Angled Hopup "pad": replacement for nub

[krap101]

I think we've all seen different attempts to improve the current hopup: the scs/pcs, h-nubs, g-hop, etc. I'm trying to develop a new design that will be a drop in upgrade, and will replace the nub.



Basically the idea behind this combines (sort of) of variable pitch in rifling and the g-hop modifications I've seen around. The disadvantages of g-hop is that it isn't very useful at higher rof (higher than semi) and that it is very fragile. Problems with SCS is that if not perfect, it will induce a sidespin, which will either cause stray shots or inconsistency.

I believe my "pad" will solve this. If you think back to high school/entry level college physics, there is an angular impulse and angular acceleration. A nub such as the scs tries to increase the surface area of contact in the lateral direction, while keeping contact time constant. My "pad" will have a small contact area for a larger period of time, achieving the same amount of hopup, but it should be more consistent. (versus a normal nub, it is nearly instant high frictional forces versus a more spread out lower frictional force.) I believe a smaller increasing frictional force (achieved through the angled nub arm) will be more effective than the traditional nubs.

In addition, the nub arm will flex, so as the bb runs underneath, it will be in contact for the entire period. It is designed to be a drop in addon, as opposed to the g-hop, which requires you to butcher a bucking and has a pretty short lifespan. The half-cylinder thing will sit where the nub normally sits, and the two sides will keep it steady against the arm.

I haven't made any measurements yet, but I expect to have a prototype "pad" in the next two weeks. The first few prototypes will be made of polycarbonate and HDPE, although I expect something like delrin will increase the bucking life, as the rubbing between the pad and bucking seems like it will wear harder than a normal nub.

Things that will need to be decided are thickness, material, angle, and type. The type being whether or not I'll need to make multiple versions for different ranges of fps.The main purpose of this is to increase consistency and the ability to use higher weight bb's, and is somewhat an alternative to shimming the nub.

Any critiques would be very helpful, as the design is entirely experimental, as calculating bending moments etc, is currently beyond my ability.

[Wrath144]

How do you plan on manufacturing something so small and complex?
Its a good design. I just don't see you finding a material that will suit the idea that can be machined that small.

[krap101]

Current candidates are polycarbonate and HDPE (cheaper), nylon 6/6 (medium), or glass filled nylon/polycarbonate or delrin (expensive).

I have a cnc that is rated to .001" step resolution, and I modeled this so it can be cut straight out. Currently I'm using 1/16" bits, which should be able to get the job done, and once we get a design out there, it won't be hard to build.

Currently, I don't believe strength to be too big of an issue. The weakest part of the design is the top left, where it loops around, and I can get rid of this; however, it increases the "springiness" of the "nub arm">>contact with the bb. I can reinforce areas that break, and polycarb is already pretty strong as it is.

[Danke]

Make it so it won't fall off the arm.

[krap101]

Originally Posted by Danke

Make it so it won't fall off the arm.

I added clips just for you . I don't have any measurements yet, so excuse the grossly estimated proportions . Going off the generic hopup arm, there's a hollow space above it, where the clips will go over. Beyond that, you're going to have to use epoxy or hot glue, but it shouldn't be hard to align to the arm, as you have flat surfaces with this



Hmm... there might be a problem with that part in the back not fitting into the hopup... you might end up having to glue it...

I don't have a hopup in front of me right now (dorms eek) but I'm not sure of the clearance on both sides of the arm. If there is enough space, I could give a second "clip" which will be glued on the free side and hold the pad into the arm, but I don't think we can avoid gluing...



I've decided that using a set screw is probably the easiest, non-invasive way of keeping the pad attached to the arm.

...ish...

[krap101]

Playing around with that idea. Insert a cylinder or semi-cylinder, and it will expand the "nub" and hopefully secure it to the hopup arm.

[Skladfin]

this looks really similar to Firefly nubs, but I'm not sure what the slope at the bottom is for?

[krap101]

Originally Posted by Skladfin

this looks really similar to Firefly nubs, but I'm not sure what the slope at the bottom is for?

