Stepper mtor - not enough friction to prevent spheres dropping

Help please I am developing a kinetic sculpture using 90 stepper motors & 11 Arduinos. Stepper with a 50mm pulley attached, with nylon to raise & lower a small 3D printed piece in various patterns. The assembly is 1200mm x 400mm with 18 x 5 matrix of stepper motors

All looking great including initial testing & prototypes. Then I decided to change stepper motors as initial ones too noisy, and stupidly I didn't re-test the concept (the original motors were geared BYJ type)

Now I'm nearing completion, and moved near completed project to a testbed where I can finally attach the spheres.

Problem With no power on the motors, the weight of the spheres (which are 3D printed & weigh 10 grams, but I want to attach a slightly heavier version at 19 gms) is enough for them to drop down to the extent of the nylon under gravity! I don't want to keep power on them continuously. Even with each stepper set to draw only about 10 mA, total current draw is in excess of 10 amps at 12 volts - and I think this too much for comfort running 24/7 ( I have 2 10A power supplies driving it)

Any suggestions on how to increase the friction of the nylon? I'm currently printing a smaller puller which will cause the nylon to rub over the hole instead of falling freely - have no idea if this might work or not.

But I'm asking if any others might have some suggestions for any possible solutions

Thanks in advance

If you post a photo of your assembly, then the possible answers could fit your assembly. Anyway, you can add a spring that presses radial on the axis of your stepper. Or simply use a rubber band that is wraped around the steppers axis between pully and casing. Or revert back to geared steppers.

RBat: Problem With no power on the motors, the weight of the spheres (which are 3D printed & weigh 10 grams, but I want to attach a slightly heavier version at 19 gms) is enough for them to drop down to the extent of the nylon under gravity! I don't want to keep power on them continuously.

Steppers are explicitly intended to be continuously powered, or they lose position. Steppers are very power hungry so an array of them is going to burn huge amounts of power.

10mA is way too small a current for even the tiniest motor.

You haven't given any details of your motors and drivers - very hard to proceed without information on the hardware you have, so please post all the details.

Thanks for your replies
Photo attached. Having thought about it overnight, I think a 10mm diameter rod that the nylon can wrap around will be my next try - don’t like the smaller pulley option at all now.

I think the 10mA for each stepper is OK - it seems to have reasonable torque for my purpose - but it will be a matter of balancing the friction to prevent the teardrop dropping versus the friction required for the stepper to lift the teardrop. I can easily increase the current / torque if required.
As per the photo, instead of spheres that I originally created, I’ve printed some teardrops to create a smaller version of the kinetic sculpture at Changhi airport in Singapore called Kinetic Rain.
As you can see, there’s not a lot of space to work with!

Maybe add torsion spring onto the pulley to offset the constant force. Maybe add counterweight to do same.

Curious, Are you using current draw as positional feedback or something else?

Thanks for your reply

I have printed some different diameter cylinders that I can attach to the motor support, and loop the nylon around it. Haven't finished testing them but it seems that it will work OK. Project now on temporary hold due to other things happening!

Positional - simply lift all the teardrops to the top and call that 0mm. Movement to xmm in time t, a simple function of pulley diameter, steps per revolution, and the time required

RBat: Positional - simply lift all the teardrops to the top and call that 0mm.

So your just blindly running the motors until you think they will be at the top position? How much current draw does that induce when you have 90 stepper motors in stalled condition?

Slumpert: So your just blindly running the motors until you think they will be at the top position? How much current draw does that induce when you have 90 stepper motors in stalled condition?

The same as usual, steppers are always in a stalled state, that's how steppers work!