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View Full Version : A shotgun frame question for Rorty



ako1
03-01-2007, 11:17 PM
Rorty,

I have had a look at your new shotgun design, and I am probably going to buy a set of plans from you. From what everyone here says, it seems to be the most complete set of plans available.

I few of the images did get me thinking though.

The crossmember that you have between the front upper suspension points seems to be a few inches away from the node. It is also intersecting the two cross braces that stiffen the upper longitudinal rails. This seems like extra fab work to me, requiring additional joints.

Why don't you move the crossmenber forward? To me this would seem a stiffer design, reducing the tendancy for the suspension pickups to deflect inwards under load, and reduce the bending loads in the longitudinal rails.

I have highlighten the member I am talking about in blue, and put the revised one in green.

What do you think? Or am I missing something?

Thanks,

Mick

http://img235.imageshack.us/img235/732/shotgunbuggy02modified1xs4.jpg

http://img235.imageshack.us/img235/5154/shotgunbuggy02modified2vz6.jpg

http://img367.imageshack.us/img367/7118/shotgunbuggy02modified3ga5.jpg

Rorty
03-02-2007, 12:01 AM
That's a fair question. The horizontal tube you've highlighted in blue is there so a panel can be attached there to seal the upper front bodywork to the front bulkhead, thereby making the whole of the under hood area and cockpit sealed against in the ingress of water, sand and muck.

The diagonals in the hood area pick up on the shock mounts , as do a couple of other tubes which tie them down to the framework below. There's no way the shock mounts or those dide tubes are going anywhere. If you wanted, you could always insert a simple length of 1" x .065" tube (as you have drawn in green) between the shock mounts.

amergin
03-02-2007, 01:00 AM
Could always do COSMOS analysis on that section. Looks to me that there would be more stress load on the shock mount tabs (not saying they are a weak point) then anything else. That diagonal brace will transfer the load straight up to the top part of the cage.

ako1
03-02-2007, 01:46 AM
Fair enough.

I was trying to think if it may have been like that for clearance for driver and passenger, but that made no sense as these members are too high up to be a problem. Just looked a little strange to me, since I know that you designed this one from scratch and had no inherent design constraints like modifiers or production vehicle manufactures may face.

I guess in real life it would make no difference either way, but I would put the larger 1.5" member where the green one is, and a smaller non-structural memeber where the blue one is for your panel.

I guess it's six and half a dozen *[smilie=biggrin.gif]

Cheers,

Mick