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PostPosted: Fri Mar 25, 2011 9:59 pm 
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Superior Bird
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This is just a sort of expression of interest type thing.

One of the major stumbling blocks with making your own automatic egg turner is the associated electronics etc. needed to control what ever design one may come up with. Similarly there is plenty of a well known brand incubator where people find the cost to upgrade from semi automatic to fully automatic prohibitive.

I have just completed a circuit that may help you with your autoturner design.

This one is DC motors only, for example BBQ rotisserre motors, windscreen wiper motors etc.

Basically you hook your 12V or similar power supply to the input leads of the unit (black box) and your motor to the output leads. The unit will reverse the direction of your motor automatically at time intervals you can select with a knob from something like every 10 mins to every 4 hours or so. If you know how often you want to your auto turner to turn, you can let me know and I will program it to that and you wont need a knob.
The unit also has 2 microswitches attached (I may not supply these) which are used to stop the motor where you want it to stop.

To try to make it easier to understand and install I have color coded it. There is a red direction and a green direction. For your design red may be Left and green is right ...
On the box is 2 LED lights, one red and one green. When you turn the power on the unit will show the red light and your motor will turn your mechanism in the red direction. It will keep on moving in the red direction until the mechanism hits the red microswitch and power to the motor is cut off. When the unit is moving in the red direction the green microswitch can do nothing.
So your turner will come to rest on the microswitch and just sit in that position.
After the hour or whatever you set has passed the unit will change direction, the green light will come on and the motor starts moving in the green direction. And it will keep on moving in the green direction until it hits the green microswitch.
When the unit is moving in the green direction the red microswitch can do nothing.

This unit could make your design brief a lot simpler in that you won't have to worry about reciprocating linkages, cams and all that stuff. Just drive it in the direction you want to go knowing the switches will stop it exactly where you want and it will turn around when you want it to.

The downside is the cost. What I pay for components makes it expensive. I'm thinking if it was made by a Chinese factory it would cost them about the same to make and deliver to you as I would pay for just the relay which is only one component. Because I have to etch the boards, solder all the parts in and program it all by hand one at time it is time consuming.

I have one for sale at $60 which is about what parts cost me.
pm me if you are interested or have any questions. If you are currently thinking of building an autoturn or attempted one in the past and the motor control was the stumbling block you are wecome to message me to see if I can help you out with a different design.
I can't see a way I can make any money out of doing this but I may be able to help someone save a few bob and have a bit of fun.


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PostPosted: Sat Mar 26, 2011 8:34 am 
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That's a good opportunity for someone Denis. Our electronics are sorted and working, in case you are wondering. With your help, it's basically what we now have working here. We have not completed the whole auto turner due to many revamps on the mechanics. Working with motors that are too small and problems with gear reduction have caused our experimental models to fail. We are back at the drawing board stage on mechanics. The motor that we'd chosen had a revolution speed of 30rpm but was not strong enough to turn the linkage arm so we put it through worm reduction gear. However, there was too much pressure/stress being put on the reduction gear causing mechanical issues such as jumping cogs etc. We rebuilt it a couple of times, but then we shelved it for a few weeks.

Reading your post hear makes now think we should go for a rotisserie or wiper motor and try again. We've invested about $100 in parts so far so we won't give up just yet. I'm just going to go and pull out the rotosserie motor from the BBQ and see what we can do. Ours has an inbuilt auto-reverse and I'm not sure if that will be a problem. The downside is that this is starting to become an expensive project.

The project had stalled so thanks for the prod.

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PostPosted: Sat Mar 26, 2011 10:37 pm 
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Hi Chicken07,

the most important requirement of the egg-turning motor is typically the torque output to overcome friction, inertia, and any imbalance in the trays.
If the mechanics are balanced then the required torque should not be large.

For example, think of Microwave plate motors. They do not run fast (~6rpm) and are high enough torque to turn a turkey around because the mechanics are set up properly.
Denis has a picure of one in his gallery being used as an automatic egg turner.

Hence, I think you should have another look at your mechanical setup.


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PostPosted: Sun Mar 27, 2011 2:02 am 
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Haan is right about balance and the rest of it.

Today I finally got my bum into gear and looked seriously at how to make BBQ rotisserre motors more effective. They are only about 3W, that means they don't have much power and maybe not a lot of torque either.

