I am intending to use a Lego power functions motor as part of custom lego build and ideally need a way for it to auto stop.

The motor will be used to power a lift and when it reaches the top or bottom I need it to stop rather than mindlessly grinding itself to death when it reaches the end. This different to if you use a motor to rotate something which could rotate indefinitely. For the lift I was planning using either a worm gear with Lego 3743 gear rack bricks, a standard gear and Lego rack and pinion.

I did think about using a clutch gear wheel but need something more effective than that as the clutch gear wheel would be not be really suited to fit in the build.

I bet this would be answered better in the technic forum! :)

I am intending to use a Lego power functions motor as part of custom lego build and ideally need a way for it to auto stop.

The motor will be used to power a lift and when it reaches the top or bottom I need it to stop rather than mindlessly grinding itself to death when it reaches the end. This is different to if you use a motor to rotate something which could rotate indefinitely. For the lift I was planning using either a worm gear with Lego 3743 gear rack bricks or a standard gear and Lego rack and pinion.

I did think about using a clutch gear wheel but need something more effective than that as the clutch gear wheel would be not be really suited to fit in the build.

Is the lift intended to be manually operated or repeatedly going up and down? For manual operation, I guess the simplest way is to have two levers to actuate the battery box switch. One manually operated lever that starts the lift and second one that switches the battery box off, actuated by the lift when it reaches top/bottom.  

Another option is to drive a rotary gear catch from the crown wheel of a diff and run the drive from the motor through the output shafts. The resistance level of the rotary catch can be adjusted using friction pins etc to allow the catch to turn when the output shaft from the diff encounters sufficient resistance. This means your lift will disengage drive if it jams at any point in its travel.

15 minutes ago, Davidz90 said:

Is the lift intended to be manually operated or repeatedly going up and down? For manual operation, I guess the simplest way is to have two levers to actuate the battery box switch. One manually operated lever that starts the lift and second one that switches the battery box off, actuated by the lift when it reaches top/bottom.  

It would be manually operated. How do I link the leaver to the battery box to turn it off? What parts would be involved? This sounds like what I am looking for if it triggers automatically when the lift reaches top or bottom.

 

You could link directly to the battery box but I think it might be easier (if you have one) to use the separate PF switch.

Have a lever at the top and bottom of the shaft that is actuated by the lift. Connect to two levers using a long rod (creating a 4 bar linkage). Somewhere along this vertical connecting rod have two pegs spaced close together. Between these two pegs will sit the switch (separate switch or battery box switch). The pegs are not directly connected to the switch, but they will press on the switch to turn it off as the vertical linkage moves, while being spaced just far enough apart to allow you to move the switch to the other way.

 

In this video, I have something like that at 1:35:

The lift is using chain instead of gear rack but otherwise that would be more or less what you describe. Note that here the lift turns on when the weight reaches the bottom, but that's just matter of simple geometry tweak. Also, I needed quite a bit of leverage advantage to actuate the battery box switch because it is quite stiff.

12 hours ago, jelockwood said:

I am intending to use a Lego power functions motor as part of custom lego build and ideally need a way for it to auto stop.

The motor will be used to power a lift and when it reaches the top or bottom I need it to stop rather than mindlessly grinding itself to death when it reaches the end. This different to if you use a motor to rotate something which could rotate indefinitely. For the lift I was planning using either a worm gear with Lego 3743 gear rack bricks, a standard gear and Lego rack and pinion.

I did think about using a clutch gear wheel but need something more effective than that as the clutch gear wheel would be not be really suited to fit in the build.

With PF you could build a mechanical stop that is engaged when the lift reaches the end, which then switches the power off from battery box.

With PU you could program the motor to stop at the correct position by setting the amount of rotations it needs to revolve to reach the end.

Maybe you can install a switch (8869) at the top of the elevator. The problem with that is that you will need to switch there motor on each time after it reaches the top... it's just an idea!

 

A clutch indeed can be an option as well, which is also the simplest, I think. But the issue of how to limit the time the motor is on is still unsolved, no?

 

 

 

40 minutes ago, allanp said:

You could link directly to the battery box but I think it might be easier (if you have one) to use the separate PF switch.

Have a lever at the top and bottom of the shaft that is actuated by the lift. Connect to two levers using a long rod (creating a 4 bar linkage). Somewhere along this vertical connecting rod have two pegs spaced close together. Between these two pegs will sit the switch (separate switch or battery box switch). The pegs are not directly connected to the switch, but they will press on the switch to turn it off as the vertical linkage moves, while being spaced just far enough apart to allow you to move the switch to the other way.

 

Thanks, I also found a video demonstrating the PF polarity switch. Its name had led me to believe it only did polarity reversal and not also on/off but the video clearly shows the mid-position is off and top/bottom are the reversed positions.

Take a look at this lift which is self reversing using a worm driven turntable & link arms.

If you can drive the lift from your motor continuosly this might be suitable.

Video

https://youtu.be/hlLElrL-vBE 

.

 

 

 

 

Brickative has something like this in their Library (video) for ground floor and upper level. It is simply using the battery box switch as a stop and reverser through a clever lever mechanism. It works very well and always goes in the right direction but needs manual activation after every stop which is logical as people need time to get in and out.

