TOW TANK
Having a test facility like the tow tank already built and right on campus was an invaluable resource. That being said, there were a few problems with the system initially. Due to infrequent use and the harsh, damp
"marine" environment of the Aquaculture Research Center, corrosion was
a problem in many places. The rails on which the carriage rides needed
to be sanded smooth to allow the carriage to travel easily. The guards,
which protected bystanders from the rails and the drive cable, had
rusted and migrated in towards the carriage to the point that they
touched the carriage in some places along the track. These rails were
unbolted from there mounts and moved back away from the carriage. Also,
the drive cable had to be realigned on the drive drum to allow the
carriage to travel the full length of the tank.Tow tank with carriage up on blocks for maintenance
Most importantly, a major design flaw was noticed on the carriage trucks. The carriage had two trucks on the drive side. Each truck had two forks, which three wheels each. Two of the wheels were non load bearing stability wheels, which wrap around the rail. The third wheel was the load bearing wheel, which was supported by a bolt that was canitlivered from one side of the fork. The major design flaw was with this bolt. Even with the carriage unloaded, these bolts were bending enough to cause the wheel to contact the top of the fork. This made the carriage movement sporadic. After disassembly of the carriage, it was evident that the bolts of the load bearing wheels had yielded. Three possible solutions were conceptualized to solve this problem:
1. Replace the existing bolts with bolts of the same size but made of harder material
2. Replace the existing bolts with bigger bolts that step down to the needed size
3. Add a support block on the unsupported side of the wheel to fully support the bolt
2. Replace the existing bolts with bigger bolts that step down to the needed size
3. Add a support block on the unsupported side of the wheel to fully support the bolt
Solution 1 Solution 2 Solution 3
After analysis, solution three was decided to be the best. This modification was predicted to raise the factor of safety of the fork system from less than one to 28. While solutions one and two would theoretically work, they would only increase the factor of safety by at most two. The trucks were removed and a slot was machined into each fork to accept a small rectangular precision machined aluminum block. This block was threaded to accept the drive wheel bolt, and was screwed into place on the fork. Installation and testing of these modified forks showed significant improvement in the carriages travel characteristics with no yielding of the load bearing bolts.
Carriage truck forks after modification