Presented with written permission from RocketyPlanet:

Product Review by Brad Shea
Tuesday, October 21, 2008

When Giant Leap first announced their new product called the Slim-Shot, I was excited. The idea of an easy-to-use motor topper that didn't break the bank was something I was quite interested in obtaining. When the introductory offer came out at roughly $100, I was sold - I bought mine within 24 hours of the announcement on Rocketry Planet.

Why was I so excited? It seemed to fill a need for accurate apogee deployments with minimal fuss and preparation. I am a spur of the moment flier but I lack enough flying experience to intuitively "know" the correct delay required for a given rocket. I tend to rely on simulations to help guide my delay choices. When I'm in the field and I have a whim, it is nice not to have to fret about delay selection.

Why not use a traditional altimeter you ask? I do on the rockets I have that are designed for dual deployment. But many of my rockets are designed for single deployment and easiest to fly in that way. I can and have added altimeter bays and flown some of them in dual deployment, but this adds unwanted weight and length to these rockets.

The Giant Leap Rocketry Slim-Shot accelerometer recovery device, as shipped, contains quite a bargain.

Very soon after I placed my order the unit arrived. I was pleasantly surprised by the speed of the order fulfillment as well as the extent of the contents. I had only expected to receive an aluminum canister, some mounting gear, instructions and electronics. In addition, the package included a set of safety goggles, extra mounting gear, an extra grommet, some Kevlar cord and a specimen jar with two small holes in the lid. Why the jar? It's used in the ground test procedure.

At this point, you need to know that I am not the kind of guy who just jumps in and starts fiddling with things like this. I learned to read instructions before getting started after years of watching my father read the "corrections" after some step was omitted and it was too late to fix. I decided long ago this was a poor strategy for success. After experiencing the results of not reading first, I became good at tinkering with things and figuring out how to fix things. However, if instructions are available I tend to read them cover to cover before starting.

The instructions turned out to be a bit harder to understand than I expected. Partially, this may be due to preconceptions on my part, but part of the blame is content related. My advice if you get one of these is to practice with it away from the field so that you can determine if you have questions or need help from Giant Leap before your first flight. My past experience with Giant Leap has shown me that they are friendly and responsive.

The Giant Leap Slim-Shot, unpacked, contains a lot of extras, including safety goggles, testing chamber and extra hardware.

Using the Slim-Shot is unlike working with a traditional altimeter in that there is no power disconnect switch. You insert the battery and rely on the accelerometer and the firmware to make the device safe. When horizontal it is DISARMED. When the Slim-Shot is vertical and stationary for a couple of seconds, it moves into ARMED mode. In this mode it waits for LAUNCH DETECT which requires a positive* acceleration of at least 1.7g's that lasts for 0.11 seconds. Once launch has been detected, the altimeter moves into the FLIGHT MODE and waits for APOGEE DETECT. When apogee is detected and the flight duration is longer than 2 seconds, the altimeter fires.

If this seems convoluted, it is and it isn't. All of this is designed to make the device safe from routine handling to and from the pad as well as accidental drops and bumps while still allowing the device to work without an external power switch safely. Once you get the hang of it, you find it easy to understand but the learning curve can be a little daunting at first.

Did it work? Yes and no. I found it to be a very reliable apogee deployment device when I used it correctly - but I found a lot of ways to use it wrong. If you could do it wrong, I did. I'm not unfamiliar with flying rockets and don't typically make stupid mistakes. But with the Slim-Shot, I shot myself in the foot repeatedly. Most of the time, my failures were a non-issue since I experimented early on using the Slim-Shot as a second deployment device rather than as the only deployment option. However, I crashed a favored rocket when I thought I had the hang of things by relying totally on the Slim-Shot for deployment. The failure was my fault - but I can't help thinking that if I had used it for redundant deployment the rocket would not have crashed.

How did I mess up when using the Slim-Shot? Here's a partial list:

• Installed upside down so that Arming and Launch Detect failed.
• Used an ejection canister that required too much output current.
• Angled my rocket too far so that Arming and Launch Detect failed.
• Flew it in a spool which, is not appropriate for this class of device.

How did I make all these mistakes? Was I careless? Was I not paying attention to the instructions? Yes and no. Despite making these mistakes, they were each single events that I never repeated.

The Giant Leap Slim-Shot uses a 38mm-diameter aluminum housing with a stepped forward end designed to fit into the ejection well of RMS-style 38mm and 54mm motor forward closures. The tiny accelerometer-based recovery device fits inside the housing.

It's true that I installed the unit upside down despite having made myself a note not to forget. In that case to be fair, I had just flown it on the top of a motor and I was moving it to the nosecone mount in another rocket. The canister was flipped 180 degrees, but the way that the wires route caused me to forget this and load it in the wrong orientation. This was a mistake I never repeated, and lucky for me, it was not a costly failure since motor backup saved my bacon on this flight.

