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Why no safety switch on motors??

Old 08-29-2010, 12:46 AM
  #1  
Shrikered
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Question Why no safety switch on motors??

This may be something of a newbie question, but there seems to be a needless safety gap in the standard procedure that we use when powering up/powering off. Why don't people use a physical switch (or a fuse) between the ESC and the MOTOR??

Here's the problem I run into. In order to test the radio, servo direction, etc. preflight, I need to have battery connected and system powered up. But once I do that, the motor is HOT. If my elbow accidentally hits the throttle on transmitter - motor turns on!

Same situation after a flight - I need to open up the aircraft and disconnect the battery to shut down the motor. But some add-in electronics (like EagleTree) prefers that you keep power going after a flight, in order to retain the memory. I had a situation where I crashed, people picked up the airplane while I was running over. They were all smart enough to stay away from the prop, and someone did disconnect the battery (which after a crash is presumably better anyway) but again a redundant switch seems useful.

A solution seems clear, but apparently nobody does it so I must be missing something. Put a switch (or a fuse, and I don't mean fuselage ) on the outside of the aircraft. It interrupts the connection from ESC to the motor. That way, all the electronics etc. can be checked out while the motor is still unpowered. (Except for briefly checking the motor itself, obviously.) Only on the flight line do you connect the motor to the ESC.

I found some old discussions around similar issues.
http://www.wattflyer.com/forums/showthread.php?t=16727
http://www.wattflyer.com/forums/showthread.php?t=1546

But these threads emphasize switches to shut off ALL power, instead of disconnecting the battery. Various switches are sold for this purpose. One person mentions removing the prop physically, which is OK except that I don't think I'm competent to attach/detach it quickly while on the flight line.

Sorry for the long post. Obviously this can't be a major issue or it would be dealt with more often. But I'm putting together a checklist, and trying to "mistake proof" my procedures, and this seems like a gap. Thanks for any insights.
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Old 08-29-2010, 12:52 AM
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spitfire
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It never seemed like to big of a problem to me...

thats why you should be careful with your transmitter, once you plug in the battery, it should be kept from elbow-knocking distance.

Spit

Last edited by spitfire; 08-29-2010 at 09:47 AM.
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Old 08-29-2010, 02:16 AM
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Insomniac
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Also, depending on how many wires the switch has diconnected, you may accidently damage your ESC. If it's only disconnected one of the three wires between the motor and ESC, it's possible that attempting to run the motor without turning the switch back on could cause the ESC to fry when it's trying to go with only two of the wires connected.
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Old 08-29-2010, 02:25 AM
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dumo01
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Depending on what transmitter you are using, you might be able to set a switch as throttle kill switch. On my DX6i I replaced the push button with a real switch. You need to do a little soldering but not too tough. This obviously is a kill switch on your warranty as well if that is an issue. If you have a different transmitter there may be a way to program that option.

There are several E Flyers at my field that do add and external interrupt of some type, swtch or jumper plug, in the battery to ESC positive wire, but that option would only do what you want if you have a UBEC or a separate battery for your electronics. If you are using the BEC in the ESC you would have to interrupt I think at least two of the three wires going to the motor which would probably get more complicated than it is worth.

For bench testing i still think it is safest to take the prop off, but that would be difficult at the field
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Old 08-29-2010, 02:32 AM
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MustangMan
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Probably one of the biggest reason we don't put a switch in either the motor wires or the battery wires has to do with power loss and extra weight. Any switch heavy duty enough to handle the currents without significant loss would likely weigh at least twice what your ESC weighs. A switch also introduces another point of failure into the system.

IF your ESC shuts down the motor upon loss of signal from your receiver, then you could switch the "signal" wire from the receiver to your ESC. Opening the switch would simulate loss of signal from the receiver which would cause the motor to be disabled. This signal only requires a few milliamperes and ANY switch would handle that fine. Again, the switch introduces a point of failure in to the system.
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Old 08-29-2010, 04:31 AM
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on a plane i fed batteries in thru the bottom of the cowel into the fuse and plugged in...it was a pain to do. if i was delayed going to the flight line it was a real pain to take the batts back out.

i made a arming switch out of deans "t" plug and i could place the plane on the flight line....put the lil male deans plug in place and off I'd go.

gotta say that once we plug in the motor its armed to cut up anything in its path and plugging in with the TX in easy striking distance is dangerouse....i place it on my flight box which is closed on the table when setting up at the field . and i always look at the prop to keep hands and wrists clear of the prop . thats why i build planes to top load batts in a way to keep behind the prop with my hands/arms...ect. also lay the TX on its back while setting up...if it falls forward its sure to throttle up.

