Well, some may have wondered about last weeks update, others already got an idea what I did. Here’s the 4th part of my tiny Shay loco, showing you a little untold secret ;-)
The Toma Shay is factory equipped with a small coreless motor. I meassured the current draw of this motor, which is 6-7mA in regular use, up to 12mA when the wheels are blockes with a thumb. Let’s combine this with a tiny 50mAh Lipo battery, which will be the base for an RC conversion.
As the Shay has limited room inside, the only spot to add RC would be the tender top and inside the firewood pile. I already had a Deltang reviever at home, so I searched for tiny Lipo batteries.
I made a 3D model of each component in Fusion360 as well as model of the tender shell. Next hours were spend in good old Tetris-manner, trying to puzzle all parts in place. A tiny SMD switch could be placed behind the timber railing, same would be possible for a charging socket. Its tight, but should work.
What Fusion360 did not show me is, how tiny tiny the space really is and how to use a soldering iron in litteraly no space at all. First, I converted the power truck. I removed the pick-ups to the wheels and replaced them with a tiny 2-pol socket. This plug-in connection allows easy desassembly if necessary.
A 3-pol-socket for charging was placed on the back side of the tank. I had to file one of the opening and add some shims to make it fit. I use 3-pol sockets for charging with “minus-plus-minus” to allign polarity. On the firemen side, I added the SMD switch with some shims underneath. The knob is sticking out of the grate.
The photo below shows the components used. To charge the battery, I use an external USB-charger with cable connection.
As I designed the whole rebuild in CAD, it was easy to create a woodpile which would cover up all the RC components. I added cut outs for the switch and socket and send the file to my dad for 3D-printing. The printed part got painted and fits perfectly in place, covering up all the electronics below.
Beside the wood pile, I send files for disconnect log cars to my dad as well. But that’s another story for another week.