Garage door opener hack

[Rig]

I modified the limit switch mechanism in an older Chamberlain 1/2 HP - I made it longer to open a taller door. It's still stopping about where it did with the original mechanism, so I'm guessing the RPM sensor is counting revs as a secondary safety feature.

Does anyone know how I can 'trick' or bypass the rev counting part of the RPM sensor function?

Removing the cap doesn't work. Covering the 'window' openings on the cap doesn't work.

UPDATE: This modification is for use of the motorhead in a DIY jackshaft system for opening doors taller than 8 feet.

 

[inphx]

i thought there were two resistor potentiometers that u turn to adjust the limits

Chamberlain/Liftmaster Travel Limit and Force Adjustment

The Chamberlain/Liftmaster group use different travel limit system and Force Limit Adjustment on their openers and it depends on the manufacture date and model

veterangaragedoor.com

 

[Rig]

Yes, the newer MyQ style do have unlimited adjustment with the up and down illuminated arrows. I'm working with an older model, mostly because they're more readily available and typically free.

The older units have two adjustment screws that move contacts forward or backward to adjust the up or down limit. Between those contracts is a lead screw with a little shuttle back and forth as the door is going up or down. When the shuttle tab hits the contact up/down contact, it stops the door.

I modified my limit switch to be longer, therefore presumably allowing the opener to open taller doors.

 

[Rig]

.

 

[kbs2244]

you should have "stops" inserted in the chain that trigger switches for the up and down gross movement
the screws are for fine tuning the movement after the chain switches stop the door

 

[Zeke]

Maybe you reached the end of the overall travel no matter where you move the trigger.

 

[Rig]

you should have "stops" inserted in the chain that trigger switches for the up and down gross movement
the screws are for fine tuning the movement after the chain switches stop the door

This is a Chamberlain (aka LiftMaster, Craftsman and previously Stanley). They don't have limit switches on the chains, just the screw adjustments - at least from about 1975-2008'

However, even in if they did, this application is for a DIY jackshaft mount system, so chain switches wouldn't work.

 

[Rig]

Maybe you reached the end of the overall travel no matter where you move the trigger.

In my scenario, the theoretical end of travel is dependent on the length of the limit switch screws pictured. As I mentioned in the original post, my suspicion is that the RPM sensor is the secondary limit so the opener can't "crash".

I can see I'm going to have to edit my original post.

 

[whateg01]

In my scenario, the theoretically end of travel is dependent on the length of the limit switch screws pictured. As I mentioned in the original post, my suspicion is that the RPM sensor is the secondary limit so the opener can't "crash".

I could be wrong but I wouldn't think in 1975 they were that fancy yet. How did they count revolutions? With nothing there but the motor, does it still stop at a specific point? Or does it spin indefinitely?

 

[kbeefy]

Welcome to the forum!

I have nothing further to add.

 

[Rig]

I could be wrong but I wouldn't think in 1975 they were that fancy yet. How did they count revolutions? With nothing there but the motor, does it still stop at a specific point? Or does it spin indefinitely?

The 1975 reference was regarding limit switches on the chains, which I actually believe never existed on Chamberlain/LiftMaster units.

Somewhere in the 80's on thru maybe 2008, they had the RPM sensor that I pictured in the original post. As I have said a few times, I suspect this is a Rev counter as well as a speed sensor, and my question is how to trick it.

 

[whateg01]

The 1975 reference was regarding limit switches on the chains, which I actually believe never existed on Chamberlain/LiftMaster units.

Somewhere in the 80's on thru maybe 2008, they had the RPM sensor that I pictured in the original post. As I have said a few times, I suspect this is a Rev counter as well as a speed sensor, and my question is how to trick it.

If you've removed it and the behavior didn't change, then I don't think that's the thing you need to override, is it?

 

[Rig]

If you've removed it and the behavior didn't change, then I don't think that's the thing you need to override, is it?

You might be right. There may be an RPM counter somewhere else in the system - possibly built right into the motor.

I was actually hoping to find an old-timer tech guru in this group that would know how that worked and be able to offer a bypass.

 

[Zeke]

You might be right. There may be an RPM counter somewhere else in the system - possibly built right into the motor.

I was actually hoping to find an old-timer tech guru in this group that would know how that worked and be able to offer a bypass.

Maybe but that seems unlikely. The motor is probably doing 1750 RPM and the reduction gear a lot less and easier to dial in. But I really don't know, just following along with an idea or 2 to explore. Hope you get it the way you want.

 

[whateg01]

Is it a DC motor? What wires go to the motor? Are there other things attached to the shaft? What of my earlier questions? Older garage door openers aren't that complex

 

[Rig]

Maybe but that seems unlikely. The motor is probably doing 1750 RPM and the reduction gear a lot less and easier to dial in. But I really don't know, just following along with an idea or 2 to explore. Hope you get it the way you want.

If I'm successful, I'll report back to this forum, including pictures of my modified limit switch setup.

