This is a marker concept that I first drew up back in 2003. Essentially, Thumper is a closed bolt redesign that was based on the current open bolt Shocker SFT. The important factor is that the pressure dump chamber be located in front, and the mechanism to move the bolt itself be located in rear (this constitutes the Shocker SFT). The design functions in a closed bolt manner by moving the bolt guide component to fire, then moving the bolt to reload the chamber.
The original design I planned was a dual solenoid marker, using a four-way solenoid for the bolt and a three-way for the piston to fire. I don't have my original plans for it, but I did recreate them in 2004, which looks something like this...
That particular design has some problems and flaws, but is on the right track. I toyed around with the marker design on and off for a few years until I eventually ended up with this model, which shows a more reliable and actually functional marker.
In essence, the marker functions by supplying pressure to the rear of the firing piston (through ports located in the bolt) which push the piston back and fire the ball. When the firing piston moves back, an additional set of ports located right behind the bolt's main sail o-ring are vented, which allows the bolt to be pushed back. When the bolt reaches the rear position, a new ball will load, then the solenoid switches and pushes the bolt/firing piston combination forward again.
These animations show the operation correctly except for one small problem, I ended up adding an internal o-ring down inside the fire piston which prevents the rear of the bolt sail from becomming repressurized when the bolt opens. When this happens (as in the animations) the bolt would get pushed closed regardless of the solenoid switching, which wouldn't work.
This design works okay but it has some issues. I won't go into all of them here but suffice it to say I begun working on a new version, which looks like this...
It works a little different than the earlier version. This model uses a three-way solenoid instead of a four-way, and the firing piston is unbalanced so it moves itself when the solenoid energizes (vents). The general principal is the same but the implimentation and parts arrangement is very different.
The design has one quirk that I can't drop due to the perplexity of the design. As long as the marker is to use a three-way solenoid, it needs to use a bolt that is provided with continuous LP air to open it. Normally this wouldn't be an issue, however due to the diameters Thumper uses, it needs to utilize an LPR for this air so less force is excerted. The problem here is an LPR acts as a one-way valve in this application, so it would only work for a few shots before pressure would amass and prevent the bolt from moving. To counter this I would have to integrate a bleed valve (or possibly something more modern like a small solenoid vent) to ensure the LP air supply stays at the same levels without compressing and rising up.
The Bottomline
I discussed the above quirk and some others by posting a general thoughts thread on the Tinkering Tech forum, which can be found here. The thread has a more detailed explaniation of the function and parts.
The bottomline to this design is that even though it's very creative and totally unseen in the industry, I doubt I'll ever actually make it. I would like to make it, but since it will have a limited rate of fire, I'd rather spend time and money on other projects. For that reason I decided to post some of the intellectual property here and on the forums.