This doesn't involve Galil products directly, but I will post the question.
I need approx. 0.1 deg dynamic pointing accuracies with a direct-drive system. There will be a position loop closed around a gyro rate loop which then will control the motor torque. The system will be taking out motion of the platform. How does one determine (rule-of-thumb?) if an exotic sinusoidal commutation scheme needs to be used (no torque ripple) or if a standard six-step with hall sensor feedback can be used (7% torque ripple). A multi-speed (1x and 16x) resolver is being used for feedback.
EricK on 02/24/2004 - 15:53
Jeff,
We have published an application note describing Sinusoidal Commutation of brushless motors and using Galil controllers. See Appnote 3414. http://www.galilmc.com/support/appnotes/optima/note3414.pdf
In general, sinusoidal commutation will benefit mostly when the application requires very slow speed control where slight ripple in current is more noticeable as the motor moves slowly between phases. At higher speeds it becomes less of an issue, since the ripple frequency exceeds the bandwidth of the system.
Sinusoidal commutation is also beneficial in systems with low friction and/or low inertial loads. As the friction and inertia decreases, the system bandwidth increases making the system more susceptible to ripple effects.
-EricK