Version 2.0
Segway RMP – User Guide
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Scale Factors
Scale factors may be applied to the maximum velocity, maximum acceleration, maximum turn
rate, and to the current limit. The scale factors limit the associated quantity to a fraction of its full
scale value. Each of these scale factors may range from 0 to 1.0. Default values for these scale
factors are:
Scale Factor
Default value
Parameter range
Maximum velocity
0.75
0.0 – 1.0
Maximum acceleration
0.75
0.0 – 1.0
Maximum turn rate
1.0
0.0 – 1.0
Motor Current (torque) limit
1.0
0.0 – 1.0
Scale factors are altered through commands from the host processor to the RMP; refer to the
“Segway Robotic Mobility Platform (RMP) Interface Guide” for more detailed information on
generating these commands.
Acceleration/Velocity Scale Factors
The acceleration scale factor provided by the software interface allows for very aggressive
stopping and starting. Attempting to drive full reverse from maximum forward speed may
command so much platform tilt that the device falls over. In an emergency stop, this may be
preferred to continuing forward (much like a person who decides to fall back and slide when
attempting to stop quickly).
The minimum stopping distance may be calculated from the maximum velocity,
V
max
, and
maximum acceleration,
a
max
:
Thus, large velocities with small accelerations produce large stopping distances. Choose your
acceleration limits with care, considering both the need to stop quickly and the top speed you
have chosen.
Turning Scale Factor
A turning scale factor parameter may be used to limit the maximum lateral acceleration of the
RMP. This may be particularly useful with tall payloads, to prevent the RMP from tipping. In
most cases though, higher turning sensitivity is useful for navigating around obstacles.
Motor Current Limit (Motor Torque) Scale Factor
The available wheel torque may be limited by reducing the motor current limit scale factor. Each
wheel is capable of producing peak torque of 122 Newton-meters (90 foot-pounds). Setting the
motor current limit to 1.0 (256 counts) results in full torque capacity; setting it to 0.0 (0 counts)
results in no available torque. Dynamic balancing requires higher transient torque to accelerate,
decelerate and traverse small obstacles. However, the torque required depends on the
environment, task, and payload. Reducing available torque may be prudent in some cases. In
Balance mode, limiting the torque too much will result in the RMP falling over during a transient.
If in doubt, test the RMP performance using a robust payload that can tip over without being
damaged.
Battery Packs
max
2
max
min
2
a
V
D
=