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Steve
May 11, 2023
In Debug Hints
Several builders have asked about setting the speed on the Silent Shield Clock Controller used in several of the stepper motor desk clocks. This post will try to summarize everything a single post. Feel free to ask questions in this post. I may condense the threads to bring the important information to the top. Summary: The Silent Shield Clock Controller (available on Etsy) includes the bare minimum components needed to control my stepper motor desk clocks. This includes an Arduino Nano, TMC2208 stepper motor driver, DS3231 real time clock module, and a small circuit board to connect the components. Four small jumper blocks can be added or removed to select various motor speeds and debug modes. The first iteration of the clock used a commonly availably board called a CNC Shield V4 to provide the same functionality as the Silent Shield Clock Controller. Its primary advantage is that it is commonly available worldwide without high shipping charges for postage from the US. It uses the same electronic components with the same algorithm programmed into the Arduino Nano. Speed settings also use four small jumper blocks with the same configuration as the Silent Shield Clock Controller. Speed Settings: The latest speed setting is selected according to the following table that is used by the latest algorithm that is accurate as of 11-May-23. The table may change over time as new clocks are designed, so double check the assembly notes that come with your clock and download the latest algorithm from the clock description page on this web site. The most current algorithm supports the six different speed settings used in four different clocks. The jumpers select the speed. For example, the SP10 clock with 400 step motors uses setting number 2 with a jumper setting of 0010. This corresponds to jumpers from left to right that are "out", "out", "in", and "out". Here are pictures of both style of boards showing speed setting number 2 with jumpers set to 0010. The Silent Shield Clock Controller uses four out of the five available jumper positions as shown below with yellow highlights. The fifth jumper at the far-left position is not used. This picture is showing the 0010 configuration. The jumper pin locations for the CNC Shield V4 are located here. This picture is also showing the 0010 configuration.
Setting the speed on the Silent Shield Clock Controller content media
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Steve
Dec 16, 2022
In Electric Clocks
My latest project is a better stepper motor driver for the desk clock. When I designed the clock, the resistor-based driver circuit was the quietest solution I could find. It was mostly silent, but over time the gears started to develop a slight rumbling sound. The motor itself seemed quiet, but the gears were starting to rattle. Another thing that really bothered me was the ridiculous cost to ship the tiny circuit board overseas. Shipping and customs costs were often 3X higher than the board itself. I went searching for something better and believe I may have found a solution. The secret is to use a board called a CNC Shield V4 which is designed to allow an Arduino Nano to control three A4988 stepper motor drivers. The A4988 is replaced with a much better Trinamic TMC2208 driver. This reduces the noise and allows everything to run on 5V. A precision real time clock was added to serve as a reference timer. Here is the bill of materials: 1) CNC Shield V4 – Amazon US$10.96 for 3 boards. 2) TMC2208 drivers – Amazon US$21.99 for 6 drivers. 3) Arduino Nano – Amazon US$16.99 for 3 modules. 4) DS3231 Real Time Clock – Amazon US$12.11 for 4 modules. 5) NEMA17 stepper motor – Amazon US$9.99 each. The CNC Shield V4 was modified to fix a known bug and to wire the RTC into one of the unused driver ports. Here is the circuit: The TMC2208 was set to 16X microstepping mode. The algorithm adjusts the stepper motor delay to stay synchronized to the real time clock reference. The DS3231 is voltage and temperature compensated to stay accurate to around 1 minute per year. And the clock is significantly quieter. One downside is that the CNC Shield V4 is huge compared to the custom driver that I was previously using. I am designing a new base to fit the larger circuit. It looks like it will fit. The ability to buy off-the-shelf components is a big advantage. It does not make sense to design a more compact custom circuit board. Updates to the existing MyMiniFactory desk clock are coming soon. A larger version of the desk clock is also in progress. I designed it a while ago but did not release it because the gear noise was too high. That rattling noise is gone with this new driver circuit. And a wooden gear version of the clock is in progress. Stay tuned for more information. Steve
New Stepper Motor Driver content media
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Steve
Apr 28, 2022
In Wood Gear Clocks
A woodworking club near me held a project challenge to make something with a small amount of bamboo material that they provided. I decided to convert the 3D printed desk clock to wood. The wooden gears are super quiet compared to the printed version. The size is about 8" tall and 8" wide. Larger versions are being planned. I am running low on the small circuit boards used to control the stepper motor in the clock. My goal is to have a new design with a real time clock added for the next order of boards. The RTC looks to be the easiest to integrate https://www.amazon.com/Sensors-Precision-DS3231-Arduino-Raspberry/dp/B08D11ZGMK and it uses a temperature compensated oscillator. I am still working on the algorithm. Hopefully it will be ready soon.
