I want to build an arduino controlled PCB etching system. I've built a set of very thin develop/wash/etch tanks mounted side by side, and I want to make a mechanism for moving the PCB between tanks.
The side-to-side movement will be quite small (since the tanks are very thin and stacked next to each other) so I think I can achieve this with a simple servo mechanism.
However, I've made the tanks quite tall (about 25cm) - to reduce the chances of splashes from one tank getting into another, so the up-and-down movement will need to be quite big.
Does anyone have any good ideas for a suitable actuator to achieve this range of movement, with a reasonable degree of control? I was considering trying to hack the mechanism in some printers that moves the head from side to side, but I'm not sure how easy this might be.
Anyone have any better ideas? - So far the project has been built largely from scrap, so I'm hoping not to need to spend too much money on this.
Have you considered doing it the other way around. Rather than move the board, you could use a few peristaltic pumps to fill and drain the tank with the appropriate fluids.
use a few peristaltic pumps to fill and drain the tank
That's an idea, I can see where you're coming from, but I can't help feeling that at some point the different liquids might get contaminated, some of the chemicals are pretty nasty so I think I'd prefer to move the board instead.
You could get plenty of movement from a servo by using a long arm or a sail-winch servo. Servos are so simple to work with both mechanically and control-wise that I would go to some trouble to try to use one. They are probably also cheaper than the alternatives.
With 25cm high tanks, I reckon I need about 30 cm of movement (to ensure I get clearance at the top of the tank)
using a long arm or a sail-winch servo
I'm not sure a long-arm servo would give 30cm of movement, but a sail-winch servo looks promising (must admit, although I've used servos in the past, I've never come across a sail-winch servo before)
Which leads me to another question.....
What are the pros and cons of using a sail winch servo compared to using a stepper motor? I've used servos before, my guess is that a sail winch will be cheaper to buy and easier to control than a stepper motor, but at the expense of less precision?
I think the "rope or chain" could be made from fishing line. Monofilament should be pretty resistant to chemical attack. You could also pass this between two pieces of foam rubber that are clamped onto it, to squeegie off the worst of the liquid matter before the line gets to any of the gubbins.
a simple roller that winds up some sort of rope would work
Yes.
The current plan (see previous post from Robin2) is to use a winch servo to lift the PCB up and down as required, using draw-slides (or similar ball-bearing races) to provide lateral stability. Then at the top I'll have a separate slide mechanism to move the PCB from side-to-side between the tanks.
Monofilament should be pretty resistant to chemical attack. You could also pass this between two pieces of foam rubber that are clamped onto it, to squeegie off the worst of the liquid matter before the line gets to any of the gubbins.
My plan is that only the PCB and it's clamp should actually be inserted into the etchant. The up/down mechanism itself should remain clear.
Fulliautomatix:
but at the expense of less precision?
Lifting stuff in and out of a tank shouldn't need much precision from the motor - well within the scope of a servo, i imagine.
If you are content to use a "rope" to lift the boards then a 30cm is about a full turn of a 10cm diameter drum or a half turn (standard servo) with a 20cm drum.
Robin2:
Lifting stuff in and out of a tank shouldn't need much precision from the motor - well within the scope of a servo, i imagine.
If you are content to use a "rope" to lift the boards then a 30cm is about a full turn of a 10cm diameter drum or a half turn (standard servo) with a 20cm drum.
...R
using some PVC pipe, I would expect a 2 CM drum. times pi() about 6.28 CM circumference, about 5 rotations for 30cm movement. Would need to use some large pipe to get less than 1 revolution.
For an application like this you could easily make a winch drum of any required size. A piece of timber with several screws in it would work perfectly well - see attached (when I find the attachment button)
Alternatively, just cut out a disc of MDF. Put a bolt through the middle, hold this in the chuck of a drill. Clamp the drill to a worktop and apply a rat tail file to the edge to create a pulley. It's just a crude lathe, but it does the job.
KenF:
apply a rat tail file to the edge to create a pulley.
I guess that is a file with a circular cross-section - a round file. I've come across the name lots of times in the past but never realized what it meant (guess I just never bothered to think)
