16 replies to this topic

[mort25]

I resently bought some rockets, one of them has 2 motor holders. I was wondering the best way to set both motors off at once?

I use the standard estes launch control box.

Thanks!

[Gillard]

For basic model rocketry there are two ways

First is to use a cluster whip, which is basically several pairs of croc clips on separate wires that join to one wire. Each pair of croc clips are wired parallel. you will need to power the clips form at least a 9V supply, but a 12V motorcycle battery is better. Anything less and you won't get both motors to ingnite at the same time or at all.

The second method is quick match. Quick Match is a BP impregnated cord inside a sleeve and comes on 500mm sections. It has a linear speed of flame propagation of 60 to 100 feet per second. That's why its called quick!

To use it, you cut suitable lengths (depending on your rocket 3 to 6 inches should be enough) and put the bare inner core inside each black powder (Estes or Quest) motor nozzle. Secure the outer wrapping (epoxy or tape) to the motor and bring the other bare end of the strands together and secure with tape. Use ONE igniter in the middle of the bundle.



Personally i go for the whip (i'm a rocketry guy and not so much pyro), but there is an initial set up fee for the 12V battery. In the long run the battery pays for itself, as you don't get many launches form 4 AA cells in an estes controller.

but alot of people swear by quick match.

[YT2095]

I wish I had known that as a kid growing up, the best I managed was the multi-stage types, double firing always ended in poor trajectory at best, or Disaster (most of the time).

[Gillard]

There is a third method -don't do it even though its the easiest.

Third method is to use two estes controllers and try and get them to light at the same time.
do not try it.
firstly one will always light first, that will launch the rocket with the second motor still attached to the second controller, if you are lucky the ignitor will fall out, if your unlucky the second motor will lit later after the rocket has pointed sideways. its dangerous and will damage you rocket.

What type of rocket is it?

If the rocket has both motors cantered towards the centre then it is much more likely to be stable if one motor fails, if the motors are side by side then you will get a asymetric lift and the rocket will arch on thrust

[mort25]

There is a third method -don't do it even though its the easiest.

Third method is to use two estes controllers and try and get them to light at the same time.
do not try it.
firstly one will always light first, that will launch the rocket with the second motor still attached to the second controller, if you are lucky the ignitor will fall out, if your unlucky the second motor will lit later after the rocket has pointed sideways. its dangerous and will damage you rocket.

What type of rocket is it?

If the rocket has both motors cantered towards the centre then it is much more likely to be stable if one motor fails, if the motors are side by side then you will get a asymetric lift and the rocket will arch on thrust

Im not sure what make it is but it says impulse down the side. The motor tubes are side by side in the center of the body! Its quite big and stands 2ft tall.

[Daedalus]

There is a third method

And a fourth - flash pan ignition. Dust a metal pan directly under the motors with BP and then put the ignitor in that - big in America where BP is not regulated (much) and quick match is

The best way though, especially when clustering lots of motors, is a single igniter and quick match - once you have the technique mastered nearly any size cluster is possible. (my biggest at the moment is 7 motors).

I find the best way is:

- Cut equal lengths of QM and strip about 1" of tube from each
- Center the tube on the QM
- Crimp the tube at one end to fit in the motor nozzle
- Insert in nozzle and hold in place with 2 strips of masking tape - one on either side of the motor up onto the QM tube and about 1/4" attached to the motor
- Insert motors into rocket
- Bring exposed ends of QM together and insert Estes igniter, tape with masking tape carefully soa s not to short or damage the igniter but ensure it is well taped in.
- Fly !!!

The key is preparing all the motors prior to inserting in the model and consistency of preparation. Trust me, I've done it before




Dave

Edited by Daedalus, 29 February 2008 - 04:39 PM.

[mort25]

Not too sure where I would get Quick Match from?

[Gillard]

Not too sure where I would get Quick Match from?

Try deepsky model shop, they charge £2 but you have to pay a courier to gat it sent, which is expensive, so its best to buy lots of motors at the same time etc

and as for the fourth method -flash pan -don't -ever.