The slope on the bottom is to "slowly" increase the friction on the bb (rather than the abrupt change in... angular momentum of the normal nubs). Once the bb begins spinning, it'll be "easier" to get the next jump, so as the bb travels through, the arm will bend, giving something (I'm assuming) near constant angular acceleration. Since the hopup action is spread out more, rather than an impulse (physics again), it should be more consistent.

I suppose it is very similar in design to the firefly nub, but I'd like to think that the improvements will justify the amount of work I'm going to put into this.

[krap101]

There seems to be some confusion about how this works, so I'll add this to all of my threads.

The cylindrical part fits into the slot where the nub normally sits, and the other flat parts on the top rest against the hopup arm. The size of this will be the same width of a bucking, but maybe 5-6 times longer, but short enough to fit into the window cut out of the barrel.

The purpose of the flat plate as opposed to a concave plate, is to reduce the chance of adding sidespin to the bb. I suppose it will be much easier to align my pad rather than a nub, so the concave idea might still work. The purpose of the SCS,PCS,H-nub, is to increase contact area to increase friction. My design uses the "normal" amount of friction, over a longer period of time to achieve the same thing. A angled, concave pad would add more hopup, but would be unnecessary until you get into ridiculous weights of bb's.

The angle on the pad makes it so the bb will *more* slowly accelerate angularly, but as it moves through, pressure will increase. In rifles, variable pitch is used to slowly increase angular acceleration, which yields a more consistent shot with less wear on the barrel. In our case, the more time the bb has with the pad, the less likely it is to slip>>greater consistency. The pad will essentially put less pressure on the bb (less friction) but over a longer period. So in physics, impulse=change in momentum=force*time. If I have 1/5 the pressure, with 5x the duration, I will achieve the same angular velocity.

I feel like I've just said the same thing over and over again, so forgive my repetitiveness.

[Mitchell12]

I believe your idea makes sense and I'd really like to see some results once your prototype it. I recommend using a quality bolt action with as consistent of an FPS as you can find.

Well that's what I'd like to see anyways

[krap101]

Originally Posted by Mitchell12

I believe your idea makes sense and I'd really like to see some results once your prototype it. I recommend using a quality bolt action with as consistent of an FPS as you can find.

Well that's what I'd like to see anyways

Well I have a fully upgraded TM vsr-10, but the hopup isn't the same (it is nubless). One of my friends offered to use his SR-25 as the test platform, so i think for now that'll be what we do. Bioval .40's will probably be the test bb.

[Mitchell12]

Excellent I look forward to it.

[krap101]

Mini-update

To everybody who thought the design was too big... you were right. Here's the newish design. The dimensions are correct. The radius of the outer circle is .1165", and it will be .1535" thick. For now, I need to get a new endmill, as the details are quite small, and to make this out of one piece of material (rather than stacking two and gluing them) I'll need a longer endmill. (trying out 2 at 35$ a piece...)

Without further ado...



The thicknesses will probably be changed, because I want the base of the half ellipse-type thing to be able to rotate. I hollowed out the half-cylinder a little bit to make this easier, and I think I need to make the "tail" a bit thicker.

[Amos]

That's still a singular point of contact, Make the part that applies friction an inverse 6mm and you may be onto something.

[krap101]

Originally Posted by Amos

That's still a singular point of contact, Make the part that applies friction an inverse 6mm and you may be onto something.

It seems like everybody wants an extended scs :P.

The single point of contact idea, is that there should be no way to cause sidespin as in an SCS; however, if I made an "inverse 6mm", and it was long enough, then I think it might actually get rid of any sidespin as it rolls through...

Yeah I think this'll work. You make something like a half cone, which terminates in a 6mm radius. The bb will be forced to the center, and I think it'll get rid of sidespin...

Alright, drawing's done. The BB goes from leftish to rightish. The bucking slopes downward, and the radius of the "concave" decreases until the end where it fits the radius of the bb.