OK, my turn:
I and R
I gives your 3 interfaces: 4-20, 0-5 and RC, R only gives you RC.
RC may be cheaper and if you used a 8 channel RC interface like I showed earlier you would not need D/A converters. 4-20 is very common in industrial environments. the reason it's used is there is no length issues or ground loop issues and it's easy to provide isolation.
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Stalling the actuator is like being between a rock and a hard place. A carefully selected spring on the end of the actuator with current protection (possibly fuse( would work just fine, but it does mean the spring has to be selected.
Remember the force on a spring is kx where x is the extension or compression of the spring. So, take a spring and your finger and determine the deflection. So, let' say that you could move the button when the spring deflects 1/4 of it's length. Now let's suppose that full travel of the button is reached at 3/4 of the spring length and now suppose that the force of the actuator is not exceeded at 100% of the spring length.
Your finger acts as a feedback device. You know when to back off the pressure, when the button doesn't move. Making the actuator have a spring-tipped would basically accomplish that. The actuator movement would have to be longer than the button movement.
So, as the actuator moved, the end spring would start to compress and eventually the button would move. Now, you can move the push button distance. Then there should be some spring left over, so the actuator won't stall. e.g. It might take 125% of the push button distance to move the button 100%. Stall might be reached at 150% (no more spring to compress).
With the tip of the actuator being a spring of the right length and k, you would be able to push the actuator without stalling it. A stall should activate some sort of protection and it might be a fuse. The reason fuses are bad is because you can replace them with a bigger one.