TageW, yes I think I could incorporate parts of a commercial pallet wrapper into the design - or even at its simplest, mount one of those small pre-stretcher units that are intended for wrapping forklift pallets by hand.
As I'm thinking of a wrapper for small square bales I don't think that there will be any lifting action needed at least in the Mk1 version.
From reading the McHale baled silage guide (Thanks Tom
) it seems that I really need to wrap the bales ASAP, so I'd be wrapping them there in the field rather than loading them and transporting them here (home) to a stationary machine - that would mean some of the bales would be unwrapped for many hours.
We have a second tractor - a 1952 (mostly) Fordson Major - that could mount the wrapper to and follow the baler round with the driver hopping on and off to wrap the bales. It doesn't sound very efficient but it would get us started.
Tom - isn't it the same - thinking relative motion - if the table rotates relative to a fixed film dispenser, or if the film dispenser rotates around the table? In both cases the bale also rotates along its long axis on the rollers, so isn't the effect the same?
One reason I had for considering a separate motor for working a rotating arm that holds the film dispenser is that it might be easier to get the timing (and therefore the film overlap) correct.
A much neater solution would be to rotate the table (rotation about the vertical axis) using a hydraulic rotor, or mechanical linkage to pto, and gear the bale rollers (rotation about bale horizontal axis) via a stationary crown gear concentric with the axis of the hydraulic rotor. BUT this would mean that the required turns ratio between the two rotational axes woluld need to be determined in advance.
Now, in theory that sounds easy. If we wanted a 50% overlap, that would obviously mean that by the time the table had rotated 360 degrees, the bale rollers should have turned the bale about 12cm at the edge, assuming 25cm wide film. Now a bale is about 130cm circumference, so it should therefore be made to rotate about 36-ish degrees on its axis for every revolution of the table.
However, years of bitter experience have taught me that nothing is as straightforward as the theory suggests (or then I'm a rotten theorist
) so for the prototype, I'd rather make something where I could control both axes of rotation independantly...
As an aside, if the calculations above are right, then after about ten turns of the table our bale has a complete wrap at 50% overlap, in other words any point on the bale is covered with two thicknesses of film (I know, the ends are going to have more). The McHale silage guide suggests 6 or 7 layers per bale, so that's a minimum 30 turns of the table. Now I've no idea how fast such a machine could be made to run without tearing the film, but assuming say 60rpm (too fast??) that would give 30 seconds wrapping time per bale, add another 30 sec for mounting, attaching the film, cutting and dismounting, that's one minute per bale, now lets say we have 2000 bales to wrap, 2000 minutes then - that's 33 hours.
