Stepper Motor and Driver

@zander

Posted by: @zander

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As well as counting steps and decelerating at the end of travel, still use a limit switch for backup. Consider coming down slower than going up. I don't know the full scenario so some suggestions might seem kooky, but what about a PIR to sense a hen or even worse a chick in the way of the door?

Also consider if a second limit switch on each end is advisable in case of a failure of the stepper to slow or a complete failure of the first limit.

Ron,

Never worry about stating the "obvious".  Many people on this forum have decades of experience and if nothing else your suggestions may validate requirements I may be considering. 

After @davee comment on looking at the 3D printer I started to list some system requirements.  The door blocked (PIR) sensor was #1 to make sure we don't hit a chicken (or I face the wrath of my wife) - this is an absolute requirement.  Varying the speed between up & down makes sense.  I like the idea of the limit switch, but this is a very dirty environment and I am concerned that the switch would become fouled (or fowled).  Will need to look at other sensors that could be placed at the top of the door (maybe a laser sensor and a hole in the door that align when the door in down.)  Will also need a light sensor for automated opening and closing.

I started looking for 3D files for a chicken door and frame but have found nothing so far.  I started looking at the 'MangoJelly Solutions for FreeCAD' youtube page.  He has many design tutorials that I could follow and design my own.  

Thanks again.  I always appreciate your comments.

Mike

@huckohio I worked in the steel industry when I was very young. I can't imagine a more dirty environment. Just look for sealed units, although they will cost more. We had lot's of those on the various mills and they seldom failed.

As far as 3D files, try to include in your searches the west coast (they are big on raising chickens) also look for groups that talk 'chicken raising' on social media.

Hi Mike @huckohio,

  Great to hear that you are trying to design solutions for the problems.

  A brief point, that comes into 'Pointing out the obvious' category ... but I since I often find the 'obvious' points, the hardest to spot, I hope you don't mind if I raise it.

You mention the possible problem of a sensor being obscured by the contamination.

Obviously, the best answer is to make a design where it doesn't happen, but sadly such designs can sometimes be harder to find than the chicken's teeth. So as second best, try to ensure the system 'fails safe'. e.g. if the sensor has been obscured, then maybe assume the chicken is in the path of the door, if you fear it will become a guillotine if it moves at the wrong time, as well as raising the alarm, that the system needs some attention.

Also, consider having more than one sensor.  Hopefully, no more than one sensor will fail at the same time. Two sensors means a system 'assume the worst', and take the safer of two alternatives. Three sensors can work in a majority vote scheme.

Just scatterbrain comments at present, but hopefully useful prompts for you to consider.

Best wishes, Dave

@lamichaney This garbage doesn't belong on this forum!

Posted by: @huckohio

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@lamichaney This garbage doesn't belong on this forum!

So true.

This appears to have been a hacked account; until today, this individual hadn't posted for 4 years.  The account is now banned.

And thanks to those members who alerted me to this; with the situation with my Mom, I don't get to check the forum as much, so I appreciate the heads-up.

😎

Bill

@huckohio I just remembered, magnetic sensors are probably immune to the types of contamination a chicken coop would have. I think it was already suggested to have multiple sensors and use a 2 out of 3 voting scheme.

@zander Ron, thanks for the suggestion.  I would assume there are magnetic sensors with different field strengths to pick from (related to how far away the two haves of the sensors are before the circuit is closed).  

When you first mentioned the limit switch I was envisioning the switch at the bottom of the door (remember...limited mechanical experience).  I was thinking today that I could embed the limit switch in the door track (on the side).  That would be a cleaner environment.

Thanks again (btw, I hope the health issues are improving).

@huckohio I have used these with decent reliability.

https://amz.run/9H70   (Canadian link)

Embedded in track is a good idea.

July 11 I have an appointment with the cardiologist for an echocardiogram and a consult. I am hoping he will tell me what my treatment options are.

@zander I hope they find everything is working well!  At least, they can fix/control whatever they find.

@huckohio I am hoping he will recommend a pacemaker. Friends who know people with one tell me it is a game changer, I will feel 20 years younger!

Hi @huckohio,

RE: I would assume there are magnetic sensors with different field strengths to pick from (related to how far away the two haves of the sensors are before the circuit is closed).

