Help on selecting a first two stage high power rocket kit

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Hi Jim,

Thank you for taking the time to write up such a detailed response. Your efforts did help to explain a lot of issues. I still have a few more questions if you don't mind.

You stated that the interstage is the weak point in a two stage rocket. Others on this forum have complained about their interstage's without stating the problem. Would it be better to replace the interstage tube with a carbon fiber one in the fiberglass rocket? Do you have a better technique to wrap the interior of the fiberglass tube with carbon fiber? I have used carbon fiber socks on the exterior of tubes with great success. The only way I could see wrapping the inside of such a narrow diameter tube would be with multiple strips of material.

Do do you place any gas vent holes in the upper end of the interstage? One of your great photos shows a band of blue painters tape securing the ignition wires to the aft end of the sustainer. Do you do anything to prevent the red motor nozzle cup from sliding off? Do you have any problems with ignition wire sliding down out of position in the sustainer motor?

Do you install a seperate switch above and beyond the altimeter power switch to break the sustainer ignition wire connection?

How much of a time delay do you use between the black powder interstage separation and ignition of the sustainer? Have you ever had the black powder charge damage the ignition wire for the motor?

Would you like to write a book? I loved your high power high altitude launch videos.

Thanks,
Bob

Getting a carbon coupler for the interstage would be just fine as long as it matches with the fiberglass tube. When I line the inside, I just use one wrap at a time, overlapping a bit, but a carbon coupler would be better.

No vents in the interstage. Generally, the little red caps stay on just fine. The picture was taken quite a while back, and I now an more aggressive in protecting the wiring from the separation charge. On the other hand, I've done it the way shown in the pic many times with no problems. I typically use a separation charge of 0.3 g of black powder. On these smaller motors, the igniter doesn't move much, but I use a stick to support it for 75/98 mm.

I use two switches beyond the power switch. The circuit is shown below. I turn on the altimeter first - no continuity. Then I close the switch that opens the path to the altimeter. There is a continuity tone. Then, I open the shunt if everything has powered up correctly. Shunts must be short, use heavier wire, and must be ground tested using the actual lengths of wire for the igniter. It is best to avoid Lipo batteries, as the amount of current they provide can overwhelm the shunt and/or burn it out. Unfortunately, the Easymega only uses Lipo's, so it's best to use a smaller Lipo for the firing battery. Also good to minimize the firing time to as short as possible.

The timing just depends. I often separate the booster a second or so after burnout. Sometimes, I let the rocket coast together and then separate after the velocity drops a little. I have found that waiting until the rocket slows to Mach 1.3 is usually OK for my carbon rockets. I previously laid out criteria for lighting the sustainer, so the coast time would be the time between the two events.

I might also mention that the way the Easymega and/or Raven gets programmed for staging is an art by itself. Ask about that when the time comes.

I've written several articles on carbon fiber construction, but not on staging. However, everything that I have ever done is documented somewhere in this forum.

Shunt_Short.jpg

IMG_0805.jpg
 
Hi Ksaves2,

You bring up good points that haven't been mentioned in this discussion. Personally I am not concerned about tracking since I have been using one of Vern's "Kate" GPS Tracker / Telemetry units. I've used Vern's Unit about a dozen times in a twelve month period. The device is simple to use, and works to over a 100,000 feet. You will have to go to Vern's website to see videos of those high altitude flights. My flights have not been that lofty.

I plan on installing a lesser grade tracker in the booster section. I have a Walston Unit from my R/C Sailplanes. I may use that for the booster unless someone has a better suggestion.

If you look at Vern's website, he has a coming soon section. Vern has an altimeter / staging device that will be available this fall. This device will communicate with the Kate unit via Bluetooth. This staging device has many safety devices built into it including a tilt function. You will also be able to abort the sustainer ignition from the ground. Pretty cool stuff.

As as far as the altitude goes, lower flights are better for testing. I am hoping to run Rocksim simulations that will confirm a small 38mm sustainer motor will work with a 54mm booster. Hopefully there will be a combination that will work and keep the rocket low.

All the best,
Bob
 
Hi Jim,

Could you explain how the shunt works? I am not familiar with shunts. Your diagram looks like the shunt is shorting out the circuit. Does current also run to the igniter which could set it off?
 
Hi Jim,

Could you explain how the shunt works? I am not familiar with shunts. Your diagram looks like the shunt is shorting out the circuit. Does current also run to the igniter which could set it off?

