R/C Combat Vehicles

Modification of a GTVe Paintball Marker

by Steve Tyng

During the Battle for Middle Maryland, the gun installed in my tank was a constant source of irritation. The gun continually refused to re-cock and I missed out on a lot of action while I was troubleshooting the marker. After that first weekend I decided that a gun upgrade was in order. My mixer (an Anvilus prototype) has two auxiliary control ports that can be used to switch electronic circuits on and off. The thought was that it would be a simple matter of interfacing an electronic marker to the mixer. This would remove a servo from the equation and give me a higher rate of fire ? an advantage on the battlefield! I began to look for a suitable candidate (i.e. low cost) for conversion.

Joe Sommer first brought the Paintball Inc. GTVe marker to my attention. He was using a GT-2000 marker in his Hetzer at the time (and still is) and thought the GTVe would be a good candidate for my project. The GTVe marker is a low cost semi-automatic blowback marker with an electronic trigger based on the GT-2000. It uses Spyder compatible parts and at first glance looked to have some features that would make it an ideal candidate for the hobby. Most importantly it was low cost. The GTVe can be found for as little as $75 from various online suppliers. I researched the GT line of markers at www.pbreview.com and owners were giving the markers high marks. PBReview also had a nice review of the GTV-1 (the mechanical triggered version of the GTVe) at http://www.pbreview.com/flash/gtv1. I contacted the designer, Doug Brown, at www.gt-2000.com and informed him of the hobby and what I was considering doing to one of his guns. Doug was enthusiastic about converting the GTVe and provided some pointers and even provided the marker and extra parts! Thanks Doug!

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Here is the GTVe as it looks out of the box. Nothing fancy about this design.
The really unique feature of the GTVe is the removable side mounted feed tube. Remove a couple of screws and the feed tube comes right off.

With the feed tube removed you can see what I consider the feature that makes this marker ideal for R/C Tank Combat - a side feed port! With a horizontal mounting (like most tanks in the hobby) it's a simple matter of fitting a magazine tray right above the gun. Unfortunately I can't mount the marker horizontally in the T005 so I'll have to be a little more creative as will be seen.


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Another great feature of the GTVe is the removable CO2 bottle adapter. With the Vertical Adapter removed it's a simple matter of attaching an inlet hose directly to the body of the marker. This makes for a nice compact installation. The Vertical Adapter Retainer was locked in place with high strength LocTite. You're going to have to really torque to get it off or soften it up with a torch before removing it. If you use a torch remove all the marker parts first before heating it up.
Here's the backside of the electronic handle (e-handle). An e-marker requires that the Sear be adjusted for best performance. This is easy to do.

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Here's the e-handle opened up.
With the handle removed the Trigger Sear can be easily seen. The Sear holds the marker hammer in the cocked position. The electronics "pulse" the solenoid, which depresses the Sear and fires the marker. I read somewhere that the Trigger Sear on the GTVe is made out of titanium.

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Here's a detail shot of the marker body with the handle removed.
Since we started with the disassembly, let's continue. Here's the Ball Stop assembly removed. The Ball Stop keeps balls from rolling down the barrel until their ready to be fired. This is accomplished by a little rubber piece that sticks inside the chamber. It is held in place by the plastic bar and screws. These pieces are all stock Spyder parts.

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The valve assembly pieces. These are all Spyder compatible pieces also. You can get a really good idea how all this works by looking at the animation at www.gt-2000.com/v1gif.htm.
Here's the hammer and Bolt assembly removed. For such a value priced marker I was really impressed with the quality of the pieces. They are mostly nickel plated aluminum and nicely machined.

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Here's a view looking through the body piece from the rear. In this photo the valve assembly is still in place and can be easily seen in the bottom tube. In the top tube you can see the ball stop sticking in from the left.
The main emphasis of the conversion of the GTVe is to reduce its size or "footprint". This is what the GTVe looks like after I was done with it. It's fully functional, compact, and fits well in my turret. The following pics outline the steps I took to get to this point.

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The first step in shedding the inches was to remove the top site rail. I removed the top rail because the marker is installed into my turret in a vertical position and I needed the extra space along the top. Removing the top rail probably wouldn't be required in a horizontally mounted installation but it all depends on your particular setup.

