this is a GoPro Pulley for GoPro i designed it after SonPop idea you will find his idea right here https://www.myminifactory.com/ideas/gopro-cable-way-1000327
it's the perfect way to do travelling or following it is often used in VTT downhill for example. To realise this object you will need, 3 axis of 3 mm diamater and 6 waher of 1 mm thick and 3 mm diamater.
I suggest you to glue the GoPro Mount with the GoPro Pulley for more security you can also glue the stopper. It works with different size of ropes but the perfect size is a rope of 10 mm diamater. If the rope is bigger than that in can't assure you that is going to work. You just have to incline the rope more or less to control the speed.
Hope you will like it