The purpose of the shunt is to minimize the current to the igniter if the altimeter accidentally triggers or is powered for some reason. The idea is that the resistance of the shunt is low relative to the igniter so that the current that does go to the igniter is below the no fire current. This is why the shunt part of the circuit has to have a low resistance (short, reasonably heavy wires). A shunt is harder to use if using a lipo battery because they can provide more current. It is possible to ground test the circuit using the same lengths of wires as the actual flight, just to verify that it will work if there is a need.

Jim
 
Yes, I've crashed a lot of two-stagers. Some of them have been interesting though. I've posted many of my staged flights here:

https://www.youtube.com/results?search_query=jiminaus50

Maybe since this is a kit thread, I'll describe what you'd get if you got a "Jim" kit. I don't make kits, but if I did, this is what it would be. My kit might not suit you at all - it's just another way to do it.

The kit would be 3" to 3". It would be fiberglass and designed to fly anywhere from 3K to 25K. The pics below are from an existing rocket I built maybe 12 years ago? That rocket has probably flown a couple of dozen times, and there are a few concepts from it that I would keep.

(Temporary rant on) My kit would have surface mounted fins. I think many fiberglass kits come with through the wall because they can be built by folks with a wider range of skill levels. But I have never understood why you would want to take a perfectly good fiberglass tube and cut slots in it. In 3" with a permanent motor mount, surface mounted fins with reasonable reinforcement will be stronger and lighter than through the wall. (Temporary rant off) My fins would be 5/32 or 3/16", and I would include just enough carbon for a couple layers of tip to tip. This would stay inside the perimeter of the fins - i.e., the carbon would stop short of the edges of the fins, and then I would use epoxy/West 410 or the like to smooth everything out.

The booster would be very simple. I'd go with a 54" motor mount with a retainer and just use motor deploy, or a chute release. A chute release is a little risky because apogee deployment might not be very accurate for a two stage booster, which increases the risk of the chute release releasing the chute early upon deployment. I calculate the delay time by performing a simulation but without separating the rocket or lighting the sustainer. I calculate the delay time in that configuration and then take 2/3 of that value for setting the motor delay. I get close most of the time. I'd design the booster with a piston as I think they greatly increase deployment reliability, so the booster would just have an open top.

The interstage coupler would be the "nose cone" for the booster and it would slide up into the bottom of the sustainer. A caliber or just a little bit more into the tubes on either side. A small switch band goes on the outside and a bulkhead goes at the appropriate location on the inside (leaving enough room for a separation charge below the sustainer motor. A good fiberglass tube would be fine for the interstage coupler in the kit, but I'd add a few wraps of carbon to the inside of the tube before adding the bulkhead. Two stagers tend to fail at this point, so stronger is better.

I suppose some electronics could go into the bottom side of the interstage coupler. This might allow better apogee detection and the separation charge could be done from that point. I don't light motors from the interstage coupler though (that voids the kit warranty). Be sure to shear pin the interstage coupler to the top of the booster, just like a nose cone. Also, if electronic apogee deployment is used, then the booster could be constructed minimum diameter.

My sustainer would be pretty conventional. Again, 54mm mount with retainer. The bottom ring of the mount could fit against the top of the interstage coupler. I'd use three rings on the motor mount and I would also mount the fins a little higher on the airframe (around those rings). The secret to sound surface mounted fins is to prevent the underlying tube from deforming.

The sustainer would have a zipperless coupler design. The wires for the motor ignition and the separation charge would pass through a brass conduit from the top of the zipperless coupler to the bottom motor mount centering ring. I connect the wires to wires from a conventional altimeter bay just using a simple twisted breakwire.

The first pic shows the altimeter bay in the upper air frame with the wires passing through the drogue section. I've done it this way for many dozens of flights and have never had a problem with the wires inhibiting drogue deployment in some manner. The wires need to be attached securely within the bay so that the electronics don't get yanked out upon separation.

The pic also shows an upper airframe that is in two parts (with the bay going between them. The kit would only have a single tube, and the bay would slide in from the top, sit on a ring and get pinned with rivets or the like. Air frame breaks should be avoided on two stagers wherever possible.