I've been bitten by the prop enough times to try real hard not to let it happen again..lol. prop + strike=stitches

one thing i'v notice with a lot of pilots powering up either electric or glow....some look preoccuppied with moving stuff around the table and pop!!!finger strike...ouch.....just not paying attension....these are the same guys who taxi there planes back to the flight line after a flight and run into the protection stand......now thats one i haven't done yet as speed returning to the gate really isn't that important...lol...
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Old 08-29-2010, 04:37 AM
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Nitro Blast
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Originally Posted by Shrikered View Post
Here's the problem I run into. In order to test the radio, servo direction, etc. preflight, I need to have battery connected and system powered up. But once I do that, the motor is HOT. If my elbow accidentally hits the throttle on transmitter - motor turns on!

What I do to 'test' the radio, is just plug a RX battery into a open socket, or open Y harness. It brings the radio to life but not the ESC & Motor since there is no motor battery attached.
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Old 08-29-2010, 05:42 AM
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kyleservicetech
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Originally Posted by Shrikered View Post
This may be something of a newbie question, but there seems to be a needless safety gap in the standard procedure that we use when powering up/powering off. Why don't people use a physical switch (or a fuse) between the ESC and the MOTOR??

Sorry for the long post. Obviously this can't be a major issue or it would be dealt with more often. But I'm putting together a checklist, and trying to "mistake proof" my procedures, and this seems like a gap. Thanks for any insights.
This is a very good question. At least with the higher powered models that pull over 50 Amps or so, it is difficult to find a toggle switch that can handle 50 amperes DC.

It does not take much to make a high power switch, using a few high current Mosfets, a resistor, and a small toggle switch. I've made a few switches in this manner, but it's another thing that can go wrong. And, you've got to worry about the very high currents that flow between the batteries and the ESC front end capacitors, which could damage the Fets.

What I've done, is NEVER get near the propeller while carrying the model, and be absolutely certain to pick up the transmitter by the carrying handle on the back side, holding the transmitter sticks away from me. After the battery plug is pulled, then it is safe. And any testing of these motors in my workshop is generally with the propeller removed.

This has worked well for the past 20 years I've been flying these electric models.
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Old 08-29-2010, 06:33 AM
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Insomniac
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Another option is just to sit your plane in a position where it doesn't matter when the prop starts... When I'm programming my transmitter I often sit my plane right against a chair, so each wing's leading edge is resting against one of the legs... go full throttle, and the plane doesn't budge.
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Old 08-29-2010, 06:38 AM
  #10  
mesh
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A jumper on one of the motor leads seems like it would be the simplest solution. The easiest way to make one would be to install a female power connector on one of the leads, then use a shorted male connector as the jumper. Of course, you could simply unplug one of the motor wires if you have them in a handy spot.
Having one motor lead be longer than the others by a few inches shouldn't matter, considering the windings are already several feet of wire.

I've ran various motors on 2 of 3 leads while debugging another faulty motor. They all just jerk back and forth, didn't seem to damage the ESC. It just goes "let's try to start.. nope, let's try again" a few times a second.

Another thing to ponder is that most motors are pretty weak when starting, so if you inserted a dowel or barbecue skewer alongside the motor into a conveniently placed hole, you would lock the prop down pretty effectively. Try holding the prop while starting the motor, not much force there. (I've only done this up to a 40A motor running 11x6 though

I've recently started just using the throttle hold function on my radio though (a switch to hold it at 0%). Since it's 2.4Ghz I feel safe about this, although I suppose the ESC could turn all poltergeist and decide to kill me on its own.
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Old 08-29-2010, 06:40 AM
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chris123sc
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All good answers, best thing is to like every one else said. Before you even think abour connecting the battery, TX on or off, keep everything clear of the prop and use a chair as suggested or something that will clear the prop and hold the leading edge of the wings. I personally have found that switches only give a false sense of security and can actually lead to accidental power ups.
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Old 08-29-2010, 07:10 AM
  #12  
Shrikered
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Originally Posted by mesh View Post
et's try to start.. nope, let's try again" a few times a second.

Another thing to ponder is that most motors are pretty weak when starting, so if you inserted a dowel or barbecue skewer alongside the motor into a conveniently placed hole, you would lock the prop down pretty effectively. Try holding the prop while starting the motor, not much force there. (I've only done this up to a 40A motor running 11x6 though
I like ALL these answers - thank you! This one has the virtue of "visual control" (in six-sigma-speak). I have metal barbecue skewers that seem quite sturdy. But I worry that a rod could become a projectile if the motor force snaps it or yanks it out! So I guess this needs some experiments, on an OLD airplane if I ever get that far. (And run the experiment from the other side of a wall.)
It's the starting torque presumably that's the danger. So could I program the ESC for a slow start? (as if it were on a heli) Something else to learn about.

