Wednesday, September 27, 2017

Worm Gear Installed

So I installed the worm gear and a temporary pulley to try it out. Turns smoothly and easily. I may have mentioned it before but a worm gear is self braking in both directions, the door can't move unless the worm gear is being operated. Since it runs smoothly I decided rather than build two systems I would go ahead with the motor drive now, the one hiccup will be if the door sticks or hangs up.

So I ended up spending half the day looking for the right switches through half a dozen boxes of salvaged electrical equipment I have saved over the years. Eventually I found the momentary normally off switch (I believe this is the correct name, I could be wrong). In industry we call it a "deadman" switch, It is spring loaded and operates when you push it in and releases when you let it go. I am an operating power engineer and we used them when blowing sediment out of our boiler water columns, if you released the switch before the water level returned to normal in the water column, the boiler tripped out and left you to deal with all the problems that comes with that, depending on the type of plant you are operating, the most critical being a steam turbine driven generating plant. Thus the name "deadman" switch.

The second switch is a 3 position switch to reverse the motor, forward, off and reverse. this switch is not powered unless the "deadman" switch is held in. So to operate the door you first select forward or reverse (raise or lower) and then operate the deadman switch. when you release the switch the door stops and locks in position because of the worm gear.

I have gone this way to avoid limit switches which would require additional wiring, and they generally require frequent adjustment. The deadman switch requires your attention and nothing is live or operates unless you physically hold it in.


Installed a temporary pulley and belt to operate manually from floor level.


On the left a momentary normally off "deadman" switch and on the right a 3 position switch, both are Allen Bradley switches.


This is the revised wiring diagram for the above switches, if you copied the previous diagram its wrong.



The motor will get a 2" pulley and the worm drive will get a 6" pulley. The worm drive has a ratio of 60:1 and the motor runs at 1725 rpm. If you do the math, for the door to go from closed to fully open will take 10 sec.

Got to catch up on chores I have been neglecting today. I'll try to make up and upload the PM highlights this evening.