Path to follow a belt / chain

I need my sketch is comprised of a belt follow a path .. the problem is that the belt is croquiz block and other times is disengaged from the pulley, as I can do to make the croquiz follow the desired path

.you Could help please follow the step.

Necesito que mi croquis que esta conformado por una correa siga una trayectoria

el problema es que el croquis de la correa se bloque y otra veces se desacopla de la polea, como puedo hacer para que el croquiz siga la trayectoria deseada

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What I need is my sketch to move in conjunction with other componetes that relationship have to apply, if you could make a small example to follow a path a belt / chain

Es un modelo de una silla de ruedas sube escalones

It is a model of a wheelchair up stairs

Me podrían ayudar por favor con los paso.