As can be seen here, I'm using wood working equipment to cut aluminum, a tablesaw in this case. You can work aluminum with wood working equipment as long as you have carbide tipped blades. When working with aluminum you must keep the pieces WELL SUPPORTED and FEED SLOWLY! And don't forget your EYE PROTECTION because little bits of aluminum will be flying around everywhere.

The cut shown here was the most aggressive during the conversion and I did it in five passes. Be safe, cut only a little at a time. If you don't have a metal shop or the equipment I used, a hacksaw will work also.

The Front Plug was cut down to size in the mitersaw.

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A quick pass though the tablesaw makes a screw slot so the Front Plug can be removed.
One issue with this marker and many other Spyder compatible types is how far back the bolt sticks out when in the cocked position. With the bolt extended like this the GTVe will not fit into my turret.

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To deal with this issue the top tube section needs to be shortened. 1 7/16" is removed from the rear of the top tube. Along with a shortened bolt, this modification reduces the space required to mount the marker.
Here's a pic showing all the modifications to the GTVe body.

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The next step is to shorten the bolt.

1 5/8" is removed from the end of the bolt. Once this shortened bolt is installed into the modified body it will no longer protrude beyond the rear of the marker in the cocked position.

The bottom bolt in this photo is the stock one that came installed in the marker. The top one that I modified is an upgrade "Vortex" bolt. It has some internal channels to direct gas flow and those two o-rings to reduce blowback into the magazine. This bolt is supposed to give you better accuracy and distance.

You may have noticed the top bolt has a longer pin coming out the bottom of it than the lower bolt. This is one area were the GT markers deviate from Spyder compatibility. The GT markers require the longer pin.

A hole is drilled through the end of the bolt and an aluminum roofing nail is press-fit through it. This gives me something to grab a hold of to cock the marker.

The rubber washer that came with the nail is installed back on the nail to hold it in place in case the nail works itself loose.


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The next step is to shorten the handle.

The electronics and trigger switch was removed from the handle. A quick cut in the mitersaw finishes this step. An extension wire (red and black wire) is spliced into the solenoid wiring so it can reach the firing board, which will be installed in the turret.

In this photo you can see the shortened bolt installed in the marker. Additionally you can see the CO2 quick disconnect fitting installed in the CO2 inlet.

Because I'm mounting this marker in the vertical position I had to come up with this adapter to receive the feed from the magazine. The next several photos detail this part.

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This photo details the mounting of the modified GTVe into my turret.

The blocks surrounding the front of the marker keep it from twisting around. The spring-loaded contraption going up the side of the marker keeps it in place. The springs also absorb recoil as the marker is fired. The blocks, the springs, and the hole the barrel is going through all do a great job in keeping the marker securely mounted.

All the background clutter in this photo is intentional. It keeps automated Tri-Pact image evaluation systems from gathering any useful intelligence from the photo!

The circuit board from the marker was mounted adjacent to the turret on/off switch. A small 5volt PCB relay replaces the trigger micro switch. The Trigger Relay is fired by an auxiliary port on the Anvilus Controller. Of course, a servo could be used to fire an e-marker. Just attach the trigger micro switch to a servo.

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Here's the GTVe fully installed with the magazine in place.

A note on the magazine. It may not be evident but the front of the magazine tray is attached to the mantlet by that metal bracket. The tray moves with the mantlet. By elevating the gun, the downward angle of the magazine tray is increased. This articulation helps in feeding ammo.

This conversion took me about two weeks of on and off labor to complete. I could have probably done it in a weekend if I had allocated the time to it. The marker performed well during its first weekend of battling. It did not jam once. The setup did have the tendency to fire on its own from time to time. This may have been due to low voltage to the electronics due to the way I had it wired up. I'll be making adjustments before the next battle to try and correct this. Additionally, the magazine did not feed as well as it had with my last marker. I think this was due to the reduced blowback into the magazine that this marker has compared to my old. Blowback can really mix things up in the magazine and help feeding. This wasn't too much of a hindrance though. I was able to cycle the elevation (articulated magazine) or bounce the tank around to get the feed going again.

All in all, I'm very happy with the GTVe and its performance on the battlefield. I highly recommend it for the hobby.