Mab Robotics MD80 x CANdle User manual

MAB ROBOTICS
MD80 x CANdle User Manual
rev 2.0 - 05.09.2022
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TABLE OF CONTENTS
Ecosystem overview 3
MD80 3
CANdle and CANdle HAT 3
Safety information 4
Operating conditions (MD80 and CANdle) 5
Hardware setup 5
Quick startup guide 5
MD80 5
General parameters 5
Connectors pinout 6
Control modes 7
Controller tuning 10
Safety limits 11
FDCAN Watchdog 12
Measurements 13
Calibration 13
CANdle and CANdle HAT 14
Principle of operation 15
USB bus 16
SPI bus 16
UART bus 16
Using CANdle and CANdle HAT 16
Latency 18
Soware Pack 20
CANdle C++ library 20
MDtool 22
CANdle ROS/ROS2 nodes 24
MD80 update tool - MAB CAN Flasher 30
CANdle update tool - MAB USB Flasher 31
Common Issues and FAQ 32
How to check if my motor is operating properly 32
Motor not soldered properly 32
Failed calibration 32
Lack of FDCAN termination 32
Different FDCAN speeds between actuators 32
Too low torque bandwidth setting 33
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1. Ecosystem overview
MD80 x CANdle is a system of brushless actuator controllers (MD80) and translator devices (CANdle)
used for interfacing with them. MD80-based actuators can be used in advanced robotic projects like
quadrupedal robots, robotic manipulators, exoskeletons, gimbals, and many more.
1.1. MD80
MD80 is a highly integrated brushless motor controller. It can be interfaced with a great variety of
motors to turn them into advanced servo actuators. MD80 can work with both direct drive (no gearbox) and
geared motors.
MD80 brushless controller
1.2. CANdle and CANdle HAT
CANdle (CAN + dongle) is a translator device between the host controller and the MD80 drivers. It is
possible to interface CANdle with a regular PC over USB bus or CANdle HAT with SBCs (such as Raspberry PI)
over USB, SPI or UART bus.
CANdle Device CANdle HAT device
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1.3. Safety information
The instructions set out below must be read carefully before the initial commissioning or installation to
raise awareness of potential risks and hazards, and to prevent injury to personnel and/or property damage.
To ensure safety when operating this servo drive, it is mandatory to follow the procedures included in this
manual. The information provided is intended to protect users and their working area when using the device,
as well as other hardware that may be connected to it.
Electric servo drives are dangerous: The following statements should be considered to avoid serious injury
to individuals and/or damage to the equipment:
●Do not touch the power terminals of the device (supply and phases) as they can carry dangerously
high voltages.
●Never connect or disconnect the device while the power supply is ON to prevent danger to
personnel, the formation of electric arcs, or unwanted electrical contacts.
●Disconnect the drive from all power sources before proceeding with any wiring change.
●The surface of the device may exceed 100 ºC during operation and may cause severe burns to direct
touch.
●Aer turning OFF and disconnecting all power sources from the equipment, wait at least 10 minutes
before touching any parts of the device, as it can remain electrically charged or hot.
●Do not remove the casing of the device.
The following statements should be considered to avoid serious injury to those individuals performing the
procedures and/or damage to the equipment:
●Always comply with the connection conditions and technical specifications. Especially regarding
wire cross-section and grounding.
●Some components become electrically charged during and aer the operation.
●The power supply connected to this controller should comply with the parameters specified in this
manual.
●When connecting this drive to an approved power source, do so through a line that is separate from
any possible dangerous voltages, using the necessary insulation in accordance with safety
standards.
●High-performance motion control equipment can move rapidly with very high forces. An
unexpected motion may occur especially during product commissioning. Keep clear of any
operational machinery and never touch them while they are working.
●Do not make any connections to any internal circuitry. Only connections to designated connectors
are allowed.
●All service and maintenance must be performed by qualified personnel.
●Before turning on the drive, check that all safety precautions have been followed, as well as the
installation procedures.
