Lighting AT DMS with e-match

[davidshewitt]

On the Sandhawk sustainer of my LOC Terrier-Sandhawk 2-stage project, I would like to use an AeroTech DMS motor. I want to use DMS because the retention method will be friction-fit with an extra few wraps of masking tape around the end. I can't use an AeroPack or similar retainer because it will interfere with the interstage coupler.

My question is can an AT DMS be lit with an e-match? Is there a low-voltage igniter I can use with DMS?

 

[tfish]

A bare ematch will not ignite a DMS motor.
Am ematch dipped in this. http://quickburst.net/qb/procast-order-page/
Will ignite it!

Tony

 

[Steve Shannon]

Or use a Pyrodex pellet with the ematch.

 

[cerving]

Dipped ematch, and you need some kind of stick and suitable retention to keep the igniter from coming out at boost or being spit out prematurely.

 

[jimzcatz]

Or use a Pyrodex pellet with the ematch.

Pellet won't fit thru noozle of a DMS.

 

[tfish]

Pellet won't fit thru noozle of a DMS.

what's the size of pellets?

They should fit the 75 and 98mm DMS motors.

The smallest nozzle on the 75mm DMS motor is .685...and the cores will be bigger then that.

Tony

 

[jimzcatz]

Right Tony, for some reason I was thinking of the smaller motors. Thanks for pointing that out.

 

[StreuB1]

How about the OP tell us what motor he is talking about? DMS is an entire family of motors and without knowing what motor (size, propellant, and core geometry), it's not possible to give any accurate guidance.

A single e-match augmented with a sliver(s) of blue thunder propellant of a wide range of sizes can light almost any motor. If the core is large, to the point where an e-match wire is not stiff enough to support the business end of the match under acceleration. Then, there is an additional associated issue to contend with. Until we know the motor though, it's nearly impossible to provide any guidance that would be actually effective.

 

[Steve Shannon]

Pellet won't fit thru noozle of a DMS.

Some carving with a knife or razor saw might be possible, unless Pyrodex pellets are now being made of granite.

 

[jimzcatz]

No, but extremely crumbly!

 

[Johnly]

Looks like the upper stage will be a 38mm diameter DMS motor based on the LOC kit instructions.
My first suggestion would be to select reliability over performance for your first flight.
Highly catalyzed propellant in your upper stage is your friend for ease of ignition and because of the high burn-rate propellant, the nozzle throat diameter is larger than the motors in their impulse class so inserting an enhanced igniter is simplified. My suggestion would be a H283ST for all these reasons. Both Blue Thunder and Super Thunder propellants are super easy to ignite, and might even light with an e-match alone, but upper stage ignition really calls for a quick reliable ignition. In the old days, we would just use an e-match and a piece of thermolite, and that would still be a good choice should you have any in your range box or have a good friend that is willing to share. A commercial or home-made igniter dip is likely your best option based on the motor size, it works best to fold over the e-match head about a 1/2" so that more pyrogen is around the e-match head. This assumes that the folded tip will still fit through the motor nozzle.

 

[tjsnakez]

Ematch dipped in pro cast will work great.

 

[rharshberger]

Ematch dipped in pro cast will work great.

Procast among the commonly available igniter dips is unique, its performance is known and the amount of pyrogen can be tailored to the volume. There is a thread by jsdemar on BKNO3-V (Procast) that has a Excel spreadsheet for properly sizing a Procast igniter for a given motor core size.

 

[tjsnakez]

Procast among the commonly available igniter dips is unique, its performance is known and the amount of pyrogen can be tailored to the volume. There is a thread by jsdemar on BKNO3-V (Procast) that has a Excel spreadsheet for properly sizing a Procast igniter for a given motor core size.

if the motor is big enough to use pellets that’s great. Otherwise it’s a reliable ematch dip for smaller motors.

 

[rharshberger]

if the motor is big enough to use pellets that’s great. Otherwise it’s a reliable ematch dip for smaller motors.

I weigh my igniter blank and dip until it reaches the proper weight no need to cast pellets.

 

[ksaves2]

Wow! Just stumbled into this thread. If I ever try airstarts or staging, I'll get a kit. I have some Boron and KNO3 too but don't want to experiment. Just get a kit where most of the hard work and testing has been done. Made some MTV igniters but I doubt they would work for low current staging. Found some Boron on sale one time, forgot where I got it from. Kurt

 

[teepot]

I put some fine titanium sponge in my dip. They look like sparklers when they light.

