37mm AT-gun M3A1 Owners Club

I have started building

[youtube2]HlJJg3LlLo4[/youtube2]

Hopefully BedsnHerts does not mind me using some of his footage as an intro, I sent him a PM.

I've just watched the first 4 videos on youtube.
I have a couple of things to say about the suspension:

1) The independent units could cause you trouble with the way they're connected to the pipe. The connection is you had looks too rigid to allow a twist - if one unit moves more than the other, it could break the shaft or its connection.
2) The rotation of the axle tube could be controlled by a parallelogram. Set up a second arm that moves parallel to the suspension arm. That would make the axle maintain a distance from the suspension mount.

These issues are the reason why rigid axle systems don't use simple trailing arm suspension units.

I've just watched the first 4 videos on youtube.
I have a couple of things to say about the suspension:

1) The independent units could cause you trouble with the way they're connected to the pipe. The connection is you had looks too rigid to allow a twist - if one unit moves more than the other, it could break the shaft or its connection.
2) The rotation of the axle tube could be controlled by a parallelogram. Set up a second arm that moves parallel to the suspension arm. That would make the axle maintain a distance from the suspension mount.

These issues are the reason why rigid axle systems don't use simple trailing arm suspension units.

2 is to be talked about in video 5 loading up now, 1 is a potential problem and this is a test to see how it works out, an answer could be to cut off the stub axles and fit a thinner stub into a rubber bushing or use a larger ID pipe with a rubber bushing over the existing stub.

That's the problem of designing something with suspension to look like something that hasn't any

[youtube2]wg1qKdg19n8[/youtube2]

Thanks for looking

WRT your comments on the arm travel: There are going to be times when all the load goes off the axles, such as bounces. You'll need to account for that, rather than assume the load will always be on.

Yes mate, I think a good idea would be to wait for the stub axles to be made so I can fit the wheels.
I can then make some secondary swing arms between the pipes and temp weld them for a test, if I also temp weld the trails on I can add a load onto the rig and jump up and down on it to see what it does.

More on the suspension, I should have stubs for the hubs next week.

[youtube2]9tPIFOJsJzk[/youtube2]

I have just noticed the hole I have drilled for the traverse point will have to be moved to the load member centre or the gun shield will hit the wheels when I rotate it

Real axle setup here.

Ok I have been looking at how the elevation is adjusted and it seems to use some form of screw jack.
I have been hunting round for something like it but not much luck yet.
Any ideas guys?
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Nearest things are car screw jacks not quite the right thing or a linear actuator with the motor removed.

http://cgi.ebay.co.uk/SERVOMECH-ATL02-R ... 8844634741

but a linear actuator would have to be turned by hand about 1000 times to move 1" so no good.

Steering rack maybe, but that would not hold the barrel up gravity would make it roll back and the hand wheel spin.
I think it has to be a screw jack or worm drive.

Anyone got something like this in their shed they don't want?

Something you might be interested in to help with your build Oddball!

http://www.dragon-products.eu/product_i ... ucts_id=53

Something you might be interested in to help with your build Oddball!

http://www.dragon-products.eu/product_i ... ucts_id=53

Yes my friend in the South has one and is using it to plan his build but he has several other things on his plate at the moment, I did think about buying the model but I think it is a kit and don't want to waste time making a small model when I want to be making a full size one.
Also the model is near £60, my friend has opted not to build the kit but just measure off the dimensions from the sprue.

In the USA there is also this guy who makes full size replicas http://users.multipro.com/brentandloria ... page_2.htm

You can see that this guy has just made prop parts that don't function, I would like mine to work.

Notice the Traverse and Elevating mechanisms and handwheels, and dummy firing plunger components installed. The gun does elevate and traverse perfectly on tapered bearings, nice and smooth! The kit has dummy versions of all of those items, but they will not actually do the elevating or traversing. You can jury-rig that yourself, if you are a Rube Goldberg, or a McGiver type.

I also like this

Towing behind vehicles (at low speeds!!) is fine. NOT recommended for road speeds above 15 MPH due to the possibility that the unit is not welded square, true, or securely. Even originals were not designed for that!!!! Has handles on trails for crew movement and set-up.

Mine is going to do over 50mph

My friend has tried contacting this US guy but he does not want to share his plan set and the diagrams he does show on his site are low-res so not so helpfull.