Wooden Desk Clock content media
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Steve
Apr 27, 2022
In Crazy Ideas
I just received two rolls of some really incredible looking dual color PLA filament that should make some great looking clock gears. The gears will change colors as they rotate. Here is the same gear with different orientations. It is a bit pricey at $37 for a 0.75kg spool. A typical clock will use about one half to one third of a roll.
Quantum PLA content media
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Steve
Apr 10, 2022
In Debug Hints
It looks like I have finally found a fix for the "sticky gear" issue that has been causing the easy-build clocks to stop. A clock can be running perfectly and suddenly the escapement stops rotating when the pendulum is moved back and forth manually. The clock can be made to operate again by pushing on the escapement, but the problem has not been fixed so the clock will only run for a short time. The root cause is gear 3 pushing against the escapement and preventing it from rotating. It takes very little sideways pressure to stall the escapement since it very lightly loaded. Straight spur gears should not have any sideways motion, but it seems like they do. The cause could be frame sag, not perfectly level walls, or gear 3 tilting so it gets pushed sideways. This problem has been particularly difficult to debug because the symptoms do not change when the drive weight is increased. Now it makes sense because a heavier drive weight will apply a proportionally larger pressure against the escepement. The fix is to add a gentle helical twist to gears 3 and 4 to push gear 3 away from the escapement. Gear 4 has five different runtime options, so the complete fix requires a new gear 3 and the appropriate runtime option of gear 4. Both the 32 day and the larger 21 day easy-build clocks are affected by this issue. Here is a picture showing a small helical angle on the large portion of gear 4 in the front and the pinion on gear 3 in the back of the image. This solution was prompted by a series of questions on MMF by Felix. I ran some tests to confirm the hypothesis. A previously buggy clock was brought back to life with a large pendulum amplitude. A clock with a reverse helical angle to exaggerate the issue will typically stall within 5-10 minutes. The new gears have been uploaded to MyMiniFactory for both sizes of the easy-build clocks. I will try to post a video describing the solution soon. Steve
Sticky Gear Solution content media
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Steve
Mar 11, 2022
In Show and Tell
Hi Massimiliano, Congratulations on getting your electromechanical clock running. It was a lot of effort and I realize that there is a language difference. Google translate does not always work very well on PDF files. I just noticed a translate feature in Microsoft Word that does a much better job. Some page layouts needed to be manually shifted to get images to fit on the same page as the associated text. Screen captured images are obviously not going to be get translated. Overall, I think it may be helpful. Do you mind checking out the translated assembly notes to see if it is readable? I only recognize a few words and mostly just lined up the pictures to match the original source. Steve
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Steve
Dec 16, 2021
In Show and Tell
I finished the prototype of an electromagnetic pendulum drive clock. It uses the electronics from a US$4 pendulum drive module. The only change needed was to run it with 3V to adjust for the extra friction from the ratchet pawls. The first overnight run was accurate within about a minute, although it can probably be tuned to within a minute per week. Electromagnetic Pendulum Clock - YouTube The design still needs a round of fine tuning and an assembly manual before posting to MyMiniFactory. Hopefully, it will be ready in January 2022. Steve
Electromagnetic Pendulum Clock content media
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Steve
Oct 25, 2021
In Debug Hints
