Ivan C wrote:... I've deliberated long and hard over the body mounting, to allow rail seperation and have decided against using springs. My (possibly flawed) logic is that springs are for bearing weight, the chassis will do that, what I want is the movement of the subframe and body damped, rather than restricted.
I've roughed up a couple of brackets to allow me to do this, how it will work in practice remains to be seen. Comments welcomed.
Ivan C wrote:... I'm planning two anti-slew mounts at the front to keep the body from moving sideways, this makes the movement of each subframe rail, relative to the chassis linear. (it's really an arc, but at 4000mm radius and 100mm travel minimal).
This set-up would work without springs or dampers in that it isolates the subframe and body from the twisting of the chassis.
The only potential issue is that of " box flop" which is why springs are used. Springs however will restrict the relative movement of the two as they compress, which will transfer stress to the box and subframe.
I don't want to restrict the movement, just dampen it. It is self limiting because at the limit of chassis twist a wheel will lift. As long as the dampers (one on each side) have more travel than the maximum separation, all is good...
Comments welcome eh?:
1. I've seen dampers used to restrict 'box flop' in pivoting-subframe systems - where box flop can be dramatic - but never in a rail-on-rail system.
2. When the full mass of the completed hab box is bearing down on the rails - even at maximum articulation - I can't see the separation at the leading edge of the subframe being that great so it's unlikely any kind of opposing-spring system would actually restrict articulation (unless the springs were very short)
3. Box flop generally isn't something that rail-on-rail systems suffer from.
4. I personally reckon slew plates alone would get the job done just fine.
5. In rail-on-rail systems springs essentially exist to counteract the forces imparted during separation - and so reduce the rate of separation. They also help control slew.
6. Dampers would counteract the forces imparted during separation too, but would introduce the prospect of a more controlled closing of the separation.
7. Ideally, it would seem logical if the dampers were set up to have minimal rebound damping (so as not to restrict articulation) but a good deal of compression damping (to take advantage of the 'soft close' benefit).
8. Using dampers would possibly replace the benefits conferred by a sacrificial hardwood (or similar) strip between chassis rails and subframe.
9. I'm not entirely convinced that a problem that requires this solution exists...
10. ...but I can see some potential advantages anyway.
11. I like the stress-relief profile at the leading edge of the subframe.
12. There are some stonking trucks being built at the moment.
13. I'm definitely and officially not an engineer.