Introduction
This short blog shows how to replace the speed control device in the foot controller on the Amazon 9.8” pottery wheel. This change may be required for anyone with irregular speed control or a damaged foot speed controller.
Determining the Part Replacement
With the pottery wheel unpowered, the internals of the foot speed controller are accessed by removing three plastic screws located in the base of the foot controller. The foot control mechanism consists of a potentiometer for setting the speed and two gears.
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| Internals of Foot Speed Controller |
To remove the potentiometer, the locking nut was loosened. This allowed removal and part identification.
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| Original Potentiometer |
As shown in the above image, the potentiometer was rated at 4.7 k 2 W. A similar device was located from TE Connectivity part 3-1625931-0 and sourced online.
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| Replacement TE Connectivity Potentiometer |
Items to Address with the Replacement Part
The TE Connectivity potentiometer is a direct replacement for its value (resistance); however, there are mechanical differences with the potentiometer, specifically the solder pins and smooth shaft. Since the original potentiometer was supplied with a D-shaped shaft, the original spur gear could not be reused, so a new spur gear needed to be created.
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| Original D-Shaft Spur Gear |
Down the Spur Gear Road
The spur gear script feature in Fusion 360 was chosen to create a compatible gear. Alternative tools are available for creating a spur gear however these alternatives were not tested for this blog. Two alternative sites may be STL Gears and Gear Generator.
Fusion 360 Spur Gear Script
In Fusion 360, the Spur Gear script is accessed from the Utilities tab under the Add-Ins icon.
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| SpurGear Script in Fusion360 |
The settings in the image below were chosen after measuring the original gear, applying them to the spur gear script followed by 3D-printed prototypes. Some important items for the spur gear were the number of teeth, shaft diameter and Fusion 360 calculated Pitch Diameter.
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| SpurGear Settings in Fusion 360 |
Fusion 360 Spur Gear Modification
To ensure that the spur gear would not rotate on the round potentiometer shaft, two cutouts were added inside the spur gear shaft area for glue. The cutout changes were made to the spur gear sketch generated by the Fusion 360 script.
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| Editing the SpurGear Sketch |
The images below show the edit to the sketch and updated 3D model.
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| SpurGear Sketch with Cutouts Added |
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| SpurGear 3D with Cutouts Added |
Ultimaker Cura was used to generate a print with a 100 % fill. The Fusion 360 file and STL files are available for downloaded at the end of this blog.
Replacing the Potentiometer
The wiring layout for the potentiometer was recorded. Using a soldering iron, the three wires from the original potentiometer were desoldered.
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| Potentiometer Wiring Connections |
For the replacement potentiometer, the centre pin of the new potentiometer was determined to be the wiper (red wire). In the configuration shown in the image below, pressing the control pedal to the angled position increased the speed. For reverse operation, the yellow and green wire positions on the potentiometer should be swapped. All connections were soldered and covered with a piece of heatshrink.
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| Wiring for New Potentiometer |
The replacement spur gear was printed in PLA and then it was placed onto the potentiometer shaft without glue to ensure it aligned with the other mechanism inside the pedal.
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| Positioning the Spur Gear |
To ensure the gear did not rotate on the potentiometer shaft, glue was added.
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| Replacement Potentiometer with Round Shaft |
Fitting and Setting the Potentiometer Home Position
With the connections finalised and the gear positioned, the locking nut on the potentiometer was hand-tightened.
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| Mounted Potentiometer with Threadlocker |
The pottery wheel was powered and set up to operate from the foot control. In the horizontal position, the potentiometer was rotated so that the pottery wheel did not turn. This corresponds to a speed of 000 on the pottery wheel display. The potentiometer was tightened further. Pressing the foot control to the angled position resulted in a speed of 320.
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| Maximum Speed Value on Pottery Wheel |
Loctite 222 was applied to the thread on the potentiometer to reduce the chance of the potentiometer coming loose.
Lastly, the base plate for the foot control was reattached and secured with the three plastic screws.
Downloads
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| SpurGear.f3d |
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| SpurGear.stl |
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