Application Notes

Loco Wiring: Auto Reversing Lights

Some models have separate forward and reverse lights that need to change automatically when reverse is selected. The 4 relay version of the HRB can be configured to do this by following the diagram below. Read More

Noise Suppression for Multiple Motors

One question that often comes up is how to best arrange the motor noise suppression components on locos that have multiple motors driven from a single controller and spread across two or more bogies. There Read More

Double Heading Pro & 4QD Series

A lot of customers are now seeking to double head [or MU] locos with different models of 4QD controller, and a common request is how to link a new Pro-160 / 360 to an older Read More

Sound System Suppliers

We often get asked about sound system suppliers, so here’s a list of all those that we know about. Brian Jones Dallee Electronics Mtroniks Phoenix Sound Sense Innovations Soundtraxx South West Digital Trax Controls These Read More

DNO and Sound Cards

When using DNO with a sound card you will need to give the sound card a signal that relates to the speed of the model. There are a number of ways to do this described Read More

Clubs with controller test boards

Here’s a list of all the clubs that have a controller test board… Ashmanhaugh Light Railway Belfast & County Down Miniature Railway Society Bromsgrove Model Engineers Budmouth College Camp Creek Railroad Cleveland Association of Model Read More

DCC / Airwire Interface

We’ve been asked by a number of customers if our controllers can be made to work with a DCC orĀ  Airwire system. This little circuit ought to do the trick…. With pins 2 and 3 Read More

Closed Loop Current Control

Although our Porters have current limiting which can be adjusted, they were not really designed to provide an active closed loop current control mode. So many thanks to Ian Beaver for making public a neat Read More

Double Heading Wiring Diagram [DNO]

This diagram shows how to connect two DNOs in different model locomotives together using the expansion port.     You can download a PDF version here. For the slave cable we recommend using a bulgin Read More

Parking Brake Voltage

We have seen a number of cases recently where a 24V parking brake coil has been fitted to a 48V motor. Generally this has been where 2 motors have been fitted to a 48V golf Read More

Mtroniks and regen braking

One of our customers has brought to our attention an issue that can arise when using an Mtronics sound card with a controller that has regenerative braking [all 4QD controllers]. The model in this case Read More

Motor Suppression in Robot Wars

Robot wars is a hostile place for motor controllers, and motor suppression should be given careful thought. The main areas for concern are; Shock and vibration caused by collisions and weapon strikes. Electrical noise spikes Read More

Overheating in Boats

If you are using the 4QD series in a boat then you should pay particular attention to airflow and cooling to prevent the controller from overheating. It’s not kind to shut your controller away in Read More

Fraser Golf Buggies, Wiring for Pro-150

Fraser golf buggies (A La Carts), e.g. the Firefly and Dragonfly originally used 4QD’s Pro-120-48. When the Pro-150 was released, we stopped making the 48v Pro-120 as the Pro-150 is just as simple and does Read More

Starting with Robots

We get a lot of of enquiries from Robot Wars contestants who don’t know where to start building their robot. I sometimes get the impression that they are starting with the robot control system – Read More


Towing an electric vehicle with a permanent magnet motor can cause major problems. If any E.V. is to be towed, you must disconnect the motors or else jack the machine so that the drive wheels Read More


Torque is not really a controller function, but it is directly related to the current flowing in the motor. The mechanical torque is proportional to the motor current and the relationship is defined by the Read More

Mobility Scooters

Mobility scooters generally operate at 24v and have a legal top speed of 4 mph on the pavement, road vehicles can have a top speed of 8 mph. 4QD controllers can be wired with a Read More


4QD have supplied motor speed controllers to the Greenpower battery powered electric car competition for many years, and our controllers are highly efficient. The event has been won more than once using our controllers. This Read More

Golf Carts – Overview

One of 4QD’s principal markets is ride-on golf carts or buggies. Now there is a different market for buggies in UK as opposed to the USA. Most American machines use petrol engines and the buggies Read More

Radio Control Wiring Hints

Any radio controlled machine with motors has potential problems, and this page of radio control wiring hints hopefully helps to identify and solve them. The block diagram shows the electrical system of a typical radio Read More

Phoenix Loco Wiring

4QD supplied the complete wiring for Phoenix locos and the wiring of the loco is shown here for the convenience of Phoenix customers. This equipment was supplied only through Phoenix and enquiries about the locos Read More

Loco Wiring: Hand Control & Horn Relay Board

4QD’s Reversing Bell throttle hand control and associated Horn Relay Board are designed to simplify miniature Loco wiring whilst maximising features available. The Reversing Bell throttle gives a dead man speed control and may be Read More

Robot Steering

Introduction Quite a few Robots have steering problems initially. These notes are to help you set up the mechanics and electronics. In order to steer in a straight line, any machine which is driven by Read More

Double Heading Problems

Systems using the expansion connector to double head with a pair of controllers (Pro-150 or Pro-120 or DNO or VTX) almost always simply work when wired correctly. But there are occasional problems with installations: Wrong Read More

Double Heading Switch

We were asked for a system such that either loco could be at front and could be facing either way. This seems to make selection of reverse very complicated, but it is in fact quite Read More

Control by Microprocessor

4QD controllers are quite suitable for use with a microprocessor e.g. Pi or Arduino etc, but may require some simple interfacing, depending on the output of the digital system used. We have a schematic and Read More

Recharging Under Sail

When an electric motor is fitted to a sailing boat, it opens up the possibility of recharging under sail by using the water flow over the propeller to turn the motor to act as a Read More