 

[waltr]

I've been using DIY igniters for air starting AT RMS motors. I make them the same as standard igniters except use 40 ga Nichrome instead of 36ga. and only do 2 wraps instead of 4. Then dipped in Procast (just enough that they pass through the nozzle).
Never had a failure firing these or getting the motor to light from an Eggtimer Quantum and a 300mA-hr, 2S LiPo.

 

[Not Quite Nominal]

Depends what you're trying to light. 29mm BT and NBT DMS will light just fight off both orange ebay matches and MJG Firewires

 

[StreuB1]

I've been using DIY igniters for air starting AT RMS motors. I make them the same as standard igniters except use 40 ga Nichrome instead of 36ga. and only do 2 wraps instead of 4. Then dipped in Procast (just enough that they pass through the nozzle).
Never had a failure firing these or getting the motor to light from an Eggtimer Quantum and a 300mA-hr, 2S LiPo.

Do you solder your nichrome to the lead wires or do you just stagger the lead wires and wire wrap?

 

[waltr]

Do you solder your nichrome to the lead wires or do you just stagger the lead wires and wire wrap?

Stagger the length of leads, about 1/4-3/8in, then strip of about 3/32in of insulation. Do 5-6 turns of the Nichrome on the stripped wire then bend the wire end over and crimp onto the turns on nichrome.
Straighten the wires so they are parallel and do 2-4 turn of nichrome over the insulation of the longer lead. Again 5-6 turn on nichrome onto the stripped wire end, bend and crimp.
Last is a dip or double dip in Procast. This gets smaller and larger diameters. Then use the largest that will fit into the nozzle.
For the Q-jet motors, I use a twisted pair of 28ga wire-wrap wire instead of shooter wire (or wire pair from used eMatches).
This makes very small diameter igniters that easily fit the Q-jet nozzles.

I have made several dozen like this of different sizes for launching and never had a failure. Most were at club launch when the AT igniters failed and someone needs another igniter.

 

[davidshewitt]

Thanks for all your helpful replies! I flew the Terrier-Sandhawk on an I180W -> H100W (the DMS motor I should have mentioned). I used an MJG e-match dipped in ProCast. The H100W lit without issue! It went to 4000', but I lost the aft section of the Sandhawk when the drogue shock cord snapped (I *really* should have replaced the undersized one that came with the kit). At least I got all the electronics (EasyMini and EasyTimer) back.

 

[waltr]

Thanks for all your helpful replies! I flew the Terrier-Sandhawk on an I180W -> H100W (the DMS motor I should have mentioned). I used an MJG e-match dipped in ProCast. The H100W lit without issue! It went to 4000', but I lost the aft section of the Sandhawk when the drogue shock cord snapped (I *really* should have replaced the undersized one that came with the kit). At least I got all the electronics (EasyMini and EasyTimer) back.

Well good news, motor light but bad news, cord broke.

I either do 3 taped bundles or braid the cords to provide resistance as the rocket part come apart. This greatly reduces Shock Load to the recovery system.

 

[davidshewitt]

I've since rebuilt the lost aft section with a much better shock cord (thanks SBR for the new cord!). I flew it successfully on an I180W -> H100W last October at Brothers, and I flew it to 6400' at Pasco on a J420R -> I140W (also recovered with no significant damage).

I used the ProCast to light the Sandhawk both times and it worked.

 

[jnmiller]

On the Sandhawk sustainer of my LOC Terrier-Sandhawk 2-stage project, I would like to use an AeroTech DMS motor. I want to use DMS because the retention method will be friction-fit with an extra few wraps of masking tape around the end. I can't use an AeroPack or similar retainer because it will interfere with the interstage coupler.

My question is can an AT DMS be lit with an e-match? Is there a low-voltage igniter I can use with DMS?

Why can't you use a CTI motor and friction fit a CTI case in the sustainer? I do this in my Nike-Apache sustainer which also leaves minimal room for the interstage coupler

 

[davidshewitt]

Why can't you use a CTI motor and friction fit a CTI case in the sustainer? I do this in my Nike-Apache sustainer which also leaves minimal room for the interstage coupler

I have a CTI 38mm 4-grain case and a couple I242 reloads I could try this with. Just haven't done it yet.