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Quick Questions and Answers

Our FAQ sheet lists most of the technical information you can possible want, but this is a series of quick questions and answers (with pointers to more detail) which may help some people. The site is now so large and complex that many have difficulty reading, and cannot find the information they want.

Page Index


4QD series

Can I use DCI-111 with 4QD series?
Yes, but you need only do this is you want to mix at the receiver.

Pro, DNO and VTX series

Can I disable the regen braking?
The reversing system assumes that the motor speed is zero when the controller has ramped the internal demand speed to zero. This is only true if the controller has full control of motor speed when the controller is decelerating. If regen braking is disabled, the controller can make no assumptions about the motor speed, so cannot reverse safely. Therefore the facility to disable the regen braking has not been included.

Dual Channel Interface.

Can I plug a radio control receiver straight into the DCI-111 ?
No. But see

Are there other interfaces available?
Yes. 4QD manufacture one and several people have designed their own.

Radio Control

Can I plug a radio control receiver into a 4QD controller?
No - but there is an interface that enables you to.


Can you tell me what motors, battery and Radio control gear I should use?
No. Choosing these is part of designing our robot and that is not a job anyone else can do for you.

See Roboteers start here

My robot's got steering problems.
Probably mechanical, but see Robots - Steering

Motor speed controllers, general

My Batteries don't last long enough
Use bigger batteries!
Batteries, as they age, 'get smaller'. The controller can only do only one thing with the current it takes from the battery - pass it on to the motors. If the controller wasted any significant power - it would simply get red hot and go up in smoke, so if the batteries don't last - it's a battery or a motor or a mechanical problem. Don't blame the controller!

Battery Charging: Can I charge the batteries from the controller?
4QD manufacture motor speed controllers, we do not manufacture battery chargers.
Yes - probably, given the right circumstances, the regeneration could be used to feed energy into the batteries but there's no monitoring of battery state of charge so doing this could easily overcharge and destroy the batteries.

Dual control: Do 4QD make dual motor controllers, to control two motors?
You should simply use two single motor controllers. In fact the number of components saved by making a dual controller is quite minimal. The advantage is one of mechanical convenience. The disadvantage can be one of cost.

Mains Transformer Use: Can I use a 4QD controller from a transformer from the mains?
No: 4QD make controllers for battery operation. battery is not simply Low voltage.
However - if you understand the requirements enough - there are certain applications where mains transformer operation is possible. See:

More MOSFETs: can I add more MOSFETs (or upgrade the existing ones) to an existing controller to increase the current.
No. A motor speed controller is complex and MOSFETs are not the only bits working hard. Adding more MOSFETs will quite possibly overload other parts.

Regen braking: Can I turn off regen braking?
Generally no. But it depends on the controller you chose. See

Several motors: Can I drive several motors with one controller?
But using only one motor speed controller - you can only control one speed. All the motors will react as one.
Controllers cannot count. All they know about is the overall (mechanical) load. However, one motor speed controller will only deliver one speed, so (assuming the motors are matched) they will all go at the same speed.
My controller seems to lack power
Power is volts times amps. What people seem to mean, when they say they lack power, is that they cannot go to full speed!

So have you read the controller's instruction manual and adjusted the gain as described therein? If not, you may not be reaching full speed.

If you have, then is the controller getting hot? If it is, your motor is taking too much current. Either you have the gear ratio such that your full speed is far too fast, or you need a bigger controller. See our Motor Current Calculator to work out what size motor and controller you need.


Can I run several motors from one controller?
Yes - but see our main FAQ sheet Series-parallel motors

Do 4QD make controllers for Brushless (BLDC) Motors?
No. Sorry!

How can I make my motor go faster?
See our roadspeed calculator. The speed of a motor is determined by its design and the voltage applied to it. A speed controller reduces the motor speed by reducing the applied voltage. So if the controller is already applying full battery voltage to the motor, the only way of going faster is either to increase the battery voltage - or to change the gear ratio.

I already have a motor, what controller do I need?
Choosing a controller for an existing motor can be the wrong way to go as both motor and controller should be chosen to suit the mechanical load. Is your gearing correct? Is the motor adequate to move the machine up the gradients it will meet, at full speed?

You should use our motor current calculator to determine all this.

However most motors can take a 300-400% overload for about a minute, so you should generally use a controller capable of giving 3-4 times the motor's continuous current (which is the current rating on the nameplate). See Permanent Magnet Motors and their ratings for more on this.

What type of motor is yours? Our controllers are designed for permanent magnet brushed motors. These generally have only two wires and are reversible by changing the wires over. See our page on Motors - an introduction for more information

Also you must decide what other features you want, such as reversing. See our guided tour explaining the available features on our controllers.

What size motor do I need for ....?
How long is a piece of string? Or, better, how hard is it to pedal a bicycle?
The answer depends on how fast you go, what gear ratio you have selected and how steep the hill is you are pedalling up. Also - how heavy are you, the cyclist? All of these factors affect an electric vehicle also - which is why we have, on site, a calculator to let you experiment with different figures.

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Last modified: Mon, 11 Aug 2014 10:56:59 BST
First published: 1st of January, 2002
Page's Author: Richard Torrens
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