Hi Darrel, thanks for your comment and contributions.
As I mentioned in the post, this is the first test with the hydraulic system. This gripper is made with cheap and small RC hydraulic pump with light duty brushless motor, there are much more powerful hydraulic motor pumps if you want more strength. On the other hand, the hydraulic bottle is also one of the smallest, with pipes and fittings of 1.8 mm internal diameter, there are larger diameter bottles with 2.5 mm internal pipes that provide more speed and force.
Regarding noise, by introducing the motor inside the watertight tube it is minimized, and if you want less noise you can epoxy seal the stator and put the motor in the water like the ROV propellers or use the M100 or M200 to obtain a noise similar to propellers, which is muffled by water.
The motor gear system that you tell us about, if I am not mistaken, is very similar to the newton gripper, of course I am referring only to the gripper system, not to the multi-movement servo system that is already more complex. I have chosen another path because it has been very difficult to find a commercial arm in Europe and more with the COVID 19. The newton gripper is discontinued because I suppose that the guys from bluerobotics are trying to improve the system, I am sure that they will soon release a new version improved and more durable, as they do with everything that gives little errors.
My intention was to open an alternative way of working that was very simple and that despite not being perfect, was cheap, functional and durable. With this system you only have to buy the hydraulic bottle, the pump with motor, an ESC, print the parts of the gripper (I used the 3D designs of the newton gripper, light modified), use a penetrator to epoxy seal the pipes and connect the esc using a pixhawk light output or any other auxiliary servos. In this way, no electrical part will be in the water and no component will have to be sealed with epoxy except for the penetrator, nor will it be necessary to build a specific watertight compartment to encapsulate, the brushless motor, the gear motor, the electronics for its operation and the DYI acme linar actuator. So anyone, who has a specific need, as it happens to me, can have a gripper easily for less than € 100.
This system also allows multiple movements to be used with a different-way valve actuated by servos, being able to build a much more complex system.
In any case, thanks again for your contribution, since it makes us think of everyone and provides new ways of development. I am waiting impatiently to see your 9 dof project running, I am sure you are making an amazing system.