WR BEAR User manual

BEARTM Operation and SDK Manual
Westwood Robotics R
Corporation
v 0.2.6
c
2020 Westwood Robotics
All Rights Reserved
1

Contents
1 Introduction 3
1.1 About This Manual ..................................... 3
1.2 Warnings .......................................... 3
1.3 Know Your BEAR ...................................... 4
2 Using BEAR 10
2.1 Power & Signal ....................................... 10
2.2 Communication ....................................... 14
2.2.1 Control Table .................................... 14
2.2.2 Detailed Description ................................ 16
2.2.3 Error Code ..................................... 17
2.3 Operating Modes ...................................... 18
2.4 PID Tunning ......................................... 20
3 SDK 23
3.1 PyBEAR ........................................... 23
3.2 LabBEAR .......................................... 30
2

1 Introduction
1.1 About This Manual
•Type of a data is enclosed with “<>”. For example, <list>is a data type in Python.
•BEAR is also referred to as BEAR motors, BEAR actuators or BEAR modules.
•CAUTION labels contain advises and instructions that, if not properly followed, can possibly
lead to damage or malfunction on your BEARs.
This is an example of CAUTION label.
CAUTION labels contain advises and instructions that, if not properly followed, can
possibly lead to damage or malfunction on your BEARs.
CAUTION
•WARNING labels contain restrictions and instructions that, if not properly followed, will defi-
nitely lead to severe damage on your BEARs, and can result in dangerous situations.
This is an example of WARNING label.
WARNING labels contain restrictions and instructions that, if not properly followed,
will definitely lead to severe damage on your BEARs, and can result in dangerous
situations.
WARNING
1.2 Warnings
To avoid structural deformation, please NEVER clamp your BEAR from the side.
WARNING
To avoid leakage, please do not loosen or tighten the screws on the cooling channel cap or
disassemble the cooling channel cap. The gasket must be replaced once disassembled.
WARNING
3

In Direct Force Mode, the output speed of BEAR is not limited by the limit velocity max
setting.
WARNING
Pay extra attention when changing mode while BEAR is enabled. BEAR will remain enabled
and execute the corresponding goal xxx setting in the new mode immediately.
WARNING
Do not save configurations when the motor is enabled. The motor may not respond when it
is writing flash memory.
WARNING
1.3 Know Your BEAR
a) Koala BEARTM V2 (KB02)
Koala BEAR V2(KB02) is a small actuator designed for highly dynamic applications with rel-
atively low loads, such as all kinds of small mobile robots, robot hands or robot manipulators.
The mechanical and electrical as well as the thermal management features are introduced
as following, with the help of figure 1.
Weight Speed Constant KVTorque Constant KTSupply Voltage
250 g 22 RPM/V 0.35Nm/A 9 ∼33.6V (3 ∼8S)
Stall Torque 15sec Stall Torque 15sec(LC) Stall Torque 1.5sec Reflected Inertia
3.5 Nm 4.2 Nm 14 Nm 1.82 ×10−3kg/m2
Table 1: Koala BEAR V2 Specification1
•Mechanical Features The dimensions and locations of mounting features are anno-
tated as in figure 1. There are six M3 screw holes and six 3mm pin holes on the output
shaft for locating and connecting the payload. The eight M2.5 screw holes, four 2.5mm
pin holes located on the front side as well as the four M3 screw holes and four 2mm
pin holes on three sides can all be used to locate and mount KB02 to its application.
Besides, there are also four M3 screw holes on the back that are axisymmetric about
the output shaft, and these four M3 screw holes can also be used as mounting points
or to mount additional bearings under certain application.
1Stall Torque is the maximum torque BEAR can deliver for more than 10 seconds under given thermal condition; LC
stands for Liquid Cooled.
4

Figure 1: Koala BEAR V2 Specs
When high axial load is expected at the application joint, additional axial support
is required instead of directly use Koala BEAR for the axial support on the joint.
CAUTION
Please refer to Table. 1for overall mechanical and performance properties of KB02.
•Electrical Features KB02 has one XT30 power port, and two Molex PicoBlade 53047
6Pin signal ports. The two signal ports make it convenient to connect multiple BEAR
modules in serial. Power supply voltage for KB02 ranges from 9V to 32V.
When driving the load dynamically, a non-negligible back EMF will be generated
by BEAR upon backdrive or impacts. In such applications, it is highly recom-
mended to use Li-Po batteries as power supply or add a big capacitor to the
power supply circuit as a buffer to protect the power supply.
CAUTION
•Liquid Cooling The headers of the liquid cooling channel on KB02 are push-to-connect
headers for 4mm OD tubes. The applied coolant pressure in the cooling channel can
5

