Whee! New MadMax ROFinator!

[dontask]

you gotta love LiPo

[Tankdude]

For a cut off there is a little circuit involving a opamp and diodes, OR get a speedcontroller for a model airplane. I'm sure you can hot wire it to fire and they (most) come with a battery cut off.

If your interested in the optamp I have the parts here but lost the diagram.

[Renegade)]

That, Carl my friend, is COOL!!! Really insane lol, show us more when you replace whatever parts you fried haha.

[Kid]

Originally Posted by Renegade)

That, Carl my friend, is COOL!!! Really insane lol, show us more when you replace whatever parts you fried haha.

Show us the parts you fried, too. Maybe a macro shot to show the damage.

[MadMax]

Originally Posted by Tankdude

For a cut off there is a little circuit involving a opamp and diodes, OR get a speedcontroller for a model airplane. I'm sure you can hot wire it to fire and they (most) come with a battery cut off.

If your interested in the optamp I have the parts here but lost the diagram.

I think I can work something out with the MOSFETs. Perhaps a comparator arrangement which compares the battery output voltage stepped down through a voltage divider against the output from say a 6v regulator.

Basically when the output of the battery drops below 12v across a 50% voltage divider (6v) it drops below the 6v reference provided by a regulator output which is also fed by the battery output.

[MadMax]

Originally Posted by Kid

Show us the parts you fried, too. Maybe a macro shot to show the damage.

Not much fun really. The first 3 teeth on the piston wore off.

The burned out switch doesn't look like much. It just doesn't go continuous when it clicks.

[Renegade)]

Originally Posted by MadMax

Not much fun really. The first 3 teeth on the piston wore off.

The burned out switch doesn't look like much. It just doesn't go continuous when it clicks.

Ya... we want more video!

[MadMax]

Well, I figured out the dying piston problem today.

I mangled two more pistons before looking at the problem really hard. I found that CA makes their piston heads differently from TM. They're shorter than the usual piston head so the piston sits about 1mm too far forward. This makes for crappy pick up engagement so the first sector tooth makes a mess of the first piston tooth and subsequently prangs the 2nd and 3rd tooth.

I changed the piston head and piston and managed to fire off about 2000rnds in very long bursts before ROF dropped considerably and I was treated to the stink of burning insulator.

I think I fired the stock CA motor on a 300-500rnd (hard to tell except for the shredded zone of cardboard) burst.

I really want a SAW which doesn't even notice that's working, but I think I'm hitting the practical limits of the AEG design. Maybe I have to go to brushless motors which have the coils on the motor casing so I can remove heat with conduction. Brushed DC motors have always had the problem of heat removal. The coils on the armature can only shed heat to the air in the can so they can overheat. Maybe I can make a water cooling jacket for a brushless motor and bolt on a radiator like a water cooled Vickers gun.

I may also have a heat buildup issue in the cylinder. Air can heat up when it's compressed rapidly so I'm wondering if I could be making the cylinder really hot when firing long bursts. It's an issue with aircompressors which are on for many minutes at a time.

[takatorikku]

are you using polycarb pistons or aluminum ones? would that even make a difference?

[MadMax]

I'm trying to avoid aluminum pistons. Aluminum is not a very good material as it sheds particles pretty fast when it wears. When this starts to happen, the particles can get welded back on making a crummy galled surface which wears even faster. Also, if the piston jams, it would be strong enough to lock up the gears and stall the motor.

While Al pistons are strong on the whole (teeth don't rip off), they kill other stuff (and themselves ) with their shedded aluminum flakes.

Conversely, polycarb pistons just get torn to bits when they bind with the sector gear. They shed bits which the gears don't even notice. Up until now, the tradeoff of a consumable piston has been worthwhile in most of my AEGs as it protected more expensive components. However, if this gun eats up pistons too fast, I'll have to try a piston with a steel rack (e.g. deepfire).

At the moment, I'm more concerned with the motor heat issue. I think the current piston may last just fine, but if I can't beat the heat buildup problem in the motor I won't be able to make the gun of other peoples nightmares.

[takatorikku]

how about heatsinks? or would they not fit into the handgrip?

[MadMax]

heat sinks wouldn't work as the heat buildup is on the armature (where the coils are) which has poor contact with anything else in the motor (it's spinning). Heat sinking the can can remove heat from the magnets, but they don't heat up much. Heatsinking the brush housings might help cool the brushes a bit, but it would do nothing for the coils which are the major heat loads.

[takatorikku]

well Carl, if anyone can figure it out, better you than me. I'd prolly somehow turn the thing into miniature nuclear device...

[Lisa]

Fan? lol. not sure where you would stick it though

[MadMax]

Originally Posted by Lisa

Fan? lol. not sure where you would stick it though

I'm actually considering that. I'm thinking of shoehorning one just behind the pinion gear to improve airflow thru the motor