That doesn't mean that they can't do a lot of work, it just means they can't do it in a hurry.

To lift a 10kg weight a distance of 1 m W=Fd or mgh =10x10x1= ~100 joules
A 100W motor will do that in 1 second but if our little motor is going to do it then we expect it to take at least 33 secs.

The way I spin my turntable isn't the best example of what I am banging on about here. Whatever work my set up has to do it has to do it fairly quickly, in the time it takes for one of the motors to complete half a revolution. Thus balance is reasonably important.

Originally I tried with microwave motors, because I had half a doz I got for 3 dollars ea. They had 3W marked on them so I wasn't real ambitious as to what they could do. I didn't think they would spin the turntable directly from the center. The original plan was to do something like is shown in this picture.
Image

Instead of teeth like a cog I had a round plywood disc, love my old router. The motor was supposed to have a rubber tube around it's shaft and friction was supposed to turn the disc. I was really struggling for a week or so with the thing that was driving me mad was not having a coupling to fit the 7mm D shaft of the motor. It was really hard to drill into the shaft and when I tried to weld it I found the shaft popped out and so on.

Then I saw a BBQ rotissere motor and thought they would be strong enough to turn the motor from the centre. I had no idea what their power rating was but they turn a roast. Just having that 8mm shaft set up was a godsend. I still persist with the motor through the centre because it is sooo quick and easy to build.
Strangely enough the motor in the 240V BBQ rotisserre motor (black plastic case) is exactly the same as a microwave one. But it has that coupling that lets me use the 8mm squre rod.
When I make an incubator that holds three trays it is too much for the 3W motors to turn from the centre.
I should do something like the original plan but it is just easier to buy a bigger BBQ motor.


Anyway back to main story. I've tried a few ways to have a motor roll the eggs. What I've wanted was something that would push a simple ex fridge or stove rack back and forth. I've tried linkages and cams etc. All them would work but none of them could I be bothered with the time and effort to build them. Their is plenty of examples of how to turn circular motion into linear motion.

If you have a BBQ rotisserre motor this would have to be the simplest.
Get yourself a 3/8" threaded steel rod. With a little bit of grinding at one end you can make it square and fit the motor. Mount the lot pretty much as you would a normal spit.
Have a 3/8" nut in the middle of the rod. Weld a hook or something to that nut. Use a cable tie or a bit of wire and connect that nut/hook to whatever it is you want to drag back and forth in a straight line.

This picture shows how I would be trying to convert an E1 to auto turn. The motor and shaft cost me $50 a plug pack costs $20 so if I can get a timer for under $230 then the all up cost is $300 which is half what it would normally cost from multiquip. :oops: :oops: :oops:

ImageImage

On the threaded rod. I had to screw a nut on mine today so I just held the nut and turned the rod with my rechargeable drill. The nut still moved pretty slowly so if you have an old drill you can't use because the battery is cactus ......


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PostPosted: Sun Mar 27, 2011 8:09 am 
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Thanks Haan. I agree that we need to go back and look at the mechanics. Perhaps I should show you what we did that didn't work. Denis, thanks for the comments. We will go back and reread.

Firstly, here's our electronics box. Denis has seen this, but it may help others understand the problem to see how we are connecting the motor. There is a little 30rpm motor with the turning arm coming out the front of the box.

Image

Image

We were planning to attach it to the E2 arm like this and have the motor pull the arm backwards and forwards on the timer.

Image

This didn't work because there was not enough torque in the motor to take the load from the linkage arm. The motor just stopped turning.

After that we introduced a home-made reduction gear box. I don't have a photo of that, but it was a 4 to 1 reduction unit built with plastic cogs bought from Jaycar. The result of this was that the motor worked. There was enough torque for it to operate. However the gearbox was not physically strong enough to take the stressors. It was not made precisely enough. There was too much slippage under load. At the end of each of the cycles from the arm, there was more load. It would move quite comfortable during the middle range of the turn, but at the end of the turn when the incubator arm was on more of an angle, there was more load and at that point the gearbox would slip or fail. It just wasn't consistent enough and was clearly going to fail completely at some point. It did actually work for half an hour but we could see that it wasn't going to be successful long term. The other thing as well was that the travel speed was still too fast at 4 to 1. It was a bit clunky. We'd basically reduced it to 7.5rpm on the arm.