be up to 1MPa. It is recommended to use DI water mixed with appropriate amount of
biological inhibitors as coolant. It is not recommended to add other additives or dyes
into the coolant.
. To prevent damage to the circuit from coolant leakage, please apply/replace
PTFE sealant tape on the thread of the cooling channel headers before attaching
them onto your BEAR and check for leakage carefully.
CAUTION
Refrain from using Copper (II) Sulphate (CuSO4) additive – common trade name
“Nuke Cu” or “Biocide Cu” – due to its tendency to react with metals usually found
in the liquid cooling loop, especially radiators (Zn, Cu, Sn) as well as BEAR (Al)
thus promoting corrosion. Using CuSO4also accelerates visually discouraging
copper tarnishing phenomena.
CAUTION
In the case of regularly liquid cooled applications, please check for leakage in the
liquid cooling loop at least weekly.
CAUTION
To avoid leakage, please do not loosen or tighten the screws on the cooling chan-
nel cap or disassemble the cooling channel cap. The gasket must be replaced
once disassembled.
WARNING
b) Panda BEARTM V2 (PB02)
With the right balance of torque, weight, and form factor, Panda BEAR V2(PB02) is our
most versatile unit. Its excellent dynamic performance and payload capability makes it well
suited for diverse applications ranging from legged mobile robots to service and entertain-
ment robots. The mechanical and electrical as well as the thermal management features are
introduced as following, with the help of figure 2.
•Mechanical Features The dimensions and locations of mounting features are anno-
tated as in figure 2. There are eight M3 screw holes and eight 3mm pin holes on the
output shaft for locating and connecting the payload. The eight M3 screw holes and
3mm pin holes located on the front side as well as the six M3 screw holes and six 2mm
pin holes on each of the three sides can all be used to locate and mount PB02 to its
application. Besides, there are also eight M3 screw holes on the back that are axisym-
metric about the output shaft, and these eight M3 screw holes can also be used as
mounting points or to mount additional bearings under certain application.
6

Figure 2: Panda BEAR V2 Specs
When high axial load is expected at the application joint, additional axial support
is required instead of directly use Panda BEAR for the axial support on the joint.
CAUTION
Please refer to Table. 2for overall mechanical and performance properties of PB02.
Weight Speed Constant KVTorque Constant KTSupply Voltage
685 g 10.7 RPM/V 0.67Nm/A 9 ∼50.4V (3 ∼12S)
Stall Torque 15sec Stall Torque 15sec(LC) Stall Torque 1.5sec Reflected Inertia
13.4 Nm 16.8 Nm 33.5 Nm 7.44 ×10−3kg/m2
Table 2: Panda BEAR V2 Overall Mechanical Properties2
•Electrical Features PB02 has one XT60 power port, and two Molex PicoBlade 53047
6Pin signal ports. Pry open the back cap to access the signal ports, as instructed in
figure 3. The two signal ports make it convenient to connect multiple BEAR modules in
serial. Power supply voltage for PB02 ranges from 9V to 48V.
2Stall Torque is the maximum torque BEAR can deliver for more than 10 seconds under given thermal condition; LC
stands for Liquid Cooled.
7

Figure 3: Panda BEAR Signal Ports
When driving the load dynamically, a non-negligible back EMF will be generated
by BEAR upon backdrive or impacts. In such applications, it is highly recom-
mended to use Li-Po batteries as power supply or add a big capacitor to the
power supply circuit as a buffer to protect the power supply.
CAUTION
•Liquid Cooling The headers of the liquid cooling channel on PB02 are push-to-connect
headers for 4mm OD tubes. The applied coolant pressure in the cooling channel can
be up to 1MPa, but it is recommended to regulate your coolant pressure under 0.7MPa
if your system’s coolant is pressurized at all time. It is recommended to use DI water
mixed with appropriate amount of biological inhibitors as coolant. It is not recommended
to add other additives or dyes into the coolant.
. To prevent damage to the circuit from coolant leakage, please apply/replace
PTFE sealant tape on the thread of the cooling channel headers before attaching
them onto your BEAR and check for leakage carefully.
CAUTION
Refrain from using Copper (II) Sulphate (CuSO4) additive – common trade name
“Nuke Cu” or “Biocide Cu” – due to its tendency to react with metals usually found
in the liquid cooling loop, especially radiators (Zn, Cu, Sn) as well as BEAR (Al)
thus promoting corrosion. Using CuSO4also accelerates visually discouraging
copper tarnishing phenomena.
CAUTION
8

