There is no question in my mind that hydraulic are the best way to go.
I agree, but "the best" means it is the most expensive solution to build, once built, different story...
AT _some_ point I intend to add a compressor and hydraulic pumps to my start-o-matic, that way I have mobile "any flavour you want" power, but I know hydraulics so it doesn't post the same challenges it does to a "virgin"
1/ ATF (automatic transmission fluid" is a very very good substitute for proper hydraulic oil, I personally would not under ANY circumstances except a life threatening emergency attempt to use any other kind of fluid.
2/ Hydraulics has to be SPOTLESSLY clean, a good hydraulic filter won't even pass water molecules, so ANYTHING you can see or feel is orders of magnitude bigger than any acceptable size of contaminants
3/ Hydraulics always always needs some sort of cooling / reservoir, and this has to be easy to fill and drain.
4/ lots of hydraulics have "case drain" so you're involved in three hoses, not just two.
5/ Hydraulics is like steam, full torque at 0.01 RPM, so spec your motor and pump wrong and you can tear your seed press to pieces (cos someone dropped a 5/16 bolt in there) at 1 RPM no worries, if you want to control torque you end up using things like pressure dump valves, and they are not cheap.
6/ Hydraulics takes the path of least resistance, so any circuit more complex that one pump + one motor direct coupled is starting to get into the realms of either using two matched pumps, or a bank of pumps (dowty type pumps just stack up) or something called a gear splitter, which is just as expensive as a pump.
7/ Hydraulics are NOT an incompressible fluid, there ain't no such animal, fluids compress 1% by volume per 100 bar, roughly, so if you have 50 feet of hose between the valve and actuator you have potential for delays and that means feedback loops***
8/ Hydraulics are potentially incredibly dangerous, either because of the power in a ram, or forgetting about the power stored in an accumulator, or because of the weight of machinery moved (crack the lines and that backhoe arm settles on YOUR arms with several hundred pounds of weight and lots of mechanical advantage)
***
We used to do a lot with yacht/ship stabilisers, there are basically extra rudders amidships, when the boat is under way, if the wave motion tends the boat to lean to the left, the stabilisers turn these rudders so the passing water produces a force the drives the bottom of the hull towards the lean, keeping the hull upright and vertical.
These rudders are actuated by a pair of rams, hyrdaulic power comes from a pump / accumulator / filter / tank set up driven off the main engines, and control is by a box of gyroscopes on the bridge producing two sets of square waves, the more offset, the more actuation and rudder angle, operating a series of solenoid valves, feedback from ram position was a potentiometer (vospers use to sell these at 70 odd UK pounds each, they were RS pots, cost all of a dollar each)
The whole circuit was timed to prevent feedback and allow for compression of the hydraulic oil in the lines, which would be many many feet long.
Mess with that timing, like when the 50 cent rubber tube that connected the potentiometer shaft to the top of the stabiliser shaft started to perish and introduce an extra bit of "play" not hard wired into the compensation system, and they could pulse so hard the whole hull would feel like it was tearing itself apart.
The moral of this story is - even an expensive and well designed hydraulic setup can still look and sound like shit and make you look like a fool, if some 50 cent component is not up to spec, and if YOU don't know hydraulic, you will pay someone like me, and I used to love hydraulic work as it was the most expensive hourly rate we used to charge out, even if that hourly rate was used to detect and diagnose and replace a 50 cent item......
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There is another story here.
Guy has a Moody 40' sailing yacht, centre cockpit, they were OK if you like floating caravans, engine was a BNC thornycroft 1.5 diesel 4 cylinder with DPA pump, can't remember the gearbox now, prolly PRM or hurth, anyway it was 20 years ago, so he asks me for a quote to replace the leaking core plug, I believe yanks call them freeze plugs or block plugs, the little dishes of steel you hammer into blocks, her is a picture of one under the guys finger
so I quoted him, and this is twenty plus years ago, 3000 bucks
he just about shit himself, before blowing up at me and calling me a crook etc.
as a result, I didn't have the chance to explain.
a/ the leaking plug was right behind the injection pump.
b/ to remove the injection pump you had to remove the timing chain cover on the front and undo a bolt, it wasn't a slide in on a master spline job.
c/ to remove the timing cover you had to remove the two pulleys driving ancilliaries
d/ to remove the pulleys you had to split the drivetrain and move the engine so it could be rotated, as the pulleys were so close to the bulkhead you could only get a new belt in with a blunt punch.
e/ to move the engine you had to life the cockpit sole
f/ to life the cockpit sole you had to disconnect the steering and control binnacle mounted in the cockpit sole
so, a 20 minute job that should have cost 50 cents in parts ended up as a 3000 buck job that wasn't done, because it was too expensive, until one day the core plug went completely and then the whole boat had to be craned out and re-engined because he siezed it solid, so the boat was craned out, placed on the hard, and a for sale sign went up on it.
Now, Moody were responsible for that fuck up, a god awful piece of design, because all they cared about was maximising internal cabin volume, which meant minimising engine bay volume.
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so the moral of these stories are this.
whenever you decide to modify something, think like a submarine designed, make bloody certain than every last piece can be removed and repaired, without you having to disturb any adjascent components or readjust or realign anything else, and never ever ever let any one design consideration (such as cabin space, which sells a boat) over rule good engineering practice (such as engine access, which can kill your customer and his family)
whether matey uses hydraulics or flat belts or electric, ac or dc, if there is a distance between the power pack (lister) and the work (seed press) then lots of bad things can happen if you are stood at one unit, and someone walks up to the other unit and starts fiddling
uh-oh, we just came up against one of those scenarios where the old style genuine lister vee belts which will always stall in overload make sense, as do old style flat belts, if you go electric or hydraulic then you need to build in a safety dvice that does the same stall in overload thing, and design it so the ONLY way it transmits power is when it is working, and EVERY mode of failure is guaranteed to stop, totally, ALL power transmission, 100% of the time.