For electronics, I have always used either an Easymega or a Raven for staging. Both altimeters have some quirks and need to be fully tested before use. But, they both allow an altitude check, which is essential for staging. There are other altimeters that do this also, including the RRC3+ and one of the Egg-things and probably the Marsa. You would use the Easymega or Raven with another dual deploy altimeter, or perhaps use a pair of RRC3+ altimeters. Back when I started staging, I used an ARTS II, which could fire a channel at a pre-set altitude on the way up, combined with a timer that actually lit the motor. The output of the ARTS II was connected to a transistor switch. If the altitude was reached before the timer fired, it would open the transistor switch and allow the timer current to the igniter. It worked well for several years. It is critical to use an altitude check with any staged rocket. Tilt is nice, but secondary I think.

The pathway to the igniter would include two switches. One would open the igniter leads and the other would short them out. The one opening the circuit would be on the altimeter side of the shunt, which is a lot like twisting the leads of the igniter together. The design of these circuits is a topic for another day.

Staging delays are another subject too. On a slower flight, a few seconds is usually OK. If the boost will approach mach, then you can let the sustainer slow down to perhaps 500 ft/sec with no problems. If above Mach, then there is a choice. I have generally let my rockets fall through mach to perhaps 700 ft/sec to reduce the top speed of the sustainer. But there are reasons to consider lighting above mach such as trying to maintain a straighter trajectory.

So, above the bay is another piston and then the cone of your choice.

Anyway, that's my kit. Thanks for letting me design it on your thread!

Jim
HI Jim very well thought out and designed rocket there .
It sounds very similar to this https://www.wildmanrocketry.com/ProductDetail.aspx?product=3915 less the zipperless booster.
 
Hi Steve,

I've looked at the PML kits. Others on the forum have called them old school. Personally I just like working with fiberglass. You spend so much time building these rockets that you want them to be durable. It is great though how PML provides instructions. Too many other kit manufacturers do not provide instructions.

Thanks for for the input.

Bob
 
Hi Tim,

I met you briefly at the June URRG 3 Day event this year. Your wife has been very helpful when I ordered a bunch of motors and cases from her.

Tim would you be able to upgrade your 3" Wildman Kit for me, at an additional cost, by upgrading the fins from 1/8" to 5/32's or 3/16's? Would you be able to substitute a carbon fiber interstage tube for the fiberglass one that comes with your kit?

Have you you extensively flow this design while you were developing it? If you have, can you recommend a CTI motor combination that provides enough thrust to be safe but keep the rocket low for the first few flights? I wouldn't mind using a lower power 38mm motor in the sustainer for the first flights.

Thanks,
Bob
 
The purpose of the shunt is to minimize the current to the igniter if the altimeter accidentally triggers or is powered for some reason. The idea is that the resistance of the shunt is low relative to the igniter so that the current that does go to the igniter is below the no fire current. This is why the shunt part of the circuit has to have a low resistance (short, reasonably heavy wires). A shunt is harder to use if using a lipo battery because they can provide more current. It is possible to ground test the circuit using the same lengths of wires as the actual flight, just to verify that it will work if there is a need.

Jim

My only concern with shunts is if they are not tested, like you say lipos can push enough current through for ignition to occur. If using an ematch augmented
igniter I doubt a shunt is going to provide any means of safety whatsoever due to the low current requirements. A higher current requiring nichrome igniter
might be safely bypassed with a shunt but one doesn't know unless the failure mode is tested to see if the paradigm is true.

Also a full up failure mode test stands a chance of destroying one's electronics if the parameters aren't controlled carefully.

My opinion is remote arming of the ignition electronics via Rf means is the way to go. One can stand a fair distance away from the stack and not
risk standing next to it when "arming". I'd rather be 30 to 50 feet away from a high powered sustainer than standing next to it if it blew.

This can be tested ad nauseam with live contained igniters on the bench (or outdoors) to be certain nothing goes haywire without risking destroying one's devices.

Kurt
 
Hi Tim,

I met you briefly at the June URRG 3 Day event this year. Your wife has been very helpful when I ordered a bunch of motors and cases from her.

Tim would you be able to upgrade your 3" Wildman Kit for me, at an additional cost, by upgrading the fins from 1/8" to 5/32's or 3/16's? Would you be able to substitute a carbon fiber interstage tube for the fiberglass one that comes with your kit?

Have you you extensively flow this design while you were developing it? If you have, can you recommend a CTI motor combination that provides enough thrust to be safe but keep the rocket low for the first few flights? I wouldn't mind using a lower power 38mm motor in the sustainer for the first flights.

