I have been trying to model a conveyor belt with a quickrelease similar to the conveyor shown in this video:

I need to animate the motion so I can show that rotating the tip of the conveyor releases the tension of the belt and enables easy removal. I have been trying to use the Belt/Chain feature which works perfectly when modelling the tense belt. But when I start rotating the tip of the conveyor and the belt is rebuilt it is still tight - which means the belt changes length instead of starting to slack. Is there any way to model this so I will be able to show it via animation in Motion Study? 

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