Installing Sabertooth 2x32 Motor Controller in GP40 Loco

This afternoon's activity was installing a new electronic motor controller in my Accucraft GP40 locomotive for 7 1/4” gauge.

Although the supplied Mini Train Systems motor controller works well in the Planet 2 loco, the two identical units installed in the GP40 have given problems. Lately, one or both controllers (there is one for each bogie) have been cutting out during regenerative braking, leading to reduced or zero braking effect.

To their credit, Mini Train Systems did suggest some changes to try to fix the problem and even sent a spare motor controller for me to try. However, the problems persisted.

The new controller is a Sabertooth 2x32 which is a general purpose motor controller widely used in wheeled robots, model tanks, etc. It can control two DC motors up to 32 amps each, continuous rating.

As it has 2 channels, the one Sabertooth will drive both bogies.

The Sabertooth 2x32 Motor Controller (circled in red)

The box to the left of the Sabertooth in the photo is an interface which I made so I can continue to use the tethered control panel supplied by Mini Train Systems. It provides a 0-5 volt speed signal and a forward/reverse control to the Sabertooth, as well as switching the lights and horn via relays already installed in the loco. The interface also drives the current and voltage meters on the control panel.

Mini Train Systems tethered control panel

The two black cables plugged into the interface unit are from the MU sockets at each end of the locomotive, where the tethered control panel plugs in. As before, the loco direction control is reversed and the appropriate headlight is selected depending on which end of the loco has the control panel plugged in.

The main difference with the Sabertooth is that the separate control for regenerative (Regen) braking no longer functions, and regenerative braking kicks in automatically when the speed control is reduced.

It is not quite as much fun to drive as the ability to shut off the throttle and coast then apply braking as required is no longer available, but it will be easier for novice drivers to manage, and the regenerative braking works reliably, which is useful.

I will investigate adding some electronics to mimic the former coast and brake feature for experienced drivers.

The Sabertooth also has inbuilt "cruise control" in that it maintains a fairly constant speed, applying extra power or regenerative braking as required. On an uphill grade, you can see the current increase. On a downgrade of about 2%, you can see the current drop to zero and the voltage increase slightly as braking energy is fed back into the battery.

Here is a link to the Sabertooth 2x32.

I ordered my Sabertooth direct from Dimension Engineering in the US as the local supplier, Robot Gear (in Perth), was out of stock. However, the delivery from the US took a long time due to the slowness of the US Postal system and it was several weeks before I received notification that it was even ready to leave the US. In the meantime, Robot Gear emailed me to say that new stock has arrived, so I ordered a second unit, which is the one I actually installed. Being a critical item, there was no harm in having a spare available when the other one arrives. From the Robot Gear, the cost was $256 plus local postage.