Falcon 9/ Heavy 1:65 Scale cluster plan check

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I was inspired by PieroAcme’s Soyuz 1/25 build to take my Falcon 9 Crew Dragon and Falcon Heavy builds from 1:90 to 1:65 scale which would use BT-70 tubes for the core body tubes.

Wow! 20 motors in the 1st stage! PieroAcme’s build really got me thinking about what a BT-70 based model would look like.

How many motors can a BT-70 tube hold? Then I realized I could cluster 8 Estes 13mm A10-3T motors around an 18mm or 24mm center motor. So I'm looking for a plan check as I scale up to 1:65.

Battery
1000A jump starter battery pack.

Project box
LeMotech ABS Plastic Electrical Project Case Power Junction Box

Relay
EHDIS Car Relay 4 Pin 12v 40amp Spst Model No.: JD2912-1H-12VDC 40A 14VDC
Will it work to have three relays operate in parallel if I try to cluster 27 motors?

Igniter
Estes 002303 – STARTECH™ STARTERS
With Quickburst Quick Dip

Clip whip
Homemade (no pictures, sorry)

Binding Posts
QMseller 10 Pcs Terminal Binding Post M6 Threaded Diameter JR2068

Launch Controller
Pratt Hobies “Go Box”

Rail buttons
https://www.apogeerockets.com/Building_Supplies/Rail_Buttons/1in_1010_Rail_Button_Standard

Source material: John E. McCoy’s “Black Powder Forever! The Art of Clustering Black Powder Motors”.

Here's my 1:64 cluster engine mount

 

[Switch]

This turned out to be way harder than I expected. The housing of the rocket motors takes up all of the free space between the BT-70 tube and the center motor. Fitting retainer clips was also difficult.



But end the end I was able to get it all to fit inside the BT-70 tube.



This was my first print. The depth of the E-motor needs to be adjusted. And there are some other minor details to work out.

 

[zog139]

Hope this works well and you get video. I knew John quite well for years. His cluster stuff worked great on my own uses over the years.

 

[Switch]

I just realized I missed at least one thing. I've been scaling this up on the assumption that I'd use the same 3/8" launch rod that I'm using for my BT-60 based Falcon Heavy and and BT-70 based Delta IV Heavy. Am I going to need a launch rail at some point?

My plan was to make this Falcon 9 easily convertible into a Falcon Heavy with most of the parts being interchangeable. The 1:90 scale Falcon Heavy weighs in at 520g without motors. So the 1:65 version is looking to weigh in at 700g...

 

[bad_idea]

Cool project!

I added rail buttons to my 7x18mm BT-70 cluster, and after watching the rocket launch on my 48" 1/4" rod, I'm glad I did. 1/4" is IMO squirrely on a rocket of that size, and if you launch on it, you might consider a short rod for less whip if you have the thrust-to-weight to get away with it. 3/8" I wouldn't even consider.

I was launching in a park with a D-impulse limit so had a slow takeoff on A motors and needed all the rod length I could get. I may not ever try 1/4" again, since the park is now closed for launches until the spring, by which time I can probably cobble together a railed pad, and both my local clubs have rails for the mid-power pads.

 

[bad_idea]

BTW, the plugged A10-PT is available again if you don't want to deal with ejection gases from your exterior ring of motors. I laid in a supply of them for a mixed cluster I'm working on which will use either 6 or 8 13mms around a larger core.

 

[Switch]

Do I have the wiring diagram correct?

 

[Switch]

So here's the relay box. I only need one relay for my current builds. But I thought I'd build it out for a Falcon Heavy with 9 motors in each core, which would require 3 relays to handle the total amperage. The relay on the bottom drives the other three relays. This gives 40A per relay which should be enough to light 27 motors.


Basically the car jump start battery and Go Box get connected on the end and the rocket igniters (up to three) get connected on the side.

 

[bad_idea]

Looking good! What cables will you be using?