Recently, I have had several clocks slow down and eventually stop running after a few weeks of months of operation. The symptoms are the clock has stopped and manually moving the escapement back and forth does not produce any movement in the escapement. Something in the gear train is completely stuck. Wiggling a few gears or winding the clock a few clicks will often allow the clock to start running again. However, it only runs for a short while and stops again with the same symptoms. All the troublesome clocks were built using silk PLA because I really like the way the gears look. My best guess is friction as the gears move. The gear profiles are correct, or at least the gears in CAD are correct. Errors could creep in if the gears do not match the expected CAD profile. I will try to find or create a test pattern specifically designed to test the gear accuracy. It could require a change to the extrusion multiplier or XY size compensation. I already have elephant foot compensation under control. The other consideration is friction as the gears slide past each other. Most of the gear movement is a rolling action with no sliding, but there is always some sliding as the teeth are starting to engage. I printed some small squares of material that allow comparing friction between different brands of PLA. The test jig would have a section with normal PLA next to normal PLA and another section with silk PLA next to silk PLA. Sideways pressure is applied and whichever one moved has the lowest friction. One thing that was apparent was that lightly loaded PLA of any type has low friction, but friction is much higher when pressure is applied before sliding the pieces. This would be roughly comparable to dynamic friction with a light load and static friction with pressure applied. I tested 12 different spools of PLA consisting of 3 silk PLA, 2 translucent PLA, and 7 normal PLA. The 3 worst performers were silk PLA, followed by 1 of the translucent, a normal PLA, then the other translucent PLA. The best 6 were normal PLA. Most of the normal PLA brands were difficult to distinguish, but the silk PLA samples were obvious that the friction was higher. The next step was to replace some failing silk PLA gears with normal PLA gears. The clock definitely runs better, but I can tell that there may still be some issues. I will continue looking for better fixes. A few other suggestions are to use the shorter runtime options where they are available. I have been running my 32 day easy build clock with runtimes of 8 to 10 days. I am also looking at different tooth profiles with lower friction. I have tested some modified cycloid gear profiles, but they were slightly worse. Involute gears seem to have lower friction in a clock. The next test is to compare different pressure angles to see if one is better than the others. I may also try finer pitch gears where they are closer to the escapement so the pinions can have more teeth. Let me know if there are any other ideas. I would like to get back to having a fully functional clock with a 32 day runtime. I know the clock works, because I have had it working. However, the high static friction needs to be fixed for the clock to be super reliable. I am looking for a fix. Steve
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Steve
Oct 24, 2021
In Crazy Ideas
I recently purchased some tiny geared motors in the hopes of making a rewind mechanism for a new clock. They are called N20 gear motors and are available with gear ratios ranging from 10:1 to 1000:1. They are incredibly tiny at 12mm by 10mm by 38mm with all metal gears. Prices are around US$10 on Amazon and as low as US$2-3 on eBay. These are the motors that seem to hold the most promise. The 1000:1 motors are incredibly quiet. I also tried some 120:1 motors that were a bit noisier. Current was measured at around 0.03A at 3V with no load and possibly 0.05A with a larger load. I am thinking that a small gear can be added to the 3mm end shaft. This gear would attach to the outside of either the minute hand gear or the nest gear closer to the escapement. A simple on/off microswitch could have enough over-travel to trigger the rewind to lift the motor. The weight of the motor falling would power the clock until it needs to be lifted again. Steve
Electric rewind content media
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Steve
Oct 24, 2021
In General Discussion
This forum was created to allow clock builders to ask questions or search for answers from previous builders. Most posts will likely be focused on clocks designed by Steve Peterson, but any clock making questions are welcome. The intent is to share knowledge. Some of the sub-forums are publicly visible and require a simple registration to post. Hopefully, this will be enough to keep out the spam. Rules: 1) Be nice. 2) No sharing of plans without permission. 3) Try to stay focused on clock related topics. 4) New threads for separate topics are preferable.
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Steve

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