In the case of regularly liquid cooled applications, please check for leakage in the
liquid cooling loop at least weekly.
CAUTION
To avoid leakage, please do not loosen or tighten the screws on the front cap or
disassemble the front cap. The gasket inside must be replaced once disassem-
bled.
WARNING
9

2 Using BEAR
2.1 Power & Signal
a) Power
The power port on KB02 is a male XT30 connector and the power port on PB02 is a male
XT60 connector. The power port polarity follows the regular convention of XT30 and XT60
connectors: the pole near flat side is positive and the pole near the rounded/chamfered side
is ground, as shown in fig. 4
Figure 4: BEAR power connector and polarity
Be cautious and never reverse power polarity.
WARNING
Power supply voltage for different BEARs are as listed in Table. 3. Connect BEARs getting
same voltage in parallel when using multiple BEARs.
To avoid fire hazard, please estimate nominal current consumption on each BEAR
when chaining multiple BEAR in parallel and select power cable with appropriate AWG,
especially higher current consumption is expected.
WARNING
Product Name Koala BEAR Panda BEAR
Supply Voltage V 9 ˜ 32 9˜ 48
Connector XT30 XT60
Table 3: BEAR Power Supply Specs
b) Indicator
Each BEAR has an LED indicator on the back side. There are three(3) LEDs with different
colors on the indicator that indicates the status of the actuator: Grean,Blue and Red.
The Grean light comes on once BEAR is powered and initialization is complete; The Blue
LED lights up as soon as the torque output is enabled, and turns off once disabled; The Red
light indicates an existing Error.
c) USB2BEAR
It is recommended to use Westwood Robotics USB2BEARTM high speed RS485 USB dangle
to connect BEARs to your computer.
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Use at own risk when using other generic RS485 dangles.
CAUTION
The USB2BEAR dangle is a USB2.0 device and its RS485 connector is a 4-pin Molex Mini-
SPOX 5268 male header. (Mating female housing: 4-pin Molex Mini-SPOX 5264, part num-
ber: 0050375043) It’s pin-out and function of the switches are as shown in fig. 5.
Figure 5: USB2BEAR pin-out and switches.
It is recommended to add a terminal resister of 120 Ohms at the end of RS485 chain when
using long signal cables and the impedance of the signal line is high enough to result in noisy
communication. Put the Terminal Resister Switch at ’ON’ when a terminal resister is applied
at the end of the chain, but be sure to have it at ’OFF’ when no terminal resister is applied
at the end of the chain. USB2BEAR can also be used to communicate with generic RS485
devices other than BEAR. Make sure the matching communication Baud Rate is selected. It
is recommended to use 8Mbps for fast communication when paired with BEARs.
d) Chaining BEAR Signal Ports
When having multiple BEARs in your system, properly chaining their signal lines not only
can make your wire management easy and clean, but also contribute to system reliability
and robustness. Just like all other RS485 devices, you can simply chain your BEARs in a
daisy chain, as shown in fig. 6. It is recommended to add a terminal resistor of 120 Ohm
at the end of the signal chain, especially when the signal line is relatively long or whenever
exceptional signal noise is observed.
There could also be multiple chains of BEARs, such as in the application of dual-arm ma-
nipulators or legged robots. In this type of situation, traditional solutions are either using a
long signal cable to connect the end of one chain with the start of another, or using multiple
RS485 adapters, one for each chain. The former solution could lead to high impedance in
the signal line thus noisy communication, while the latter could result in control complication
and a demand of too many USB ports on the controller.
In the above situations, the unique pass-thru channels on all BEAR signal ports become very
handy. Fig. 7illustrates a simple example of using the pass-thru channels to achieve a fork
chain. Again, it is recommended to add a terminal resistor of 120 Ohm at the end of the
signal chain, especially when the signal line is relatively long or whenever exceptional signal
noise is observed.
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Figure 6: Daisy chain BEARs.
Figure 7: Fork chain BEARs.
It is fine to chain different type of BEARs together, but be careful to make sure that all BEARs
get the correct power supply voltage. All BEARs in the same chain should have the same
baud rate setting, and there is no ID conflict as well.
e) Connect to USB2BEAR
There are three ways of connecting the signal line from BEARs to the USB2BEAR dangle,
as shown in fig. 8. The GND, A and B terminals are always connected to corresponding
pins on the USB2BEAR dangle, and the only difference between these three configurations
is how the ESTOP signal terminal is handled. The minimum connection is to connect the E-
STOP terminal to signal GND, but doing this will eliminate the function of E-STOP protection
thus depreciated. A basic configuration which adds a E-STOP switch between the ESTOP
and the signal GND terminal is preferred over the minimum configuration. Disconnecting the
ESTOP terminal from the signal GND terminal via the E-STOP switch triggers the E-STOP
protection on all connected BEARs.
Our recommended configuration is to connect the GND and ESTOP terminal to a Westwood
Robotics Wireless ESTOP module, which enables the user to trigger the E-STOP protection
12