 

[Switch]

So because I'm stupid, I realized when I started to test this configuration that I don't need 4 relays. And I can use the same battery source for both the ignition power and igniter switch. So here is a much simplified box that actually works.




In the photo above, the car jump-starter battery pack connects on the left + and - terminals and a simple switch connects to the right + and - terminals. The "Go Box" I was planning to use does not work and I don't care. All I need to do is close the circuit on the right + and - connectors to activate the relays.


And, in the meantime, I've got a draft version of the Falcon 9 Crew Dragon at 1:65 scale almost ready to fly.



Right now, I'm working against a deadline of 11/19/21 to have everything "flight ready" . Lots of challenges still to face on this build.

 

[Switch]

Well here it is:



That's 6 of the A10-OT engines igniting without the center E12-0 Engines and hence the belly flop.

Two of the landing legs broke, but more important was a fracture in the main engine assembly. So I'm working on fixes for the next launch opportunity....

 

[Dipstick]

Well here it is:



That's 6 of the A10-OT engines igniting without the center E12-0 Engines and hence the belly flop.

Two of the landing legs broke, but more important was a fracture in the main engine assembly. So I'm working on fixes for the next launch opportunity....

Nice try! How did you ignite the cluster?

 

[Switch]

Nice try! How did you ignite the cluster?

I'm glad you asked and I forgot to included that detail. I tried 1st with igniters on all 9 motors using a relay and a parallel igniter lead configuration. It should have worked perfectly, I tested continuity on every igniter. But only two A10-OT motors lit. I didn't bother to post that (failed) launch. My 2nd attempt was using one electrical infighter and quick fuse to the 6 remaining A10-OT motors and center E12 motor. If I had used tape to the E12 motor fuse like I did with the A10-OT motors, I'm 100% positive it would have worked. This is literally my 5th attempt at a cluster launch, so I'm sure I have much to learn still...

On a positive note, as I watch the belly flop, I realize the aerodynamics look good..

 

[Dipstick]

I'm glad you asked and I forgot to included that detail. I tried 1st with igniters on all 9 motors using a relay and a parallel igniter lead configuration. It should have worked perfectly, I tested continuity on every igniter. But only two A10-OT motors lit. I didn't bother to post that (failed) launch. My 2nd attempt was using one electrical infighter and quick fuse to the 6 remaining A10-OT motors and center E12 motor. If I had used tape to the E12 motor fuse like I did with the A10-OT motors, I'm 100% positive it would have worked. This is literally my 5th attempt at a cluster launch, so I'm sure I have much to learn still...

On a positive note, as I watch the belly flop, I realize the aerodynamics look good..

Might be worth going to flash in the pan method. There must be a different ignite time between mini A and E motors.

 

[kramer714]

Flash pan is way better!

 

[bguffer]

turn rocket upside down, insert igniters into motor nozzles, pour bit of black powder into each motor nozzle, tape over each motor nozzle so that powder and igniters cannot fallout.

Worked on a 3xcluster of Apogee F10 motors.

 

[Dugway]

I have no trouble getting all seven motors going simultaneously on my NCR Cluster Ducks and upscales, with both black powder and composite motors. Just build one of Boris's cluster boxes (https://bpasa.com/Cluster-box.htm), use a big LiPo battery with fat wires running to beefy clips, use MJG igniters, black powder or composite as appropriate. Never had a motor not go.

 

[DaHabes]

I'm glad you asked and I forgot to included that detail. I tried 1st with igniters on all 9 motors using a relay and a parallel igniter lead configuration. It should have worked perfectly, I tested continuity on every igniter. But only two A10-OT motors lit. I didn't bother to post that (failed) launch. My 2nd attempt was using one electrical infighter and quick fuse to the 6 remaining A10-OT motors and center E12 motor. If I had used tape to the E12 motor fuse like I did with the A10-OT motors, I'm 100% positive it would have worked. This is literally my 5th attempt at a cluster launch, so I'm sure I have much to learn still...

