This week the Spice of Pi project has seen incremental steps in both the right direction an the wrong direction along with a lot of spinning of wheels both figuratively and literally. Last week I got the jar lifting servo mechanism built and this week I worked on getting the platter rotation mechanism working.
The first few days were spent trying to assemble and tune a low-cost 3-D printer that was large enough to print the platter. It is together and printing but I'm still not happy with the performance. It did a reasonable job on some tripod brackets for my camera, but I'm sure it can do better, I just need to adjust the temperatures I think. Anyway, I'm waiting for a new roll of filament before attempting the big spice jar platter shown in my last blog.
Next I designed an adapter to allow a servo motor to rotate a 15 tooth pulley. I am using a rubber belt pulley drive because I want to minimize shock to the servo gears. The adapter worked pretty well as seen in the next video, but I discovered the set screws in the pulley were not actually at 90 degrees as I had assumed from looking at them. The actual angle is around 112 degrees. I carved the adapter up to make things fit but it was going to require a new adapter to make things fit well.
When I tried the servo motor I discovered it was a continuous rotation servo instead of a 360 degrees servo. I was sure the motor spec indicated it was a 360 degree servo, but the terminology seems to be loosely used.
I happened to have a 180 degree servo, but to make it work for 360 degrees, I needed to have a drive pulley with twice as many teeth as the platter pulley, so I did not fix the adapter for the old pulley - I worked on a new pulley instead.
China is shut down for 2 weeks and an order now might not get here in time, so I designed the entire pulley to be 3-D printed. Fortunately it came out beautifully and fit the belt perfectly.
Then it crossed my mind to check why the servo wasn't the 360 degree servo that I expected. It turns out that it was a spare servo I ordered in case we need to build a second unit for Glenn (my partner on the project). The original servo actually works the way I intended, although I was surprised that without power the gears are completely locked. So now I had a nice pulley with the wrong number of teeth since this servo needs a 1-to-1 ratio.
So back to the drawing board to design a corresponding pulley for the platter. Again the print came out great, so I put a couple of bearings in a vise to demonstrate the belt drive does indeed work.
By the way, I find these rubber-jaw, ball joint vises indispensable for working on the bench. They make super third and forth hands for holding wires, components, PCBs or anything else at any angle and as shown above they are useful for mechanical mock-up and assembly as well. Suppose you want to hold a wire up to a component while you solder them together with solder in one hand and soldering iron in the other hand.
The next step is to design mounts for the bearings and the drive motor with a way to adjust belt tension.
This blog documents that incremental progress is being made on the project, although this last week was pretty hard slogging.
Design Challenge Links:
Project Links:
Blog Glenn 1 - AIY Voice Kit Unboxing
Blog Doug 2 - The Block Diagram and Bill of Materials
Blog Doug 3 - Spice Jar Lift Mechanism
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