After much looking and thinking, I found the reason why the 4th axis
table was moving in an unsteady, jerky fashion. It was not
mechanical.

I took off the servo motor and when directed to rotate steadily, it
would, instead, accelerate and slow down four times over a complete
rotation, which was kind of severe and led to quite a bit of vibration.

It was narrowed down as a resolver issue, since the slow downs were at
each 90 degree position and also because the table moved exactly 360-
degrees when instructed to do so.

Long story short, it turns out that the voltage to the resolver
primary was too high, which at times caused bad reading of the sine
and cosine outputs of the resolver. I lowered it and the motor turns
smoothly. I discovered this because I INCREASED the voltage at first
and that made a bad problem MUCH worse -- but it told me where to go,
that I had to go the opposite way.

I reassembled the rotary table and put "Pennzoil marine grease" into
the place where rotation of the servo motor is turned 90 degrees. The
"brown grease" that I took out, as I realized in the morning, was
Shell Alvania. I should have used the same thing but I did not think
about it. I think that for the amount of use that this RT will see,
Pennzoil marine grease will be just fine.

This is a place where the servo motor's rotation is turned 90 degrees,
and also reduced by some good factor, with a pair of 45 degree gears.

I packed about 80% of the volume with grease and left 20% empty.

i

Ignoramus17662 wrote:
After much looking and thinking, I found the reason why the 4th axis
table was moving in an unsteady, jerky fashion. It was not
mechanical.

I took off the servo motor and when directed to rotate steadily, it
would, instead, accelerate and slow down four times over a complete
rotation, which was kind of severe and led to quite a bit of vibration.

It was narrowed down as a resolver issue, since the slow downs were at
each 90 degree position and also because the table moved exactly 360-
degrees when instructed to do so.

Long story short, it turns out that the voltage to the resolver
primary was too high, which at times caused bad reading of the sine
and cosine outputs of the resolver. I lowered it and the motor turns
smoothly. I discovered this because I INCREASED the voltage at first
and that made a bad problem MUCH worse -- but it told me where to go,
that I had to go the opposite way.

I reassembled the rotary table and put "Pennzoil marine grease" into
the place where rotation of the servo motor is turned 90 degrees. The
"brown grease" that I took out, as I realized in the morning, was
Shell Alvania. I should have used the same thing but I did not think
about it. I think that for the amount of use that this RT will see,
Pennzoil marine grease will be just fine.

This is a place where the servo motor's rotation is turned 90 degrees,
and also reduced by some good factor, with a pair of 45 degree gears.

I packed about 80% of the volume with grease and left 20% empty.

i


If you had a scope on the output of the resolver you would see the wave
being clipped because of saturation of the core of the resolver the
other problem that can occur is clipping occurring in the amplifier
itself causing the same problem. I went through this problem many years
ago when i was supplied with a bad set of installation prints on a
Bendix flight director A/P system that I was doing an STC on. They had
the resolver inputs and outputs reversed on the print and it had an 6:1
ratio.

John

On 2011-01-30, John wrote:
If you had a scope on the output of the resolver you would see the wave
being clipped because of saturation of the core of the resolver the
other problem that can occur is clipping occurring in the amplifier
itself causing the same problem. I went through this problem many years
ago when i was supplied with a bad set of installation prints on a
Bendix flight director A/P system that I was doing an STC on. They had
the resolver inputs and outputs reversed on the print and it had an 6:1
ratio.

I have not used my oscilloscope, but I think that the wave was not
really clipped by the resolver -- it was clipped when used as an input
to the resolver to encoder converter board, by the board itself.

i