Build A Net Gun

Step 8: Assemble Tractors

Tractors are what slip on to the launcher arms and are propelled with compressed air to pull the net outward. You can build two kinds of tractors. The simplest are just four empty soda bottles. They must be bottles that were used for a carbonated beverage as they were designed to withstand pressure. Other bottles, especially water bottles, are much flimsier and likely to burst. The bottles can be filled with a little bit of hot glue, silicon adhesive, or wax to give them a bit more momentum. The soda bottle tractors are free, nearly indestructible, but suffer slightly shorter range. The high performance tractors are more efficient, due to lower internal volume, so have greater range. They are a bit more fragile, SDR-21 (Class 200) PVC pipe may be hard to locate, and they take a little more time to fabricate.

• Tractor supplies

4 per net 16 or 20oz carbonated soda bottles
Hot glue/silicone sealant/wax to pour in bottles to add weight
Optional additional items needed for high performance net tractors
4 per net 3/4" couplers
4 per net 3/4" caps
4 per net 8" lengths of SDR-21 (Class 200) 3/4" thinwall PVC note: regular 3/4" SCH-40 will NOT work!
4 per net 12" lengths of non-adhesive 1" ID foam pipe insulation
Super glue
Utility knife
Dremel with sanding drum

Assembly

• When selecting soda bottles I would advise digging through a recycle bin with a launcher arm in hand. You want a bottle that slips over the launcher arm, and, ideally, will not slide off under its own weight. Make sure the bottles are identical volume, don't mix in a 16 oz bottle with three 20 oz.
• For the soda bottle tractors, there is very little assembly. You may want to test your net gun with unweighted bottles, as you can always add weight later. Use a scale, or melt/pour identical pre-measured amounts into each bottle. I don't recommend adding more than 40 grams to each bottle.

---

• For the high performance tractors, begin by cutting the necks off of the 4 soda bottles Fig 1. Use the Dremel tool to sand down the threads Fig 2 so the neck can be pushed into one end of a 3/4" coupler. Once it fits snugly, super glue in place Fig 3.
• Take the 8" lengths of 3/4" SDR-21 (Class 200) and glue the soda neck couplers on one end and a 3/4" cap on the other Fig 4.
• Cut four 12" lengths of pipe insulation. These will be slipped over the net tractors leaving 2-3 inches of cushion at the end . This will protect the tractor from shattering if it hits the ground. It will also minimize damage if the tractor accidentally hits something valuable, like a car, plasma TV, or a cranium. Wait until the tractors are tied to the net (next step) before putting on the insulation.

Comments

[ToolTech]

I know this has more than likely previously been questioned, but is the thinwall PVC necessary? I have plenty of 3/8" laying around but as with others I have had troubles finding thinwall. Will performance severely lack if I use the regular PVC?

[crispyjones]

I am assuming you meant 3/4" PVC not 3/8". Regular 3/4" PVC will not actually fit over 1/2" PVC, that was why I recommend using the thinwall. Additionally, the 3/4" couplers are very close in size to the bottle necks. The next closest sch40 PVC that would fit would be 1". I think it might be a tight squeeze fitting the bottle neck into one end of 1". If you do get 1" tractors working, let us know in the comments.

[Danno420]

I used 1" sch 40 tractors with 1" caps on the ends. The bottle necks of certain bottles fit perfectly. I added rubber cement to help keep em in. I used black plastic, 1/4" hole bird netting I bought at Home Depot (comes in 14' x 14'). The tractor launcher arms are set at 10 deg and the net at the moment is 7 x 7 foot. I used a little electrical tape to hold the net to the tractors. It fires great. We have fired it 50 times or more and the net is still not ripped or coming off of tractors. I am still going to buy the recommended net though at some point. Took about 3 hours to get all my parts together at home depot, but me and my buddy assembled nearly the whole gun in the isle just to be sure we weren't going to need to make a second trip. The funny thing is we used all 2 foot pieces for everything including all couplings and the gun was about 14 feet long on the ground in the isle of Home Depot. LOL ....Then we knew we had everything correct (except for tooo many 2 foot pieces we don't need) but then we put back all the extras. The only thing we deviated from on this project to keep the cost down a hair, was the trigger. Instead we just bought a 1" ball valve and mounted it with the T-handle on the left side of barrel in the exact spot the sprinkler valve would have gone. It works great. If we wanted to add the sprinkler valve later we can just unscrew the ball valve and screw in the sprinkler valve, but I don;t see the need. Also we made the pressure chamber with 2" pipe and about 16" long. We are going to be replacing the front net holding tube with 4" pipe. We currently have the center net tube capped off so we are not using any air to push it out and it still works great with extra power for the tractors. We have come to find the 4" tube will hold more net and looser. I have left a easily removal 1/2" cap on the center tube though so if I choose to use it I just pry off the cap. I can cap the tractors and uncap the center tube, load it with backing and some fish gravel and now I have a shotgun too. Thanks for all the instructions. Everything went without a hitch.