By the way, it seems there are two topics on this with the same title and same initiator.

 

Edited May 1, 20222 yr by Berthil
typos, video added, added double topic

Double topic with this one:
 

 

18 minutes ago, Berthil said:

Double topic with this one:

I accidently posted originally in the Star Wars theme forum and as advised posted (then) in the Technics forum. It looks like someone kindly then moved the original post also to the Technics forum so we ended up with two in their. (I could not move it myself.)

does it matter if the motor is running continuously? You could just make the gear rack slightly short at the top, thereby making sure the lift doesn't climb higher. Gravity will easily get it back on track in reverse. You could add a spring or a tensioned lever at the bottom for the inverse effect.

Edited May 1, 20222 yr by Carsten Svendsen

10 minutes ago, Carsten Svendsen said:

does it matter if the motor is running continuously? You could just make the gear rack slightly short at the top, thereby making sure the lift doesn't climb higher. Gravity will easily get it back on track in reverse. You could add a spring or a tensioned lever at the bottom for the inverse effect.

It would likely make a noticeable noise and of course continue to draw power. The answer below seems what I was looking for.

I will therefore buy a PF polarity switch via Bricklink and explore designs for pulling the switch back to the centre off position at top/bottom. I will also try and make it harder for a 'guest' to accidently try to use up when already at the top and down when already at the bottom.

2 hours ago, jelockwood said:

I will therefore buy a PF polarity switch via Bricklink and explore designs for pulling the switch back to the centre off position at top/bottom. I will also try and make it harder for a 'guest' to accidently try to use up when already at the top and down when already at the bottom.

I use the same switch for GBC trains (see video) when they change direction, the switch requires quite some force to switch. The older types not but most sellers do not know the difference so you don't know what you will get when you buy. The switch can be made to switch with less force by cutting away a view notches for which disassembly is necessary.

 

I would definitely do this with PU instead of PF, that's exactly what it was designed for due to the position sensors in the motors. For example the controls in the Liebherr do this exactly, and you don't even need to turn it back on when you want to reverse. I haven't ever tried programming that in the PU app though, wonder if it's possible..

Or are you after the fun and complexities of solving it all mechanically?

48 minutes ago, gyenesvi said:

I would definitely do this with PU instead of PF, that's exactly what it was designed for due to the position sensors in the motors. For example the controls in the Liebherr do this exactly, and you don't even need to turn it back on when you want to reverse. I haven't ever tried programming that in the PU app though, wonder if it's possible..

Or are you after the fun and complexities of solving it all mechanically?

Unless there's some complication I missed, it's really easy to do with PU. And yeah, definitely much easier than with PF and mechanical linkages to turn the switches.

6 hours ago, gyenesvi said:

 I haven't ever tried programming that in the PU app though, wonder if it's possible..

it is possible

it is set to run the motor 10 rotations when button "0" is pressed and when button "1" is pressed it will set the motor back to the 0 position

Edited May 1, 20222 yr by Jayden

For a pure PF solution, connect the motor to one side of a differential, and the PF switch to the other.  Drive your mechanism from the differential housing.  When your mechanism reaches its limit, the motor will drive the switch, turning itself off.

https://bricksafe.com/files/Hrafn/technic-misc/trim.5D0469E9-E870-4EB2-8010-7C0F3476E099.MOV

Note that this isn’t a 100% solution since it only drives your mechanism in one direction.  

Edited May 3, 20222 yr by Hrafn
Added video

On 5/2/2022 at 12:14 AM, Jayden said:

it is possible

That's a solution for a very simple scenario, but it all depends on how sophisticated it needs to be. With this program you could only start it from one end, and it would go all the way to the other end. You could not for example move it by a manual controller, like the Liebherr, and avoid going over the ends. Also, if you want to stop it in the middle and restart moving, this would need to get more complex. For these scenarios, you'd need some kind of a variable to store the actual position and cap that with the end positions, and I am not sure if/how that's possible.

Also I suspect that this system does not need actual remote control, it would be just a button/switch on the model itself I guess. So even if one would use the simple 2-switch PU hub from the Osprey, that's not possible to program, as there is no app involved in there, right? So it essentially functions like a PF system would..

12 minutes ago, gyenesvi said:

You could not for example move it by a manual controller, like the Liebherr, and avoid going over the ends. Also, if you want to stop it in the middle and restart moving, this would need to get more complex.

Something like this could work for that scenario:

15 minutes ago, gyenesvi said:

Also I suspect that this system does not need actual remote control, it would be just a button/switch on the model itself I guess.

This is probably true.

24 minutes ago, Jayden said:

Something like this could work for that scenario:

If I understand correctly, this would move the elevator to any position dictated by the slider, and the range (end position) could be set with the multiplier number (the other end being 0). This could actually be an interesting solution. One remaining question though is calibration, i.e. what is the zero position. I believe that will be the position the motor is in when the app starts, right? So if the elevator stopped in the middle, and the app is restarted, the middle becomes the zero position after restart, which is not ideal.. Is that any solution you know of for that problem?