SpudFiles

Hi,

My freind Tom asked me to build him a tennis gun. I had all the stuff sent to my place, and I finished it today....

http://www.peter-hoare.co.uk/tennisgun2.jpg

http://www.peter-hoare.co.uk/tennisgun1.jpg

http://www.peter-hoare.co.uk/tennisgun3.jpg


http://www.peter-hoare.co.uk/tennisgun4.jpg
This breech is temporary. Unfortunatly teh 75mm 10bar pipe is too loose a fit. I have some 16bar on the way, but I am meeting with Tom on saturday so we want to be able to use it, so i cut a rough breech out.


I have a can of propane from a blowtorch, and I also have a screw on regulator. The chamber is just over 50cm long and 110mm wide, how much gas will I need? I intend to build metering onto this gun for tom, but at the moment we are just going to leak some gas in from the canister. How long should I open the valve for to get a good mix?[/url]

Looks very nice. You did a great job with the spark strip mountings. What are those grommets(?) that the screws are passing through? And what are the white caps on the outside?

Chamber volume is (Pi)(5.5cm)²(50cm) = 4750cm³ (290ci). 4% is 190cm³ (12ci).

A standard Benzomatic torch head supplies something in the vicinity of 20cc/sec. So about ~ 8 seconds of fuel would be a good starting point. I would unscrew the air mixer from the Benzomatic torch head and add a piece of rubber hose so you can inject the fuel deep into the chamber.

The gun is just begging for a chamber fan. A fan will help the performance more than will a meter.

Thanks very much, im planning to use a fan eventually.

The rubber grommits were there primarily to stop any chuffs of flame burning my/toms hands but it worked out fairly well to hold the strips up off the wall of the chamber.

I got them from B&Q, they are seals designed for taps. They callt hem rubber washers.

the little white caps are a great find, they cost £2 for a bag of 100 caps. They are great because you can put the bolt head through and snap the cap over the top.

http://www.screwfix.com/app/sfd/cat/pro ... 5&ts=71551



Thanks a lot for the torch advice, i will have a go with that.

Thanks.

BTW, you want to remove the air mixer, not the flow control orifice from the Benzomatic torch head. Where it says "unscrew" below


The orifice is extremely small, less than 0.01".

Yeah, i got one of those torches. Thanks very much

That looks really nice you friend will love it. Did you get the pipe from hendersons? I'm planning on making an order there soon.

the p ipe came from hendersons, but unfortunatly its 10bar, not 16 as we all thought. The fittings came from pipestock.

Are you a a spuder from the UK?

join my forum: www.uksgc.co.uk

OOh looks ood I'll join now.

Heres a video:

http://www.youtube.com/watch?v=aTUZWqORz-Q



We shot some unopened coke cans too. They went about 100m then made a right mess when they landed 8)

A quick update on the tennis gun:

It fired a tennis ball about 100meters in the air and the same with an unopened coke can. I decided it needed a chamber fan, so I put a 90mm coaxial fan inside and clamped it in with four bolts.

In order to let the air in the back so the fan could clear the chamber, i decided a valve in the back would be a good idea. It seems screwing the end cap on and off takes a while caus there are so many threads. I got a 50mm thread from pipestock and welded it in with solvent weld.

Looks like this:

That looks really good. Only one thing I cant establish:

you wrote:went about 100m

and then:

you wrote:It fired a tennis ball about 100ft in the air

Which is it, meters or feet, or both respectively?

Opps, sorry I got my units confused. They are both meters. 100 FEET int he air is pittiful

If you didn't have the extremely-non-manly-hobby of Model Railways you wouldn't have made that mistake

Michael

...I fail to see how that makes sense.

how come your not called himszy

OK, Im sensing an inside joke here... who does railways and who doesnt? Do you know each other?