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1.4. Operating conditions (MD80 and CANdle)
Ambient Temperature (Operating)
0°C - 40°C
Ambient Temperature (non-operating)
0°C - 60°C
Maximum Humidity (Operating)
up to 95%, non-condensing at 40 ºC
Maximum Humidity (Non-Operating)
up to 95%, non-condensing at 60 ºC
Altitude (Operating)
-400 m to 2000 m
1.5. Hardware setup
A typical hardware connection/wiring scheme is presented in the picture below:
CANdle MD80-actuator string (USB bus)
CANdle HAT MD80-actuator string (SPI/UART bus using Raspberry Pi 4)
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1.6. Before first use
Here are some things to look out for while playing with the MD80 x CANdle ecosystem for the first time:
1. Always stay cautious when dealing with actuators. Even though they don't seem like it, they may
severely hurt you when unintentional movement occurs. Itʼs recommended to fix the actuator to the
workbench.
2. Get accustomed to the safety limits section of this document. While developing your application be
sure to keep the limits low, and only if you are sure you know what you're doing - increase the limits.
3. We recommend using power supply sources that have the ability to work in two quadrants -
meaning they can supply and dissipate some of the energy produced by the motor in case it works
as a generator. Old trafo-based power supplies usually block current coming into the power supply,
causing overvoltage events on the MD80s. The best choice is to use LiPo batteries or at least SMPS
power supplies.
1.7. Quick startup guide
Please see the quick startup guide on our YouTube channel: Md80 x CANdle - Getting Started Tutorial
2. MD80
2.1. General parameters
MD80 is a brushless servo drive. It may come with a variety of motors and reductors, that can be precisely
matched to the usersʼ specifications. All MD80 variants are using an advanced motor control algorithm (FOC),
a high-resolution encoder, a high-speed FDCAN communication bus, and a common communication
interface. The servo drives have an integrated high-frequency position PID controller (at 1 kHz), velocity PID
controller (at 5 kHz), and impedance controller (at 40 kHz), as well as a direct torque controller. MD80 also
features a daisy-chaining mechanism, for easy connection of many drives in a single control network.
Parameter
Value
Input Voltage
18 - 28 VDC
Nominal Input Voltage
24 VDC
Max Input Current
20 A
Max Continuous Phase Current
20 A
Max Peak Phase Current (t = 4 s)
40 A
FDCAN Baudrate (adjustable)
1/2/5/8 Mbps
Position PID Controller Execution Frequency
1 kHz
Velocity PID Controller Execution Frequency
5 kHz
Impedance Controller ExecutionFrequency
40 kHz
Torque Control Execution Frequency
40 kHz
Torque Bandwidth (adjustable)
50 Hz - 2.5 kHz
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2.2. Connectors pinout
The connectors used in the system on the CANFD side are MOLEX Micro-Fit series 3.0. Both connectors are
connected in parallel for easy daisy-chaining. The connector pinout is presented below:
The colors of the corresponding wires in the Molex socket, as supplied by MAB (looking from the side of the
wires):
2.3. Control modes
TL;DR: MD80 x CANdle - motion modes
To control the motor sha with the userʼs command MD80 is equipped with multiple control
loops. All controllers are based on a regular PID controller design with an anti-windup block. The saturator
(anti-windup) is an additional module that acts as a limiter to the ʻIʼ part of the controller, as in many
systems, the error integration may grow to very large numbers, completely overwhelming ʻPʼ and ʻDʼ parts of
the controller.
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Velocity PID
Velocity PID controller calculates velocity error based on target velocity (set by user) and estimated
velocity read from the encoder. Its output is a torque command for the internal current/torque controller.
