How to convert a Bachmann class 66 for radio control and slow speed running.

In BRM magazine of November 2015, I described my early experiments with converting a Lima class 66 for radio control, and how the motor can be controlled to make it run slowly.

Power for the loco is taken from the track, and speed commands are sent via a radio link to an onboard microprocessor. The demanded speed is compared with the actual speed of the motor, and the motor drive is varied as necessary to obtain the desired speed.

Unfortunately, the ringfield (pancake) motors in the Lima models are not able to perform too well at these speeds as there are too few poles, making them more than a little jumpy when run slowly, even with the microprocessor doing its best to keep them going steadily.

The Bachmann motors, on the other hand, are much better and offer the ability to do some spectacular slow running when properly controlled. Since all 6 axels on the Bachmann class 66 are driven, the pulling power of these models is excellent. With speed controlled motors, long freight trains can be driven slowly and smoothly at very realistic slow speeds and gentle acceleration and deceleration to suit the heavy loads.

The conversion process is fairly straightforward and I have designed drop in PCBs for both the main control board and the head/tail lights.

This is what the PCB inside a class 66 looks like. There are different versions but they all look pretty much alike. The DCC socket is centre right.

All this gets removed and is no longer needed. Unscrewing it provides access to the centrally mounted motor underneath.

This has two brass fly wheels and then a drive shaft takes the rotation to a worm drive on each bogie. The motor needs unscrewing for modifying so that its speed can be monitored. The capacitors are removed as they are incompatible with the high speed pulsed motor drive signals which will be used.

The modifications to the motor are simple. Just add strips of black paint at regular intervals around one of the brass flywheels. On some I have also put white paint in between the black strips which does make setting it up easier. These stripes are read by an optical pickup, and are fed to the microprocessor so that it knows exactly how fast the motor is turning.

While the loco is apart, then the replacement head and tail light PCB is fitted under the driver's cab.

This makes controlling the LEDs easier as they all share the same supply to their anodes, and turning one on is as simple as grounding the cathode through a resistor. By modulating the light (ie rapidly turning it on and off) it is also possible to adjust the brightness.

Here is the driver's end with 'day' headlights showing, one headlight being brighter than the other.

The other important thing needed is some stay-alive capacitors as at such slow speeds, it is not possible to guarantee a supply through the track even with 4 axles (or even 6 on some models) having pickups. There are two of these high value super-capacitors rated at 12VDC and they are wired in series and wrapped in black PVC tape so that they don't come into contact with the chassis.

This is what the assembled unit looks like with the marker lights in the cab soldered to the PCB as well. The small blue module is the radio transceiver.

Once screwed to the chassis the only thing left to do is to make sure that the light sensor on the underside of the PCB is at the correct distance from the striped flywheel to pick up the rotation of the motor.

For controlling the loco, I have made this hand controller.

It controls the loco's direction, speed and head/tail lights all with two toggle switches. There is also an on-off switch.

Another type of controller is based on a Raspberry Pi with a touch screen using a programming language called Python to control the loco, in fact this program can control 2 at the same time using a simple touch screen.

I am now working on linking the Raspberry Pi to track detectors, point motors and signals. This will mean that a timetable can be developed, routes set, trains sped up and slowed up all with extremely realistic movement.

If you want to know more about this project, then please email me.