Author Topic: Shut-offs (Read 3518 times)

James_Mynes · « **on:** August 19, 2013, 05:30:11 AM »

Seems like I was hearing about fuel shut-offs some 20 years ago. I thought they were a good idea back then, and now that I'm coming back to Control Line once again, I still think they're a good idea.
But after 20 years, one would think the technology would have matured by now. From what I read, some people are still not convinced they work as needed. Problems of arming, launching, brief loss of line tension, flyaways, and on-demand shutdown should be easily solved given modern miniature electronics.
Now, I'm no whiz-bang electronic guru, but I know there are small transmitters which will activate a device at short distances. I use one to get in and out of my car every day. So why hasn't someone adapted this stuff to pinch a fuel line? No need to maintain line tension, no need to sense G forces, simply push the button to cut off fuel. Put it on a carabiner and hang it off a belt loop. Or build it into the handle. It could even have a flip cover to prevent accidental bumping. If you want to get really fancy, include a limited range, which, if exceeded, actuates the shut-off.
I must be thinking too simplistically, because if it were that easy someone would have done it by now.
There are a bunch of smart guys reading these forums, at least one of you can cobble up a lightweight, reliable shut-off. Seems like there would be a market for something like this.

Brad LaPointe · « **Reply #1 on:** August 19, 2013, 06:08:23 AM »

Trust me it's been done . They will be tested shortly in a real world contest .

Brad

Paul Smith · « **Reply #2 on:** August 19, 2013, 07:45:12 PM »

There are plenty of mechanical and electronic shutoffs available.

Remember, this is a backup device added on in addition wrist straps, oversize lines well beyond design loads, and a really pull test. There aren't all that many flyaways and existing shutoffs have performed well. Remember, the model frequently sustains damage in the crash that triggers the flyaway, so ANY shutoff could be disabled in the pre-flyaway incident.

Organizers of combat contests should use venues with adequate clear zones to allow for the occasional mishap.

qaz049 · « **Reply #3 on:** August 20, 2013, 04:41:18 AM »

Yep people are working on radio frequency cutoffs for F2D combat at least.

It's not exactly rocket science any more.

The key is a range of tiny microcomputer boards known collectively as "the Arduino".

The one shown below is less than an inch long, runs on battery power, and is programmed via a usb cable from a PC,

and costs less than $8 (inc postage from China) on ebay. The PC user interface etc is free off the internet.

See: http://www.ebay.com/itm/Mini-USB-Nano-V3-0-ATmega328-5V-Micro-controller-Board-Arduino-compatible-TR-/181188882200?pt=LH_DefaultDomain_0&hash=item2a2fb2ef18

The Arduino will run a micro R/C servo directly.

The radio link from the pilot can be a matched set of 433 Mhz transmitter/receiver similar to those used on our car locks.

This set is $1.50 post paid off ebay.

http://www.ebay.com/itm/1pcs-433Mhz-RF-transmitter-and-receiver-kit-for-Arduino-project-/261041100836?pt=LH_DefaultDomain_0&hash=item3cc7431824

The receiver connects directly to the Arduino via a single input and acts on a changing digital signal from the former.

Currents are minimal with the most required for the servo.

The real question is not whether it can be done.

It's more of whether the system can be robust enough to withstand the rigors of combat flying.

The electronics can be "potted" in a slow-set epoxy. Not so the battery.

I can imagine the possible carnage form a midair causing a split or shorted LiPO.

They may make Combat even more "interesting" to watch.

Also imagine an unscrupulous competing team with a radio device designed to saturate the 433 MHz band with rf signal.

Paul Smith · « **Reply #4 on:** August 20, 2013, 05:23:56 AM »

Somebody who enjoys that sort of thing should just fly RC. The shutoff is just none of several systems on a mechanical model. F2D flyers routinely prepare a DOZEN models for a contest and damage or destroy quite a few of them. This is not Scale or Stunt where a model lasts for years.

What we need a reliable device you can buy, install, and trust. Nobody trusts that a whole population of contestants will assemble reliable devices from Radio Shack parts. The key hurdle is the fuel line pincher or shutoff valve, not the receiver that controls it.

The "at will" requirement is nothing but a monkey wrench thrown in to disrupt the event when ingenious designers were able comply with the flyaway requirement.

qaz049 · « **Reply #5 on:** August 20, 2013, 05:50:08 AM »

Quote from: Paul Smith on August 20, 2013, 05:23:56 AM

Somebody who enjoys that sort of thing should just fly RC. The shutoff is just none of several systems on a mechanical model. F2D flyers routinely prepare a DOZEN models for a contest and damage or destroy quite a few of them. This is not Scale or Stunt where a model lasts for years.

What we need a reliable device you can buy, install, and trust. Nobody trusts that a whole population of contestants will assemble reliable devices from Radio Shack parts. The key hurdle is the fuel line pincher or shutoff valve, not the receiver that controls it.