From there, we moved to a worm gear kit that we bought from Jaycar to give that a go. It was 40 to 1. The good thing about it was that the motor was powerful enough to sustain the amount of torque. The problems were in making a gearbox that was going to take the secondary loads. We had some trouble connecting the wormgear to the motor to withstand sideways forces. As soon as the load came on, the plastic wormgear would bend and jump off the drivecog. It would disengage and the teeth would slip. Under load the wormgear needed to be supported more effectively. We were going to try that in some way but decided that we were probably trying to work with materials that were a bit too flimsy. That's when we got frustrated and put the project away for a while.

Failed worm gear option:
Image

If we were to go to the rotisserie motor option, the one we've got here is a 240V A/C synchronous motor. It appears to randomly turn in either direction once it's turned on. Accurate control direction of rotation can't be controlled with the rectifier and current circuit. If you can remember our circuit, Denis, we built the rectifier to convert A/C current to D/C to be able to control direction of the current flow so we could reverse the directional rotation of the motor. We'd have to revisit that issue. I was hoping to speak to my son about this problem last night but he didn't come home before I went to bed. He has previously mentioned something to me about introducing a capacitor to the circuit to regulate the current direction. I don't understand this so I'll probably start cooking bacon and eggs soon and hope that the aroma gets him out of bed. He doesn't respond well to these questions this early in the morning. Coffee & brekky might do the trick.

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PostPosted: Sun Mar 27, 2011 10:19 am 
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The verdict here seems to be that our rotisserie motor has been designed so that direction of rotation doesn't really matter. We can't practically change the D/C excitation windings as it's all internal and permanently set up. He explained how it's theoretically possible but it went straight over my head, I'm afraid. He tells me that he'd change the polarity of one of the sets of windings. He thinks that on a tiny little motor it would be so fiddly he wouldn't bother. He thinks a D/C motor would be better to use for this job if we want to control direction.

So ... where now? Do we stick to the little motor we've got and go back to trying to improve the gearbox in some way?

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PostPosted: Sun Mar 27, 2011 11:49 am 
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Chicken07,

I think I need some bacon & eggs to get my brain working.

Don't worry too much about which way your motor turns.
If your linkage connection point moves 180° each time, then it does not matter whether it turns clockwise or anticlockwise - it ends up at the same place.

Your 2nd picture shows you have the motor driving the load directly, with the load & motor having different radii from the centre of the shaft.
Your setup shows that the load has a Mechanical Advantage (MA) over the motor. (see http://en.wikipedia.org/wiki/Mechanical_advantage)
Hence any Force or Torque applied by the load is multiplied, and the result is then applied to the motor.
From your picture, it looks like the difference in radii is of the order of 11, but let's say it's 10, hence the MA = 10.

The result is any small force due to the previously mentioned friction, inertia or tray imbalance, is multiplied/amplified by a factor of 10, so essentially a small force becomes a large one resulting in the problems you described. ie. motor stalling, stressing gears etc.

The solution is to provide the MA to the motor instead.


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PostPosted: Sun Mar 27, 2011 4:46 pm 
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Without knowing all the details, I would think the motor you are trying to use is not suited to the task. It looks like a small DC motor which probably has a reasonably high RPM - is that correct? Not sure how much torque the turning handle requires but I am guessing it is a bit too much for the motor. Trying to add a gear reduction arrangement is often very difficult due to the mechanical stresses (as you have found). Options as I see it are:

1. Higher torque motor - a BBQ rotisserie motor might be suitable but I would go for a DC one so that reversing it is easier. Other higher torque motors might be suitable are some of the ones available from Oatley:

http://secure.oatleyelectronics.com//in ... c4d245b98f

2. Use something like a servo motor. These little motors can produce an amazing amount of torque. Control of the motor is a bit more complex but I have made some turners using a servo and a small micro (such as a PIC). These turners were for a parrot incubator though and the PIC also controlled the temperature so the incremental effort was reasonable small. If you need servos get them from somewhere like Deal Extreme (much cheaper than Jaycar etc):

http://s.dealextreme.com/search/servo

If you can provide some more information (i.e motor size & RPM, torque required etc) then I might be able to help some more.


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PostPosted: Sun Mar 27, 2011 5:41 pm 
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What happens to the servo motor and our racks when the power is cut off?