There are lots of 'integrated circuit' package style magnetic sensors around, often based on and called Hall-effect sensors. They can be very sensitive ... if you have a smartphone, there is a high chance you will have one, or even three mounted at right angles to each other, to measure the Earth's magnetic field, and operate as a Compass for map applications, etc.

Depending on the intended application, the output may be any of a logical 0/1 type, an analogue voltage, or a digital number from an A/D that measures the analogue voltage, related to the magnetic field strength. There are some that measure the angle of the magnetic field.

I do not claim any particular expertise in the area, but like all 'chips', there are lots of data sheets, etc.

In addition, there are 'packaged' devices in various mountings, but with a 3D printer, packaging such devices should be a lot easier than it used to be.

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Interestingly, Ron (@zander) has used his long experience to provide a link to a far more 'traditional' sensor, that is cheap and remarkably effective, but easily overlooked when considering its more contemporary competitors, namely the reed switch. Wikipedia says it was invented in 1922!

It is effectively the contacts part of a small relay, usually offering a single pole, either on/off or changeover function. The actual reed relay is usually a thin, sealed glass, with the connections at the ends of the tube. The actual part is quite fragile on its own, but encapsulated in a plastic box, it can be pretty robust. Depending upon the actual design, it can also be quite sensitive, with switching when a small magnet is brought within a few centimetres of it. Of course, it depends upon the actual device, but I would generally recommend it as a low current, low voltage device, which is fine for driving the input to an Arduino, etc., but avoid directly switching inductive loads, like a relay coil, that produce an arc when the switch opens, as it easy to arc weld the contacts together! Similarly to the 'chip' based sensors, it is easy to buy the 'bare' reed switches, and maybe encapsulate it in a housing or similar, with a 3D printed design.

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You have probably seen it, but just in case, Bill (@dronebot-workshop) has one of his excellent video + blog reports combining both Hall-Effect switches and stepper motors!!

https://dronebotworkshop.com/stepper-motor-hall-effect/

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So lots of choices to research and consider ... maybe too many!

I am sure you will already know some of the above, but I hope there is something you will find helpful.

Best wishes, Dave

@davee I am going to add an item to my ToDo to compare the sensitivity and reliabilty of the reed swict to the hall effect. I think I have 3 or 4 different types of Hall effect devices. The reason I said reed, is it is sealed and fairly robust but may not be as sensitive as a hall effect device.

Hi Ron @zander,

  I think reed switch is a good idea ... simple and providing you don't subject it to arcing, or put any strain on the glass seals, has a good reliability record. Of course, 'sensitivity' adjustments are down to mechanical tricks, which can be a tricky in some cases.

The Hall-effect sensors seem to be everywhere, from monitoring the camshaft on a petrol engine (which is usually a hot, oily location), to magnetic compass, and more. Those that provide an analogue voltage or digitised equivalent, provide a convenient way of making the sensitivity, a software based scheme, which is handy.

One £2 AliExpress angle measurement device, as a chip on a board, to be linked with magnet attached to a rotating shaft or similar, are claiming 14-bit resolution 1 in 16384 .. around 0.02 degrees, albeit I haven't seen any independent proof of the claims.

So plenty for your to do list, including proving or disproving the more dramatic claims, I reckon! I look forward to the reports(s)! 

Best wishes, my friend, Dave

@davee The magnetic sensors that I have are encapsulated so far more durable than a glass reed switch. If in fact it can be embedded in the door track, it will work very well.

@huckohio Here is a link to my favourite tools/hardware store Lee Valley. They and many others sell UHMW plastic. You can work it with woodworking tools and it is super slippery. This would make an ideal chicken coop door track. Just rip a piece say 1" wide, then route a ~3/8" slot down the middle for the door to slide in. It's a simple matter to then cut out a part of the track to place the magnetic reed switch and a second small but robust limit switch (may be overkill). If you are in the US, order on-line at LV or google UHMW to locate local or other on-line sources. It just occurred to me, the magnetic switch and probably the emergency limit switch could be mounted higher such that the activator is at the top of the door thus keeping the switches further from any contamination. Maybe a warning switch at the door top such that the door bottom is at 120% of max chicken height. OR what about a truck inner tube door (free at your local tire shop) with that round but slightly stiff under door weather stop as the frame. This way the chickens (not sure about chicks) will survive any collisions.

Ok, I promise to stop now.

https://www.leevalley.com/en-ca/shop/hardware/jig-and-fixture-parts/32045-uhmw-polyethylene?item=46J9014