Hi all,
I've read lots about radio activated kill switches for Electronic ignition engines but have seen little for the Magneto driven types. I have a sweet running little Fuji 32A but the carb has no choke (doesn't need one really) so can't use a choke servo to kill the engine so I installed an "electronic switch" in parallel with the standard toggle type switch to kill the ignition by grounding out the system. While it checks fine with an Ohm meter, in practice the switch provides enough of a path to ground that the ignition will not run with it installed regardless of whether the electronic switch is off or on!
Of course the old toggle works well but I'd love to have a way to shut the engine down remotely if the throttle servo fails/becomes disconnected, strips a gear or whatever. Just additional safety and peace of mind. My question is whether the optical type kill switches will be any different or is it just that all the electronic switches are just not made to isolate a 20K volt (or whatever) kick like you get from a magneto. With an electronic ignition all your doing is turning on/off the power source but with a magneto you have to open up and not allow that big spike to ground when the "switch" is open (thus allowing the ignition to work) and reliably ground it out when closed.
Anyone have any experience here??

Magneto equipted engines can be shut down by grounding out the mag's contact set, that's how it's done in full scale piston aircraft engines.

IIRC, DuBro and others made engine kill switches for magneto equipted engines and it was basically a micro switch setup in a holder which was wired into the contact set. This holder also had an arm on it for a servo controlled rod to attach, so hitting the "kill switch" on the radio would activate a servo which closed the micro switch and grounded out the mag.

Try a search on say Tower for kill switch.

Great Planes has one for around $7 that I have a couple of-they work great! The switch has a manual on/off to mount on side of fuse and then a servo operated switch to mount in the fuse.

Thanks guys. I suspected that a toggle/micro switch would work such as these use, just hadn't looked for one yet as it was not my preference. Thanks for the references for these devices. I was kind of hoping for an electronic version though. Either optically operated (my preference) or electrically without the need for a mechanical relay or an extra servo. If no one has seen/used such a device however I will go with this method as the next best alternative.

Well I'm afraid you're stuck with the method mentioned, the reason you still see magnetos in full scale piston stuff is precisely because the mags don't require any electrical power to operate. So in the event of a power system failure the aircraft engine will continue to run.

Sooo.... the only way to kill a mag is to break it or ground it out.

http://www.rcatsystems.com/electronics/rc100.php

RC100X - connected Normally Closed between magneto and ground.

Works great

Mike

Here is another option:

http://www.chiefaircraft.com/rcmsec/...ff/Cutoff.html

Both of the units sited seem similar to the one I tried to use. At this point I hate to invest another $30+/- to have another failure... Here is the one I used:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCJD6

When I attach the E switch and turn it off/open the engine still won't start. On and of course it won't start. VOM shows low resistance to ground when closed/on and very high when open/off as expected. Perhaps the wire I used is just not very well insulated or has some minor crack in the insulation that is allowing the spark to jump across the wire somewhere....??? I think I'll run some heavier/new wire tomorrow and give it another try. It certainly seems this unit should work just like the ones you guys cited. Thanks for the references and I'll keep you posted.

Well, ran new wires and switched the reversing jumper... still no joy. No matter what, if it's in the magneto circuit, engine won't start. I sent an email to the manufacturer to see if they have any suggestions. On a side note, while testing this today I also had time to test the smoke system in the same airplane and it seems to work very well. Won't know 'till I fly it but I think I'm going to like it! [8D]
Engine also ran flawlessly throughout.

How about one of these Dimension Engineering Pico switches? Seems like it would work great to remove/restore a ground and plugs in just like a servo.

http://www.dimensionengineering.com/PicoSwitch.htm

I suspect this wouldn't work as it is only rated for fairly low voltages. Keep in mind it needs to withstand a multi thousand volt "jolt" when the magneto supplies spark. If it's not a MUCH higher resistance path to ground it's going to drain away valuable spark. They do not mention it's use in this arena and do warn about high voltage applications. Interesting device for some other uses however....

Ah, I don't think the thousand volt thing is accurate, you aren't grounding the spark plug wire, which is essentially on the secondary side of the magneto. You are grounding the low voltage primary side of the magneto and that certainly doesn't have thousands of volts on it. I've been using the RCATS 100X switch for a number of magneto engines. No problems at all. It is essentially a relay and a signal from your receiver closes the contacts and shorts the magneto input to ground.

Yep, a day or so after I posted that I realized that I was wrong. I believe you're correct. This is effectively grounding the primary side of the "transformer" if you will and therefore probably sees a much smaller voltage. Still, the one of I have won't work so I am begining to think it's just a matter of having a bad one. Unfortunately the manufacturer is not responding to my email and I just didn't have time to call this week. I'll try to call them this coming week and hope I can resolve it. I just hate to go buy yet another similar device and find out that something else is wrong, or it just won't work in this application so I could end up with two useless parts! I'll get back to you all if I ever get a resolution.

Just a quick note. Looked into the RCATS device mentioned previously and even emailed the manufacturer and it will not work in my application as it is limited to ~6 volts and my 2 cell A123 pack will exceed that... pretty much always! Don't want to run a regulator (one of the main pluses to A123 over LiPo... no regulator). Could do some modifications to make that work but buying a nice neat packaged (hopefully reliable) device and then having to modify it sorta defeats the reason I would have bought it to start with! Looking at the servo/microswitch route for now. I'll post at least once more when I have it all working. Just an FYI and thanks to all who have posted and PM'd.

Zenoah offers a great mag only switch. Its transmitter operation only (no aircraft mounted switch). I have one on my G62 and it workes great. Dons Hobby Shop sells them. Just tell them
you need a mag shut off switch, no part # needed. If you need more info email me.