on all connected BEARs remotely, which we consider to be an extremely important safety
feature for high power or high complicity systems, or any system that works around a human.
Please refer to section. f) for detailed explanation on E-STOP protection.
Figure 8: Connecting BEARs to USB2BEAR.
Do NOT leave the ESTOP terminal floating, as this keeps BEARs in their ESTOP status
and prevents them from being enabled.
CAUTION
f) E-STOP
When the ESTOP terminal on a BEAR is not pulled low to signal GND, the BEAR module’s
E-STOP protection will be triggered. The 3rd bit of its error code will be come HIGH and
the torque enable status will become 3. If the E-STOP protection is triggered while BEAR is
enabled, such BEAR will go into hardware damping mode preventing any potential damage;
if the E-STOP protection is triggered while BEAR is disabled, such BEAR will stay disabled
and will not enter hardware damping mode.
The E-STOP protection can also be triggered by writing ”3” to the torque enable status reg-
ister and does not necessarily require the ESTOP terminal to be disconnected from signal
GND.
To release a BEAR from its E-STOP protection, first make sure that the ESTOP terminal is
pulled low to signal GND, then disable the BEAR by writing ”0” to its torque enable status
register. This will also reset the 3rd bit of its error code to LOW.
Refer to section. 2.2.2 for details on torque enable status register and section. 2.2.3 for details
on error code.
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2.2 Communication
Communication with BEAR is achieved by using BEAR SDK to interact with the Control Table.
The Control Table is a structure that consists of multiple Registers to store status or to control the
device. Users can check current status of the device by reading from specific Registers in the
Control Table, or to control the device by writing specific data to some Registers.
The Control Table is explained in detail in this section as following. Please refer to Section. 3for
complete instruction of using BEAR SDK of various languages to interact with the Control Table.
2.2.1 Control Table
All Registers in the Control Table are divided into two groups: Configuration Registers(CONFIG)
and Status Registers(STAT). All values in the Configuration Registers will be saved in the flash
memory when “save config” command is received by BEAR. All values in status registers and
all unsaved configuration registers will be lost when power-off and reset to default or last-save at
power-on.
Do not save configurations when the motor is enabled. The motor may not respond when it
is writing flash memory.
WARNING
It is recommended to save config only when necessary. Internal flash guaranteed endurance
is 10K write cycle.
CAUTION
Please refer to Table. 4for complete lists of CONFIG and STAT Registers.
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Configuration Registers
Name Description Access Type Unit Default Min Max
id Unique motor ID R/W uint32 1 0 0xFC
mode R/W uint32
baudrate R/W uint32 Mbps
homing offset R/W float32 rad
p gain id P gain for Id current loop R/W float32 0.001 0 10
i gain id I gain for Id current loop R/W float32 0.0001 0 10
d gain id D gain for Id current loop R/W float32 0 0 10
p gain iq P gain for Iq current loop R/W float32 0.001 0 10
i gain iq I gain for Iq current loop R/W float32 0.0001 0 10
d gain iq D gain for Iq current loop R/W float32 0 0 10
p gain velocity P gain for velocity loop R/W float32 0.2 0 1000
i gain velocity I gain for velocity loop R/W float32 0.001 0 1000
d gain velocity D gain for velocity loop R/W float32 0 0 1000
p gain position P gain for position loop R/W float32 0.01 0 1000
i gain position I gain for position loop R/W float32 2E-05 0 1000
d gain position D gain for position loop R/W float32 0 0 1000
p gain direct force P gain for direct force loop R/W float32 0 0 1000
i gain direct force P gain for direct force loop R/W float32 0 0 1000
d gain direct force P gain for direct force loop R/W float32 0 0 1000
limit acc max Maximum Acceleration R/W float32 rad/s25 0 100000
limit i max Maximum Iq (torque) and Id R/W float32 A 5 0 100
limit velocity max Maximum absolute velocity R/W float32 rad/s 100 0 10000
limit position min Position limit min. R/W float32 rad -8π-8π8π
limit position max Position limit max. R/W float32 rad 8π-8π8π
min voltage R/W float32 V 6 6 60
max voltage R/W float32 V 40 6 60
watchdog timeout R/W uint32 µs 0 0 10000000
temp limit low Limit power at this temperature R/W float32 ◦C 80 0 125
temp limit high Shutdown at this temperature R/W float32 ◦C 100 0 125
Status Registers
Name Description Access Type Unit Default Min Max
torque enable Enable output R/W uint32 0 0 3
goal id Goal Excitation Current R/W float32 A
goal iq Goal Torque Current R/W float32 A
goal velocity - R/W float32 rad/s
goal position - R/W float32 rad -8π8π
present id Present Excitation Current RO float32 A
present iq Present Torque Current RO float32 A
present velocity Present velocity RO float32 rad/s
present position Present position RO float32 rad -8π8π
input voltage Present input voltage RO float32 V
winding temperature Winding temperature in ◦C RO float32
powerstage temperature Powerstage temperature in ◦C RO float32
ic temperature IC temperature in ◦C RO float32
error status *Not implemented yet RO float32
*R/W: read and write RO: read only
Table 4: Table of Registers
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2.2.2 Detailed Description
Config Registers
•id The ID of a BEAR. This should be unique for every BEAR in the same chain.
•mode Operating mode. Refer to Section. 2.3 for detailed explanation.
•baudrate Baud-rate for the RS-485 communication. Unless needed by system setup, it is
recommended to leave it at default 8Mbps.
•homing offset present position = raw position + homing offset. When setting up new hom-
ing offset, always take the existing homing offset into account.
•PID Gains Refer to Section. 2.4 for more details.
•limit acc max Absolute maximum limit for acceleration (unit: rad/s2). Effective in mode 2
(position mode) for trajectory generation.
•limit i max Absolute maximum limit for torque current Iq and excitation current Id (unit: A).
Effective in all modes. Since Iq is proportional to torque, this is effectively the torque limit.
•limit velocity max Absolute maximum limit for velocity (unit: rad/s). Effective in modes
1(Velocity) and 2(Position).
•limit position min/max Lower/upper position limit for BEAR (unit: rad). Going out of bounds
triggers internal damping mode and generates an error. Disable, then bring motor within limit
physically or by limit adjustment clears the error. Effective in modes 2(Position) and 3(Direct
Force).
•min/max voltage When voltage goes below min voltage or above max voltage , hardware
fault triggers with an error generated. Disable, then regulate the supply voltage within limits
clears the error.
•watchdog timeout Safety watchdog timeout value in micro seconds(µs). When communi-
cation times out, BEAR goes into internal damping mode and generates an error. Disable
clears the error. This ONLY applys to modes 0(torque).
•temp limit low From this temperature(◦C) to temp limit high, the Iq limit will start to decrease
linearly from limit iq max, and an error will be generated.
•temp limit high From this temperature(◦C) above, the Iq limit will be reduced to 0. The tem-
perature limit functionality uses the maximum between Winding temperature and Powerstage
temperature.
Status Registers
•torque enable Enable status and control of BEAR.
When write:
0 - Disable BEAR, also clear latching errors;
1 - Enable BEAR torque output;
3 - EStop protection triggered. If motor was enabled, motor goes into safe damping mode.
When read:
16

