the motor will not run. With brushless motors, most catastrophic esc failures will result in improperly timed pulses to be sent to the motor, so to motor won't function at all.

As far as I know, all of the currently available timers have on/off switch or start/stop button. Usually, this is all that is needed. My wife is my pit person, and she is very non-technical, but she can push a start/stop button in the event of a problem. When I landed inverted at the Wichita contest this fall(long story), the motor continued running (after grinding the prop to a nub on the concrete...in a matter of seconds), she walked over and pushed the button, stopping the motor. She also knew to disconnect the battery (by simply disconnecting the external battery connection in this case), which she did without prompting. This is not rocket science, folks.

Bob

Guys, I think you asking for troubles, disconnecting battery during run can lead to damage and even to burning of ESC/battery. If you want arming plug, use it as an arming plug, not a device which will shut off running motor. Instead of safety you can burn your house.

If you have a (highly recommended!) arming switch or plug, using it would be practical. A button on the timer is of course handy for most "normal" situations.

Igor is absolutely right. Yanking the arming switch on a motor running at speed can destroy the ESC due to the voltage spike created.
If you must, disconnect the control cable from the timer.

Regards,
  Dean P.

If you must, disconnect the control cable from the timer.

I must be stuck, thinking about the arming before flight and disarming after shutdown... or emergency shutdown if the timer is not responding due to some crosswise bit in the SW.

On a built up fuselage, the control cable is unlikely to be accessible from the outside but disconnecting it should stop the ESC, unless there's something seriously wrong with the ESC.

I do not think that diconnecting of battery while motor runs is risk for firmware ... but teoretically also that can happen. The problem are high voltage peaks as Dean wrote. The motor is induction, and when transistors switch current to coil off, the self induction pushes the current further, and it goes via diodes back to the battery as short charging peaks. If battery is not present, the current will make high voltage on transistors and it can damage them. It will lead to burn next time you connect battery. I know minimally one of completaly burned model because of exactly this reason. Unfortunately it was so bad, that damaged was only one transistor, so after connecting of battery everything looked well, but after first throttle up, ESC started to burn, it shorted the battery and pilot could only look how it burns. It was F3A model with 10 cells, but also 4 or 6 cells can do bad thing.

It does not need too much imagination - disconnect battery on field because of something, go home, connected battery to repair the error ... and your hose burns.

So ... never do that. If you need to cut off the e-motor, use either function of timer, if not available, use switch of the ESC wchich will cut the run and also cut the power to timer - both leads to motor stop, if your ESC does not have switch, make switch on power lead to timer (some ESCs has switches only for that connector anyway), it will do the same, and if you do not want it (for example my indoors do not have any switch) then just disconnect timer from ESC connector, it will stop as well.

To prevent problem of voltage peaks, it needs to properly choose large capacitors, which will flat that voltage out, but as I say - it is not trivial task, not for beginners. Additionally capacitors tend to lose capacity during the time, and it is not so easy to chceck them. That is also reason why producers of ESC recommend to use additional low ESR capacitors in middle of long battery leads, and that happens if we install arming plug. So if you use arming plug, and leads are not direct and short, if it needs to add longer lead, it will be good idea to add the capacitor close to the plug.