[mort25]

Try deepsky model shop, they charge £2 but you have to pay a courier to gat it sent, which is expensive, so its best to buy lots of motors at the same time etc

and as for the fourth method -flash pan -don't -ever.

Would a local gun shop sell it?

[Gillard]

Im not sure what make it is but it says impulse down the side. The motor tubes are side by side in the center of the body! Its quite big and stands 2ft tall.

Sounds like its an Estes Industries Pro series Impulse (early 90's rocket)
recommended motors are:
D12-5 x2, D12-7 x 2, E15-6 x2, E15-8 x2

Although E15 have been replaced by E9's which have much less push than the old E15.
The reviews i've read about this rocket suggest that a pair of D12-5 are best.

If it is an estes impulse then it should be over three feet tall, make sure that you have not got a damaged rocket that has had a foot of body tube cut off - check stability before you fly.

[mort25]

Sounds like its an Estes Industries Pro series Impulse (early 90's rocket)
recommended motors are:
D12-5 x2, D12-7 x 2, E15-6 x2, E15-8 x2

Although E15 have been replaced by E9's which have much less push than the old E15.
The reviews i've read about this rocket suggest that a pair of D12-5 are best.

If it is an estes impulse then it should be over three feet tall, make sure that you have not got a damaged rocket that has had a foot of body tube cut off - check stability before you fly.

That sounds like it! It is over 3' tall now Ive been and had a good look at it! I got a load of rockets off a chap for a bargin price and just sorting them out! Im a bit new to it all so any tips would be good!

[Daedalus]

and as for the fourth method -flash pan -don't -ever.

It's big in America, personally I never would - we have better ways in the UK.

[icarus]

if you go the cluster route as you parallel more igniters together the resistance drops so more current is drawn from the firing source (battery ). Assuming the igniters have same resistance then from ohms law resistance of 2 in parallel is halved. The supplied current has to double, from kirchoffs law with multiple igniters the same amount of current flows through every igniter and total current flow is sum of branch currents. when we fire an igniter from a small dry cell or partly discharged battery the internal resistance of a small battery limits the available current .the voltage drops , so the energy heating the element of the igniter to the point where its temp results in ignition of a chemical compound is less .( energy in joules =current in amperes Xvoltage X time in seconds J=ITV ) we therefore introduce an unknown time delay of unreliable duration .dry cells especially cheap eastern ones will not reliably fire more than a couple of paralleled igniters. Rechargeable cells deliver far higher s/cct current and are a much better option . a 12v lead acid battery will fire multiple parallel igniters reliably and is especially valuable for home produced igniters . The theatrical industry fire their igniters in series !! this surprised me as once one fires the line is open cct ,Arthur Brown assures me no problem multiple series firing. Electrical firing of H E over long lines uses potentially lethal higher voltages so the firing box is designed to measure the resistance of the attached line, if it is open cct,short cct or correspondsto a human touching the terminals the box will not fire and indicates a fault condition

[Arthur Brown]

Parallel igniters can present so little resistance that any safe cable length has too much resistance to allow the igniters to fire reliably some may fire some may not. If fired with too little power an igniter can gently go open circuit without firing the match head.

Series igniters have the risk of total misfire but by careful use of tools this can be minimised. The advantage is that with 2 to 10 ohms of command wire resistance the series igniters fuse at little current and the cable doesn't limit the current ad much.

Yes good batteries help and good connections too.

In theatrical pyro most things are series wired. There is an assumption that the total circuit could have 30 ohms resistance, and still need to fire..

Theatrical pyro circuits are likely done in bell wire or 3 amp mains wire. Often even for pyro ccts are connected with bulgin 3 amp plugs, or bare wire speaker connectors, or for wire to wire IDC crimps are used . Reliability is critical. Use good kit and wire it well.

[phildunford]

The series thing is weird! It goes against everthing I know about electrics...

I can only assume that all the fuse wires get hot enough to ignite the comp before one goes open circuit.