 

[Rig]

Is it a DC motor? What wires go to the motor? Are there other things attached to the shaft? What of my earlier questions? Older garage door openers aren't that complex

I don't know if it's a DC motor, but it isn't as simplistic as you're making it sound. There are a number of safety features built into the systems, I'll almost all based on obstructions, whether "seen" or "felt" by the opener.

Am I the only one in this group that's ever pulled apart a garage door opener motor?

 

[mrb1]

Am I the only one in this group that's ever pulled apart a garage door opener motor?

Check out ...garagedoormotoropeners.com..

 

[whateg01]

Most of those "obstruction" circuits are based on the load, or current draw, of the motor. Aside from IR beams, there aren't usually a lot of hardware associated with it. But that results in the smarts telling the motor to reverse to stop smashing the kid. That's different from the up/down limits.

 

[Rig]

Most of those "obstruction" circuits are based on the load, or current draw, of the motor. Aside from IR beams, there aren't usually a lot of hardware associated with it. But that results in the smarts telling the motor to reverse to stop smashing the kid. That's different from the up/down limits.

Here's what I can tell you -

- The limit switch contacts are farther apart than standard by approximately 3/4"

- The opener still stops approx where the contact max is on the standard limit switch assembly

Conclusion - the system "knows" its at the top height of the standard limit switch design, by some method other than the mechanical limit switches. Most logical is that it's counting Revs.

Side note: these standard openers are capable of opening a 12' door. I know this because I've built many custom traditional overheard openers with extended rails for outbuilding doors.

 

[Rig]

Check out ...garagedoormotoropeners.com..

Funny

 

[Rig]

...That's different from the up/down limits.

The "secondary safety' considered with a rev counter has more to do with equipment damage, like the shuttle "crashing" into the top hard stop or something.

 

[inphx]

Are you sure the contactors at a and b are not being hit? It would maybe then be the load limit sensor with the new travel?

 

[Rig]

Are you sure the contactors at a and b are not being hit? It would maybe then be the load limit sensor with the new travel?

Yes, I have the cover off the motor while testing the modified assembly. I'll see if I can attach a video so everyone truly understands the issue.

 

[Rig]

Here are a couple pictures of my modified limit switch assembly. The first shows the extended length (blue lines). The second shows where the shuttle stops every time - right where it *would* limit out with the standard limit switch assembly (red line).

 

[LXCam]

If the truck will disconnect from the drive. It’s an easy test to see if it is accounting for travel in some other fashion cause the drive will just keep rotating until you intervene.

 

[Rig]

So far, anything disconnected from anything causes it to error out.

Because the middle (driven) shuttle stops in about the same place on my extended assembly as it does on the stock assembly, I'd say that's a pretty clear indicator that there's a secondary (equipment) safety in the firmware based on the number of revolutions.

 

[whateg01]

You seem really stuck on it being a number of revolutions thing but you've yet to show anything that points to that being the case other than the stop not corresponding to the limit switches.

 

[Dagny]

He sent pictures of what looks like a counter remove every other wing on the counter.

 

[whateg01]

He sent pictures of what looks like a counter remove every other wing on the counter.

He says it's behaving the same without that attached

 

[inphx]

If i understood corrctly he eliminated that optical(?) sensor like @whateg01 said.

 

[Rig]

You seem really stuck on it being a number of revolutions thing but you've yet to show anything that points to that being the case other than the stop not corresponding to the limit switches.

Can you think of any other feature or method that would stop the main drive motor at almost the exact place as the limit switch maximum?

All I can add to support the rev counting theory is that it stops without an error, as though it hit the limit switch. No clicks, no lights flashing.

 

[Rig]

If i understood corrctly he eliminated that optical(?) sensor like @whateg01 said.

The "windows" are the openings between the tabs/flags on the black cup. The sensor (left) reads what passes thru it. I didn't alter the sensor

I removed some tabs to presumably make fewer windows, but it still operated as normal.

I removed the cap altogether which caused it to stop after a few revs and return, but no blinking light error.

I left the cap on but removed all the tabs - same result.

I covered all the windows with black tape - same result.

One thing I haven't tried is to put this extended limit switch assembly on a different motor.

 

[whateg01]

I removed the cap altogether which caused it to stop after a few revs and return, but no blinking light error.

Sorry. I misunderstood your earlier post about this. I thought you said removing it made no difference.

 

[Rig]

Sorry. I misunderstood your earlier post about this. I thought you said removing it made no difference.

No harm, no foul, brother. It seems to be a more sophisticated system than one would expect from the older tech!

I will probably give it up soon and bite the bullet with the MyQ (unlimited adjustment) for my purposes.

 

[CoogarXR]

Maybe it has a maximum run time, and it's just timing out?

 

[Rig]

Maybe it has a maximum run time, and it's just timing out?

After exhaustive searching, I finally confirmed this run time to be correct. By law, starting in about 2000, all garage door openers are required to have a "30-second clock" to assure the door closed completely in that time. You can override it by holding the button down, but finding a way to do that "automatically" may be impossible.