Yet another controller idea thread + MYTHBUSTERS!!!

[worldofglenn]

Okay, I'm sure I had you all at Mythbusters

That being said, if you've ever seen Mythbusters and episodes involving rockets and/or rocket motors, you'll know that most of the time, Grant just grabs an 18V rechargable drill battery to light igniters. To me, this seems fairly ideal, as I can just pull a battery out of my drill and go. Of course, touching two wires to a battery may fall within NAR codes.....

I had always thought about building a small launch controller that would fit over the top of the battery and I was going to talk about that here. I'd flatter myself if I said that Grant and I think alike, but in a recent episode he created one! Fortunately someone posted the youtube version, because the edited version on the official website doesn't show it.

Take a look / freeze frame at 6:21 into the video...
https://www.youtube.com/watch?v=x-YxhAszYic

Is there any reason why these types of batteries may be unsuitable? I have these currently: https://www.homedepot.com/h_d1/N-5yc1vZ1xit/R-100086262/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

Grant's design looks nice and compact, complete with safety switch.

I'd like to be able to reliably launch(is there any other desire) a 4 motor cluster....

Would it be possible to power a pratt go box with these batteries?

Thanks as always!

 

[Rex R]

if you can keep the amp draw under 20amps it oughta work w/o killing the pack.

 

[scsager]

This looks like a very workable project! :clap: Attached is a screen cap from the MythBusters video.

 

[BEC]

That's actually a great idea. For that matter, a good nickel-based battery can deliver much more than 20A for a short time. It's too bad that the different drill makers have different contact configurations or a controller like that would be a great thing for a company like Pratt Hobbies to make.....

 

[Rex R]

the main problem isn't the cells...its the wiring. the intercell connectors just isn't set-up for high amp loads. plus many of the packs I've looked at don't have a high amp hr rating (which also limits the amp draw), the 3.8 amp hr Nimh cells (when they have decent wiring) are good for up to 40 amp loads (for about 5-6minutes)
rex

 

[BEC]

Agreed, the cell interconnects between the cell stacks aren't high current straps typically. But how long does it take to fire an igniter or even a cluster? If it's more than half a second something is wrong. That's a much different demand on interconnects and cells than 5-6 minutes.

I have some 20-year-old Sanyo 1200 mAh NiCds (sub-C sized) that would happily source over 100A for short periods of time with no ill effects and routinely would give 30-40A for the entire rated capacity. Current NiMHs that are the same physical size but over 3 times the rated capacity aren't that capable.....unfortunately.

In any case a launch controller that snaps on to a 12-18V drill battery should work wonderfully even for three-four motor Estes igniter clusters if the leads from the controller to the pad are of adequate gage. THAT would be the limitation, not the cell interconnects.