0 - BEAR disabled
1 - BEAR enabled
2 - BEAR disabled and critical error preventing enabling the motor
3 - BEAR in safe damping mode due to non-critical error.
•goal id Reference excitation current Id input. Leave it at 0 for normal operation.
•goal iq Reference torque current Iq (unit: A). Can be written to when BEAR is in mode 0 and
3. Iq is roughly proportional to the output torque.
•goal velocity Reference velocity (unit: rad/s). Can only be written to when BEAR is in mode
1.
•goal position Reference position (unit: rad). Can be written to when BEAR is in mode 2 and
3.
•present id/iq/velocity/position Present status value of BEAR. Read only.
•input voltage Present power supply voltage to BEAR (unit: V). Read only.
•winding temperature Winding temperature reading (unit: ◦C).
•powerstage temperature MOSFETs temperature reading (unit: ◦C).
•ic temperature Temperature reading (unit: ◦C) of the micro controllers.
2.2.3 Error Code
A BEAR will always return its present error status by returning an 8-bit error code together with
every returned data. The highest bit of the error code is always 1. Refer to table. 5for detailed
explanation of every bit in the error code.
bit Type Name Note
0 Warning Communication
1 Warning Overheat
2 Error Absolute Position
3 Error Watchdog Timeout & ESTOP
4 Error Joint Limit
5 Error Hardware Fault
6 Error Initialization Error
7 1 Always 1
Table 5: Table of Error Code (little-endian)
17

