TechComm Labs

The door got halfway up and then there was an unpleasant sound. A bit of a push got it up far enough to get the car out. 

A garage door opener is just an example of the robotics exercises except that is has a long history and runs a motor a bit more potent than is typical of the home robotics devices. There is a logic board, sensors, and a gear driven activator. There is also a lot of help on the I’net for proper maintenance, diagnosis of problems, and repair.

In this case, the problem was a worn out main drive gear. That gear engages a worm gear on the motor shaft and appears to be the most common source of failures of the type I encountered. A new gear is available on Amazon for about $6 (Drive Gear for Sears Crafsman Liftmaster Chamberlain Garage Door Openers 1984-Current affiliate link). You can get replacement kits for the entire drive train if you want to do a complete overhaul for about an order of magnitude higher cost. 

Since the door had been neglected for a couple of decades, I thought it was probably a good idea to do some preventive maintenance. There are number of suggestions about what to use to lubricate the door hinge parts. I ended up using Reese ball lube as it was a heavy motor oil I had handy in a convenient applicator. A spray can might have been better for getting into the hinges and whatnot but it doesn’t appear that the actual lubricant is all that critical.

For the gears, I had a tube of bona-fide Garage Door Lube which was probably a lithium based white grease. Brake-Clean (CRC Brakleen Brake Parts Cleaner – Non-Flammable) was used to clean old grease from the trolley track. The chain (this is a chain drive model) was left alone as that seems to be the primary recommendation from the manufacturer. A film of grease was applied to the trolley track and the drive gears got a liberal dose.

The spring on the door was holding the door open at the halfway point so its tension was OK. It was wiped down with oil and some oil was applied to the bearings on each end of the spring shaft.

This device was installed just before the mandate for an electric eye at the base of the door opening. Safety features it did have included motor sensing to reverse travel when an object was encountered. That means there was some need for detecting motor rotation. Adjustments included both a force up and down and limit sensors. The force adjustments were to find a balance between enough push to get the door moving but not so much as to squash any obstacle encountered. That implies some form of motor torque control. The limit sensors were switches on a shaft connected to the gear train to stop the door at the desired open and closed positions.

The biggest hassle in this whole R&M task was getting the roller pin out of the drive shaft. It probably would have been easier with the right tools. There are some good YouTube videos are out there on how to get recalcitrant roll pins moving and some rather innovation home built presses for the task. I just used some 2×4 lumber on a solid table with a carefully selected bolt as a punch. Even then I had to upgrade from a ball peen to a small sledge and apply a bit of patience and persistence to clear the gear. Getting the pin in to hold the new gear was almost as much of a hassle, too.

It is always nice when everything gets back together and the thing actually works!

The chain tension was adjusted so it would hang just above the trolley track. The limit adjustments were trimmed to stop travel at the right points. I probably ought to check the blockage reversal function, too.

The control board on this garage door opener is now ancient technology. The sensors and motor control could be implemented these days with a micro-controller and a lot fewer parts. That probably contributes to modern openers having enhanced security and I’net access for control and other features. 

and on the topic of security – there are a number of suggestions about how to inhibit someone from reaching in through the top of the door to pull the trolley release catch with a coat hanger in order to gain access to your garage. It looks like a simple twist tie to hold the latch closed is the simplest solution to this security hole. A pull on the release rope will break the tie but a coat hanger stuck through the crack at the top of the door won’t be able to do that.

It looks like old garage door openers being replaced with new ones might be a good source for robot parts. If you’ve got an older opener, it might be a target for a bit of hacking to extend its features and communications capabilities. There’s opportunity over your head!