Hey Everyone, I'm currently looking at designing a device that would allow people to escape from working at heights quickly and safely in the event of an emergency (up to 33 m) I know there are some products on the market already but since I don't have a great deal of experience with them I'm not overly familiar with how they work but what I'm hoping to achieve is to design a device which can be used for a set range of weights (as if the device is specific to a certain weight range, it is easier to create the amount of desired friction) which would allow a working to step off a platform in an emergency and just lower down the rope unassisted, so the device is controlling the friction force. the downward force will be equal to m*a and since mass is constant Im going to want acceleration to be 0 after an initial acceleration to get the person to a safe desending velocity. Therefor, what I need is an equation that would give the friction on the rope according to the velocity of the rope passing through this. Is there anyway to do this or does velocity have no bearing on the friction between the rope and the device? If so, does any one know of a device I could research that would allow me to control the maximum speed at which the rope could pass through a device. At the moment I'm thinking more electric motor with chain but if I can keep it all mechanical (and thus probably cheaper) that would be preferred. On closing I would like to say this is ONLY a theoretical project, so Im not going to go jumping off building or anything so no one is any danger:) Thanks for your help!