Thanks,
Bob
Hi Bob
I can do the upgrade to the fins but it is not needed unless you want to go minimum diameter on the booster. and the same thing with the carbon coupler.
I have never heard of anybody breaking one of these. As a mater of fact I guarantee it.https://www.wildmanrocketry.com/Instructions/2%20stage%20final.pdf .
I have flown the 2stage 3" Wildman on more motor combinations than I can think of.
A good combo to start with would be Vmax or White thunder in the booster and something with lots of smoke in the upper (so you can see it).
The thing to remember when flying a 2 stage, is high initial thrust is a must on the booster and not to play with upper stage ignition timing( leave it at0- 1) to start with. After you get comfortable then , start messing with timing and different motor combinations.
 
HI Jim very well thought out and designed rocket there .
It sounds very similar to this https://www.wildmanrocketry.com/ProductDetail.aspx?product=3915 less the zipperless booster.

Tim, my belief is that your kits are better than most for sure. I'm pretty sold on the zipperless coupler concept, though. I have had flights in the past where the coupler has failed at very high speeds. So, over time, my design has evolved to a lined zipperless coupler with several bulkheads supporting it (which is why I buy so many bulkheads from you!). I don't know how your dual deploy wildman is designed (instructions not posted), but if it is a lower tube section and an upper tube section joined by an ebay as a coupler, then that is something I would modify.

My other comment is that your two motor sections are too long and would allow oversize motors. What, are you crazy?

Jim
 
Hi Steve,

I've looked at the PML kits. Others on the forum have called them old school. Personally I just like working with fiberglass. You spend so much time building these rockets that you want them to be durable. It is great though how PML provides instructions. Too many other kit manufacturers do not provide instructions.

Thanks for for the input.

Bob

My first two-stage was a PML quantum leap. When I got it, I spent hours trying to figure out how to modify it to be more like what I wanted. I didn't quite get there, though, because I managed to shred it. So, I rebuilt it but with even more modifications. It's quantum-leap-like, but not a quantum leap. It's that purple rocket and has worked for years. That particular rocket used a couple wraps of fiberglass on the phenolic tubes, and they have been very durable over time.

Jim
 
Hi Bob
I can do the upgrade to the fins but it is not needed unless you want to go minimum diameter on the booster. and the same thing with the carbon coupler.
I have never heard of anybody breaking one of these. As a mater of fact I guarantee it.https://www.wildmanrocketry.com/Instructions/2%20stage%20final.pdf .
I have flown the 2stage 3" Wildman on more motor combinations than I can think of.
A good combo to start with would be Vmax or White thunder in the booster and something with lots of smoke in the upper (so you can see it).
The thing to remember when flying a 2 stage, is high initial thrust is a must on the booster and not to play with upper stage ignition timing( leave it at0- 1) to start with. After you get comfortable then , start messing with timing and different motor combinations.

But you would only use Vmax in the booster if electronic deploy. White Thunder is perfect.

Jim
 
My only concern with shunts is if they are not tested, like you say lipos can push enough current through for ignition to occur. If using an ematch augmented
igniter I doubt a shunt is going to provide any means of safety whatsoever due to the low current requirements. A higher current requiring nichrome igniter
might be safely bypassed with a shunt but one doesn't know unless the failure mode is tested to see if the paradigm is true.

Also a full up failure mode test stands a chance of destroying one's electronics if the parameters aren't controlled carefully.

My opinion is remote arming of the ignition electronics via Rf means is the way to go. One can stand a fair distance away from the stack and not
risk standing next to it when "arming". I'd rather be 30 to 50 feet away from a high powered sustainer than standing next to it if it blew.

This can be tested ad nauseam with live contained igniters on the bench (or outdoors) to be certain nothing goes haywire without risking destroying one's devices.

Kurt

Kurt, many good points. Regarding the Lipo's, I think the only way to use them and test them safely is to use small ones where the current is limited. This is based primarily on the recommendations Adrian has provided for the use of Lipo's with the Raven. In the case of the Easymega, the firing time can also be reduced. I'm in the process of ground testing some modified boards. I'll report back.

Jim
 
My other comment is that your two motor sections are too long and would allow oversize motors. What, are you crazy?

Jim

LMAO! Yes. Yes he is crazy...
This rocket is perfect for Airfest...
If only I could ever get to go. :-(
 
Dear Jim & Tim,

Thanks for the back and forth. This a great way to learn. What is a zipperless coupler? All of my 4" diameter Level 2 rockets and my 5.5 inch Level 3 Rocket use dual deploy. Some have the AV Bay coupler epoxied into the payload tube. I lower the AV Sled down the payload tube until it seats on the top edge of the AV Bay coupler. Then I bolt on the rear AV Bay bulk plate from the bottom.

