Linear actuators with built-in limit switches: feasible to modify?

Thread Starter

jw11432

Joined Jul 28, 2019
8
I don't know how a limit switch works, per se, but I understand that in this context, once the motor reaches a certain point, it stops the motor from spinning any further and over-tightening/loosening the arm. I have built a circuit that handles my automation, but these linear actuators (Zoom Industrial Z1000WH) have built in limit switches that I'd like to modify to perfect my driveway gate setup. I installed it with the gate closed to make sure it closes the way I want, but when it opens, it simply opens way too far and it occurred to me that if I can modify the limit switch (I assume there are two switches, one for extending and one for retracting movements) that I can get it to work exactly how I want it to. Is this a feasible pursuit?
 

AlbertHall

Joined Jun 4, 2014
8,514
I suspect it will be more feasible to either alter the leverage to reduce the movement of the gate at the limits of the actuator or to fit your own external limit switch for the open position.
 

Thread Starter

jw11432

Joined Jul 28, 2019
8
I'm using a fixed arm, anchored on a stationary part of adjacent fence, connected to gate to push and pull gate. I'm capable, but very rusty, with my geometry, so what's the formula(s) needed to figure where to attach on gate and how long an arm I need for it?

Edit: visual example of style of opener I'm using https://www.google.com/search?q=driveway+gate&client=ms-android-verizon&prmd=sivn&sxsrf=ACYBGNTgFIpq7uHHz63knRawMXeklSbsHg:1574105521553&source=lnms&tbm=isch&sa=X&ved=2ahUKEwi7yM2DwPTlAhUBSq0KHfkRAJcQ_AUoAnoECBUQAg&biw=412&bih=761&dpr=3.5#imgrc=l6r3yzBbV-sG0M
 

LesJones

Joined Jan 8, 2017
2,349
You will have to provide some actual facts for someone to work out suitable fixing points.
1 - The distance between the actuator fixing points in the closed position.
2 - The distance between the actuator fixing points in the fully extended position position.
3 - The angle through which you require the gate to swing between the fully open position and the fully closed position.

Some pictures of your actual installation would also be helpful.

Les.
 
Take a look at the PDF I did on this post: https://forum.allaboutcircuits.com/threads/need-some-direction-on-relays-and-limit-switches-for-greenhouse-roof-window-control.134958/post-1131056

You might want to read the entire thread as well. Usually a lot of info pop up when looking for "chicken coop door".

What I might suggest is to add a current sensor. https://www.pololu.com/category/118/current-sensors

And add some sort of logic that:
if its trying to open and senses an object, it returns to closed.
If it's trying to close and senses an object, it returns to open.
If the motor runs too long - do something as well.

Try using shear pins if possible.

You can also look for "car window reference designs". Some of the things, they do is auto-calibrate the first time it;s used. they know, RPM, position, current and voltage and can stop anywhere if overloaded.

I believe the internal sensors will stop the motor, but will not stop overrun. The standard SPDT automotive relay circuit used for door locks and motors will. The open/close relays if both activated at the same time will result in no movement. The motors are dynamically braked (winding shorted) when it's at a limit thus when stopping the DC motor is acting as a generator with the output shorted, so it stops very quickly.

The automotive relays have a fairly substantial coil current, so the limit switches have to handle that.

If you use open/closed contact closures, no current is used by the motor circuit at a limit. To reduce the overall power consumption of the "system" power can be taken away once the open or closed limit is reached.
 
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