Instructables

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.
 
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ToolTech4 years ago
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?
Do you have to use soda bottle necks? Could I just use the necks of water bottles for the high performance tractors?
crispyjones (author)  pingpongplaya9114 years ago
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.
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 (author)  pingpongplaya9114 years ago
Yes, that is exactly it. The outside diameter of 1/2" PVC closely matches the inside diameter of most bottle necks.
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! )
murdock14504 years ago
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.
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?