On a positive note, as I watch the belly flop, I realize the aerodynamics look good..

If you are using stock Estes igniters, enhance them by dipping in Testor's aluminum paint. If you really want to enhance them, dip the wet aluminum in a tiny bit of black powder. Instantaneous ignition.

As for power, I built my own 12V relay system. I find clip whips a pain to build, so I built a breakout box, one lead in from the relay box, seven leads out, parallel design (14 GA). That's how I launch my Cluster Duck. If I only have four engines (or less) I skip the breakout box and use the relay, which has four outputs. No need for LiPos, a 12V SLA battery provides plenty of juice.

 

[Switch]

I think I never followed up on this post. I used the following igniter configuration:



and I have successfully ignited all 9 motors twice:

Here's one launch:

But now I have a related question. I'm working on this project: Falcon Heavy 1:65 scale

and I want to design a circuit that has an led indicator for continuity on each motor. 27 motors is just too many to check continuity on the launch pad...

And I don't know if my jump starter battery has enough power to ignite 24+ igniters.

This is what I'm trying to ignite:



So how do I wire LED lights for continuity? What kind of connectors can I use for so many igniters? and how many Amps do I need on the battery? I'm looking at connectors like this:

Amazon.com: uxcell 20Pcs 300V 25A 10mm Pitch Pluggable Type 2-Position PCB Mounting Plastic Screw Terminal Block Connector Black for 22-12AWG : Industrial & Scientific

Amazon.com: uxcell 20Pcs 300V 25A 10mm Pitch Pluggable Type 2-Position PCB Mounting Plastic Screw Terminal Block Connector Black for 22-12AWG : Industrial & Scientific

smile.amazon.com

What I envision is an ignition platform that holds all of the igniters and gets mounted on the launch rod with the rocket, so that everything is wired and ready to fly just by attaching two battery leads.

 

[waltr]

A jump starter battery should be able to output several hundred Amps. So should be no issue with available current.
This however, I produces a Voltage Drop of wiring (I * Rwire = Vdrop). Use a Relay launch system that has the battery close to the pad and use heavy gauge wire up to the igniter pig-tails.

Continuity indicator of each igniter would be fairly complex. That requires a circuit for each igniter which also means separate leads to each igniter.

Your photo of igniters inserted and wired seems odd.
You have 3 motors at the bottom in series then the top 5 motors in series. Then the top 5 in parallel with the bottom 3 in parallel with the central motor. I would think you would do top 4 and bottom 4 in doing the series/parallel combination.
If the battery Voltage is high enough and available current (Battery and heavy wiring) high enough then this should work as you have already proven.

Typical clustering is usually with all igniters wired in parallel. Series can work but if one igniter opens, breaks connection, before the others in that series gets hot then multiple motors can fail to ignite.
Tradeoffs....

 

[Switch]

On the Falcon 9 with the 9 motors shown above, my clip whips only had 4 leads on each whip, which is why the center motor was wired in that way.

With the new design, I'm going to wire each igniter separately into a screw terminal, so I can build what ever circuit I need.

I have three weeks to figure this out before my next launch opportunity.

 

[Switch]

OK, time for some remedial education...

Background reading

https://estesrockets.com/wp-content/uploads/Educator/2811_Estes_Model_Rocket_Launch_Systems.pdf

While I've found more complicated circuits, the basic idea is simple enough. Provide enough current to light an LED but not ignite the igniter.


And how to use the breadboard that came with my Raspberry Pi that I never needed:


My relay box (the original point of this post) is configured with three relays so I can power the Falcon Heavy core and two boosters separately with 9 igniters on each relay with the full power of the car jump-start battery. So I can configure three separate breadboards (one tied to each relay). But can the breadboards handle the current of ignition? If so, the circuit would be pretty straightforward.

Nothing is easy:




So I can use the bread board for proof of concept only...

