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On this page, you will find the answers to many questions related to the technologies and applications of our controller. This FAQ is a permanent work in progress so come back often. If you have a question you wish to see added to this FAQ, feel free to send us an e-mail.

Applications FAQs

How can I use the Roboteq controller to build autonomous robots?

An autonomous robot is a machine that will move without an operator guiding it. Autonomous robots always imply that there is a Microcontroller that will sense the environment and make motion "decisions". Truly autonomous robots, featuring vision and artificial intelligence, are the stuff of science fiction. However by providing a minimal amount of "senses" in the form of limit switches, video cameras, GPS, compass and other sensors, it is possible to build robots with limited but useful autonomy. Examples would be automatic guided vehicles following marks on the floor, automatic lawn movers, robot patrolling a preset perimeters, an more. For such robots the controller must have a way of talking with the microcomputer, which in the case of the AX2550, can be done using the serial port

Can I remote control a robot via the Internet?

Yes. Using a microcomputer connected to the AX2550 on one hand and the Internet using a 802.11 connection on the other, in addition to some customized software, it is possible to remote control a robot from any point on the planet. With a video camera mounted to the robot and Internet videoconferencing software running on the computer it is even possible to see what the robot is doing. Details schematics, mechanical drawing and software for such a project can be found here

How can the controller be used to build super strong servos (jumbo-servo)?

The AX2550 supports a closed-loop position mode. In this mode, the axle of a geared down motor is coupled to a potentiometer that is used to compare the angular position of the axle versus a desired position. This unique feature makes it possible to build ultrahigh torque “jumbo servos” that can be used to drive steering columns, robotics arms, animatronics, life-size models and other heavy loads.

How easy is it to to connect the controller to an R/C radio?

Very easy. The AX2550 will connect directly to two R/C radio channels for commanding each motor. One additional channel can also be connected to the controller to trigger on-off outputs for commanding accessories.

How can the controller be used to remote or computer control a full size car

The challenge with a large gas-powered vehicle is the force with which to activate the controls which far exceeds this of the heaviest-duty RC servos. This is particularly the case of the brake and steering activation. When operated in the position mode, the AX2550 can be used to create very high-power servos capable of such operation. See a detailed description on how to do this here.

Can the controller be used in Underwater Robot applications

This is a common application of the controller. One controller can be used to control two thruster. Typically, a second controller is needed for a third axis.Best performance is achieve by incorporating the batteries in the sub.

Motor FAQ's

What kind of motors can I connect to Roboteq's controller?

The controller will connect to brushed DC motors. It is recommended to use permanent magnet (PM) motors.

Can I use brushless motors with Roboteq's controller?

No. Brushless motors have a different construction requiring the controller to output three sin waves 120 degrees apart to create a rotating magnetic field. Roboteq's controller has only two outputs and may not be used.

Can I apply a higher voltage to motors than the recommended value?

In most cases, yes. The voltage rating is a value at which the manufacturer will guarantee a motor's continuous operation. DC motors will run at a higher voltage for a reasonable amount of time before starting to heat up. If the excess voltage is only applied for a short time, then this will not be damaging.

Can I use a 12V motor on one output and a 24V motor on the other?

Even though the controller has two battery power wires, they are joined internal and thus a single battery voltage must be applied. However, when the controller outputs 50% power, it effectively applies half of the battery's voltage to the motors. So a 12V motor can be driven using a 24V battery if, as long as the power level on the 12V motor never exceeds 50%.

What are the benefits of running at a higher voltage?

Higher voltage is an easy way to get more power out of the motor. In fact, the motor's output will increase to the square of the voltage: going from 12 to 24V on a given motor will quadruple the power delivered by the motor.

Can I use a car starter as a motor?

It is possible, but this requires hardware modification to the motor. The main problem is that starter motors do not have permanent magnets to create the armature's (the part of the motor that doesn't move) magnetic field. Furthermore starter motors are designed to deliver high power for relatively short periods of time, and, therefore, do not make very effective or efficient continuous motors. Information on how to modify starter motors can be found on the Internet. Starter motors are not recommended for use with Roboteq's controller .

How can I know how big a motor I need for my robot?

