Trouble adding an A axis

I have added an A axis to rotate work pieces under the spindle tool.
Things mostly work but I am experiencing fallowing errors with this
axis when I attempt to increase the rotational velocity.

I have checked the HAL and integrators manuals concerning HAL
variables maxaccel, maxvel and INI variables MAX_VELOCITY & MAX_ACCELERATION. I have tried using the pncconf wizard as a
way of learning how this works. But I still can not spot the problem.

How do the maxaccel, maxvel, MAX_VELOCITY & MAX_ACCELERATION variables relate to one another? or are there other variables I have
over looked? I am having trouble understanding this

I am using a Mesa 5i25 IO board to drive the step motor with no
feedback loop so I should be able spin this axis rather fast.

Some other observations :

If I relax FERROR to = 0.010 I can set the feed rate F30000 and G1 A1000
The axis will spin up to the max velocity 21600 deg/min or 360 deg/ sec
this is as it should be and works fine.

But if HOME_SEARCH_VEL is greater than 12.00 deg/sec I get a joint
fallow error when homing.

Or if I attempt to jog the A axis at a speed greater than about 600 deg/min
I get a joint fallow error.

On thing to remember if you change acceleration is that
the stepgen maxaccel parameter must be about 1.2 x the machines MAX_ACCELERATION value for each axis

Tried another approach I let Pncconf generate a complete new configuration
letting it compute all the values in the INI and Hal files.

This did not solve the problem when I attempt to home the A axis it
begins the cycle but generates an fallow error near the end of home
process.

I would verify that the stepgen maxvel and maxaccel values are correct in the ini/hal files

Here are the values created via the Pncconf wizard

setp hm2_5i25.0.stepgen.08.maxaccel 1350.0
setp hm2_5i25.0.stepgen.08.maxvel 450.0

MAX_VELOCITY = 360.0
MAX_ACCELERATION = 1080.0

1350.0 / 1080.0 = 1.25
450.0 / 360.0 = 1.25

They seem correct as per your comment about the 1.2 ratio

In that case its probably higher up
(the axis may be requested to do a motion its not capable of)

I do recall that DEFAULT_ACCELERATION needs to be set for
non-trivial kinematic machines

Would the DEFAULT_ACCELERATION be set in the TRAJ section of the INI file?

would it equal setp hm2_5i25.0.stepgen.08.maxaccel 1350.0 or
MAX_ACCELERATION = 1080.0 or some value in between?

A solution to this problem has become of great importance since
I am now experiencing fallow errors during G1 Annn moves thus
preventing useful work.

The top step rate is 72Khz, should be a piece of cake for the Mesa 5i25.
The drive is a quite happy with 1us pulse widths and probably can accept
a 200Khz step rate or more, never tried to find out.

But this problem is not a hardware issue. Since there is no feedback in
the system other than homing switches and the spindle encoder Linuxcnc
is unaware of what the X Y Z & A axis are actually doing.

By experiment I have stumbled onto a solution that appears to solve the
problem. If I change MIN_FERROR = 0.0005 to MIN_FERROR = 0.0010
and FERROR = 0.005 to FERROR = 0.1000 for the A axis the problem
disappears.

This may affect the positional accuracy of this axis but is small enough
that it has not caused a problem and way better than not working at all.