POWER ASSIST FOR THE MAIN BAY DOORS (PART 2)…
Here's the completed door chain hoist ready to go back up. The assist motor has the run capacitor just hanging from its cord temporarily for this first test. Just to give you some sense of scale, the motor diameter is about 4".
My front loft hoist (
See Reply #904) got used for the first time lifting the door hoist. It's a little hard to see here, but an olive green strap is looped through the chain wheel and it is hanging on the hoist hook. It’s headed up to the spot indicated by the arrow.
Here it is mounted up in place. I added the wooden strut, not to support it vertically, but to keep it from swinging side to side. It has a slot in it for the white bracket to engage in.
So how did it work?
It worked rather well, but start-up was a bit more abrupt then I was expecting. When I was calculating what RPM motor to use, I estimated how fast I normally pull the chain. This, in turn, determined the RPM needed at the jackshaft. What I calculated almost matched my 95rpm motor perfectly.
What I didn't plan on was the fact that the gearmotor was going to try and hit that speed almost instantly when the voltage was applied. I guess my arms are a natural "soft start" for the door when pulling on the chain. I think it's best to build some cushion in to protect the drive parts and door, so I'm starting to research the alternatives. Choices range from using a slower motor (I have a 72rpm version to try), mechanical cushions on the power transmission parts, or electrical circuits to ease into full rpm.
The other good thing I found out in this test was that the original chain can still be used to open the door. You barely can tell a difference with the extra drag of back-driving the gearmotor. That is great because I want a backup method for operating the door in case the power is out or some drive component breaks.
Here's a quick video to show the current speed of the door. Sorry about the light levels - I wasn't expecting things to go completely dark like that when the sunshine started coming in.
If keeping the original pull chain available as backup, I want some type of wheel at the lower end to keep the chain from flinging all over the place when the door is doing its thing. I found these at the surplus store and I think I will be able to use them as the lower chain block. I would like to shorten the chains up and locate these wheels out of the way above my head. In an emergency, I could climb up the library ladder and open the doors.
Another detail that still needs to be addressed is a way to lock the door at any given height (for safety reasons). So there are many more details to work out yet, but this has proved to be quite feasible.