The "at will" requirement is nothing but a monkey wrench thrown in to disrupt the event when ingenious designers were able comply with the flyaway requirement.

Whatever!

I should have added the following as a disclaimer.

My interest is in constructing an rf controlled stooge so I can fly my Flitestreak on other than club days.

The F2D cutoff is just a similar problem that I know people are working on.

Ray

Michael Alurac · « **Reply #6 on:** August 20, 2013, 10:50:49 PM »

Here's something that I've had in-mind for a self-contained electric shut-off device set-up to release an extension spring to pinch off super-soft latex fuel tubing when it senses a prolonged change in the centrifugal forces, such as a flyaway, that it learns in the first couple laps. It's a bit of a challenge at the moment to find the miniature parts needed to form the electromagnetic triggering device operated on a few button cells. My idea is to be able to mount this on any combat wing and profile suction design with shut-off on-demand functionality programmed in. Our field runs adjacent to a major highway so any combat flown at our field requires fly-away shut-offs.

The programming of the logic is another small hurdle... Here's my concept would anyone like to elaborate upon it?

phil c · « **Reply #7 on:** August 26, 2013, 08:56:12 PM »

I've tried a $20 car radio from HobbyKing or HobbyPartz. The radio is more than adequate, the Rx weighs <8 grams, a servo 8 gr, I used it on a Half A electric combat plane, so a separate battery wasn't needed. For a standalone setup I'm pretty sure one lipo(3.7 v) would work. Maybe 3-400mah. 15 gr for the battery and wiring. The servo can be set up to use a small wire loop to twist a piece of small fuel tubing to kink it shut with very little load.

This gives you a funtional shutoff on demand. F2D and other events also require it to work automatically, so some sort of failsafe to kill the engine would be required. I figure that trimming the attenas and using a pulse train detector failsafe would work. Trim it so the failsafe would activate when the plane got more than 100 ft. from the pilot. The pilot could back that up by also shutting the engine down as soon as he realized it had been cut away.

For ease of use the transmitter could be repackaged into a small project box with the on/off switch and a second switch to move the servo.

Phil C

Larry Davis · « **Reply #8 on:** September 30, 2013, 05:16:18 PM »

Steve Stewart has one that seems to be working pretty well. The "pinch off" was indeed his biggest hurdle. I think he is on gen 3 or for but pretty happy with it now. He uses stock park flyer bits for the other stuff.
FYI Texas Timers has a really nice supple fuel line.

ChrisSarnowski · « **Reply #9 on:** November 06, 2013, 06:22:38 AM »

Quote from: Michael Alurac on August 20, 2013, 10:50:49 PM

Here's something that I've had in-mind for a self-contained electric shut-off device set-up to release an extension spring to pinch off super-soft latex fuel tubing when it senses a prolonged change in the centrifugal forces, such as a flyaway, that it learns in the first couple laps. It's a bit of a challenge at the moment to find the miniature parts needed to form the electromagnetic triggering device operated on a few button cells. My idea is to be able to mount this on any combat wing and profile suction design with shut-off on-demand functionality programmed in. Our field runs adjacent to a major highway so any combat flown at our field requires fly-away shut-offs.

The programming of the logic is another small hurdle... Here's my concept would anyone like to elaborate upon it?

Hi Mike,

So basically you have an accelerometer sensor on the board used to sense when line tension (centrifigal force) is lost. That is a neat idea to use the spring as a pinch. Nice 'extension' of the line-tension spring shut-off idea.

-Chris

Michael Alurac · « **Reply #10 on:** November 20, 2013, 11:33:06 PM »

Hi Chris,

Yes exactly! My thoughts are that once the accelerometer loses the centrifugal force the processor has learned from a couple of laps for instance and has a continued change of CF that varies from what the processor has learned in the first couple laps such as in a fly-away or upon command with a succession of rapid inward pulls an electromagnetic plunger would be activated releasing the spring to pinch off the fuel. Or possibly even ditch the spring idea and have the electromagnetic plunger device pinch the fuel line directly. I got a quote of about $2500+ to engineer the device and write the operating code so it's a bit out of budget. Not to mention a miniature electromagnetic triggering device has been hard to source. What I've found on the shelf is much too large for this application. I'll keep this idea simmering on the back-burner in the meantime...

Thanks for your input,

Mike

tom hampshire · « **Reply #11 on:** November 21, 2013, 06:25:13 AM »

Wouldn't the mechanical effort be less to open a fuel dump tube as opposed to clamping it shut?

