In article ,
Eric R Snow wrote:

On the front of the tractor the bucket keeps it's angle the same in
relation to the ground. What I want is for the thumb to follow the
backhoe bucket. So when it grabs something the bucket can be curled
without either dropping the load or being prevented from curling
further.

Not really a needed mode of operation - does not buy you much,
excessively complex. A manually set thumb is quick, easy (and
inexpensive) to build, stays out of the way when not in use, and works
quite well for those tasks you might want a thumb for. Reach, grab,
pick, drop. It also does not add a lot of dead weight to the bucket
area; weight which will work against picking up whatever you are trying
to grab. My hoe can supposedly apply 9000 lbs of force to dig with
(curling in at the bucket lip), but it can only pick _up_ about 1500 lbs
at full reach. Add a bunch of hardware and plumbing, and you subtract
payload.

If you are seeking the full pick & place mobility a log loader offers,
you need a log loader. If you get your superthumb, you still won't have
rotation, and your reach is awfully short. A TLB is a great general
purpose machine, and I have moved a lot of logs with mine, since it the
only thing I have to to that with - but turning it into a log loader is
no more practical than turning it into a bulldozer.

The "easy" way to do what you describe is to have a "thumb" (or perhaps
"fingers") that is mounted to the bucket itself, ala a clamshell bucket.
That way moving the bucket moves the thumb, and you can apply the
pressure you want to the tumb, then curl the bucket without changing the
clamping pressure. But it will probably get in the way of digging.
Someone may have tried this, so go look for design ideas and design
flaws by seeing if you can find such a thing, prefereably well used, so
the flaws show up.

I doubt the accumulator would work - the load can squeeze it and make
room to fall out. If the load can't squeeze it (too strong), then the
load is likely to get crushed as you try to squeeze it with the bucket,
since the load is in between.

IMHO, YMMV, etc....

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