Army R85 Semi Auto Firing Problem

[BigEd]

That is a very interesting setup, glad you worked it out.

 

I know there is not enough room in most guns for an auto relay, but here is a wiring diagram for a $5 mosfet, with active braking.

I put them in most support guns that have room. Just wanted to share the info.

 

///ed///

[Docv400]

That is a very interesting setup, glad you worked it out...

Well, I did, then it started doing it again, now it's OK again .

Before I took it apart for the last pictures, it was working beautifully, pre-cocking every time, reliable as you like.

Then while it was apart for the pics, I stuck the battery (Vapex 8.4V 2200mAh) on charge so it was fully charged for the owner to use at a game today.

Put it back together with the freshly charged pack and it started the pre-cock-then-two-round-burst nonsense again, which settled down after a few dozen shots to a reliable 'normal' AEG-type semi function (i.e. no pre-cocking).

I whipped out one of my 7.2V packs (2700mAh), plugged it in, and hey-presto, perfect pre-cocking action restored.

Which is what the owner will probably go for now, using a 7.2V pack, as he's not a ROF junkie, and with the 8.4v pack it spins over too fast for his liking.

 

So, in a nutshell, it can be sorted, but it takes a fair amount of 'fiddling' to get it pre-cocking reliably, particularly if anything has been done to it's electrical circuit upgrade-wise.

 

I like the relay option BigEd, I've seen that mentioned in another topic for the same application (was that you? )

You're just replacing one set of mechanical contacts with another of course (better quality I grant you), but the advantages are that they are cheap and easy to replace once they do start to deteriorate.

That's passive braking though, not active.

Active braking puts a reverse current to the motor momentarily to stop it, whereas passive braking just connects the +ve & -ve terminals of the motor together when the trigger is released (as in the L85), there is no electrical input to it.

In your diagram, the trigger is released (contacts 'open'), and the positive circuit from the battery ends at the 87 contact in the relay.

The motor +ve & -ve are joined by the closed circuit through the relay (30 - 87A) and via the battery -ve terminal.