The parameters of the controller are:
●Velocity Target (in [rad/s])
●kP (proportional gain)
●kI (integral gain)
●kD (derivative gain)
●I windup (maximal output of an integral part in[Nm])
●Max output (in [Nm])
Position PID
Position PID mode is the most common controller mode used in industrial servo applications. In MD80, it is
implemented as a cascaded PID controller. This means that the controller is working in two stages, firstly
the position error is calculated, it is then passed to the Position PID, which outputs target velocity. This value
is then passed as an input to the Velocity PID controller, which outputs commanded torque. This mode uses
both Position PID and Velocity PID and thus needs the following parameters:
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For Position PID
●Position Target (in [rad])
●kP (proportional gain)
●kI (integral gain)
●kD (derivative gain)
●I windup (maximal output of an integral part in [rad/s])
●Max output (in [rad/s])
For Velocity PID:
●Velocity Target (in [rad/s])
●kP (proportional gain)
●kI (integral gain)
●kD (derivative gain)
●I windup (maximal output of an integral part in[Nm])
●Max output (in [Nm])
To properly tune the controller, it is recommended to first tune the velocity controller (in Velocity PID mode),
and then the Position PID. The controller can be described with a diagram:
Impedance PD
Impedance Control mode is a popular choice for mobile or legged robots, as well as for any compliant
mechanism. The main idea behind it is to mimic the behavior of a torsional spring with variable stiffness and
damping. The parameters of the controller are:
●Position Target
●Velocity Target
●kP (position gain)
●kD (velocity gain)
●Torque Feed Forward (Torque FF)
The torque output is proportional to the position error and velocity error and additionally supplemented
with a torque command from the user. Here are some of the most common applications for this control
mode:
●Spring-damper mechanism - when Velocity Target is set to 0, Impedance Controllers kP gain acts
as the virtual spring stiffness and kD as its damping coefficient.
Example use case: a variable suspension for a wheeled robot, where suspension stiffness can be
regulated by kP, damping by kD, and height (clearance) by changing the Target Position;
●High-frequency torque controller, where its Targets and Gains can act as stabilizing agents to the
torque command.
Example use case: In legged robots, force control can be achieved by advanced control algorithms,
which usually operate at rates below 100 Hz. It is usually enough to stabilize the robot but too slow
to avoid vibrations. Knowing desired robot's joint positions, velocities, and torques, drives can be
set to produce the proper torque and hold the position/velocity with small gains. This would
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compensate for any high-frequency oscillations (vibrations) that may occur, as the Impedance
controller works at 40kHz (much faster than <100 Hz).
●Raw torque controller - when kP and kD are set to zero, the torque_ff command is equal to the
output controller torque.
The impedance controller is quite simple and works according to the schematic below:
2.4. Controller tuning
TL;DR: The best way to get started with tuning is to copy the default gains and tweak them. You can
treat this section as our recommendation for tuning the controllers, but online articles can be useful as
well (link)
The first step to correctly set up the gains is to start with our default gains. There are three sets of default
gains that are set on each motor power up and thus they allow for restoring the actuator to a default state in
case some gains were set incorrectly by the user. These gains are also a great starting point for user
modifications when the actuator has to be used in a specific application requiring high positioning accuracy
or very dynamic movements.
Note: Default gains are set to work with CANdle examples. This way they can be assumed to be
universal but it does not have to always be the case.
Note: When something does go wrong during the tuning process just power-cycle the actuator - the
default gains will be restored.
Warning: Always keep your safety limits low when experimenting with gains. Gains not suitable for
your system may cause oscillations and unstable operation of the MD80-based actuators.
Velocity PID
The velocity PID controller can be used to command different velocity profiles to the motor. This mode uses
a regular PID controller architecture and has four user-defined parameters: kP, kI, kD, and windup. Since
velocity readout is somewhat noisy, it is recommended to keep the kP value as low as possible and play with
kI gain. It is necessary to find the sweet spot that makes the actuator response resistant to disturbances, but
also not too noisy (too high kP gain may introduce oscillations). Usually, the kI gain is set to a higher value,
however, do not treat it as a rule of thumb. Setting the kI gain to a too high value can cause an overshoot
when the target velocity is changed rapidly. The kD gain may be used to partially overcome this issue. The
windup parameter is used to limit the integral action which could potentially rise to high values when
velocity error is present for longer periods.
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