The size and type of motor you need will depend on your robot's weight, how fast you intend it to move, how quickly you want it to accelerate and stop, and how long you want the batteries to last. The heavier the robot, the faster and the quicker to accelerate, the more powerful the motors will need to be. Enigma Industries makes an extremely interesting Drive Train simulator that will let you define your robot's specification, including batteries, motor type, gear ratio, weight. You can then drive your robot in a 3D software simulation and watch its behavior and current consumption as it moves. This is a truly amazing piece of software which will take much of the guesswork out of robot design. Note that the simulator does not yet include a simulation for the controller's features (current limiting, programmable acceleration). A link to this company can be found on the links page.

Where can I buy motors?

In the USA, NPC Robotics (www.npcrobotics.com) carries and excellent selection of DC motors, batteries, gears and wheels. In Europe, Technobots (www.technobots.co.uk) has a similar offering.

Power FAQ's

What is the Amps rating of Roboteq's controllers?

There are two versions of the controller: the standard version and the High Efficiency (HE) version. The standard version is rated at up to 120A. At 40V, this is up to 4,800W on each side, or nearly 10,000W total. This is a very high amount of power which in practical cases cannot be sustained for more than a few seconds before wires, motors and the controller begins to overheat. The standard AX2550 uses SmartAmps technology to keep track of the total heat generated by the controller and adjust the power automatically as it operates. The High Efficiency version can handle up to 140A but generate significantly less heat.

What is the difference between the controllers' standard and the HE versions?

The High Efficiency version controls twice the number of output transistors, which in turn cuts the generated heat by half. While this could theoretically mean that the HE could handle twice the amount of current, above 140A other components, including the wires, reach temperatures above their approved specifications. Roboteq deliberately set the software limit at 140A and recommends this version for applications requiring the improved reliability of a cooler running unit. The HE version is also fitted with extended temperature components and can operate in -40 to +85 oC ambient temperature.

How does the AX2550's SmartAmps current limiting works?

On the AX2550, the current limiting is based on the measured temperature of the heat sink, near the mounting point of the Power MOSFET transistors inside the controller. While the measured temperature is below 60oC, the controller will deliver up to 120A (140A on the HE version) of Continuous Amps. For every degree of temperature rise above 60oC, the limit is reduced from this absolute maximum amount. Furthermore you can select one of 6 current limit settings based on your robot’s component capabilities (motors, battery, wiring), up to the controller’s own limit. The current limit that is applied at any given time is the lesser value of your selected value and the maximum Amps the controller is allowed to deliver at its current temperature point. This capability ensures that the controller will be able to work safely with practically all motor types and will adjust itself automatically for the various load and environmental conditions.

How much Amps can the standard AX2550 deliver in practical applications?

Because the maximum current is dependent on the actual temperature of the standard version of the controller at any given time, this will depend on the actual operating conditions. Practically, assuming the maximum Amps limit setting (120A), the controller will allow up to 1 minute of operation at 100A or 15 seconds at 120A before dropping the output. Extended continuous operation will be at 80A. These numbers can be improved by ensuring proper ventilation to the controller and/or having the controller's case making contact with a large metallic surface for additional cooling. In practical robot maneuvering situations where stop and go is very common, the controller will be capable of delivering up to 120A whenever needed.

How much Amps can the High Efficiency version deliver in practically?

Because it generates almost half the heat of the standard version, the HE version will deliver 140A for up to a minute and 120 practically indefinitely in a 25o ambient environment.

What is peak current, and how much of it can the Roboteq controller sustain?

Peak current refers to short spikes of current due to switching, sudden overloads, and other exceptional events. The AX2550 will sustain well over 250A of peak current. On most controllers, this current level, if sustained will damage the controller or blow the fuse if one is used. On the AX2550, the current limitation feature will cause it to automatically drop the output until the current drops to an acceptable level.

My motors have a stall current of over 150A. Can the AX2550 handle them?

Yes. The whole idea of active current limiting is that the controller will never give more current than it is safe to. If the motors are hungry for more current because of peak demand, the controller's maximum current is all they are going to get. In most cases, this kind of peak demand is exceptional and giving the motor less current makes no visible difference. If the controller does not have active current limitation, then it must be large enough to be capable of delivering these very high and often accidental current load or risk destruction.

How can I tell if the AX2550 will be sufficiently powerful for my robot

Roboteq recommends that you use Enigma Industries' Electric Drive Train Simulator. This amazing software will let you simulate your robot's components (motors, gears, batteries, wheels) and drive it around in a 3D arena. You will be able to view how much current is drawn in the various driving conditions. You will need to remember that if you see Amp loads above 120A (140A on the HE version) at times, the controller will automatically limit its output. Roboteq is collaborating with Enigma to incorporate a model of the AX2550 controller inside the simulator.

