I like the solonoid cutoff idea. Could you tell me more about the routing of the fluid. Did you hook up the bucket and the thumb in series or parallel? I dont see how it could work in series, but I thought hydraulics are supposed to be in series? I see how it could work in parallel.
Do you have any difficulty getting the thumb to return to the open position? I guess if you push the bucket against something the thumb will move regardless of bucket position.
Go ahead and read my project description. But yes, the plumbing is in
parallel, which allows the thumb to perform more like a traditional grapple,
vs. a fully independent thumb. The bkt or thumb experiencing the least
resistance moves first. This is particularly valuable when picking rocks or
working near an immovable object. With an independent thumb, the force
acting against the immovable object will lift the tractor. Not so with a
parallel connection.
I operate my thumb to the fully open position to get it out of the way when
I am ready to return to dig-only action. I can turn off my solenoid valve with
the thumb in ANY position, which gives me the equivalent of a mechanical
thumb. An hyd thumb is much better than a fixed thumb, but the add'l costs
for pivots and hydraulics are quite significant. (See story.)
RE the B21, I offered a mech thumb kit to the guy who bought my B21, and
he said he wanted it, but he has never come back for it. I made 6 of these,
one of which I beefed up for my current hyd unit. The B21 has a very
similar dipper width to my Prairie Dog hoe.
I am using the same solenoid valve installation for my current 4-in-1 FEL
bkt project, which is only waiting on hyd fittings I ordered. I plan to post
a thread soon on that project.