Actuated Display using motorized pots

Preface: I’m quite new to the world of Arduino (and also to electronics), so please don’t berate me too much or assume much background knowledge*.

I’m planning to create an actuated display, where small sections can be raised and lowered, kind of like this. Eventually, I’d like it to be 10 x 10. Right now I’ve gone as far as creating a 2x2, actuating segments using these (sliding) motorized pots (one for each segment).

Equipment for a 2x2 section:

  • Arduino Uno (1)
  • sliding motorized pots (4)
  • h-bridges (2)
  • 10 uF caps (2)
  • (jumper wires, breadboard)
  • powering sliders with a 9V battery and the board via USB cable

Function-wise, I’d like to monitor the position of each slider and (obviously) to be able to set their positions. Capacitive touch would also be fun to add.

I have quite a few questions-- I’m not sure if I should include them all in one post, but perhaps some of them are related… so I will this time 'round. Here goes.

I’m not sure how easily this will scale-- how many actuators per Arduino (I realize this depends on the board and number of pins-- maybe a Mega would be best to minimize the total number of boards), how many PWM pins I need per slider etc. I think I only need PWM pins if I want to control the speed of the slider? Maybe I’ll run out of analog input pins first…

I’ve also read of folks using motor drivers which contain h-bridges, rather than just h-bridges. What are the advantages of this?

I’m most worried about the footprint of the slider. Without staggering the sliders, I think each would have about a 1 1/2 inch2 footprint-- this is larger than I’d like. I think it might be possible to stagger them, having two levels of sliders, with each slider attached to a long rod. This would allow the the size of the sections to be halved… which is better. Ideally they’d be even smaller, but I’m not sure if I can make this happen using this size of sliders. I could maybe use servos and push and pull rods? I’m not confident in how these work-- could I get enough travel? I’d like the segments to be able to move up and down at least a few inches. Servos would certainly be cheaper, but knowing the height of segments might be tricky…

I am not sure what I’m going to do to power this. Right now I’m using a few 9V batteries and powering the board via USB cable. I don’t want to continue using batteries, and I’m not sure how I’d connect a larger power supply (a wallwort?) /determine current/voltage requirements.

I’m thinking jumper wires on a breadboard is not what folks do for semi-permanent projects… but I’m not sure what’s done for more permanent projects. Should I eventually figure out how to design a PCB? Or use veroboard and solder? How much (ballpark) might a PCB cost?

I realize some of these probably sound quite silly/perhaps require additional information to answer - I’m a complete n00b, so I don’t even know how to ask the appropriate questions yet ! But pointers/suggestions/thoughts/discussion about anything related will likely be helpful.

Posts I’ve consulted:

http://blog.codyhazelwood.me/motorized-faders-and-the-arduino/

*Suggestions for resources to gain this knowledge are most welcome!

Hi,
Looks good, "Motorised Pots", do you mean Servos?
Have you got a spec or picture of the "Motorised Pots"?

Tom..... :slight_smile:

Hi,
Sorry I see why motorized pots, you want to be able to move the sections not just with software but manually and feed the position back to the controller.

Tom...... :slight_smile:

I'm guessing the motorized pots can be moved manually without damaging the motor mechanism. That is not normally possible with regular servos which are designed to resist movement. However it may be possible (i.e. I don't know, I am just thinking aloud) if you use servo.detach() to stop the Arduino providing a signal. I think you could also modify the servos so that the connections to the position resistor would be accessible to the Arduino so it could detect the position if the servo was moved manually. It would be very cheap to try this idea.

The great advantage of a servo is that it only needs a single connection to the Arduino to control it - plus perhaps another connection if it is modified so the Arduino can read the position.

If you connect the servos to the sort of "wire in tube" push rods that are used in model aircraft the servos don't need to be close to the moving segments in the table. That way the segments could be as small as (say) 5mm square.

You would buy a lot of servos for the price of 4 motorized post.

It looks like a complex project, but lots of scope for interesting experimentation.

...R

Hi
These would be the motorized pots that used to be on early software controlled audio mixing panels.

Tom..... :slight_smile:

Hi Tom and Robin,

Thank you for your replies!

Tom: By motorized pots I do indeed mean motorized sliding pots, not regular servos! There is a link to the SparkFun product page corresponding to these in my original post. And here's the datasheet, if you're interested.

It's not necessary for this project to be able to move the sections manually (at least, not at this point), but it is necessary to track their position. I chose sliders because they provide linear motion, eliminating the step of converting rotational motion to linear motion. But if there's a straightfoward way (pardon the pun) of doing this that doesn't require much space, I'd consider servos again. With servos I'm also worried about the amount of travel I'd get-- I'd like a few inches at minimum.

But they (servos) are much cheaper! I'd like to be able to use them if they'd somehow work.

Robin: Thanks for the helpful suggestions. Your comment:

"If you connect the servos to the sort of "wire in tube" push rods that are used in model aircraft the servos don't need to be close to the moving segments in the table. That way the segments could be as small as (say) 5mm square."

is intriguing! "Wire in tube" is what I was referring to when I mentioned push and pull rods. I went to a hobby store and looked at some, but I'm not entirely sure how they work. The way I'm imagining, they don't allow for much linear motion (a couple cms with a micro servo - I promise I'm not a SparkFun promotor-- I'm just linking so you can have an idea of the size if you don't already). Am I right in thinking this?

How might I have such small (5mm) segments-- would I have several tiers of servos (say 2, so the segments could be 1/2 the size of a servo) with a rod coming up from each? Might you know of any projects that use this sort of mechanism-- even using a single servo along with a 'wire in tube'?

Thanks again for your comments!

During the search on “wire in tube” I came across the well known Bowden cable (control, wire…), and throttle cable. When I remember the throttle cable on my motor cycle, such a construction could be activated by a servo motor as well. But friction may require powerful (big) servos, and disks of a big diameter, not really practical for your purpose. A piston rod might be moved with less efforts, but the total dimensions of such an crank drive may become quite large.

A toothed rack or threaded bar also could be used with motors, but positional feedback will have to be added, and manual operation is rarely possible.

A vertical rope loop or kind of a chain drive could be used, with a stick attached that moves the section tops up and down.

Finally I can imagine some pneumatic solution, blowing the sections up by use of small (notebook cooling) fans. But without high pressure or hydraulics and precise control that’s usable for shape forming only, not for lifting bowls.

Also consider the number of (PWM) output and analog input (feedback) pins, where 100 of each kind are already required for a 10x10 matrix. You’ll have to spend a couple of Arduinos for that or even larger planes. Also a big power supply or multiple smaller ones may be required, in detail when the drives are not self-blocking and draw current even for holding the positions.

If you don't need to be able to move the segments manually - i.e. only the Arduino will move them - then servos would seem to be ideal.

Why would you restrict yourself to a micro-servo? With wire-in tube/push-rods (in the model aircraft business it is actually one low friction plastic tube inside another) there would be plenty of room for big servos. They could be 20 to 30 cm from the table and don't have to be in a direct line.

Unlike a bowden-cable the push-rods can push as well as pull.

You can also extend the lever arm on a servo to get more motion.

...R

Cool, this sounds quite promising. It sounds like it's not necessary to use micro-servos, so I could use larger ones which would allow for more travel (and then maybe wouldn't have to extend the lever arms!). Though I suppose micro-servos are still cheaper...

How are push rods attached to a servo?

Would something like this be appropriate?

That link you posted shows the correct idea. Look in model flying magazines or websites. Or visit a local model flying shop and see what they have. I think it will be very obvious once you see the stuff.

Usual advice - buy one and experiment before committing yourself to a particular product.

...R