James_Mynes · « **Reply #12 on:** November 21, 2013, 06:41:28 AM »

I saw a picture of a burnt string approach a while back. A small string held the spring shut-off open. If a shut-off event happened, a small wire got hot, burned the string, allowing the spring to snap closed and pinch the fuel line. I think it was driven by a button cell battery, which also powered the receiver/cutaway sensor.
Several strings were staged and ready to re-arm the device. Using this approach, all of the mechanical strength needed for pinching the line was controlled by the string, the electrical stuff only sensed line tension or centrifugal force, powered a receiver, and in case of a problem sent some juice to the hot wire to burn the string.
It would seem that a battery would last all day unless a burn was triggered, in which case you reset the spring and pop in a new battery. Might be able to drive it with a small lipo as well. Some of the little quad copters have a tiny lipo that should pack enough juice to do the job.
If I had any electronic smarts you would all be paying me for my invention.

don Burke · « **Reply #13 on:** November 21, 2013, 02:59:14 PM »

Quote from: tom hampshire on November 21, 2013, 06:25:13 AM

Wouldn't the mechanical effort be less to open a fuel dump tube as opposed to clamping it shut?

I think it's not a very good idea to dump a load of fuel either on the ground or the competitors, just on the ground in the pits is bad enough.

Bob Mears · « **Reply #14 on:** May 20, 2014, 01:59:10 PM »

http://microflierradio.com/F2DCOMBAT.html

Tim Wescott · « **Reply #15 on:** May 20, 2014, 02:07:34 PM »

Quote from: tom hampshire on November 21, 2013, 06:25:13 AM

Wouldn't the mechanical effort be less to open a fuel dump tube as opposed to clamping it shut?

Howard Rush showed me his electronic Combat shutoff (with a PIC microprocessor and an accelerometer) at one point. I asked that exact question, and the answer was that the engine stops much more promptly when you starve it than when you flood it.

Paul Smith · « **Reply #16 on:** May 21, 2014, 06:00:32 AM »

The best cutoff at this time is the Jacko DeRidder magnetic slide weight unit only 40 Euros.

It is a single module that bolts right on the outside. It has both flyaway and on-demand functionality.

It is based on a ballcheck value the is closed by fuel pressure. The ball is held open by rare earth magnets embedded in a brass slider which is held out by centrifugal force. The on-demand feature is actuated by a quick snap of the wrist.

If I were to get active in the event again I would just buy six units for 240E and not be concerned with preparing three battery-powered electric systems (in addition to the two I already need) for every match.

Paul Smith · « **Reply #17 on:** May 21, 2014, 06:04:50 AM »

PS: I am not totally against electricity. 2.4 works OK for scale and carrier where you only need one plane per event.

In F2D you need six toys for starters. In a double elim contest you can go through a dozen in a day. That's a lot of receivers, batterys and servos to deal with while your changing engines and lines.

phil c · « **Reply #18 on:** May 21, 2014, 05:42:40 PM »

Quote from: Michael Alurac on November 20, 2013, 11:33:06 PM

Hi Chris,

Yes exactly! My thoughts are that once the accelerometer loses the centrifugal force the processor has learned from a couple of laps for instance and has a continued change of CF that varies from what the processor has learned in the first couple laps such as in a fly-away or upon command with a succession of rapid inward pulls an electromagnetic plunger would be activated releasing the spring to pinch off the fuel. Or possibly even ditch the spring idea and have the electromagnetic plunger device pinch the fuel line directly. I got a quote of about $2500+ to engineer the device and write the operating code so it's a bit out of budget. ....Mike

Keep in mind that the popular swing arm centrifugal shutoffs only seem to work about 65% of the time. Apparently a cutaway combat plane can get into a looping/skid/barrel roll that can provide quite a bit of sideways acceleration. You'll have to do more real life testing to get a better handle on the actual forces on the plane after a cutaway. The swing arm shutoff does work, mostly, but it is mainly a pacifier for contest management/rules committees. In F2D they serve a real purpose in reducing the number of lost motors more than anything. For safety the shut off has to detect when the plane is no longer attached to the pilot, not just when it's lost centrifugal pull. Maybe GPS?

or a sensitive, adjustable detector in the plane to tell when a RF signal has weakened enough to tell that the plane is no longer on the circle.

Paul Smith · « **Reply #19 on:** May 21, 2014, 07:19:55 PM »

The fellure modes of the swing arms were:

1. Air resistance prevents the arm from going forward.
2. Not enough force to squeeze the fuel line against bladder pressure.
3. Arming device malfunctions or was not properly set.

The DeRidder sliding weight system addressed 1 & 2. I don't see how 3 will ever be addressed for any system.

We need to attack the root cause and prevent flyaways to begin with, not just try to minimize the distance. The original sin that triggered this whole issue was the refusal to increase fast & slow lines beyond .018' x 60' despite massive increases in power since 1965 when we had the last increase (.015" to .018").

Author Topic: Shut-offs (Read 3518 times)

James_Mynes

ChrisSarnowski

James_Mynes