What is the impact of wires on the current drive capability of a controller?

Electrical wires have an electrical resistance. The thinner the wire, the higher the resistance. When current flows through a wire, an amount of heat equal to the wire's resistance multiplied by the Amp to the square is generated. If the wire is too thin (i.e. its resistance is too high), then the wire will heat up, potentially melting its insulator, or even melting the copper. Wire thickness is defined using the AWG metric, which in turns specifies a typical maximum current that can safely flow through it. AWG 10 wires are rated to 50A max. by most manufacturers. Thicker AWG 8 wires are rated up to 80A. The AX2550 is fitted with AWG 8 wires on its power stage. Note that most competing controllers are delivered with wires or hook-up terminals that will not withstand, according the their manufacturer's specification, the advertised maximum current of the controller.

Does the controller need a fan?

The AX2550 is built into a aluminum extrusion shaped as a heat sink. Consequently, the controller is able to operate without a fan in most typical applications. In the most demanding applications, the controller may generate more heat than the heat sink is capable of dissipating. In this case, it is recommended to add an external fan that will blow air on the controller's fins. You may also physically bolt the controller to a large metallic chassis of the robot so that excess controller heat dissipates through conduction. Providing additional cooling will allow the controller to deliver higher current for longer periods of time

How does Overvoltage protection work?

The AX2550 includes a battery voltage monitoring circuit that will cause the output transistors to be turned off if the main battery voltage applied on the thick red and black wires is above 45V. This protection is designed to prevent the voltage created by the motors during regeneration to be “amplified” to unsafe levels by the switching circuit. This circuit will not protect the controller against powering the controller with a power source above 45V. The controller will resume normal operation when the measured voltage drops below 45V

How does Overvoltage occur practically?

Other than using a higher voltage source, overvoltage may occur during regeneration as the controller will attempt to push back current into the battery. See Regeneration FAQ.

How does Undervoltage protection work?

In order to ensure that the power MOSFET transistors are switched properly, the AX2550 monitors the internal 12V power supply that is used by the MOSFET drivers. If the internal voltage drops below 9.5V, the controller’s output stage is turned Off. The rest of the controller’s electronics, including the microcomputer will remain operational as long as the internal voltage is above 7V.

Can the controller's two outputs be combined to drive a single load at twice the Amps?

Yes. However, this requires a different wiring of the controller which must be set at the factory. This version of the controller is a special order. Price is the same as the standard version.

Regeneration FAQ's

Does the AX2550 support regeneration

Yes. Power will typically flow back into the battery during deceleration, or whenever the motor is spinning faster (because it is pushed, or inertia) than it would at the applied power level.

Does all the regenerated power go back into the battery

Unfortunately not. Some of the energy is lost in heat inside the leads and the controller. The amount of regenerated energy also depend on the switching ratio on the PWM stage. In the extreme case when PWM is at 0, the motor is essentially shorted and all the power is dissipated in the motor windings, wires and transistors.

What happens if there is no battery

During regeneration, current will try to flow back into the battery. If none is present, voltage at the controller's main power wire will keep rising. Eventually, the overvoltage detection circuit will turn off all the transistors so that the motor is practically disconnected. While no damage should occur, it is recommended that a battery is always present.

Batteries, Wiring, Power Supply FAQ's

How many batteries does the AX2550 need to operate?

At a minimum only one. The battery should have a voltage no lower than 12V and 40V max. An on-board DC/DC converter will take that voltage and convert it very efficiently down to 12V to operate the controller's electronics. Another on-board regulator creates a 5V supply which is brought to the DB15 connector to power the R/C radio or external microcomputer.

When should I use a separate 12V battery in addition to the main battery?

When operating the motors, the current consumption is very high and the batteries will eventually discharge to the point that the controller's DC/DC converter is no longer capable to generate the supply needed to operate the controller's electronics. It also may happen that the voltage at a weakly charge battery drops to below 12V as motors are started or load peaks. To keep the controller and operating in these conditions, the AX2550 can be supplied with a separate and stable external 12V power source.

Why is there a separate set of power cables for each motor channel?

The controller's drive power is too high for all the current to be driven through only one set of cables. 120A x 2 channels is 240A continuous, well above the safe rating for AGW 8 wires if a single wire was to be used. When wiring the controller, you should wire the two thick positive wires (red) together to the positive terminal of the battery. You should wire the two think negative wires (black) to the negative terminal of the battery.

Can I power the motor and the controller out of a single battery?

