a clock which rewrites time again and again

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This project is a continuation of my quest to build a robotic clock which can write and rewrite the time continuously day in and day out and keep going doing it. My first attempt with doodle clock was a failure due to the marker drying up and the second attempt with doodle#2 failed as the display got scratched very soon .

This clock was inspired by my daughters t shirt with the pattern changing sequin cloth glued to it. After getting some stock fabric from a vendor i figured out the size of the clock based on the minimum resolution of the cloth . The fabric has circles of 5mm stitched 3 mm apart. Also another limit of the clock was my printer bed size of 245x170mm . H

The kinematics

The kinematics of the clock consists of a mix of h-bot and Cartesian system. The y axis consists of the two rings on the extreme ends of the clock driven by 2 24byj48 motors . The rings are basically gears constrained in outer rings similar to a hubless wheel. The x-axis consists of a strut holding the two rings together and driving a belt routed on a h-bot based path. The belt is driven by two motors. The motors when moving in the same direction move the pen carriage left or right on the x-axis while when then move in the opposite direction move the pen up or down. 

Figuring out the cloth backing 

The Sequin cloth consists of disks which are stitched to a a fabric backing. The Disks flip easily with a finger as they are mounted on a t-shirt or a bag which has a soft backing .But the moment i mounted it on cylinder it stopped flipping as the disks got over constrained by the hard backing . First i tried a ribbed structure as a backing with the fabric stretched on it. It worked but made it very complicated to construct. 

Finally i figured it out that a simpler way was to just add a 3 mm sponge as a backing to the cloth to give the disks the freedom to flip.

The tip of the pen

The tip of the pen was very tricky to figure out. Getting a material to act like the tip of a human finger is not very simple. The disks are very slipper and need just the right friction to flip them.  The final solution was tip make of Tpu with a split hook. 

  • 1 × arduino nano
  • 1 × nano cnc shield
  • 3 × stepstick a4982
  • 1 × hall sensor
  • 2 × ir reflective sensor

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  • prototype #2

    ekaggrat singh kalsi01/25/2020 at 11:24 0 comments

    this one i redesigned again ground up to make it more cleaner. the y axis is now a hubless axis which moves in a contained outer ring. The y-axis homes to a hall sensor on the back side and the x-axis homes to a optical sensor on the right side with the help of a white mark on the rubber belt. The pen homing is very tricky. After a lot of trial and error i found a way out by first homing the x-axis , then backing up a bit and then homing the pen at a known belt mark to a sensor on the left side of the clock and then finally moving a fixed distance to zero it. This is not perfect as it sometimes overshoots the mark , but a error of 1mm on the pen is ok in this case. 

  • prototype 0.5 and 1

    ekaggrat singh kalsi01/25/2020 at 11:12 0 comments

    the first two prototype was just figuring out the frame and kinematics . I didnt want the the pen to have any kind of ugly wires hanging outside which would be the case had i used a normal solenoid or a servo to lift the pen. To avoid that i used a h-bot mechanism to drive the x axis and the pen.  

View all 2 project logs

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aldolo wrote 12/22/2020 at 06:47 point


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Roy wrote 02/11/2020 at 18:04 point

Okay, this is a fascinating, clever, wildly original piece of brilliant, sparkly engineering!  You have my vote, I love this thing!

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ekaggrat singh kalsi wrote 02/12/2020 at 01:33 point


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pete.j.morrison wrote 02/05/2020 at 17:46 point

This is a beautiful project! <3

I have a couple of pathing suggestions for overcoming your speed challenges:

1. Have your circumferential axis (z-ax?) return to the *top* of the unit (rather than the bottom) while writing - then it's ready to turn over new sequins immediately. Once you're finished writing, you could have it return to the bottom (then it's ready to erase immediately, too).

2. Given your 'sequin-specific problem" - I wonder if you can use a "scanning" movement path for the pen, whereby you flip all the sequins in one vertical "slice" in the same movement (similar in principle to old CRT displays)? That way the pen doesn't go back on itself in the axial direction so much: it's less pretty to watch, but it should be faster.

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Kelly Gann wrote 02/03/2020 at 15:28 point

Fascinating to watch it, well done!

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Sophi Kravitz wrote 01/31/2020 at 22:59 point

this is incredible! 

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ekaggrat singh kalsi wrote 02/03/2020 at 06:09 point


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mpinner wrote 01/30/2020 at 18:43 point

i love this!!!

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Mike Szczys wrote 01/30/2020 at 15:36 point

Belt tensioning trick is a brilliant way to add Z to this. Very cool!

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Jan wrote 01/30/2020 at 15:39 point

What! I didn't get how he moved the "pen" until you wrote your comment. Awesome!

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ekaggrat singh kalsi wrote 02/03/2020 at 06:08 point


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Maximilian Laurenz wrote 02/05/2020 at 17:00 point

I agree, this is a very nice and simple solution. Well done :)

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Richard Hogben wrote 01/28/2020 at 18:50 point


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sjm4306 wrote 01/28/2020 at 15:45 point

Awesome project! I need a giant wall of this fabric and a little spider-like robot to climb along and draw stuff.

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sjm4306 wrote 01/30/2020 at 13:37 point

Oh I'll definitely add this to my long list of projects I want to make.

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ekaggrat singh kalsi wrote 02/03/2020 at 06:10 point

too fast and u tear apart the sequins. my limitation was the 28byj48 motors.. I am looking for faster ones . maybe servos

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Dan Maloney wrote 01/27/2020 at 17:50 point

That sequin fabric is endlessly fascinating stuff. Nice application for it.

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Michael Erberich wrote 01/27/2020 at 02:42 point

That 2DOF belt drive is really very clever!

One potential optimization I could see is only redrawing the segments of digits that actually change. This would be fairly straightforward if the digits are partitioned like a seven-segment display.

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ekaggrat singh kalsi wrote 01/27/2020 at 03:36 point

thanks! yes initially the idea was to replace only the segments of the digits. but if you look carefully the disks are interlocked and starting and stopping the drawing of the segment is complicated and removing just one segment is impossible to do without disturbing a adjacent segment! 

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Michael Erberich wrote 01/27/2020 at 03:45 point

Oh, I hadn't noticed that before... interesting, a sequin-specific problem. In that case I'm really curious to see what kind of optimizations you can come up with instead!

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bobgreenwade wrote 01/25/2020 at 15:34 point

I'll be watching this. Once you get it to work right, I may try to follow your work and make one for myself. It'd look really cool in my home (I'm sure I can find a good spot if I try hard enough).

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ekaggrat singh kalsi wrote 01/25/2020 at 21:33 point

sure , i need to now see the durability of the motors and the fabric

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Ken Yap wrote 01/25/2020 at 15:26 point

Very creative. One could spend a lot of time just watching it.

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ekaggrat singh kalsi wrote 01/25/2020 at 21:32 point

ya , now i need to see how long the fabric lasts. 

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kristina panos wrote 01/25/2020 at 15:06 point

This is so cool! Definitely the best application for that reversible sequin stuff. :)

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ekaggrat singh kalsi wrote 01/25/2020 at 21:31 point

thanks a lot

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davedarko wrote 01/25/2020 at 09:20 point

This looks awesome! Definitely want one for my hackerspace :D

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ekaggrat singh kalsi wrote 01/25/2020 at 11:16 point

thanks .. sure i will publish more details after i sort the files out

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Jan wrote 01/27/2020 at 18:15 point


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