Detailed Description
•Communication A corrupted data packet was received. This warning resets automatically
and is only associated with corresponding round of communication.
•Overheat The temperature of at least one component among IC, powerstage and winding
in this BEAR has exceeded the value written to temperature limit low. This warning resets
automatically when the temperature limit low value is higher than the highest temperature
measured in this BEAR module.
•Absolute Position Absolute position reading error.
•Watchdog Timeout & ESTOP When in mode 0(torque mode), motor enabled and watchdog
timer configured, watchdog timeout triggers this error.
External ESTOP signals also triggers this error. Including physical signal and writing 0x03 to
torque enable.
•Joint Limit Joint limit exceeded.
•Hardware Fault Input voltage out of range or MOSFET driver fault.
•Initialization Error Corrupted save file in flash, calibration needed.
2.3 Operating Modes
BEAR actuator can run in the following four different modes:
Pay extra attention when changing mode while BEAR is enabled. BEAR will remain enabled
and execute the corresponding goal xxx setting in the new mode immediately.
WARNING
0 - Torque Mode
The torque current(iq) in BEAR is directly controlled in this mode. Control commands in-
structing the torque current iqis written to status register goal iq, and the unit of the input is
Amps. BEAR tracks goal Iq and goal Id using PID gains for Iq and Id.
The output torque T can be roughly estimated using the torque current iqand the torque
constant KTof the BEAR module as shown in Eq. 1:
T=iq×KT(1)
When the current command goal iq is higher than the limit iq max setting, the BEAR
module will not execute the command.
CAUTION
18

The actual maximum torque of BEAR is limited by the maximum current the power
supply can provide as well as the limit iq max setting.
CAUTION
1 - Velocity Mode
The output speed of BEAR is directly controlled by user input via status register goal velocity.
The unit of the input is rad/s. BEAR tracks goal velocity using PID gains for velocity loop, and
the PID output feeds into Iq.
When the speed command goal velocity is higher than the limit velocity max setting,
the BEAR module will not execute the command.
CAUTION
The actual maximum speed of BEAR is limited by the supply voltage and the maximum
speed it can achieve under the given load conditions; The actual maximum torque of
BEAR is limited by the maximum current the power supply can provide as well as the
limit iq max setting.
CAUTION
2 - Position Mode
The output position of BEAR is directly controlled by user input via status register goal position.
The unit of the input is rad. BEAR tracks goal position using PID gains for position loop, and
the PID output feeds into velocity.
When the position command goal position is out of the range defined by the settings in
limit position max and limit position min, the BEAR module will not execute the com-
mand.
CAUTION
The actual output speed of BEAR is limited by the supply voltage and the maximum
speed it can achieve under the given load conditions as well as the limit velocity max
setting; The actual maximum torque of BEAR is limited by the maximum current the
power supply can provide and the limit iq max setting.
CAUTION
19

3 - Direct Force Mode
In this mode, BEAR tracks position and velocity using PID gains, goal Iq and Id feed-forward
terms are also added to the loop. In another word, user can use this mode to command
BEAR to track a trajectory that contains all of position, velocity and torque data. The diagram
in fig. 9shows how these goal commands are mixed internally.
Figure 9: Direct Force Mode Diagram.
When the speed command goal velocity is higher than the limit velocity max setting,
or the goal iq is higher than the limit iq max setting, the BEAR module will not execute
the command.
BEAR will still execute the command even if goal position is out of the range defined
by limit position max and limit position min in this particular mode.
CAUTION
The actual output speed of BEAR is ONLY limited by the supply voltage and the maxi-
mum speed it can achieve under the given load conditions; The actual maximum torque
of BEAR is limited by the maximum current the power supply can provide and the
limit iq max setting.
CAUTION
In Direct Force Mode, the output speed of BEAR is not limited by the limit velocity max
setting.
WARNING
2.4 PID Tunning
It is very important for the PID gains to be well tuned for a BEAR to function as desired, and there
can be multiple sets of PID gains that need to be tuned to suit a BEAR into it’s designated tasks,
depending on the BEAR’s operating mode.
20