Yes, as long as you are confident that the voltage will never drop below 12V.

Can I power the R/C radio or a microcomputer from the controller?

Yes. The controller has a 12V to 5V internal regulator and will output the regulated 5V supply on the 15-pin connector. However, powering the radio from a separate battery, and thanks to the opto-coupler on the R/C channel inputs, will help create a more robust and noise immune system.

How long will batteries last?

It is dependents mostly on how much driving is done. The motors by far consume the most power in a robot. Battery capacity is rated in Amp/hours, which is the amount of Amps it can deliver for one hour before it is empty. So if a robot has two motors that draw an average of 20A each (40A) total, then the robot will be able to move for up to 1 hour on a 40A/h battery. When the motors are idle, the controller's output stage draws no power. At all times that it is turned on, the controller will consume approximately 150mA for its internal electronic circuitry.

Where can I find connectors that are big enough to handle the current?

Robotcombat.com sells several type. The two models at the bottom of the linked page will fit the AX2550's AWG8 cables and handle the current in most case. Beware never to pull plugs while current is flowing as this will often result in arcing and potential damage to the connectors.

Control FAQ's

What does PWM mean?

PWM stands for Pulse Width Modulation. It is a method for applying a variable amount of power by changing the on and off time of a periodic signal. For example, an output that is fully on 50% of the time, and fully off the other 50% this will average in an actual average power to the motor of 50%. For PWM to work well, however, the on-off cycle must repeat at a relatively high frequency.

What is Roboteq's controller PWM frequency?

Roboteq's controller PWM frequency is 16 kHz This means that the variable on-off cycle will repeat every 64 microseconds. 16 kHz is a high frequency value for PWM control that will result in smoother and more energy efficient motor operation than at lower frequencies. The use of high PWM frequency will also result in silent motor operation.

How fine is the AX2550 PWM control?

In the AX2550, the PWM cycle is divided into 128 steps. Other than always on and always off, the AX2550 can generate any ratio ranging from 1/128th to 127/128th. Another way to put it is that the controller output can range fro 0% power to 100% power in 128 steps of 0.8%. This is a very fine level of control by any practical measure.

What is programmable acceleration and what is it for?

Programmable acceleration is the controller's ability to limit the rate at which speed is allowed to change. Transistors are very quick and can switch from full forward power to full reverse (a worse case scenario) in a matter of microseconds. Because of the motor's and the robot's inertia, such changes will result in a very high, sudden and potentially damaging overcurrent inside the controller. Such changes can also create significant mechanical stress to the robot's structure as well. The AX2550's current limiting feature is one way the controller can limit the effects of such changes. With programmable acceleration, the controller will take the user's command and automatically "smooth" the change. In the full forward to full reverse example, the controller will gradually reduce the speed to 0 and then accelerate to full reverse.

Closed Loop and Encoder FAQ's

What is the difference between speed and position mode?

As the name implies, in the speed mode, a variable command value will cause the motor to move at a given speed or another. In the position mode, a command value will cause the motor to move to a given position. In both cases, the controller will cause the motor to spin, but in the position mode, the controller will also cause the motor to stop when the desired position has been reached. To do this, the controller must "know" what the actual position of the motor's axle is. In the AX2550, the position is determined by an external potentiometer that the user must affix to the motor.

What does open loop and closed loop mean?

Open and closed loop refers to whether a feedback mechanism is included in the controller-motor assembly for the controller to verify that the motor is actually moving as expected by the command. In open loop, there is no feedback, so a command will vary the controller's output to the motors, but the actual speed will depend on the friction, slope, load and the presence of obstacles. In speed closed loop, the controller will measure the actual motor speed and adjust the command accordingly. In position closed loop, the controller will measure the angular position of the motor's axle and move the motor until the desired position is reached. The AX2550 supports all three modes described here.

What is a PID?

PID stands for Proportional, Integral and Differential. It is a common and proven closed-loop algorithm that measures the difference between the actual and desired speed or position and processed this "error" to adjust the output. See this short tutorial for more details. The AX2550 uses a PID algorithm for its close loop modes.

When should I use a potentiometer for position feedback?

Potentiometers are convenient because they are very inexpensive and deliver an absolute position information. Being mechanical, they eventually wear. They also have a fixed and small travel angle of approx 270 degrees, unless multi-turn pots are used. They are best suited for building high power servos.

What kind of speed sensor do you recommend for closed loop?