I think that that this method is stronger than the other standard method of using rivets to attach the AV Bay to the payload tube.

Jim, you think that this standard attachment method isn't strong enough for a two stage rocket?

Tim I need one of your filliment wound Von Karmen nosecone's for this build. Mike from MAC Performance has been buying them from you. Mike has been modifying them to take a special container for Vern's Kate GPS Tracker / Telemetry units. I actually have six of your nosecones for different rockets that are all setup for the Kate unit.

How do you Gentlemen suggest that I proceed on the sustainer. I cannot utilize the nosecone for recovery gear. That space is rented to "Kate".

Tim I definitely want to try out one of your 3" two stage kit options. I am just trying to incorporate in some of Guru Jim's long term wisdom.

Have either of you Gentlemen had a problem where the black powder separation charge fails and the sustainer ignites while the two stages are still attached? Could that blowup the interstage?

All Le the best,
Bob
 
Bob my first flight of WM Jr. had a similar event. It has a really loose fit and had 0.2 grams of BP for separation charge. For what ever reason, it did not separate due to drag nor did the charge cause separation; however ignition still occurred with booster attached and that cleanly separated the two assemblies. No damage to the ISC as it kicked right out on ignition and there was only a little cleaning required. No damage at all. Since then I've used a bigger separation charge and add a little baby powder. Three subsequent flights and separation has been on queue every time.
 
What is a zipperless coupler? All of my 4" diameter Level 2 rockets and my 5.5 inch Level 3 Rocket use dual deploy. Some have the AV Bay coupler epoxied into the payload tube. I lower the AV Sled down the payload tube until it seats on the top edge of the AV Bay coupler. Then I bolt on the rear AV Bay bulk plate from the bottom.

I think that that this method is stronger than the other standard method of using rivets to attach the AV Bay to the payload tube.

Jim, you think that this standard attachment method isn't strong enough for a two stage rocket?

How do you Gentlemen suggest that I proceed on the sustainer. I cannot utilize the nosecone for recovery gear. That space is rented to "Kate".

Have either of you Gentlemen had a problem where the black powder separation charge fails and the sustainer ignites while the two stages are still attached? Could that blowup the interstage?

Bob

The first two pics I posted previously (657 and 640) showed the zipperless coupler. It's just the coupler glued to the top of the fin section instead of into the upper air frame. The reason that it's called a zipperless coupler is that during dual deploy, the fin section has to turn 180 degrees when the drogue catches. Just picture how that works. In the event of a high speed deployment, that change in direction happens fast and causes a zipper. The zipperless coupler avoids that. The other advantage of the zipperless design is as a means of retaining the motor, at least for 75/98 motors (although I use it for all motors by one means or another). Just to beat this to death, I also reinforce these zipperless couplers and add at least two bulkheads to them. The idea is to keep the coupler from deforming as this leads to failure. I normally use a U-bolt on top of these couplers, and it attaches through two of the bulkheads in the coupler. One other advantage of the multiple bulkhead approach is that it is enough resistance to stop a motor in the event of a motor cato. Believe it or not, this has saved two of my rockets from being gutted. This is why I only build zipperless.

I think your method of attaching the couple with epoxy is better than rivets only. It would be fine, although I would still recommend the zipperless approach for the benefits it provides that aren't directly related to staging.

I think if you have Kate, you don't need much more from a recovery standpoint. I recently had an unfortunate Mach 3.7 shred, which was my only flight with Kate aboard. Kate didn't like it much, but she kept on ticking. Very impressive! You might consider sticking an RF transmitter next to Kate just for insurance.

I haven't had a case where I had a motor light within the coupler, so I don't know what to say there. I would speculate that this becomes more of an issue as the motor gets larger, but that's a guess. I have never tried to design for that (vents for example). I did have a case once where the sustainer lit while the booster was still under thrust. That was very bad.

Jim
 
Dear Jim & Tim,

Thanks for the back and forth. This a great way to learn. What is a zipperless coupler? All of my 4" diameter Level 2 rockets and my 5.5 inch Level 3 Rocket use dual deploy. Some have the AV Bay coupler epoxied into the payload tube. I lower the AV Sled down the payload tube until it seats on the top edge of the AV Bay coupler. Then I bolt on the rear AV Bay bulk plate from the bottom.

