diff --git a/content/zettels/torque_motor.md b/content/zettels/torque_motor.md
index 96d137d..9d84d30 100644
--- a/content/zettels/torque_motor.md
+++ b/content/zettels/torque_motor.md
@@ -1,5 +1,5 @@
 +++
-title = "Torque Motor"
+title = "Torque Motor (3-phase)"
 author = ["Dehaeze Thomas"]
 draft = false
 +++
@@ -10,6 +10,11 @@ Tags
 Nice tutorial: <https://www.youtube.com/watch?v=3XcvjC2anM8&list=PLmklAQtFT_ZKcaI21UHgi0cm2Y3Yxu90p&index=3>
 
 
+## Error period for 3-phase motors {#error-period-for-3-phase-motors}
+
+Due to cogging, the fundamental period of the error is: number of pair poles \* 3 (because 3-phases).
+
+
 ## Manufacturers {#manufacturers}
 
 | Manufacturers                                                                                                      | Country     |