While I admit that I used it with ejection canisters that needed too much current, the instructions and the website did not offer a list of compatible ejection initiators. I ground tested but my sample size was too small. Once again the rocket involved had only minor damage from this mistake since this was a piggyback flight with an altimeter. From then until GLR offered their capacitor upgrade I used flashbulbs and never had an output current problem again. After the capacitor upgrade, I successfully flew with M-Tek e-matches but have not yet tested the unit with anything other than flashbulbs and M-Teks.

The failure due to launch rod angle was a real shock. It never occurred to me to do the math and find out that a mere 8 degrees from vertical was enough to drop the unit back to DISARMED status. The lack of any kind of feedback once the unit is placed into the housing made it impossible to know that this had happened until the rocket came in ballistic.

The 38mm-diameter aluminum housing feeds the wires to the ejection charge through the forward aluminum closure, which is held on with a snap-ring, through a rubber grommet outfitted with two pass-through holes.

The spool flight was something that seemed like it should have worked. During the flight everything looked great. The parachute deployed right at apogee. The spool came down under chute and landed, and then BANG! The ejection charge went off as I was walking towards it! The parachute had apparently been deployed by drag separation. I had expected that it might drag separate - but it had not occurred to me that the Slim-Shot had not fired.

After discussions with the designer and others knowledgeable about accelerometers, it appears that a tiny bias applied to the calculations was sufficient to keep the unit thinking that the spool was flying very slowly up until it came to rest on the ground and tipped over. The moral of the story is that spools are bad choices for accelerometer based deployment devices. This subject is not covered in the instructions and should be updated by Giant Leap ASAP.

After the incident with the spool, I was nervous about the safety of the Slim-Shot. At that time I had no explanation for why it had gone off. I began removing the battery just after testing during prep. In all other respects, I followed Giant Leap's process for preparing the unit. Until I reached the pad - I kept the battery out of the rocket. This allowed RSO's the option to shake and push and drop the rocket - without either of us worrying the unit might go off. It also allowed me to not worry that the tiny A23 battery might go dead before the rocket got off the pad.

Now you may be wondering - with this history - how do I feel about the product? The answer is - it depends. For a redundant deployment at apogee that is easy to mount and requires no external switches - I love it. As a primary deployment device to replace motor ejection - I can not recommend it. The inability to get any kind of feedback as to the status of the unit makes it very hard to recommend as the only deployment device in any rocket.

Here is a Slim-Shot retro-fit mount in a nosecone using 38mm tube and Kevlar recovery cord held in place with epoxy.

So here are my recommendations:

1. Get the unit with the capacitor added. This is a must unless you want to only use flashbulbs or home-made low-current e-matches.
2. Fly it as a redundant deployment device. It appears to get apogee just right and can be used in conjunction with motor ejection or an altimeter to give you a redundant option for apogee that is pretty simple to install.
3. Install the battery during test and prep - and then remove it. Reinstall at the pad if possible. This prevents RSO's from rolling their eyes and handling the rocket like toxic waste. In addition it preserves battery life and just seems safer.
4. Only use the altitude and time measurements for entertainment. Put no stock in these unless you are able to validate them against another source.
5. Ground test as recommended and USE THE SAFETY GOGGLES AND WEAR GLOVES while working around ejection charges. This is a good practice when using any electronic deployment device.
6. Observe the known limitations of the device: 2g's minimum acceleration / 30g max acceleration; Flight time greater than or equal to 2 seconds and less than or equal to 24 seconds; Altitude less than or equal to 15,000 AGL; "This end up" pointing in the right direction. Make a checklist and check it twice.
7. Take care when and if the unit has not fired. Give it some time before approaching if the flight might have been outside the design envelope. Ensure that the Slim-Shot is horizontal before handling it and use caution when approaching the rocket. Consider all charges "live" and avoid touching them while removing the Slim-Shot from the rocket.

What might make it better? An option for remote LED or remote buzzer to signal the state of the unit would be very helpful. Once the Slim-Shot is placed inside the canister, you have no idea what state it is in. It can disarm or fail in some other way without any feedback. The rocket that I flew with the greater than 8 degrees from vertical flight profile is a prime example. I had no way to know that it had disarmed until the rocket came in ballistic.

Would I buy it again? I think so. For what I originally wanted to do with it - it isn't quite there. I don't feel comfortable flying it as a motor topper - but I do like the ease of use and accurate apogee deployment. I also like the simple way it can be mounted in an existing rocket - I have installed it and flown it in a 12" diameter rocket as a 3rd apogee deployment device in as little as 5 minutes.

NOTE: Recently Giant Leap began offering the aluminum housing as a separate product without the electronics. This small housing is offered at a great price and would make a great place to put a small timer or other electronic device that does not need barometric data. Even if you don't buy a Slim-Shot, you should give serious consideration to the canister.