The AX2550 can use either analog tachometers or digital optical encoders to measure actual motor speed. Optical encoders are a far superior solution as they do not require calibration and deliver a very accurate reading. Tachometer can be a good quality small DC motor used as a generator.

 

Optical Encoder FAQ's

Can you recommend a source for optical encoders?

US Digital (www.usdigital.com) has a very complete offering at reasonable prices

Can the encoders consume more than the published 50mA limit?

50mA is a recommended maximum value. In reality it is possible to go as high as 125mA each, however at these values it will not be possible to power any external accessory using the 5V output on the DB15 connector.

Can the Encoder be used in position mode?

Starting in version 1.7, the AX2850 and AX3500 can use optical encoders for closed loop position feedback. In position mode, the encoders are made to "emulate" a potentiometer, delivering a position feedback value of 0 when the current counter position is equal to the value contained in the destination register (set to zero at power-up). The encoder module will report a position moving to -127 or to +127 depending on how much the counter position differs from the destination register. Once -127 or +127 is reached, the reported value no longer changes as the distance increases.

Can the Encoder be used in position mode?

Note, however, that optical encoders do not give an absolute position but a distance relative to a reference point. The reference point (or home position) must be searched and registered every time the controller is powered on or reset.

R/C Radio FAQ's

How many R/C channels does the controller use?

Typically 2 and up to 3. Two channels are used to set the commands for motor 1 and motor 2. The two R/C channels can me "mixed" to cause one channel to set the forward/reverse direction and the other the left/right direction when both motors are used together to move and steer the robot. The third channels is used to activate up to two voltage outputs on the controller and to drive miscellaneous accessories (lights, weapons, horn, solenoids,...).

Do I have to use a special R/C radio?

No. But because the AX2550 is capable of good precision in capturing joystick commands and adjusting power, it will be able to take advantage of a higher quality radio.

What will happen if the robot goes beyond the radio's range?

The controller constantly checks that it is receiving valid commands. If it stops receiving commands for a preset amount of time, it will cause the robot to stop.

Why does the AX2550 not detect the loss of signal on my PCM radio

PCM radios have their own watchdog circuitry and will output a signal (normally a “safe condition” value) when radio communication is lost. This signal will be interpreted by the AX2550 as a valid command and the controller will remain active. To benefit from the AX2550’s radio detection function, you will need to disable the your PCM radio watchdog.

What happens if the joystick rest position is a little off-center?

Normally, when the joystick is centered on the radio, this corresponds to an off command on motor 1 and motor 2. In reality, the center position on the radio may not be the "ideal" center, causing a small command value to be sent to motor 1 and/or motor 2. To prevent this, the AX2550 can be configured to use one of several possible deadband values. The deadband will cause the controller to acknowledge radio commands only when the joystick as moved significantly from its center position.

How does joystick calibration work?

The AX2550 can be made to "learn" the joystick's min, max, and center positions specific to your radio system, during a special calibration sequence. This allows the controller to always start in a safe "idle" position and use the full joystick travel as commands.

If the controller is turned off, is the calibration data lost?

No. Calibration data is stored in the controller's Flash and will stay there permanently until it is changed by a new calibration session.

If the controller is turned off, is the calibration data lost?

No. Calibration data is stored in the controller's Flash and will stay there permanently until it is changed by a new calibration session.

Serial Port (RS232) FAQ's

What is the serial port used for?

The serial port allows the AX2550 to be connected to microcomputers or wireless modems. The connection can be used to send commands but also to read various status information. The serial mode enables the design of autonomous robots or more sophisticated remote controlled robots.

What is the baud rate used in the RS232?

The AX2550 serial port operates at 9600 bits per second and uses 7-bit, 1 start bit, 1 stop bit and even parity. This rate is equivalent to approximately 1000 characters per second. Considering that a motor command takes 5 characters, the controller can be updated with a new command up to 200 times per second. While serial ports, including the one in the AX2550, could reach significantly higher bit rates, the 9600 value has been selected because it is universally found on all microcontrollers and is the maximum rate supported by many wireless modems.

What is parity and what is it for?

Parity is a method for ensuring that characters received by the controller do not have errors. While communication errors are very infrequent if the controller is close to the microcontroller issuing the commands, they could cause the robot to seriously misbehave, especially if an error occurs in the middle of a command in a manner that alters its meaning. A character with a parity error will cause the character and the entire command it was part of to be discarded.

How can I tell that the controller has received an RS232 command?