I am off to the Garstang auto jumble (Preston) next Sunday so may find some sort of screw jack I can adapt for the job.

The mounting point for the gun and shield will be modified from the one in my above photo, I am going to cut it shorter and drill the mounting hole through the center of the load member. It will have to be 20 - 25mm diameter shaft to take the weight without bending, so I also need barings to fit on this.

This sexy item would be nice to find
It is called a SCREW ACTUATOR

Here is an idea to save money
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If I have to send off for one this looks good for conversion but I am sure the scrap yards are full of them.

http://shop.x19spares.co.uk/original-fi ... k-67-p.asp

Proper Mini (i.e. not BMW) jacks work like that too.

I used an old 40s/50s screw-type bottle-jack mechanism for the elevation screw on my Vickers MG tripod. Cost me 50p from War and Peace 2009! Go down your locals car breakers and they'll probably let you have an old screw-type jack for free.

I used an old 40s/50s screw-type bottle-jack mechanism for the elevation screw on my Vickers MG tripod. Cost me 50p from War and Peace 2009! Go down your locals car breakers and they'll probably let you have an old screw-type jack for free.

Yes I was looking at the old screw bottle jacks but the real old ones were cast iron so I would not want to weld onto them and the shape is quite off for this job. If I use one of these jacks above it will give me a good right angle and all the parts can be enclosed, I could even shape it to look right if I tried. I think the real unit would have an internal gear setup like a old hand drill.
Is it a crown and pinion maybe, in fact one of these could be used but no point now as the jack will do the job. I would think the small gear would have been larger and run on the thread of the central shaft that runs straight through the unit.

For a short time I considered an old angle grinder gearbox but without the screw jack part of the design it would back drive the hand wheel.

The 90 degree transition would probably be done by some kind of worm drive - that can't be back-driven.

It's the general shape that leads me to think it has that sort of system inside.
If it was a worm drive the input spindle would be to one side by my way of thinking, but it looks like it is directed straight at the vertical shaft. Also the roundish shape of the casting gives me that feeling.
Looking at the way the casing splits makes me think crown wheel, like a rear axle diff.
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Any more progess Nige?

Any more progess Nige?

I have started the traverse unit and decided to just have it free swivel due to wanting to make it look like a real one to some degree, other than the suspension addition that is.
The elevation will be with a jack I got a Garstang for £10.
I was set to start welding on Sunday morning when my CO2 ran out (familiar story you may say ), so no sweat I thought get my reserve tank .
Got the tank to the welder then found the SO****G tank had the wrong gas nozzle on it, they had given me a CO2 pub mix gas not welding CO2. So I had 2 tanks I could not use, got one refilled easy on Tuesday, took other tank to the address on the bottle which was different from the place I got it.
Well I just thought must be the same people as I had the contract with, got to the place they said they had nothing to do with the place I got the bottle from and hence confiscated the bottle I had saying the other people had no right to rent out one of their bottles or fill them.

So that left me with nothing to take to the place I got it from to exchange it, went home found the original invoice and rang the company on it to tell them the story.
They spun me a line saying they used to get their gas from that supplier but didn’t anymore, so I should ring them and get the bottle back and they would exchange it.

So I rang the company that had confiscated the bottle, they said it wasn’t true and they had tested the gas in the bottle and found it to be pure CO2 not Pub mix that should have been in that bottle as stated on the label. They said if this had been used in a pub it would have ruined the beer and they could have been fined £200 as it was their name on the bottle.

So I and the real bottle owner are going to visit the place that gave me the bottle on Friday to sort this out with them as they have broken the law.

What a waste of time for me

Heh, I have been photographing welding for 35 years and your post was a surprise to me that you use CO2! I've never even looked at the bottles. Of course, I know of of argon welding so stupid of me not to know about CO2.

So, to drift OT a little as my mind is wandering - why is the world bothered about car (and the like) CO2 emissions yet wilfully use the stuff for welding, beer pumping and fizzy drinks. There must be billions of tones of that released into the atmosphere every year!

why not use an electric welder nige?

nice gun idea btw

i did look at doing a single barrel 20mm flak a year or 2 ago, but fireing blasts of bb`s useing a co2 bottle, i binned it, as fps would be all over the place and probably far too hot to use on people

as for your screw actuator, ill post a picture tonight of one i have here at work, or its a simmilar shape