 

[Switch]

So I spent some time on the breadboard this morning. Basically, I learned that the current required to light a decent 12V LED bulb doesn't ignite an Estes igniter when wired in series.


So I could make a circuit that isolates each igniter to check continuity, and then joins every igniter to a common power source for ignition:

The NC connector on each relay would allow the default path for power to the igniters from the Launch Controller & the continuity tester would only be active on the NO circuit.

 

[Switch]

Tonight I figured out how to use a 12V 8 Channel Relay Module



with 27 motors on the Falcon Heavy, I'll need 4 of these for a total of 32 relays.

 

[RocketScientistAustralia]

So a relay is a mechanical object operated by an electrical signal. However it can be operated purely mechanically by dropping the relay in the worst possible orientation. Or , as did happen, have your box of relays fall on the ground....

You can mitigate against that possibility by having a second relay in a different mechanical orientation.
I've actually seen this happen so it's not hypothetical.

 

[RocketScientistAustralia]

The single relay carries all the current and your firing relays carry the unique current..

 

[Switch]

The single relay carries all the current and your firing relays carry the unique current..

I had an "ah ha!" moment on the breadboard last night & realized I had the whole thing (above) wrong. My circuit should look more like the following. Although I may have more than one battery in the actual setup.


Basically this is what I actually built for my previous 3-relay project. What changes with this build is the continuity check LED light and the fact that I'm jumping from 9 motors to 27.

 

[Switch]

So a relay is a mechanical object operated by an electrical signal. However it can be operated purely mechanically by dropping the relay in the worst possible orientation. Or , as did happen, have your box of relays fall on the ground....
View attachment 517149
You can mitigate against that possibility by having a second relay in a different mechanical orientation.
I've actually seen this happen so it's not hypothetical.

That is a really good point. I was thinking about how to arrange the relays & will run them anti parallel. Also maybe plan to not move the relay box once it is connected to the battery.

 

[RocketScientistAustralia]

With all your igniters in parallel, your continuity light is not going to provide much useful info other than at least 1 igniter is connected.
Your diagram works if all your bits are at the firing position and you run cables to the launch position.
If the relay box is at the launch position, the safety switch becomes a relay in opposite mechanical orientation to the firing relays.
You have a safety switch at the firing position to arm that relay. Put a superbright 8or10mm LED on the remote to indicate when it's powered.

 

[Switch]

Each igniter and each LED is going to be on its own relay. The diagram above shows only one relay and LED but there will be 32 relays with 32 separate igniters/LEDs in total. Actually, I will only need 27 relays for the Falcon Heavy's 27 motors. But since I have some extra relays I'm going to use 1 for each relay block directly to an LED to indicate if that relay block was activated during ignition. So, I'll be using 31 of the 32 relays. Using the above schematic, I've successfully bench tested 4 igniters/LEDs in parallel (including firing the igniters). Each LED only indicates continuity of igniter that closes its circuit back to ground.

This photo shows the strong back used for transportation and sliding the rocket on to the launch rail. The strong back then gets removed leaving only a metal plate that attaches to the launch rod and supports the core motor and the screw posts binding blocks. Each igniter gets its own screw post mounts. And each igniter's positive lead goes back to a relay. With 56 positive leads plus a grounding wire, I call this "the clip whip from hell".



Each igniter's positive wire is attached to one of the wires in a motherboard power cable that I cut in half. Each igniters ground will be on a separate 18AWG wire.

Here is the LED display board:


It is 1/4" ABS plastic that I had laying around. The LEDs will be wired to the corresponding igniter on the rocket for faster troubleshooting.

I had to use a hot glue gun to secure the LEDs so it made a bit of a mess



But nobody is going to see the ugly part, just the dashboard...


The LED's a way brighter than I expected

Today I started soldering the screw posts to the motherboard cable. I learned that I don't know how to solder PCB boards. I'm only about 1/3 done with soldering.

Here's the layout of the boards in the project box