What I am searching for is something that can go inside a metal pipe and hold in place without having to resort to using a pressurized bladder. I need it to be adjutable for piples of various internal diameters perhaps one to three inches, but it does not have to seal the pipe. I envision some type of mechanism that has distal protrusions that move towards, then press against the inside of the pipe at several points. Once tightened against the inner walls, the mechanism will hold in place. I find lots of pneumatic bladders, but for my purposes this is impractical because there is no way to attach an air source when needed. I plan to use a very small electric motor to activate this piece. Thank you.