Toms Tennis Gun

[hoarp001]

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]

[jimmy101]

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.

[hoarp001]

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.

[jimmy101]

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".

[hoarp001]

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

[dauphinoise potato]

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.

[hoarp001]

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

[dauphinoise potato]

OOh looks ood I'll join now.

[hoarp001]

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)

[hoarp001]

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:

[spud yeti]

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

went about 100m

and then:

It fired a tennis ball about 100ft in the air

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

[hoarp001]

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

[Gepard]

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

Michael

[hoarp001]

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

how come your not called himszy

[spud yeti]

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