Hey guys! I’m an art student wanting to make a large clock, but instead of hands, I want a 30cm diameter disc of plywood to make a full rotation every 24h. The “clock” will have a chunk of charcoal dragged across its face every time someone opens or closes the front door of my school. So, over time, we’ll see an accumulation of marks denoting the comings and goings of students and staff.
I currently have on hand a raspberry pi zero, prototyping tools, decent programming knowledge, basic electrical knowledge and a few tutorials under my belt. I’m still firmly in the “tutorial following” stage of learning.
To rotate the clock face, should I use a stepper motor, or a heavyweight servo? I’m also a bit confused about what the best motor controller will be for this project. I own a few DC motors and a dual sparkfun motor driver, but I’m assuming that I’ll need something different (I got the stuff for https://core-electronics.com.au/tutorials/how-to-control-a-motor-with-the-raspberry-pi.html and have completed that tutorial)
Can you please recommend an appropriate motor/controller combination, and suggest the most appropriate motor head fittings? If you have any additional information that might help me to figure this out, that would be great! Thanks so much!
Interesting idea, if you’ve got a Pi zero, some practice soldering, and some knowledge with C or Python to control the GPIO on the Pi you can easily add a bonnet to the board in order to control a stepper motor (for a light wooden arm a Nema 17 should be more than powerful enough and easy to use as you’ll just need to break the 24 hours into 200 steps each being 1.8 degrees) I’ve linked some parts for you below in order to set this one up. Make sure to let us know how you go with the project ! Or if you have any further questions feel free to post them here.
PS. You’ll also need a 12V supply (wall or battery) with sufficient power, you can find some on the site if you don’t have one already.
Btw, you can get a store credit by applying to have your project put on the site from the link below.
Hey Bryce! Thanks heaps! It’s really nice to have support with this sort of thing, you guys are the best.
Just wondering, if I wanted to extend the wires on the stepper motor so that it’s further away from the HAT, what should I use?
That adafruit tutorial is really helpful, thank you! I often feel intimidated looking at hardware and not quite knowing how to put it all together. I should have a 12v power supply kicking around the place somewhere. Thanks for the reminder about sharing projects too, I’ve got a completed one which I’d love to share for store credit! Cheers.
Thanks, it’s much appreciated . Given the low current, I’d go with some 22AWG hookup wire of some description and solder that to the currently existing leads covered with some heatshrink. All the best with the project!
Also, one last question for today - if I want to mount one of those NEMA-17 motors directly on to some wood, I can only see options for L-brackets. Does that mean that to mount it in a U fashion (with the motor shaft sitting at 90 degrees to said wood), that a long screw could go all the way through the corners of the motor chassis directly in to said wood? I had a read of the data sheet for the NEMA-17 motors, but it’s not obvious as to whether the screw holes go all the way through.
You’re welcome, unfortunately, they only go around halfway down the metal faceplate as I’ve shown in the image below. But yes, you should be able to drill some holes in the wooden face of your clock then put some bolts down to the NEMA 17. It doesn’t matter if they’re slightly too short, just as long as they get some bite on the threads. Not sure about what you mean by whether the shaft is machined. NEMA17 usually use D shapes for their shafts as standard, should go fine with that mounting hub just make sure that grub screw is over the D and you’ll get a much stronger connection. Good luck with the project, we’re excited to see the final result!
Ah! Of course! Thank you so much Bryce and Jim. Seriously grateful for the effort you’ve gone to to explain things. Hope you have an excellent weekend, and I’ll check back in with some progress! Thanks all!
Interesting idea. I was thinking the inertia of a large disk attached to a stepper motor directly might cause some problems. Also with 15cm of leverage it might be easy to knock the disk and move it a few steps. According to the specs the suggested motor has a hold of 2kg*cm which means a force of 133gm at the rim is enough to knock it. That’s not much.
A possible solution is to put a large gear on the back of the disk and a worm drive on the stepper. The disk couldn’t be accidentally rotated, and a smaller stepper can be used because it has a huge mechanical advantage. The disk would rotate without much visible jerking. A direct drive with a 200 step motor gives an almost 5mm (at the edge) step every 432 seconds. You’d get a lot of lines in 5mm increments.
I have not used a 3D printer, but I’m thinking the big gear could be made in segments and the worm drive made out of a suitable shaft. The mechanism used on cheap work benches to move the moving section comes to mind. Or a bit of an old G-clamp.
Stepper motor drivers have a micro stepping ability. The one I used (below) has up 1/16th of a step, meaning there are up to 3200 steps available per rotation.
Another consideration.
Stepper motors draw current all the time. I was surprised how hot it got at the maximum current level. Backed off to half it was cooler but its holding ability decreased significantly. The link by Liam might be a better choice although much larger and more expensive.
Hey guys! Back with a project completion update for you.
Thanks heaps for your help. I ended up going with the adafruit hat and a nema 17 doing full steps (microstepping made the motor mad for some reason). I also ended up ditching the heavy chipboard clock face for some very thin ply - the motor wasn’t keen on such precise movement with heavy weight and high torque “ticks” of the clock.
I learned that stepper motors get really hot when always engaged too, so decided to release it after each tick, which let it sleep for a good 6 minutes between activity.
The aidafruit tutorial was amazing - very succinct, and the clock itself was only 4 lines of code! I learned how to solder, and in general feel really empowered now to make anything I want to move.
Well done, I especially like the paintbrush pendulum, very creative! If you would like to submit a write-up for a store credit feel free to use our link, I’m sure that there’d be plenty of other customers interested in this kind of project. Have a great day!
super cool, always awesome to see projects go from ideation to a finished product, would be interesting to see what it looks like after a couple of months
I love this project - (especially the paintbrush pendulum ) . It’s a great combination of creativity and stem skills. Sounds like there was plenty of creative problem-solving involved too. I’m sure It will make really interesting marks over time, as the density builds up and it shows the data from the traffic in and out of the door.
It’s great to see art students exploring and making this kind of work. Hopefully, it will inspire others to play around with more interactive & time-based works like this. I look forward to seeing what you make next.
! Or if you have any further questions feel free to post them here.
love this project - (especially the paintbrush pendulum ) 
. It’s a great combination of creativity and stem skills. Sounds like there was plenty of creative problem-solving involved too. I’m sure It will make really interesting marks over time, as the density builds up and it shows the data from the traffic in and out of the door.
