Help on selecting a first two stage high power rocket kit

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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

Sounds good. Only thing about smaller lipos is if one is stuck on a pad with a delay and the ignition device is armed, on one hand if it's not remotely activated one might get anxious if the launch is delayed. If the staging/ignition device can be remotely activated, then one doesn't have to be as concerned about a delay. Remotely activate, confirm it's armed and reconfirmed the flight/deployment are still good to go and launch. The larger projects I see folks flying, onboard room is not as likely to be a premium
so adequate battery capacity for the flight/deployment devices can be a plus for long waits. I think remote activation is where we're headed and when it has fully arrived I think the risk factor will drop even further. I'm sure the folks who've stood next to
a very large rocket to arm the ignition electronics would enjoy the peace of mind of being able to put some distance between them and the project on the pad. Kurt
 
Sounds good. Only thing about smaller lipos is if one is stuck on a pad with a delay and the ignition device is armed, on one hand if it's not remotely activated one might get anxious if the launch is delayed.

With the EasyMega, you can use two batteries. A small pyro battery is not a problem.

If the staging/ignition device can be remotely activated, then one doesn't have to be as concerned about a delay. Remotely activate, confirm it's armed and reconfirmed the flight/deployment are still good to go and launch.

The Egg WiFi uses the altimeter battery to power the WiFi and battery consumption is high. Workable, but a good-size lipo is best.

The larger projects I see folks flying, onboard room is not as likely to be a premium
so adequate battery capacity for the flight/deployment devices can be a plus for long waits.

On my three-stager, I would need to use WiFi in two locations. Neither bay has room for much more than a couple of postage stamps. I suspect it is a lot easier to design around the WiFi than to retrofit it. But, we'll see.

I think remote activation is where we're headed and when it has fully arrived I think the risk factor will drop even further. I'm sure the folks who've stood next to
a very large rocket to arm the ignition electronics would enjoy the peace of mind of being able to put some distance between them and the project on the pad. Kurt

I hope you're right. I would like nothing more than to stay at ground level.

Jim
 
Gentlemen:

Vern Knowles from Multitronics informs me that his new altimeter / stager will have the ability to radio control arm the sustainer ignition system. This unit will Bluetooth connect to his Kate GPS Tracker / Telemetry unit. You will be able to receive live status reports on your staging device on Vern's Kate handset unit.

Bob
 
Jim & Tim,

You Gentlemen agree that the two stage booster needs substantial thrust. How much over the 5 to 1 thrust to rocket weight ratio do you like to go when selecting a booster motor?
 
Far be it for me to contribute to the conversation among rocketry Gods, and...

There is an extensive thread about thrust to weight running now:
https://www.rocketryforum.com/showt...to-Weight-amp-Getting-Off-The-Pad-Calculation

Suffice it to say, initial thrust to weight is different from average thrust.

Isn't it about getting the stack moving sufficiently quickly off the pad/tower/launchrail so that the fins can operate effectively.?

Then about securing the velocity you need to achieve certain other flight parameters? E.g. Jim has written about slowing down to 700 ft/s somewhere for one flight - in preparation for separation and staging.

Good luck
 
Vern Knowles from Multitronics informs me that his new altimeter / stager will have the ability to radio control arm the sustainer ignition system. This unit will Bluetooth connect to his Kate GPS Tracker / Telemetry unit. You will be able to receive live status reports on your staging device on Vern's Kate handset unit.
Bob

I should probably correct this statement. The new deployment module and staging controller do indeed connect wirelessly with the Kate transmitter in the nosecone but not via Bluetooth. They use the existing 900 MHz RF link. This allows for live status information to be sent to the ground. It also allows for commands from the ground to be sent to the deployment module or staging controller. For example, it is possible to send manual deployment commands. Some pre-release advanced information is available at this link.
 
Sorry I got the Bluetooth connection to the Kate part wrong Vern. At any rate I cannot wait for your altimeter / stager to be available. Being able to give commands safely from the ground to the rocket is really cool. Everyone at the launches loves hearing your Kate unit talk to the crowd over the launch PA system in realtime.

All the best,
Bob
 
Hi Everyone,

I want to thank everyone whom has responded to this thread with helpful advice. I bit the bullet today and ordered a 3" Wildman two stage kit today from Tim.

Thanks for for all of the help,
Bob
 
Hi Everyone,

I want to thank everyone whom has responded to this thread with helpful advice. I bit the bullet today and ordered a 3" Wildman two stage kit today from Tim.

Thanks for for all of the help,
Bob

I have to ask... Because I'm nosy like that... Did you get extra parts to make it zipperless? LoL! No need to answer.
Good choice. Looking forward to the build thread that you're now obligated to do...... ;-)
 
I have to ask... Because I'm nosy like that... Did you get extra parts to make it zipperless? LoL! No need to answer.
Good choice. Looking forward to the build thread that you're now obligated to do...... ;-)

I'm sure that Tim will extend the kit warranty for any of my suggestions. Tim......Tim.....?

Ditto on the build thread. Bob, two stagers are fun. Enjoy.

Jim

PS - I have a WiFi winging it's way in my direction. In discussing this with Cris, my carbon fiber tubes are going to be an issue. They are probably thicker than what has been tested in the past, and it may not work. But I'll try it and see (and keep my fingers crossed).
 
Jim,

Thanks for all of the advice. I will keep you informed as the build progresses. I am sure that I will be hitting you up for more advice when the avionics are being setup.