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PostPosted: Sun Mar 27, 2011 7:50 pm 
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Denis,

Not quite sure whether you mean when power is turned off for a short time or a long time.

If it is a short time, then the servo will hold its current position. Yes you can move the arm of a servo that is not powered but it takes quite some effort. The holding force is quite strong. You need to make sure that the current position of the servo is stored in the PIC's non-volatile memory so that when power is resumed the PIC knows the current position of the servo (all key data has to be stored in EEROM anyhow).

If it is for a long time (i.e a power failure), there are two options:
1. Battery back up (both the PIC and the servo draw very little power and are able to operate off a battery for quite a long period of time - think a RC airplane and rechargeable batteries). Of course the battery back up is (unlikely) to be able to power the heating element but at least it can trigger an alarm (have got audible alarms and have the alarm working over the Internet and I am now looking at a mobile text message alarm capability - I know, if you loose power you have probably lost your Internet connection as well!!).
2. Removeable coupling and go back to manual operation (but without a heating element!).

I have used servos for a number of egg turning mechanisms. I typically have a 8-bit counter that gives a resolution of 256 "steps" over the 180 deg range of movement (one design uses a 16-bit counter but that level of resolution is greater than most servos). I then have a user adjustable time to move across the 180 deg range of movement (either set via a visual interface or a potentiometer interface - believe or not, most prefer the pot). A timer based interrupt is then used to increment the counter and move the servo to a new position. I do not apply power to the servo in between the timer interrupts - it relies on the servo holding force. On one particular egg turner I used a rotary position indicator to check that the egg turner was in correct position but that was for a *special* incubator. Some of the designs have microswitches at the end of the travel in both directions - the servo keeps going in one direction until the microswitch is tripped and then it reverses direction until the other microswitch is tripped etc. Like I said, by using a PIC the incremental effort is minimal - some of the small servos can be driven by the PIC directly (no interface electronics needed).

Just to be clear, the incubators I have used servo egg turners on are much smaller than what we are looking at here but I have developed some high precision mechanisms for other applications using much bigger servos so it can be scaled up (but the cost might be high - that is why I was trying to find out how much torque is required). Another option would be a stepper motor or a larger electric motor (perhaps with a built in gearbox) - once you get past a few (~10 - 15) kg-cm of torque they are generally more cheaper but the interfaces are also generally more complex.


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PostPosted: Mon Mar 28, 2011 12:17 am 
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Image
Here is one of the motors used in the 240V BBQ rotisserre, the $35 black one, not the more powerful ones you see in the stainless steel case $90. This time however it appears in a different product. The is a mirrorball motor. It hangs upside down, an S shaped piece of wire provides a hook to hang the mirror ball on. You have to supply your own music, lights and lime green stretch denim trousers.

I use these to turn a 40 egg rack turntable which is just a plywood disc with a diameter of about 30cm.
To get a feel of how much torque these have you just turn it on and see how hard you have to work to stop these motors and make them turn around. When my turntable is running I can stop the motor with my little finger, easily. So it doesn't seem to have much torque. Indeed, when I stack 3 racks (120eggs) on the turn table I need to use a bigger motor.

But tonight I threaded a piece of builders string through the hole in the shaft, turned it on and allowed the string to wrap around it like a winch. I couldn't stop the motor from turning by holding or pulling the string. It just kept winding the string in. I had to wrap the string around a kitchen utensil to stop it cutting into my hand and still I couldn't stall the motor even when I pulled as hard as I could.

I stuck a pop rivet --------|-- through the hole in the shaft and tried to stop it and only bent the rivet.

But the motor has the same amount of torque in all three scenarios. since T = F.d
Image
what I saw was the motor can deliver quite a large force if the perpendicular distance from the centre of the shaft that force is acting through is very small but as the distance increases the force the motor decreases. That is true for all motors etc.

TO MAKE SOMETHING MOVE it is all about FORCE.
Image

Shown above is the incubator handle, further along the handle the less force is needed to move it.
Also shown is what the motor can do, further along the handle the less force the motor can exert etc.
The pink line shows that the motor can certainly move the handle if we stay close to the motor shafts centre and if we apply that force at a reasonable distance along the handle.
If we apply that force using a linkage system the motor can't move the handle enough, there is just not enough travel to be had.
But if we were to apply that force using something like a winch method we have all the travel we need because the motor can turn as many times as it likes.
Image
To make the BBQ rotissere into a simple reversible winch would be something like this. Not shown is the pulley at the other end. It will move faster than the threaded rod which could be too slow.


