Hey! I‘m completely new to Steppers and would be happy about some advice for my project and purchase.
I want to tension three dyneema cords with Steppers that hold a mass of 1-2 kg in place. The mass will be 3D printed and sliding on a low Friction Surface like teflon. My first step would be just to tension the Cords so the mass is stabilized.
Then I want to try to move the mass by adjusting the cord lenght with Steppers. The movement should be possible in percision mode (1mm per second or even less if possible) and in fast mode (up to 10 mm per second). The goal is to move the mass for a few hours in precision mode and then recenter. It will be an art Installation.
As my budget is kind of small, im searching for a cheap but long lasting Solution. Maybe that combination is the biggest Problem. I got about 150$ for the whole setup.
I‘ve read a lot but im not sure if I should use Steppers with worm gears or planetary?
Or brakes because sometimes the mass should stay stationary even when touched (preventing wobbling).
I can to code the logic by myself except the Stepper Controller. Any suggestions to get good results Are very welcome! I Hope the information is enough.
With stepper motors, you don't need worm or planetary gears. Research the various stepper libraries and then look at the example sketches that come with the libraries.
Read the pinned post re 'How to get the most from the forum'
Try doing your project, and when you get stuck, draw the wiring and take a picture of the drawing. Post all code in code tags, then ask your specific question.
Just a bit of thinking on my part. See if you can get, beg, borrow a small scale. Put together the mechanical part then using the scale see what amount of force it takes to move your mass. Be sure to take in to account the force to get it “UN-stuck”. You will need this information to size your motors etc.
You will also have to know the maximum distance you need to move so you can determine the line length and how you will connect to them.
This should get you at a point where you can size your hardware. With care you should have enough left over for your favorite sandwich.
Horizontally, you could add a spring to tension the third cord in order to hold the mass securely against the constraints from the first two cords without causing binding or slippage.
By the OP original spec, there needs to be tension three ways, but no mention of sensor to give values to that tension. If gravity is pulling the object, then all three tensions will be identical. But who knows!
I mean that two ropes/steppers are enough to completely define the position, and the third rope (if it doesn't have a spring) needs to be carefully adjusted to keep proper tension on the other two ropes.
The vertical Makelangelo uses gravity to tension against the two position-defining lengths of belt, but in a horizontal configuration with a stepper for tension and low-stretch dyneema, you'd need excellent coordinated control of the third stepper.
I'd consider completely replacing the third stepper with a drum and a spring or weight to eliminate the 3-axis coordination of steppers to manage tension.
For example:
That would probably cost the whole $150 budget from McMaster Carr, but one could do something cheap using a drum with two diameters and a weight.
All these suggestions are crystal ball readings until @daneben234 exactly tells us what he wants to do. What he wrote so far is definitely not enough to get an imagination what he really wants to do.
Atm. this is all just an idea I want to bring to life.
I think a sensor to measure tension sounds like a good idea.
And yes, having tension on all three sides to fixate the Object also when moving (as good as possible) is crucial, as the Object will be touched and people will try to move it a bit. Maybe with a max force of 0.5 N?
And while talking about it, I noticed that I need a mode where I can move it by Hand of needed (on Button press) or in case the Battery is empty. Are wormgears useful then or do I need brakes?
I cannot give much more information as i am new to the field and I dont know what I need. This is why I ask. Unfortunately I think this is all I can say but every Input is welcome and helps me to find out what I need. Thanks for all replys so far!
Are confident you can write a program than can track the tension of three sensors in real time and make your system react correctly in real time? What is your estimation of the time you will need to complete your project?
How big is it? How far does the object have to move? How much of the triangle between the three points does it have to cover?
At 0.5N max force, there are a lot of cheap UHMWPE/Dyneema fishing lines that might serve. And the tension on one line, taken with the lengths/geometry of the three lines, (almost) determines the tension on the other two lines--you could put just one sensor on one of the lines and calculate the other tensions from the geometry as needed.
With the maximum lengths, 10mm/sec max speed, and 0.5N max force, you could spec the motors.
See the OP will encounter oscillation problems when he gets the tension sensors working. Something to think about while building the physical structure, whatever that may look like.
That is a good point. But what could I do about it? Would somehow syncing the steppers help? When thinking about it, I have concerns that the Steppers also try to fight each other. But maybe if I just apply the right amount of force it balances out?
I know some things will need to be taken care of when building it. Its just about preventing to buy wrong steppers and so on.
Thanks for taking your time and helping to figure it out!
So, you are worrying about stuff so far in the future! Your plan will change 10 times before you actually get something that works the way you want! You actually have to begin building the project.
I don't think you are far enough along to get help here; it very much sounds like you are still in the blue sky and what-if phase. I have always found that the months spent building it in my head over and over resulted in a very fast build, but if enough time was not spent designing, the build took forever.
I’d start by building a simple prototype with three inexpensive steppers and code that is as simple as possible but that still demonstrates the most basic desired functions. Then find out what happens when:
a child (or adult) grabs your puck and yanks it around while the system is energized.
you move it around when the system is not energized (as you said you need to do, to reposition it).
your steppers fight each other (as they will; @DaveX’s good advice regarding constant tension device for one of the cords would help reduce the odds of that)
Edit to add a comment regarding your question about using motors with worm gears: among other issues with worm gear motors, many/most worm gears are self-locking, so unless you built in a clutch, you wouldn’t be able to manually reposition your “mass”.
That would be one way to start, but the whole project only works if the OP can make a tension sensor with output readable by an Arduino. I have yet to see anything from the OP relating to such a mechanism/sensor.
I may be missing something, but I’m not sure there’s a need for tension sensors if one of the cords is connected to a constant tension device. Otherwise, another way to design in some forgiveness and possibly eliminate the complexity of tension sensors: connect each cord to the mass via a spring. Not sure that would satisfy the OP’s somewhat mysterious goals. In any case, the geometry must be reasonable. Gets back to @davex’s first question, still unanswered, in post #12.
