I'm putting in the hours but when I look at what gets done
I start to wonder if I'm in a "Twilight Zone" where someone
is stealing hours out of my life.
Mind you I have an acquaintance who believes he sees UFOs !!!!
He keeps sending me photos of what looks like blobs of light
in various places which he is convinced are UFOs.
If he disappears some time maybe I'll believe it . . .
To continue :
In order to keep weight down I decided to use a tubular shaft between the bearings on each end of the drive. As it all is supposed to work in synchronisation in order for the bed to stay level the shaft needs to be fairly rigid but there is no point in carrying extra weight. 22 mm OD with a wall thickness of 1.6 mm seemed about right.
In keeping with the re-embraced KISS principle simple sleeve bearings from acetal were turned and pressed into simple pipe supports.
These were lined up by use of the shaft itself and tacked into place.
Spins in your fingers . . . luverley !!
Now of course comes the tricky part :
a single motor has to provide drive to both shafts (one each side)
each turning in the opposite direction.
Having decided that the original motor is not quite strong enough
to lift directly some sort of gearing is needed in order to lift the weight.
While commercial gearboxes etc are readily available
they are not necessarily inexpensive and still don't solve the
problem of two drives in opposite directions.
For example a visiting sales rep the other day suggested using
a "roller door" drive. Absolutely perfect at first glance :
powerful, self programming for limiting rise and fall and provides
the output via a chain.
And only $800 !!!!
Of course not the size chain I elected to use
(only because I hadn't thought of a roller door drive - DUH!).
So after much thought and trepidation and because
I have more time than money to waste at the moment
I decided to build it custom!
Completely ignoring my own rule :
"If you can buy it - don't make it."
Of course on that basis I would just mortgage everything I own
and steal a bit more and buy a UNICAT.
Back to reality . . .
First to provide two drives in opposite rotations :
just put two gears together and the shafts go opposite ways.
I am sure that I have seen little "gearboxes" somewhere that have
one input shaft and two outputs in opposite directions -
but I can't remember where the hell I saw them.
But I used to design and make sprockets and gears recently
so why don't I just make some to do the job.
Unless you have very specific tools and machinery making
things less than a certain size is almost impossible so what I
have dictates the size to a considerable degree.
As it will be built into it's own compartment this is not a very big problem.
For me (and I am sure I mentioned it before) acetal is an amazing product.
Strong, light, easily machinable and slippery, and
I have some left overs that will probably come in handy.
Of course not having done this for a while it took a bit of stirring
of the grey matter (and a computer disaster when I accidentally
destroyed the spreadsheet I created to calculate all the important
dimensions and shapes for sprockets while adapting it to do gears.
But that's another saga !!)
I also originally decided to use aluminium for the drive gear off the motor as a mental lapse caused me to think that that would be the gear with the highest loading.
Of course it is the lowest loading!
That's the whole purpose of the gearing in the first place.
I'll remake that in acetal tomorrow.
Now it's all set up it will only take 20 minutes.
So the primary part of the drive layout looks like this:
I still need to get the drive over to the shafts from here by chains so I will also make some chain sprockets which will bolt to each gear to provide the chain drive.
While I was at it I thought I would also put in another level of reduction so another set of sprockets was quickly whipped up to do this.
They wont be used exactly in this arrangement but it gives the idea.
Yes. I could have used another set of gears but then the mounting of the shafts for the gears becomes problematic in order to provide proper meshing etc. and chains are so much more adaptable in this regard.
This arrangement will allow me to stretch it all out across the back of the "house" in the lower part of the rear wall all out of sight when finished.
Hopefully tomorrow will allow for a test run and another day to get this whole saga over with.
Then on to stuff where it actually looks like progress.
I know this all seems like a huge shemozzle for this part but the lifting bed is an extremely important part of the design in order for the whole house unit to be kept compact enough to go on the truck without modifications and into a sea container for transport.
I just have to keep reminding myself of that basic overriding premise.
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