I think that that this method is stronger than the other standard method of using rivets to attach the AV Bay to the payload tube.

Jim, you think that this standard attachment method isn't strong enough for a two stage rocket?

Tim I need one of your filliment wound Von Karmen nosecone's for this build. Mike from MAC Performance has been buying them from you. Mike has been modifying them to take a special container for Vern's Kate GPS Tracker / Telemetry units. I actually have six of your nosecones for different rockets that are all setup for the Kate unit.

How do you Gentlemen suggest that I proceed on the sustainer. I cannot utilize the nosecone for recovery gear. That space is rented to "Kate".

Tim I definitely want to try out one of your 3" two stage kit options. I am just trying to incorporate in some of Guru Jim's long term wisdom.

Have either of you Gentlemen had a problem where the black powder separation charge fails and the sustainer ignites while the two stages are still attached? Could that blowup the interstage?

All Le the best,
Bob

Hi Guys
The new kits are coming with the red tubing and filament wound cones.
Jim the ziperless coupler is the one thing that we will" I hope" to agree to disagree.
I have had to remove a bulk plate on the filed with a dremal tool to put a bigger motor in because of a bulk plate on top of a motor tube with a u bolt and swore I would never use one again.
With that said I have put small zippers in fiberglass tubes but not many and not often , but always deserved.
 
Hi Guys
The new kits are coming with the red tubing and filament wound cones.
Jim the ziperless coupler is the one thing that we will" I hope" to agree to disagree.
I have had to remove a bulk plate on the filed with a dremal tool to put a bigger motor in because of a bulk plate on top of a motor tube with a u bolt and swore I would never use one again.
With that said I have put small zippers in fiberglass tubes but not many and not often , but always deserved.

Tim, my friend, we can disagree with no problems, but I think you're overlooking the obvious. With a zipperless coupler you can retain the motor on the top. Then, with no pesky motor retainer to get in the way, you just let the motor grow to however long you need. Or you could just plan better.

I must admit, though, it has never occurred to me to cut out a zipperless coupler bulkhead to fit a larger motor. I may have to file that one away.

Jim

Overhang 1.jpg

Overhang 2.jpg
 
It's something of a religious thing with him. I call it "Tim's Second Law: No Motor Blocks!"

I take it with the overhang, the coupler takes all the thrust? Rather than transferring it through thrust plate or motor mount?
 
It's something of a religious thing with him. I call it "Tim's Second Law: No Motor Blocks!"

I take it with the overhang, the coupler takes all the thrust? Rather than transferring it through thrust plate or motor mount?

Well, the motor overhang was intended just to be humorous (although I guess I actually did it). Yes, in the two cases shown, it was intended that the zipperless coupler takes the force. It's not going anywhere though. I actually had one more situation where a smaller ring inside the air frame would have taken the force. For that one, I constructed a fiberglass sleeve over the exposed motor as a second push point. In all such examples, the case pushes on the air frame, not the closure.

Best is just to design for the motors you plan to use. In my defense, there is no conceivable way that I could have anticipated using those motors on those rockets. Just unusual circumstances.

Jim

PS - the second pic I posted also had a phenolic sleeve over the exposed motor, which was intended just to streamline things. It wasn't intended to handle the motor thrust and it wouldn't have.
 
Kurt, many good points. Regarding the Lipo's, I think the only way to use them and test them safely is to use small ones where the current is limited. This is based primarily on the recommendations Adrian has provided for the use of Lipo's with the Raven. In the case of the Easymega, the firing time can also be reduced. I'm in the process of ground testing some modified boards. I'll report back.

Jim

OK, I did the ground testing of the shunt/short on a new altimeter board. The two switches on the right side of the pic are the shunt & short switches (Aerocon PVC). The wires to the ematch connection point are short, which is the key. The smallest Lipo I have that I can wire to the easy mega was 200 mAh. It was fully charged. The EasyMega was set to a 0.05 second firing time. The ematches I use typically show about 1.3 ohms.

First test was a 10' length of 24 gauge stranded wire to the ematch and then the length of the ematch itself. This is about the configuration I would actually fly. The shunt was open and the match fired as expected.

Second, with new ematch, I did the above with the shunt closed. The ematch did not fire. I repeated the test and the match didn't fire. Then, I opened the shunt and the ematch fired.

