Any interest in a new micro electronic bomb drop product?

[chris@morsetec]

I have a scratch-built parkflyer P-51 Mustang and I was looking for a way to add an external fun-scale bomb drop. Something like this (http://hobby-lobby.com/atricks.htm - 2nd from bottom) but sized for a parkflyer. I did a few google searches and couldn't find anything related... a couple of plans for various concepts but nothing that looked authentic.

So, I got to thinking and I believe I've come up with a way to build a micro sized bomb drop that could be electronically activated and very lightweight. My current prototype can easily hold a 20 gram payload yet each release mechanism weighs about 0.5g. I haven't built the electronics yet but my guesstimate total is under 5g giving a total weight of under 7g for a 4 bay system.

The way I'm thinking this would work is you would build the releases into your model's pylons and use tiny magnets on your bombs. The release would repel the magnet using a tiny electromagnet. I think this could allow us to build some pretty realistic looking pylons without all the heavy mechanics used on the larger models (but this should scale up as well).

Now, my questions are:
1) is there a micro bomb drop system already out there that I've missed?
2) if not, is there any interest in something like this?

I'm making this a poll to gauge interest. If there's enough I'll try and build it, otherwise it'll probably remain a cocktail napkin...

[BushmanLA]

I got a bomb drop module for a Hobbyzone Firebird Freedom.

They use a similar method but they use an electromagnet to hold a small clasp in place that in turn holds the bomb in place. When you activate it, it releases the magnet.

The downside is that is always drawing a little current.

Here is the product link.
http://secure.hobbyzone.com/catalog/HZ/fierbirdfreedom/fierbirdfreedom_parts/HBZ6023.html

The little orange blob you see is the magnet, its hard to make out but it is connected to two elastic bands that attack to the other side of the basket.

[chris@morsetec]

Ok, so it seems there is some interest. I am currently (re)building my stick & wing park flyer and will use that as a test bed for the project.

I'm currently plan a fully open source & hardware project and if the interest continues I'll try to make a kit. I'm expecting the parts count to be quite low.

[Tomapowa]

Just curious what micro you plan to use... ?

Also, have you tested/proved this idea of repelling a strong permanent magnet with an electro-magnet? (curious if this idea will work with heavier payloads...)

[chris@morsetec]

my test platform will be a 24-30" custom built stick and wing but my ultimate plans are for my Guillow's 17" P-51D Mustang. I plan to replicate the twin 1000lb bombs.

I have done some basic tests... I have a 0.9g coil that is easily carrying 20g of weight yet is able to authoritatively release it. The 2 key variables I've found is the size of the magnet (obviously) and the voltage through the coil. I haven't worked out the driver circuit yet (using a AA holder now for testing) but I am planning to build something with a voltage boost into a storage cap that will be slow charged from the main battery (somewhere between 0.1 - 1 sec) and a power transistor to dump the charge through the coil. The basic idea being to build up a large enough charge to get good current through the coil but still protect the rest of the electronics from voltage or current spikes.

Using a tinyAVR or similar uC would allow for programmable release sequences (sequential, pairs, alternating, etc.) and decoding the servo channel. All-in-all, I think it will be quite simple it's just a matter of some testing and to keep the weight down.

My back-of-a-cocktail-napkin math says that a 1000lb bomb scaled down to a 17" would be around 13g so my current rig is plenty powerful enough but the good thing is that once the driver circuit is built that changing the scale of the release only requires scaling up the electromagnet (more turns) and the permanent magnet.

One thing I have found with the current prototype is that the amount of material separating the iron core of the electromagnet from the permanent magnet is kind of sensitive. Too little and it can't release, too much and there's not much holding power. I am hoping that the driver circuit will allow me to get enough power out of the electromagnet that this will be less of a problem. The good news here is that the biggest problem with high power electromagnets is cooling and since this will be a very short duration pulse heat won't be an issue.

What are your thoughts?

[BushmanLA]

The higher the voltage you can put across that coil at your ejection command the better off you will be.

You could setup a charge pump circuit and get it to 20 or 30 volts or even more you'd pop that magnet away with quite a bit of authority.

[chris@morsetec]

I was thinking along the same lines. However, I would really like to make it configurable. I think the ability to change the release sequences as well as tuning the power is important. From my testing I found it was a balance between the size & strength of the permanent, the gap between, and the voltage across the coil. Using the uC make varing the power easy enough to do but I don't have any good ideas about the programming interface. I'm afraid USB is too much overhead for me to develop, on-board switches/jumpers are too heavy, and a programming card could be too expensive. The only thing left I can think of is a complicated sequence of programming commands through the radio which I don't think is very popular. Do you have ideas about that?

Also, have you built a charge-pump before? I know about them and I think Dallas/Maxim has an IC for it but I haven't actually built one before...

[K9000wner]

I was toying with just pulling a bit of metal away from the bomb/droptanks
(with rare earth magnets ) away in a shearing motion (makes for easy release)
and using a 5g servo and small wire in a pulling only motion
may need some Manuel fiddlin to reset..but looks good otherwise.
just fyi