Note: This design is untested. While I expect it to work well, I have no idea how much power it will have or how long it will last. Order it at your own risk. If you do build a truck using this design, I ask that you contact me and share photos, videos, or any thoughts you have on the design.
This is a frame for a powered truck in TT scale, using a 10mm x 12mm motor and 39" wheels. The wheelbase is 13'7", suitable for an EMD Flexicoil C truck. The total drive ratio is about 38:1, and the no-load top speed at 12 volts is 75 scale MPH. With 13mm inside a shell, this truck will rotate over 12.5° in each direction, more than enough to run on 12" radius curves.
There is currently no provision for sideframes or electrical pickups. Both are left up to you. I will try to accommodate both eventually.
To complete this truck, you will need the following parts:
From Northwest Short Line:
- P:87 28" unassembled wheelset on 2mm flush axle. Note: You will need to shorten the axle to suit TT instead of P:87. Also, wheels of other thicknesses and diameters will work as well, provided that the axle is 2mm.
- 1.5mm axle stock. Note: This is also available from Nigel Lawton, below. The NWSL part is slightly more expensive, but it is considerably cheaper per unit length
From Nigel Lawton:
From VXB Bearings
*Optional, if ball bearings are desired
- 8x - 00-90 round head screws, at least 3mm long
- 2-56 screw
The design includes printed bearings for the axles and worm shaft. If you will be using these instead of ball bearings, check that they turn freely on the shafts, drill/ream if needed, and saturate with oil before installing.
There are three printed parts, not counting the bearings. The top cap fits on top of the motor and included the mounting screw hole. Tap the hole for the 2-56 screw. The center piece holds the motor and worm shaft. Tap all eight holes for 00-90 screws. The axle retainer keeps the axles from falling off, and helps retain the worm shaft bearings. It simply screws into place using the four holes. Note: The top cap and axle retainer are symmetrical, but the center piece is not. The motor and pulleys will only fit in one way.
Assemble the worm shaft with two worms, two bearings, and two 4mm pulleys. Add washers or other spacers as needed to keep end play to a minimum. There are 2mm long bearing retainers inside the center piece, so do not put anything against the inside face of the bearings.
Assemble the axles, with two wheels, two bearings, and a worm gear in the center.
Place two belts on the shaft, and thread them through the hole in the center piece. Position the shaft and motor in place in the center piece, and pull the belts over over the pulleys. Place both axles in position, and screw the bottom retainer in place. Screw the top cap in place.
Add wheel wipers and truck side frames as needed.
There are dimples on the outsides of the worm covers, marking the centers of the shafts. If you want to drive a second truck from this one, drill a suitable hole and leave the shaft long enough to connect to the universal joint of your choice.