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PostPosted: Mon Mar 28, 2011 7:28 am 
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Thank you all for thinking about this and responding.

Haan, We started with a single direction motor with an arm of an appropriate length to create the horizontol travel on the incubator with a complete rotation. We had some difficulties with the timer turning the motor off at exactly the 180 degree point. Seeing as the timer was not accurate enough to control both the seconds required to control the 180 degree turn, and also the frequency of rotation, we had to look at alternatives. That is a limitation of our timer. We now have microswitches turning it off at either end which requires a reversible motor.

We get your point regarding MA. We're thinking about this now with regard to the motor.

Grunto, the motor that we are using is 120 g-cm. It's 30rpm. The worm gear produced enough torque to run it, if that gives you an idea of torque required. The wormgear was 40 to 1, so 120 X 40 would give us a rough estimate of about 4.8kg-cm??

Thanks for the site links to motors available. We'll look at those. The problem from our point of view is that going to a servo motor would mean that we would have to buy a whole lot more electronics as we couldn't use what we already have. We'll investigate a stronger DC motor first I think.

Denis, we take your point regarding the winch system. That's a clever way of getting the force we need. We initially thought about different types of linkage, but if possible we'd prefer to have something that is neat and tidy and easily removable. The winch system is an option, but so far not our preferred one. If putting a system of pulleys across the front we'd have to avoid the door but that could be done. If we can find something that fits neatly and simply I think it would be better. It would look better. We were also trying to minimise the amount of equipment protruding past the front of the incubator as things sticking out are likely to be knocked by people walking past it. That's why we initially fitted the box to the side of the incubator cabinet rather than the front. The threaded rod idea (which someone mentioned) is also a good one and based on a similar principle. If we have to scrap our current design and start again we could look at that.

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PostPosted: Mon Mar 28, 2011 8:56 pm 
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Chicken07,

from the replies above, there appears to be several ways to give the "MA to the motor" ...

Denis's 1st diagram is quite instructive. You could drive the smaller cogwheel (with your motor), and attach your linkage arm to one side of the larger cogwheel.
As the larger cogwheel turns, the linkage arm would move horizontally left and right producing the required stroke motion.

The gear required could be obtained from old bicycle parts (at your recycling centre). ie. 1 large/1 small sprocket, and a connecting chain.

Or alternatively, if your motor has to be upgraded, grunto mentioned oatleyelectronics.com, and they have the SC300 motor with a small sprocket already attached. NB: "although they are built for 24V use they still produce lots of torque at 12V". Cost $39.00.
Thic could be purchased with the (80 teeth) CHAIN & SPROCKET SET [CHAINSP] http://secure.oatleyelectronics.com//pr ... cts_id=662 for $12

Driving the 80 teeth cogwheel using the 11 teeth cogwheel gives an MA of about 7. This, and higher-torque of the SC300 motor, should get you out of trouble.
The only thing to work out is how the mount the large cogwheel on a free-wheeling ratchet (or similar), but this is where old bike parts could be used.

Please note that in providing this idea I am not stating that mine is superior to the others ... it's merely an alternative.

PS: denis, thanks for your excellent diagrams and ideas.


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PostPosted: Tue Mar 29, 2011 9:27 pm 
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Thanks for the ideas. I looked up the SC300 motor but it was out of stock.

We decided to go with a bigger motor so I ended up ordering a new 12VDC motor from Jaycar. They may be expensive, I know. The torque of the motor is 50kg/cm at 55rpm with a stalling torque of 75kg. The link's here.

I also ordered a speed controller which is here. The potentiometers would have needed extra circuitry to make them suitable, so we decided to get a speed controller where that was already done.

We'll see if it works.

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PostPosted: Tue Mar 29, 2011 9:54 pm 
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4kg rotissaire motor, the DC ones that take batteries, these can be reversed with polarity as they are a true DC motor, rather than a universal motor.
the 8mm square drive can be sorced from a door lock.

use a plug pack rather than batteries to run the motor, just jack the wires in..

its not like we are trying to land a man on the moon..


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