Third, I tried the above with 5 feet of wire instead of 10 feet - same results (and then I fired the match with the shunt open).

Fourth, I tried the above with the ematch wire only - same results (and then I fired the match with the shunt open).

So, with the shunt closed, the ematches never fired (and I did not fry my altimeter - woohoo!).

Although I've done this before, and I expected this result, it is always good to see it work. I again recommend the combination of a shunt/short combination for two-stage flights.

Jim

Edit - Now, I'll take a look at WiFi options and see if that is something that I can incorporate into my my design. I'll report back.

IMG_1287.jpg
 
Hi Jim & Tim,

How do you Guys recommend attaching Launch Lugs on this two stage 3" rocket? Do you install two lugs on the booster with no buttons on the sustainer, or do you install rail buttons on the sustainer too? I assume that you want to use a longer launch rail than you would for a comparable 3" single stage rocket.

Do you put a tracker in the booster's interstage? I assume that the booster is being recovered with a single parachute fired off by the interstage altimeter at apogee?

The shunt sounds problematic. One of you mentioned using a RF radio to arm the sustainer motor. That sounds a whole lot safer. What equipment manufacture produces the RF arming system?

Thanks,
Bob
 
Hi Jim & Tim,

How do you Guys recommend attaching Launch Lugs on this two stage 3" rocket? Do you install two lugs on the booster with no buttons on the sustainer, or do you install rail buttons on the sustainer too? I assume that you want to use a longer launch rail than you would for a comparable 3" single stage rocket.

Do you put a tracker in the booster's interstage? I assume that the booster is being recovered with a single parachute fired off by the interstage altimeter at apogee?

The shunt sounds problematic. One of you mentioned using a RF radio to arm the sustainer motor. That sounds a whole lot safer. What equipment manufacture produces the RF arming system?

Thanks,
Bob

Eggtimer Rocketry produces wifi switches that can be used to remotely turn on an altimeter or to arm deployment charges. Cris also produces an altimeter that can be completely controlled by wifi from a smartphone, the Eggtimer Quantum, and a flight computer/GPS unit that can be controlled by RF using a handheld remote, the Eggtimer TRS. I'm planning to use the Quantum for my first foray into electronic staging in the next couple weeks. The Quantum does not have tilt sensing capability like the EasyMega, but it can lock out ignition if the rocket hasn't reached a set altitude or speed (much like the RRC3). I have everything built; I just need to get a good day to launch, so I can actually report flight data.
 
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Thanks for the information Absent Minded Professor. Good luck with your first multistage launch. I will �� up the Eggtimer Rocketry website.

All Le the best,
Bob
 
Bob I have 2 buttons on the booster and 1 on the sustainer. Longer rail definitely a plus to have. I think it's mentioned in Wildman instructions that if you put 2 on the sustainer you can fly that solo.
 
If cerving is monitoring this thread, I would LOVE to see a WIFI switch that is able to handle the short/shunting duties instead of switching the altimeter on. Basically, it becomes a 2 channel generic NO switch. The way the switch is configured now it looks like it automatically connects battery power on the one side of the switch instead of giving you the option to connect something to the other side. I could be wrong though.
 
Hi Jim & Tim,

How do you Guys recommend attaching Launch Lugs on this two stage 3" rocket? Do you install two lugs on the booster with no buttons on the sustainer, or do you install rail buttons on the sustainer too? I assume that you want to use a longer launch rail than you would for a comparable 3" single stage rocket.

Do you put a tracker in the booster's interstage? I assume that the booster is being recovered with a single parachute fired off by the interstage altimeter at apogee?

The shunt sounds problematic. One of you mentioned using a RF radio to arm the sustainer motor. That sounds a whole lot safer. What equipment manufacture produces the RF arming system?

Thanks,
Bob

For a 3" like we're discussing, I would put two buttons on the bottom maybe 18" apart and then a third button higher up or on the second stage. I have one of each. Two buttons further apart on the booster could also work with a long rail. I have those too. I don't put buttons on my high performance second stages because I don't want the drag, but on a sport flyer, no problem.

The shunt isn't problematic at all. You just build it. But it would be nice to be able to use WiFi arming. On my three-stager, I would love to not be 20' in the air next to two big motors. The biggest problem I see so far is that you need a big Lipo for the switch, and if you're electronics are not compatible with that, then a Plan B would be required. It would be much easier on a new bay than an existing one. But, I'm still going to look into it.

Jim
 
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