The R/C Chute Sled: simple R/C chute release unit

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tab28682

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Some background.

I have a lot of years flying and experimenting with RC models. Over time, I have rigged up lots of little devices to carry small RC gliders and RC rocket gliders on top of larger RC models, plus parachute drops, skydiver drops, candy drops, water balloon drops, bomb drops, etc. These drop units tended to be activated by servos releasing an elastic band. Simple and easy and it works at least 99.9% of the time.

One of these devices is shown below. I did this custom unit early this year year to test drop my RC A4b rocket glider from a large Carbon Cub model. You can see the servo and elastic band. The unit is rigged do that the servo rotates and releases the elastic band at the flip of a switch on the TX.

Have thought about making a similar self contained unit for large LP and MP and HP rockets since the mid 1990s. Servos and RX units and batteries were a little larger and heavier and more expensive then than now.

Took a rocketry break from about 1998 untill 2014. Started up rocketry again in 2014. In fall of 2014 I thought about the RC controlled chute deployment again. The state of the R/C art had improved a bunch, with good inexpensive micro servos, low cost and great performing 2.4Ghz RX units and tiny lightweight lithium batteries.

Built a little sled late last year with a small box to hold a 9 gr servo, a 2.7 gr 2.4 RX unit to match my Spektrum TX and a small one cell lipo battery. Did not like the mechanics of the release pin on this one. Put it on the shelf for a while.

Decided a couple of weeks ago to simplify and get the RC Chute Sled finished........

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tab28682

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RC controlled chute release is not new. Numerous scale rockets have used it, water rockets have used it and RC controlled ejection has been around for a long time. But never in a format that I really liked.

I wanted to start with a small self contained RC sled for my mid powered F and G rockets and use motor ejection. Most of my mid power models have 2.6 or 3" airframes, so easy to make a sled that fits. I wanted to be able to instantly swap it from rocket to rocket.

Decided to directly release the elastic band retainng the chute using a rotating servo arm on the outside of the sled, much like my piggyback glider release in the previous post. There is a small metal ring on the band that slides easily off the servo arm. It is also too small to ever get caught on the servo output shaft.

Sketched up a new little sled to be constructed of 1/16 basswood and 1/32 and 1/64 plywood. The box is about 1.2" wide and 3.5" long and rides on top of a longer basswood chassis that is about 5" long. This gives a nice base to strap a mid power chute to. The sled is about .5" thick.

The first pic shows the chute in place with the servo engaging the band. This is not how the chute gets packed, it was simply strapped on quickly for a pic at today's launch.

The box contains the servo, with the output shaft outside the box, plus the small RX unit and a 150 mAh lipo. One the side of the box opposite the servo arm, there is an anchor for a short elastic band made of 1/4" sewing elastic. The long base gives a stable chassis to strap the chute to.

One end of the sled base is reinforced and has a hole for a tether that gets attached to the same point on the shock cord harness as the chute.

The second pic shows the side opposite the side the chute gets strapped to.

So, how did it work today?

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tab28682

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Well, color me a happy camper!

Tested the RC chute deploy today and it worked as expected. I have witnesses, but no action photos, darn it.

The RC parachute "sled" was installed in my venerable NCR Eliminator. Chute was a stock AT yellow 24" light weight nylon. First launch was on an AT G40-7. A pretty breezy day, with winds 10-14 or so.

Nice boost in a clear blue sky. Motor ejection was on time a bit after apogee. Sled and shock cord deployed nicely. Due to the light weight of the rocket and the generous size of the fin can, I got a long floating decent with the fin can flying happily above the payload bay part of the time, with the chute strapped in place on the sled. At about 200 AGL, about 800 feet south of the pads, I did a short countdown for the spectators and hit the switch on the TX. Instant chute deployment in less than a second at around 100-150 AGL.

Without the RC chute deploy, it would have been a two mile walk....or a much smaller chute...

................

After flying a few other rockets, I swapped the sled over to my brand new, never flown AT Strong Arm. Left the small 18" chute on the Strong Arm. Installed an AT G40-7, dog barf and a little Estes wadding. Packed the sled and headed to the pad.

Another nice boost into the clear blue sky. Edged over a little to the east this time. Motor ejection just after apogee.

This airframe with the long strakes liked to fly around as well. With the chute strapped to the sled, the Strong Arm also drifted about 800-900 feet downwind, this time towards a small tree line. Held off a bit more to try to get the rocket past the tree line. Hit the switch, again at about 200 feet or so. Chute took a hair longer to deploy, most of a second this time. Nice low chute deployment. Just caught the far side edge of the tree line, with the rocket about 4 feet off the ground. Easy recovery.

So. Two for two the first day out!
 
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tab28682

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image.jpg

This unit is by no means opitimized, but it does work nicely.

I am using my Spektrum DX9 TX. The servo is a $3.00 9 gram HTX900, very popular for small RC models. The RX is a Spektrum DSMII 6 channel end pin unit made by Lemon. About 6 bucks. The battery is one of the little long and thin 1S 150mAh lipos used in the popular Parkzone micro electric aircraft. Versions of it can be had from a buck to about 6 bucks.

This particluar micro RX has a tested range of around around 1500-2000ft, minimum, in the air. Good enough for todays test with 2.6" airframes and G motors. Other Spektrum RXs can be had with ranges tested to 2-2.5 miles.

So: here is an option for pyro free, altimeter free and AV bay free dual deploy, using motor ejection at apogee, with the fun of being able to pick the exact point in real time and apparent altitude that you want your main chute to deploy. Being an RC guy, I like to have some control....::)

Also an inexpensive solution if you have a suitable RC TX on hand.

I have a rearranged version with other tiny components that I think can be made to fit a BT50 or BT55. I also have a larger heavy duty version of the sled in mind for larger HP rockets that will use dual larger servos, if needed.

This last pic shows the TX screen name for this "model".
 
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