If this has come up before, feel free to point me at the appropriate thread.

What do folks use for safety cutoffs?  What's your preferred approach?  What is done that looks good?

I can think of two basic ways to do this: one, disconnect the ESC from the timer.  This can be as simple as an itty bitty switch in the red wire from the timer, or a honkin' big battery plug with equal sized wire.

Personally, I think the cutoffs that are designed to carry full battery current are butt ugly.  They certainly cover just about all contingencies, except maybe garnering appearance points.  The 'just turn off the timer' method is only as positive as your trust the ESC not to start up on its own -- but I feel that's pretty unlikely.

So -- what do you do?  How does it look?

I was thinking maybe a knife switch that's built into a panel on the fuselage, so if you need to shut down fast there's an obvious depression that you can get a finger into and pull.  Or build it into the battery hatch (assuming it's not holding the batteries in!) so that you can just yank it off.

So there's still a honkin' big switch in there, but its "handle" is part of the outer skin of the airplane, and is therefore in a position where it can be blended in and decorated to a fair-thee-well.

I saw your suggestion about spring contacts.  That's a cool idea, and one that I've toyed with.  The problem is that high-current contacts need a lot of force on them to be reliable, which means a big spring, which means heavy.

Hi Wynn:

There is nothing ugly about it. It is simple, elegant and, most importantly, effective. I think perhaps we should only worry about the aesthetics of the "dead man's switch" when we are capable of building 20 point airplanes in every other respect first. The switches that Buddy and I used are no less obvious than yours and we got 18 and 17 points respectivley at the Nats in appearance. The top score was 19 this year, and I don't think that an external switch would have cost them a point.

Let's focus on what's important; a light, straight, rigid, well powered model with a robust and adjustable control system, that also looks good. Use the switch that makes sense to you. Nicely done, Wynn!

Bob Hunt     

Well said Bob.

Hi Wynn:

There is nothing ugly about it. It is simple, elegant and, most importantly, effective. I think perhaps we should only worry about the aesthetics of the "dead man's switch" when we are capable of building 20 point airplanes in every other respect first. The switches that Buddy and I used are no less obvious than yours and we got 18 and 17 points respectivley at the Nats in appearance. The top score was 19 this year, and I don't think that an external switch would have cost them a point.

Let's focus on what's important; a light, straight, rigid, well powered model with a robust and adjustable control system, that also looks good. Use the switch that makes sense to you. Nicely done, Wynn!

Bob Hunt     

FWIW the dead man switch looks better to me than a muffler, needle valve, cylinder/jug, and tank vents/plugs/pressure lines....

True.

I was thinking that, and my mind leaped from "true" to "hey, you could color-coordinate the wire!" to you could make a vane to hide the wire in, that you could finish to match the plane.

Personally, I gotta build something electric that flies, so I am jumping the gun.  But one must be ready for these eventualities.

Also very true.

Your point is well taken and an example of one of the details in a true electric design.

Guys,
I have used the battery lead disconnect simple two pole 40 amp switch from Home depot (about $3) for a couple years on three different ships with no problems. My setup is a CC 45 ESC and Ztron II timer. The Ztron does not have a start switch and starts once power is connected. I use a deans plug to connect the battery to the ESC. I break the red lead with and connected it to one side of the switch and then connect the other side to the deans plug. When I'm ready to fly I connect the battery then on the flight line flip the switch to start the delay time count down (20 sec) to the motor start.

The switch is very positive not to heavy but allows a neat clean installation. I have mounted it on profiles through the fuse (hollow our a section and mount to inside plywood doubler) so that only the flip switch is sticks out and the wires are neatly on the motor side. In my Stuka I put the switch inside the cowl out of sight but easy to reach but still neat.

Best,              DennisT

Guys,
I have used the battery lead disconnect simple two pole 40 amp switch from Home depot (about $3) for a couple years on three different ships with no problems. My setup is a CC 45 ESC and Ztron II timer. The Ztron does not have a start switch and starts once power is connected. I use a deans plug to connect the battery to the ESC. I break the red lead with and connected it to one side of the switch and then connect the other side to the deans plug. When I'm ready to fly I connect the battery then on the flight line flip the switch to start the delay time count down (20 sec) to the motor start.

The switch is very positive not to heavy but allows a neat clean installation. I have mounted it on profiles through the fuse (hollow our a section and mount to inside plywood doubler) so that only the flip switch is sticks out and the wires are neatly on the motor side. In my Stuka I put the switch inside the cowl out of sight but easy to reach but still neat.

Best,              DennisT

Have you thought about only cutting the power to the timer instead of the ESC?  That ESC won't start if it doesn't have the proper signal going to it.

Hi All,
Hi Crist,
Sure, if all the circuits are operating properly, killing the source of control pulses will prevent the motor from running, but ............
I think that it is entirely resonable to protect ourselves against any single dramatic point of failure.
The dead-man switch in the big red wire from the battery is our friend.
Now to come up with a weightless and resistance-less solution. Hey, we're modellers: we can solve anything!

I think the most probably advantage that I see isn't that some messed-up electronics might make the motor turn with the ESC disconnected.  It's much more likely that messed-up electronics might make the motor and/or battery go up in smoke and flames -- you won't stop that short of pulling the big plug.

Here's a pic of the switch that DennisT and myself use.  I too started off with the Ztron II, so it worked to turn on the system and also
disconnect the battery.  I have since switched to the FM-9.  At contests, I turn on the power with the big switch, then have my helper
push the start button once I've signaled the judges.  It's really handy to have that switch in case you need to shut down NOW.

Robert C

Crist,
The switch is rated on the package. I have used the heavy 40 amp for the AXI 2826 -10 motors, and the smaller 20 amp pre-wired for the small "35 size" motors that pulls about 18 amps static. These switches have worked 100% for over 2yrs in my profile ship and 6 months in my Stuka. They might be a little over kill but I like the ability to quickly turn on the system and shut it off if needed.

At a contest on pavement I will have a assistant hold the ship, I flip on the switch, system beeps to indicate it is on, walk to the handle and get set, have assistant release the ship, motor spins up and off we go. If on grass I will have the assistant hold the ship until the motor spins up then release. When the ship lands we flip the switch off, clear the circle and remove the battery once in the pits.

Best,          DennisT
 

Floyd makes a good point. The ESC will draw current whenever the battery is connected. This means that the idea of using a switch to interrupt the timer to ESC circuit, while it will prevent accidental starts, will allow battery drain. It depends on how long a time is going to lapse between battery connection and flight as to whether the timer to ESC interruption switch would be practical. If the battery is to be plugged in and the plane immediately (or very shortly) taken to the flight line, then a timer to ESC interruption switch should be practical.

Guys,
Attached is another picture of the battery line switch that Robert posted, this one is on my test stand.

Best,    DennisT