[crispyjones]

That's great that you got bird netting to work. I can definitely see using a larger net holder, I remember that stuff being pretty stiff. I would love to see a photo or video of it in action. I am also interested in what kind of range you get out of a 10 degree launcher angle. Thanks for posting!

[ToolTech]

(My bad spelling error) Thanks alot, I'll mess around with it a bit. Im using a air chamber from a previous potato gun with a one inch ball valve. It is two large fire extinguishers linked with galvanized steel elbows. I need to adapt your net design to one inch at the open one inch ball valve. My design has a pressure gauge built in as well. However I still need a net before I can test the setup.

[pingpongplaya911]

Do you have to use soda bottle necks? Could I just use the necks of water bottles for the high performance tractors?

[crispyjones]

I think that would work. My only concern would be, water bottles are generally a bit flimsier, the neck might get compressed when you put it in the 3/4" coupler causing it to be overly tight on the launcher arm.

[pingpongplaya911]

OK thanks. But I'm confused. What is the purpose of the soda bottle necks? Does it make it a tighter seal so less air escapes when launched? Thanks

[crispyjones]

Yes, that is exactly it. The outside diameter of 1/2" PVC closely matches the inside diameter of most bottle necks.

[xepteregicide]

Worst coming to worst, as I could not find this thinwall PVC anywhere in stores around me, (in fact, most plumbers even looked at me quizzically and said that the stuff didn't exist) another possiblity is to just glue the cap and connector together and then add the pipe insulation over that, attaching the string to the lip on the exposed bottle top, and then simply having stubby tractors. I'm not sure if this hinders performance, as it was a temporary thing. (i ended up finding the proper materials on this pvc webiste: Click! )

[crispyjones]

 Sorry about the trouble finding the thinwall stuff.  Apparently is also called Class 200, I've updated the instructable to reflect that.  What area of the country do you live?  I wonder if the stuff is not code certified in some places, here in Colorado I've only seen it at Lowe's, not at Home Depot.

Interesting link, they sure have a lot of odd-ball connectors.

[xepteregicide]

I'm in Rhode Island, and around here i'm not sure of the codes and regulations, so i can't be of any more help there.

and it turns out that rigid sdr 21 is a little different than class 200, based on the fact that one is more expensive and a different color than the other.

not sure what the difference is

and yes, it does seem to be a strange site...

[murdock1450]

Just an FYI: SDR-21 pipe is more commonly referred to as Class 200.  You can find it easily at any sprinkler supply house especially in southern states where PVC is still used for sprinkler laterals. But, even in northern states it should still be easily available.

[crispyjones]

 Thanks for the info, I've updated the instructable with "(Class 200)" next to every instance of SDR-21.

[ducktapeman55]

can your substitute the 3/4" pipe with 1" pipe and glue the bottle tops to the 1" pipe its self? its is a pretty good fit that hot glue would easily fill. the only problem i run into as doing this is that there is nothing for the zip ties to catch as they shoot off. could hot glue be strong enough to hold the zip tie or some duct tape? i guess the real question i'm asking is how hard are the tractors going to be pulling on the net?

[crispyjones]

That's a very interesting idea.  The duct tape would probably work.  Perhaps you could put a groove or recess around the outside of the PVC pipe that the zip tie could ride in to keep it from slipping.  A couple things to keep in mind, the tractor will be a bit heavier, and the overall diameter will be larger, so you might have trouble getting pipe insulation to fit.  I am interested to hear how this works out. 

[ducktapeman55]

i'll test out different combinations of glue, duct tape and grooves and post pictures for future instructaneers. the pipe insulation problem seems easily solved by covering up as much as possible with the diameter i have then cutting up a stripe to fit the gap.