Here's an odd idea I'm toying with, but I can't quite work out a decent practical way of implementing it.
I want to have a device which will form a kind of gauge, with the value being represented by the fluid-level in a small cylinder. I'm thinking in the range of ~2cm diameter for the tubes.
What I really need is some inspiration for some mechanism that will raise and lower the level to particular points, whilst not becoming to large.
Here are some initial thoughts (bearing in mind there will need to be several of these in the display):
A syringe with the plunger fixed to some sort of linear actuator
Some sort of compressible bladder
A reservoir behind each tube, into which a mass can be lowered to raise the fluid-level
A cheap and/or home-brew peristaltic pump
A future-tech nanofluid that expands directly proportionally to a voltage applied through it*
Any comments? I'm hoping I've missed something obvious
A syringe with the plunger fixed to some sort of linear actuator
Some sort of compressible bladder
A reservoir behind each tube, into which a mass can be lowered to raise the fluid-level
A cheap and/or home-brew peristaltic pump
A future-tech nanofluid that expands directly proportionally to a voltage applied through it*
Looking at your list the first one appears to be practical, cheap(ish), controllable, and keeps the fluid in a contained system. Doing the maths, your tubes can be up to 30cm tall at that diameter, and still only contain 95ml of fluid, which means a cheaply available 100ml size jumbo syringe* would be able to do the job of the unseen reservoir.
I'm pretty sure you'll need your cylinders to be open-topped to allow the liquid level to rise though.
Good luck ! Geoff
A quick search on eBay shows they commonly come with 80cm of tubing in this size too
Thanks, that's what I was thinking so far. I probably just need some sort of servo strong enough to pull/push the plungers (which can be very stiff), or perhaps use a threaded rod/motor combo of some sort. I probably need to draw some more ideas, maybe prototype some stuff together. I'm really good at the whole "coming up with ideas but never getting anywhere with them" thing, so need to change things around a bit
Okay, I've ordered some larger syringes, as the only ones I had lying around were little 5ml ones. They would require both a thin "display" tube to make a decent difference in level, and also a long "draw" to move the level up and down.
I've ordered some 50ml and 100ml syringes, and I'm hoping that if I have a small-ish (5-10mm) display tube, then the fatter syringes will need much less movement to affect the water-level as required. That way I can cut the syringes as short as I need.
The problem then will be how to connect a servo to the plunger in a useful way. I've seen some linear servos, but they are a little pricey for testing, and eventually I'll need 8 of these. Can anyone suggest a simple alternative? Currently I was thinking of a simple lever attached to a servo-horn. Which reminds me, I need to buy some more servos
Basic requirements would seem to be:
20-40mm travel distance
powerful enough to push/pull a syringe plunger
accuracy not critical, as long as I can get maybe 10 positions from "lowest" to "highest"
A syringe is intuitively a good fit to the problem, but ordinary syringes in that sort of size need a lot of force to move. Given that the system is unpressurised and does not really need to be sealed, I think the alternative DIY approaches of either connecting your vial to a bag and squashing the bag, or using displacement to change the level of a second container, would be mechanically much simpler and more reliable.
This certainly is different.
Connect the lower end of the water tubes to a very flexible rubber nib, like an inch worth of water balloon.
Twisting the end of the water balloon increases pressure and forces the water up.
You can then use regular rotational servos to do the rotate, with quick response.
I think a pump will be way over-kill, the amount of water is only going to be enough to fill some little tubes
Great idea with the balloon-twisting though Techylah!
I found some tubes virtually free on eBay, that have a mere 4mm internal diameter. That means for even a 5cm maximum-deflection, I'll only need to move less than 1ml of fluid. I'm hoping that the perspex tubes will still show the level enough. Throw in a bit of coloured light and they should look pretty enough. Experimentation is key here, I think
I was going to suggest using colored water. Then I realized your colored light has cool possibilities.
Use a single milky RGB led with PWM. As the green water level rises near a threshold it becomes cautionary orange-yellow. It switches to red when it goes above a threshold.
If you can get a slight, not fully opaque, non-settling cloudiness to the water, the whole column of water can be colored and have high contrast.
Perhaps a simple bulb or length of highly flexible tubing can be used at the bottom.
The servos simply squeeze the bulb or pinch the tubing a little.
It will be highly non-linear, but you can linearize it in software with a lookup table or multi-map.
Ooh! Got a linearity fix. Pressure does correlate linearly with fluid height! If a pressure sensor is connected to the tube and it is sensitive enough (big if?),
your software can simply take a pressure reading at fluid level 0 and one at fluid level 100.
To display level 67% your software starts cranking the servo, increasing the repeatedly measured pressure until it reachs exactly 67% of that between level 0 and 100!
I'll play with the balloon idea this evening, now that I have my new servos. (The old ones I burnt out in other experiments :))
The level will be more than accurate enough just using software-based calibration I think, no need for anything so precise as pressure sensors. I'm not sure how much I'd need to spend to be able to detect the difference in pressure of a column of water only 4mm across over 5cm (at max!) of movement! Someone opening the room's door would probably have more impact.
