3 — APPLICATION-SPECIFIC FEATURES
Curtis AC F2-A, F4-A, F6-A Motor Controllers – FOS 4.5 – April 2022 Return to TOC
pg. 32
3 — APPLICATION-SPECIFIC FEATURES
Some of the controller features aect more than the electrical connections or the parameter settings.
is chapter provides background information on application-specic features, to assist the vehicle
designer in the design and vehicle-development process.
MOTOR SPEED CONSTRAINTS
e maximum motor speed (RPM) the controller will allow is constrained by the number of motor
poles, the encoder pulses per motor revolution, and the maximum speed constraint imposed by the
Max Speed parameter. e Max_Speed_Controller_Limit is always the lowest of the Max_Speed_
Encoder_Limit, Max_Speed_Frequency_Limit, and the Max_Speed_RPM_Limit.
e overall maximum motor speed is the least of the following three constraints:
1. Electrical Frequency Constraint
e controller’s (fundamental) electrical frequency goes to 599 Hz. It accomplishes this by clamping
the Max Speed allowed, using the equation:
Max Speed Frequency Limit = 71880/Number of Motor Poles
For example, an 8-pole motor running synchronously at 599 Hz can rotate to a maximum rpm
of 71880/8 = 8,985 rpm (max). In this case, the control soware will limit the max speed to 8,985
rpm for an 8-pole motor. ere is a limited over-speed, should the motor exceed this speed (e.g.,
going down a hill). e controller will still attempt to produce the correct frequency for maximized
torque and proper control; it will not simply clamp to 599 Hz.
2. Encoder Pulses/Revolution Constraint (quadrature encoder)
e maximum Encoder frequency the controller will accept without the external pull-up circuit
is 30 kHz.
1
To determine how fast the encoder steps constraint will allow the motor to spin, use the equation:
Max Speed Encoder Limit = 15000000/Encoder Steps
Due to the high encoder frequency ability, encoders with lower pulses per revolution (ppr) will
not be the limiting factor in motor rpm (e.g., a motor with a 256-pulse encoder can run up to
58,593 rpm, which is greater than the rmware limit, yet a 1024-pulse encoder will be limited
to 14,648 rpm).
3. Max Speed Parameter Constraint
e maximum motor speed the controller will allow is 30,000 rpm.
Max Speed RPM Limit = 24,000
2
1
FOS versions 4.0 and higher are able to support input frequencies up to 250 kHz, provided there is an external pull-up resistor
for encoders > 30kHz. The external supplies (5V or 12V) may be used as a source for the pull-up resistor. Follow the Encoder
manufacturer recommendations when sizing this resistor, but typical values would be 220Ω for 5V and 470Ω for 12V. See the
external circuit in the Encoder specifications, Table 15.
2
The variable, Max Speed Controller Limit (0x30AF 0x00) displays this maximum limit. See the Motor Setup parameter menu.
Note: In the case where the Max Speed parameter is the prevailing constraint, greater RPM is possible.
Contact the Curtis distributor or support engineer to discuss the particular application.
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