Enjoy the rest of the summer. My Level 3 flight is scheduled for October. Realistically that means this two stage won't fly until April. Vern's staging computer isn't even available till the fall. I will be starting the build as soon as Tim mails out the kit.

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

My preferred method of mounting motors is to use the Aeropack -style minimum diameter mount that holds the motor at the top end. I position that inside the rocket to accept the largest motor that can be fitted in that size. For shorter motors an extension rod (has to be strong enough to not buckle under the thrust) is used to fill the shortfall between the motor and the mount at the top. I also usually work it out so that all the thrust is taken to the rocket at the top mount, and what most people call a "thrust plate" takes no thrust. A small gap between the thrust plate and motor at the aft end helps with that, and if the front motor mount does give a little then the thrust plate will take up the thrust. For me that keeps more of the fincan in tension, rather than compression, which is where composites work better. It keeps the natural frequencies of the assembly a bit higher too.

You can also change the amount of overhang (if you are doing a two-stage) by changing the spacer, or tuck the motor back into the sustainer for solo flights. That's what I am doing on my Nike Apache.
 
For shorter motors an extension rod (has to be strong enough to not buckle under the thrust) is used to fill the shortfall between the motor and the mount at the top.

I always thought pushing on the forward closure was a no-no?

Jim
 
I do it all the time. I make sure the front mount is strong enough to be able to transfer the thrust to the airframe.

What is the rationale for not doing it?

Well, I guess the idea is that the thrust would be being carried by the liner. It sounds like in your case that if the closure moved much, you would hit the thrust plate?

Jim
 
It sounds like in your case that if the closure moved much, you would hit the thrust plate?

That is always Plan B. Never happened yet.

I suspect the thrust is carried by the liner anyway. Given the nozzle is slid into the CTI casing, the internal pressure will be pressing it rearwards, and thrust will be balancing back against that. I don't think it is a problem. I'll think about it a bit more...
 
That is always Plan B. Never happened yet.

I suspect the thrust is carried by the liner anyway. Given the nozzle is slid into the CTI casing, the internal pressure will be pressing it rearwards, and thrust will be balancing back against that. I don't think it is a problem. I'll think about it a bit more...

I suspect you're right although maybe the liner never sees any force. I think I've heard not to do this dozens of times. Oh, well....

Jim
 
Jim,

Do you vent the interstage coupler on the sustainer side? Do you always use a black powder separation charge, or do you sometimes just use drag separation?

Bob
 
Jim,

Do you vent the interstage coupler on the sustainer side? Do you always use a black powder separation charge, or do you sometimes just use drag separation?

Bob

I don't vent there because I always use a separation charge. Most of the time, the separation force is pretty minimal one way or the other. I use a charge to separate when I want it to happen.

Jim
 
Hi Jim,

Do you use the CTI igniters that are supplied with the motors on the sustainer? I would imagine that they require a lot more current to trigger than a standard match. What battery are you using for ignition of the sustainer motor?

Bob
 
Hi Jim,

Do you use the CTI igniters that are supplied with the motors on the sustainer? I would imagine that they require a lot more current to trigger than a standard match. What battery are you using for ignition of the sustainer motor?

Bob

As far as I know, the CTI igniters are low current ematches, although the style of some of them seems a little different. Some are dipped and some are not, depending on the motor. While there would be no issue using them, I typically dip my own if something more than a bare match is needed because sometimes the coating on the match is damaged. If just a bare match, no problem, although always check the impedance before using any match.

Jim
 
Hi Jim,

Could you please explain how you are testing for impedance? I have just been testing ematches for continuity. I check batteries for voltage. Are you dipping the factory's ematches or a different ematches? What product are you using for the dipping?

By the way, I was looking at some of your active stabilation videos. Quite impressive.

All the best,
Bob
 
Simply means measuring the resistance of each e-match with an Ohm meter. Typical ematches are about 1.2-1.6 ohms.
 
Hi Jim,

Could you please explain how you are testing for impedance? I have just been testing ematches for continuity. I check batteries for voltage. Are you dipping the factory's ematches or a different ematches? What product are you using for the dipping?

By the way, I was looking at some of your active stabilation videos. Quite impressive.

All the best,
Bob

I just use a volt/ohm meter, looking for nominally 1.2 ohms. I've used maybe a thousand of them and only found a handful that didn't "pass", but I still check each one I use.

I use the factory matches for lighting motors on the ground or testing. I use J-teks for staging and deployment. For dipping, I really like the magnablend stuff from PML.

I'm sure my next stabilization flight will be perfect!

Jim
 
Thanks Tim & Jim,

Is it possible that an ematch could pass a continuity test but fail an impedance test? What ohm reading would you expect on bad ematches?

Bob
 
Thanks Tim & Jim,

Is it possible that an ematch could pass a continuity test but fail an impedance test? What ohm reading would you expect on bad ematches?

Bob

I've had two ematches that failed to ignite but which passed the altimeter's continuity test, even after the flight. That was years ago and they were both Oxrals. I'm sorry I didn't measure the impedance but it must have been higher than specs.
 
I got a bad batch of igniters once from Quick Burst. Since it was used only for single stage ignition I didn't check impedance. At the pad I got a continuity beep but when it didn't ignite I checked that one & the rest of the batch that I bought when I got home. If I remember, I found a few with 300+ ohms resistance. But anything I use for for staging & deployment gets checked beforehand and if it's not in the 1.2 ohm range I toss it.
 
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