Too many people get hung up on the "model railroading is 12 volts" thing.
There are a lot of little, low voltage motors available in discarded cell phones--the vibrators, also in the little R/C cars that sell for under $10 at Wallyworld. When geared way down, their whiz-bang RPM becomes sufficient power for a critter.
Three volts would make track pickup that much more problematic but with on board batteries--
____________________ Fix it again, Mr Gates--it still works!"
The first example I have is a simple HO Piko loco. It goes so fast at full speed with the standard mains controller that it comes off the tracks on curves. Trains like these are ideal for a single lipo. Even full throttle with a 1S lipo is much more than I need.
I removed the ballast (shown on the right) to make space for a single 330mAh lipo (bottom left). Rx41d-v5 is shown in the middle at the bottom. I prefer to plug everything together so I have soldered on small sockets and battery lead. Inside the black body you can see wires from the switch. One white plug goes to the battery and the other goes to the receiver.
Last edited on Wed Oct 3rd, 2012 06:34 pm by DavidT
Here you can see where the Rx and lipo are placed. The rx is not insulated so I have some masking tape on the motor can. The outer shell is plastic so no risk of shorts from that. I have removed all the track pickups.
And finally, there was a square ventilation hatch or similar on the top of the cab. I cut that off and installed a switch inside. The 'switch' is actually 3 magnets which when orientated correctly allow the battery to feed the Rx. A slide switch would probably have been simpler. Magnets or a socket could have been installed for charging but the shell on this train is easy to remove and charging is infrequent so I did not bother. Rx41d is again shown for scale roughly above where it sits inside.
Here is a metal N gauge Minitrix. It was orginally 0-6-0 but I've made it 0-4-0 to handle 103mm Tomix track. At the bottom of the photo is my smallest receiver Rx45 along with the lipo that powers it. The lipo is cylindrical and has 80mAh capacity. The boiler was solid metal so I had to bore that out for the lipo. A hollow body would be much easier.
Last edited on Sun Oct 7th, 2012 03:00 pm by DavidT
The white square leaning against the motor contains the receiver. It is wrapped in some thin spongy foam to insulate and protect it from vibration. Another way would have been to mount it on the chassis with double-sided foam tape or velcro. Between the two axles is a tiny switch. It is glued into a existing recess in the chassis and can be moved on/off from the outside with a small screwdriver.
I have again used plugs between all the main components. Even in a tiny model like this I've been able to find a gaps behind the motor and under the lipo. The plugs have a 0.05" pitch (1.27mm). It would take up less space if some of the things were just wired direct.
The original motor was faulty so I replaced it with one of similar size from an old servo. I thought I needed a fast motor due to the low 1S lipo voltage so I chose the fastest I had. However, this train does not have much gearing with only a worm drive and it ran too fast for its scale and the tight Tomix track. To give better speed range I reduce the volts applied to the motor with diodes mounted on a board on the side of the motor.
If you look back over the photos you will see one gold magnet at the front and two at the back. These are on both the chassis and body. These hold the top and bottom together quite securely but allow easy access for charging the battery.
Although small, this conversion is not ridiculously difficult and I think it makes a very practical RC model.