Using motorcortex api to stream position commands.

MankaranSingh

Hi,

So I am trying to use the c++/python mortorcortex APIs to give motion to the motor. I am able to engage and stream velocity and position commands on topic root/Control/jointManualVelocity and root/Control/jointManualPositions. There are many more attributes regarding position and velocities, are these documented somewhere ?

My goal is to control the acceleration, velocity and position. Right now the motion is quick with very high starting and stopping accelerations and decelerations and drive goes into fault if these the positions and velocity commands are too high. Are there some attributes that we can set to make the motion a bit smoother (less initial and stopping jerk) or do we need to write a custom trajectory generator for this ?

Thanks.

Philippe

Obviously you are using the Generic-App.
What you are doing is correct. Currently you can only command either position or velocity (not at the same time).
Velocity setpoints are integrated to a position command. This happens in root/Control/jointJogIntegrators/. These are integrators with limiters on the inputs and outputs. So make sure your limits are setup correctly for your application.

Once the signal is a position command this is fed into PVA-Limiters. These smooth and limit the signal. You can find the settings of the PVA limiter in the Desk tool.

Here you can set for instance the maximum velocity and acceleration.

root/Control/actuatorLimiters/pvaLimiter01/maxVelocity

root/Control/actuatorLimiters/pvaLimiter01/maxAcceleration

MankaranSingh

Thanks for pointing out the limits. The velocity one works well, but on setting the maxAcceleration to 10, the motor starts to oscillate slowly after reaching the setpoint. I was using the generic app gui slider to control it.

philippeH

The maxAcceleration should always be factor 10 higher as your maxVelocity (rule of thumb) . So that with a certain velocity the motor is able to decelerate in time, to prevent overshoot. The oscillation you are experiencing is probably caused by not applying this factor 10.

MankaranSingh

Thanks, that rule of thumb seems to fix the oscillations.

The robotic manipulator we are working on has a gear ratio of 100:1. I set the gearbox/nLoadSide to 100 and now the outer shaft's degrees matches with what's displayed on the gui. I am using 10 deg/s and 100 deg/s as maxVelocity and maxAccel in pva limiter. Now on pressing the manual jog up/down arrows, it commands +- 40 degrees and the motion is discontinuous, there are stops in-between (I could hear the ticking sound).

How do I make the step size to be low (around 2 degrees) ? and solve this discontinuity/ticking sound ?
Thanks!

philippeH

If you have a step of +-40deg you probably filled in the gearbox incorrect.
Gearbox ratio 100:1 so it is an reduction, n-Motorside = 1 and n-loadside = 100
I checked the documentation site, how this is currently described is a bit unclear. This part of documentation will be improved.

n stands for number of teeth of your gear.
n-Motorside you define number of teeth moterside
n-loadside you define number of teeth loadside