Wobble due to oversized hole in key
After putting charge into a car battery, we looked for ways to improve the system's robustness and efficiency. The first step was to take the wobble out of the bicycle rim. We had Chuda Mani Upadhyaya manufacture a second shaft-and-key system, this time with tighter specs in mind. Also, we made it out of only 2, rather than 3, pieces, welding the shaft directly to the bicycle rim. The small square fixture to the key was made to be closed on top (a male piece), so as not to interfere with the grinding process.
We also investigated ways to mount the wooden box directly to the floor (avoiding the necessity of holding it down in place). Half of the ghatta's floor is covered in stones. The water flows underneath these stones. The other half, however, is just dirt. We sharpened two pieces of rebar and drove them a good foot into the ground, right where the stone met the dirt. Ghattas that do not have dirt floors will presumably have to have a stone removed or a hole made for this approach to work.
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Wobble due to oversized hole in key |
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Returning to the ghatta, we were disappointed to find that we had made the hole in the center of the key too large. We were informed by the ghattera that the width of the rectangular hole in the key needs to be almost exactly the width of the shaft. However, the length of the hole can be longer without much adverse affect. Even with several layers of thick cloth over the shaft, there was still too much slop in the width of the hole in our new key; any tension in the belt essentially pulled the bike rim forwards and out of alignment. We took a careful measurement of the dimensions of the ghatta's turbine shaft, and went back to Chuda's workshop.
New key in hand, we returned to the ghatta and found that our improvements had indeed helped. The wobble on the bicycle rim was significantly reduced with the new shaft and key. We attached the wood box to the rebar with a short piece of rope. We had also purchased and brought a rubber mat to place under the box and reduce any sliding. It proved unnecessary, however, and the rope-and-stake approach worked well to maintain constant tension on the belt, without any intervention on our part.
We hooked the alternator up to a new (and mostly charged) battery we had purchased. The alternator was able to put a very steady 13.05V across the battery, which drew between 3.5A and 4.5A. It put the same voltage across our sealed lead-acid battery.
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Standard alternator with smaller pulley |
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We returned to the ghatta within two days with a lowered box. We also took one of our alternators and replaced the standard pulley with one smaller. Unfortunately, we were unable to test either scheme to increase the alternator rpms. The ghattera had become convinced, since the last time we saw him, that our machine was going to significantly damage his ghatta’s grinding stone (which was quite thin and cracked from years of use already). He threw us (and all of our equipment) out of the ghatta.
Key Lessons from this Test:
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