I realize I'm being pretty obsessive, since standard solutions almost always work. ("Be really really careful.") But I've been researching accidents with real jets, and they are always caused by a chain of improbable events. And accidents in General Aviation are often caused by carelessness, to which I am prone...
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Old 08-29-2010, 12:22 PM
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mclarkson
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I gotta say, I would love an 'arm motor' switch on my Tx. I've thought of rigging something manual with a rubber band, etc.
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Old 08-29-2010, 02:33 PM
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I have an ESC from Hobby-Lobby that has an ON-OFF switch wired into it. I mounted the switch into the nose of my plane. It was great, I could plug in the battery put the plane together get everything together and then turn on the ESC. It was great. I wish all ESC's came with those.
-Andrew
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Old 08-29-2010, 02:43 PM
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If you have a DX6I or DX7 you can set the model up in heli mode.Leave the pitch curve flat.This works the same as setting up in airplane mode. The difference in heli mode is the throttle hold switch disables just the throttle.The swash mix obviously needs to be set up for 1 servo
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Old 08-29-2010, 03:40 PM
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ArneH
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My Transmitter has a throttle cut switch:



The long switch cut the throttle. Smart solution if you need it.
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Old 08-29-2010, 06:33 PM
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Red Scholefield
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My Futaba 9C 72 mHz and 7C 2.4Ghz can be set up with a throttle kill feature. This can also be done on some JR and Spectra systems. Send me an e-mail for instructions. [email protected]
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Old 08-30-2010, 12:34 AM
  #18  
Victory Pete
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I have a switch on my T-34 that I mounted on the side of the fuselage, It came wired to the E-flight ESC but was just dangling in the battery compartment. It kills power to the Rx so the motor can not start up. When I have the plane on the bench for tests I take a thick rubber band and tie it around the throttle stick and send it down the front and under to the back and up around the top and tie it to the trainer switch.
VP
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Old 08-30-2010, 01:10 AM
  #19  
Henry111
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Default Safety switch

On my larger airplanes I always install a safety switch harness available from Atlanta Hobbies. It has an inlet located on the outside of the fuselage. To arm, a plug is inserted, removed to disarm. Since I also use a separate RX pack, there are two switches on the outside of the airplane. To check the controls I throw the RX pack switch. The motor is not armed. When ready to fly I insert the safety plug to arm the motor.
By the way, the safety switch harness weighs only one oz, not even a factor on larger airplanes.
On smaller airplanes were I use BEC instead of an RX pack, I find that Nitro Blast's suggestion is the best. When you want to test the controls without arming the motor just keep an RX pack handy and plug it into the receiver.

Last edited by Henry111; 09-01-2010 at 04:32 AM.
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Old 08-30-2010, 02:14 AM
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I really want this on the Tx, not the plane. My biggest problem is hitting the throttle with my gut or a forearm etc., when the plane is live. I'd like to be able to safe the motor from my radio.
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Old 08-30-2010, 02:27 AM
  #21  
Turner
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This works:
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Old 08-30-2010, 02:51 AM
  #22  
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I bent over to set my plane on the ground and plug the battery in with my transmitter hanging from my neck by a strap. When I went to stand up the transmitter swung back into me hitting the throttle. The plane shot across the street and slammed into a curb before I could do anything about it. It was the shortest maiden flight I have ever had .

A throttle kill switch on the transmitter is not such a bad idea.
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Old 08-30-2010, 03:40 AM
  #23  
mclarkson
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Originally Posted by Turner View Post
This works:


I'm not arguing against any of that.

Think of it like a safety on a gun, though. Yes you should never put your finger on the trigger until the sights are on the target, check if it's loaded, etc. etc. etc. but guns have safeties on them, anyway.
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Old 08-30-2010, 03:42 AM
  #24  
old grump
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Smile SWITCH

In the old day's of electric all the esc's had a switch . But now with brushless motors ,i see none. I have been nicked a few times . So now i tie a few small rubber bands "tied to trans.top handle " & looped around throttle stick. It works. THE OLD GRUMP
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Old 08-30-2010, 04:06 AM
  #25  
kyleservicetech
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Originally Posted by old grump View Post
In the old day's of electric all the esc's had a switch . But now with brushless motors ,i see none. I have been nicked a few times . So now i tie a few small rubber bands "tied to trans.top handle " & looped around throttle stick. It works. THE OLD GRUMP
Having designed my own brush type ESCs, adding a low power "Kill Switch" for these brush type ESCs is fairly easy to do. But, with the three phase drivers using a combination of six Fets as used in our brushless motors, I don't think it can be done.
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