Now that I have a couple simple pneumatic props under my belt, I am quickly wanting to expand! (or course!) So I have seen several props with people that are clearly using a rotary pneumatic device to make a fast spin. Not having seen one of these for sale, I went to ebay and found some that looked like they may fit the bill but were upwards of $100 or more each (ouch). Does anyone have any sources or more information on where to find these and what I should look for?