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added acceleration PV to Motor device #9

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added acceleration PV to Motor device #9

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1 change: 1 addition & 0 deletions src/ophyd_epics_devices/motor.py
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ def __init__(self, prefix: str, name="") -> None:
self.setpoint = EpicsSignalRW(float, ".VAL")
self.readback = EpicsSignalR(float, ".RBV")
self.velocity = EpicsSignalRW(float, ".VELO")
self.acceleration = EpicsSignalR(float, ".ACCL")
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I suggest acceleration time, so it's clear this is not acceleration rate...

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self.acceleration = EpicsSignalR(float, ".ACCL")
self.acceleration_time = EpicsSignalR(float, ".ACCL")

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The .ACCL field in EPICS is always acceleration time (the time to change the velocity from before to after). Always a stumbling block for experienced control engineers new to EPICS. I believe a change to acceleration_time here introduces some ambiguity which makes this component seem like a special case, somehow different from .ACCL.

Also, it is not typical for a user to want to change .ACCL field of every motor from ophyd. I suggest that for those motors which need this additional feature (or others), subclass locally and add the additional component:

class MyEpicsMotor(EpicsMotor):
    steps_per_revolution = Component(EpicsSignal, ".SREV", kind="omitted")

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So, please do not add support for the motor .ACCL field to every motor.

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I agree with the comment on SREV but I would argue that ACCL is quite fundamental, for instance the use case here is to work out how long it will take a motor to ramp up to velocity so we can work out where the "move to start" position should be for a flyer. Not sure if it should be an EpicsSignalR or an EpicsSignalRW though...

Also, it was there in the existing Ophyd EpicsMotor:
https://github.com/bluesky/ophyd/blob/5a0f1f3e8c2f453eb5a3262c610714bee67f84db/ophyd/epics_motor.py#L54

I agree with the comment about naming, acceleration is a better name.

self.units = EpicsSignalR(str, ".EGU")
self.precision = EpicsSignalR(int, ".PREC")
# Signals that collide with standard methods should have a trailing underscore
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