The controller will "echo", or send back, every character it has acknowledged as valid. By reading back the returned characters and comparing them to those that were sent, it is easy to verify that there was no communication error. Furthermore, at the end of each command, the controller will send back a "+" (OK) or "-" (error) character to indicate whether the command was acknowledge and executed properly.

How does the RS232 Watchdog work?

The watchdog function may be enabled or disabled by configuring the controller's settings. When enabled, the controller expects to receive at least one character every 5 seconds. The character can be part of a command, or may be a dummy character that causes no action. If not character is received, the controller will cause the motors to stop. The controller remains active and ready to execute the next command as soon as it arrives. This function is designed to place the robot is a safe (stop) position in case the microcontroller, or wireless modem attached to the controller, fails.

How does the controller switch from R/C or serial mode?

At power up, the controller can be set to expect commands from the R/C radio input, the RS232 port, or from the analog voltage control input. The startup mode is one of the configuration parameters that is stored in the controller's flash memory. However, even if it is not set to the RS232 mode, the controller will monitor the RS232 input lines and switch to the serial mode automatically if a predefined character pattern has been received.

How can I remote control a robot using the serial port?

The simplest is to use two wireless modems: one that is connected to the AX2550's serial port and the other connected to a PC, laptop or single board microcomputer. It will be necessary to write a program on the computer side that converts commands received from a joystick to RS232 commands that will be sent to the controller via the wireless modem. Depending on the brand and type, wireless modems have a longer range than R/C radio, can send very precise commands, and are able to read back sensor and diagnostic information from the controller.

Where can I find low-cost microcomputers to control my robot with?

For simple applications, microcomputers such as Parallax's Basic Stamp, or controllers from Z-World Engineering are low-cost, easy to program solutions that will work with the AX2550. For applications requiring more processing,a large number of single board computers are available from several manufacturers. It is even possible to use a low cost PC motherboard or laptop if size or power consumption are not an issue. In short, any computing engine with a free serial port may be used with the AX2550. A Palm Pilot can be a good and low cost controller since it has a serial port that can be connected to the AX2550.

Can I use the controller to turn on/off electrical accessories?

Yes. The controller has one switched output which can be used to turn on or off any electrical device consuming up to 2A at 24V. A low power outputs is provided to drive additional devices using external (user provided) power transistors.

Can I record the controller's operating data for later analysis?

Yes. The Roborun utility can record over 30 minutes of operating data, including Amps, command value, MOSFET temperature, and battery voltage. The logged information can then be saved in a format directly readable from Microsoft Excel.

Can I modify the controller's software myself to add or modify features?

Roboteq will consider any request for custom functions to be added to the AX2550's controller. Modifying the code is a complex process requiring access to the proprietary source code, which Roboteq will license under the right conditions.

Can the controller switch automatically between RC and RS232 mode?

Yes but this requires external hardware as one of the input pins is shared between these two modes and that the software can only handle one mode or the other at a time. See our application note. Switching modes can be useful in computer controller robots to take over controls via radio in emergency situations.

Analog Mode FAQ's

What is the correlation between output voltage and speed/direction

The motor output is 0 (stopped) when the analog input is at 2.5V. Full reverse speed is reached when input is at 0V. Full forward speed is reached when input is at 5V. A programmable deadband is provided to keep the motor stopped even as the analog input is not exactly 2.5V. When nothing is connected to the analog input, a pull up and pull down resistor of 47k bring the input to 2.5V so that the motor is stopped.

What analog joystick do you recommend?

Users have reported successfully using professional joysticks from Penny & Giles, model JC400. Analog PC joysticks are not recommended as they do not have the right value potentiometer and do not travel from full min to full max.

How does the "dead man" button works

One of the controller's digital input can be configured so that the motors are active only when a button is pressed. This button would typically be located on the joystick to prevent accidental motion. Transistor are off (motors freewheeling) when a button is inactive.

What happens if the joystick is not centered at startup

For safety reasons, the controller's output will be at 0 if the joystick is not centered after reset. Once centered, motors will move according to the joystick's movement.

Can the controller operate in closed loop when used in analog input

The controller has only two analog inputs. When connected to an analog joystick, these inputs are no longer available for connecting either a potentiometer or an analog tachometer. It is possible to use an optical encoder, however. See Encoder FAQ.

Can I switch from Analog to RS232 mode and back

When the controller is operating in Analog mode, it will not recognize or accept RS232 commands. It will however scan the RS232 input and switch to RS232 mode when 10 consecutive "Carriage Return" characters are received.