Drive Motor and Sheave
Entry posted by DonB
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Under the platform at the top station is a Sheave, which is based on colliery design.
I contacted Hornby Customer Services, to ask what was the diameter of the Sheave in their Colliery Headgear model and if it was available as a spare. They just directed me to their spares dealers, who had no stock and could not help.
A plea in the Help and Tips forum drew a response from Arthur (Thanks again!) who had acquired 3D printed Sheaves (57mm dia?) from Shapeways via Ebay, He tried to get his supplier to contact me, which did not happen.
Mention of the requirement for a sheave at 34mm in my Blog resulted in two offers within 24 hours!
First was Etched Pixels who had a 3D drawing / file in which all he had to do (he said) was to put in the appropriate numbers to get a 12-spoked sheave with grooved rim for the ropes. He has been a great help, and obtained the three of them for me, so that I have spares, 3D printed in Nylon by Shapeways.
Nylon was recommended to withstand the loads imposed by being a tight fit on a shaft, and the torque loads applied in use.
The second response again for a Shapeways product was from Dazzler Fan
Thanks to both for their interest and offers of help.
A picture of the nylon Sheave as supplied by Etched Pixels (His copyright!)
A reminder that this is only 34mm diameter. It has 3 grooves in the rim to guide the ropes attached to the carriages.
The operation of the model's passenger cars has been considered, and a suitable 12volt motor and gearbox, together with mounting bracket, obtained from Technobots (http://www.technobotsonline.com ).Their description is:-
"The 360:1 Mini Metal Gear Motor looks much like our other mini metal gear motors, except the motor is longer. And the gearing is in an enclosed cylindrical casing!
These also have a beefier set of mounting holes, threaded for 2-M2 metric screws.
Even more interesting are the motor characteristics. This compact brute of a gear motor offers a measured stall torque of 7.434 kgcm at 6V - thats considerable! Of course, with something this small, we trade the increase in torque for a decrease in speed at 23RPM at 6V. A suitable mounting bracket from our Pololu range is available."
Elsewhere in their site they describe similar motors as having "Finger-twisting Torque" !!
The prototype travel time from top to bottom is 1 minute ( +/- a couple seconds depending on the controller's braking of the operation.)
The sheave at the top station scales at 34 mm and needs to rotate 17 times to move the carriages over the length of the track. So I need to control the sheave to about 17rpm. The motor / gearbox chosen has a 6volt no-load speed of 23rpm so will do the job admirably.
The 15.5mm dia motor / grearbox and mounting bracket with a pack of the M2 screws.
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