APD Hopup Arm
 

Hey Guys,

I'm planning on designing a new hopup arm, because the cylindrical nubs are quite outdated so the retention system for them is as well. What sort of retention system would you guys want? I was planning on doing something like a dovetail, and I'm still trying to figure out how to make the spring attachment point at the front.

Edit: I've worked out all the foreseeable problems, and right now I'm leaning towards selling only the keyed nubs which work with my hopup arm. I'm not sure whether I want to force you guys to buy the arm, but I think that using the nubs with the stock arm would reduce performance. What do you think?

Ares has a round nub that is a figure 8. The top "o" slots into the arm and the bottom "o" presses on the rubber.

Something like that would work well with a new shape of lower fixture.

I thought about that, and it seemed sort of weak. I've drawn up what I was thinking about.

http://farm8.staticflickr.com/7150/6...4fe6f90f_b.jpg

http://farm8.staticflickr.com/7020/6...a51ca672_b.jpg

Looks fine, easy to change and captured by the chamber when installed & if you wanted you could add a grub screw to help keep it located.

you can even do a optional version with the traditional groove for the holdouts.

What you want to do is capture that spring at the front end or put a leaf spring in the rear that's in another groove so it can't pop out and vanish.

I've changed the way the spring is attached, because I wouldn't be able to machine the little cone, but It serves the same purpose. I suppose you want a way to permanently attach the spring? It might be a little easier to epoxy attaching the spring this way, but it should be relatively secure.

As to the grub screw, it is something I could add, but the main reason I'm making the arms is to work better with my nubs, but it would also help people out who want to design their own nubs, as the arm will grab the nub and won't allow it to rotate. That and if the nub needs a grub screw to hold the nub in, then I didn't do a very good job designing the pair.

I'm assuming the "traditional groove" is the normal half circle cutout? Yes, I could make them, but I'd imagine they'd rather go with a mass produced arm, since it is not a high stress part.


http://farm8.staticflickr.com/7160/6...abdb5ef9_b.jpg

That T would capture the spring nicely Something to really locate the nub would be good. If it walked sideways you'd be side hopping. A grub screw or roll pin put through back to front would nail it down.

One other thing would be the mass of the arm. I think if it was heavier it would be less likely to wander from the vibration going through it.

I suppose I'll add a grub on request, but most of these will probably be used with my nubs, which will be rubber. The upper portion of the nub will be larger than the socket, so the compression/friction will keep it in place.

I'll see what I can do about weights as well

Thought I might play around with the idea of a rotatable nub, although I don't think my nubs would use it...

http://farm8.staticflickr.com/7032/6...97b45fc0_b.jpg

The arms are $12 as of right now, but would anybody be interested in an aluminum arm for ~$25 or possibly a weighted arm for $15-18?

so if something works well for a while it's considered outdated? the only benefit i can see with your design is that it would be less likely to loose the nub when disassembling the hopup. so for like 3x the cost of a normal plastic hopup arm and nub that do the job just fine, you have solved the issue of loosing the nub. great.

sorry if it sounds like im bashing you as it's not my intension, it's just that it seems like you're over thinking and over engineering something that already works really well. if you could make something that works like a PTW hopup for AEGs, i'll take 3.

My point was that many consider cylindrical nubs to be outdated. I know it is different in Canada, but most people on ASF are moving away from cylindrical nubs, and moving on to flat extended nubs, and most of ASF are from the US. I believe that the SCS was a good start, but having a cylindrical nub leads to very short contact times (can be seen as a single line of contact), and the use of a hard plastic nub exacerbates the flaws in the bb. In addition, the short contact time/area makes it necessary for the nub to protrude further into the barrel, displacing the bb more vertically within the hopup as the bb goes by, which is another source of inconsistency within the hopup itself.

Oddly enough, losing the nub hints at a larger "problem", which is that the nub is allowed to move and rotate. This is mostly not a problem with cylindrical nubs, but with flat nubs, as the bb goes by, it creates a torque, and not securing the nub to the arm is an area which can be improved upon. I am offering nubs which are compatible with the stock hopup arm, but I do not think they will be as effective.

As to the ptw arm, I was really looking forward to the deepfire aeg ptw hopup upgrade, but apparently they cancelled it...

I think one of the classics used a long nub like that to get legendary range.

Have you thought about using some kind of "friction system" to keep the arm stable instead of having to manufacture it out of a heavier material ?
Like some kind of rubber bands in the body of the arm.

I could add some o-rings and shims, which is what I might do. I haven't fully decided on a heavier arm, so it sort of depends on the demand. I honestly prefer milling polycarb and HDPE over aluminum, but there are some advantages to having a heavier arm beyond that of o-rings and shims. My third gun analogy of the day is recoil vs the weight of the weapon, as well as thicker barrels dampening vibrations. I'd imagine you'll see more benefit as you start shooting heavier rounds.