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Aeroengineer
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Re: Motion solutions: motors- a mammoth post
Aeroengineer   6/24/2014 7:56:08 PM
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I had actually known about the AMS site for some time.  They have a great app note about using RFID tags under water in salt water.  It was pretty impressive.  They also have an interesting line of noise canceling chips.

 

The thing that impressed me about this chip is that it seems to be a full quadrature encoder replacement that is programmable.  This is something that is pretty ideal.  The cost was not too awful, and the other thing about it was that it essentially applies a predictive value to compensate for lag while maintaining pretty high angularity accuracy and precission.  It seems like a chip that I need to look more into.  I like that it is a drop in replacement for an encoder and that it can be programmed with different scaling factors.  It can also output the valueas a digital word value, or as just a quaderature style output.

 

On belts, I am specifically referring to the toothed timing belt style.  These are not bad, and are used in a lot of systems.  It is not so much the belt that I am opposed to, just that they are sometimes notas clean to integrate.  They are effective solutions.

salbayeng
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Re: Motion solutions: motors- a mammoth post
salbayeng   6/24/2014 3:00:17 AM
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Yep , You have the gist of the motor comparison. Each sort of motor has its weaknesses and strengths.

I see you have found the Austria Micro Systems = AMS website !  ,  these guys were relatively unknown about 6years ago, we had to go through all sorts of weird purchasing arrangemengts to get the stuff from Austria, now you can buy from your favorite distributer. 

Selsyn: just a kind of Synchro ,  check them on wiki , too hard to explain without pictures. They were antecedents of the resolver. Quite common on 1940's ships and aircraft for relaying the position of say the rudder to the bridge (some still in use on DC10 era aircraft for fuel gauges). You just wire two together, put AC on each end , when you turn one shaft , the other turns, it's bidirectional, great fun for kids of all ages. The other neat thing from back then was the amplidyne: before the days of high power servo amplifiers, you could, for example, attach a synchro to the hour hand of a wind up clock, and a 1000ton radio telescope would follow the sun across the sky, just like leading a bull with a ring through the nose. 

Belts: Do you mean toothed belts like a timing belt? or multigroove like an automotive fan belt. Belts have the desirable property of adding damping, most stepper motors without micro-step drives are unstable if a high inertia load is directly coupled to the shaft (That's why you see so many timing belts on stepper driven items). Timing belts are more accurate than you might think (if they are tight enough) and used on most PnP machines of 10yrs vintage.

Aeroengineer
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Re: Motion solutions: motors- a mammoth post
Aeroengineer   6/24/2014 12:25:48 AM
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"Closed loop control dramatically improves holding accuracy and stiffness. Closed loop control can double available accelerations, but no effect on limiting speed."

 

Though the speed will be present by the very nature that you are using a bldc motor over a stepper.  Though the fact of adding closed loop to the bldc motor will not change its nature in speed, but only increase its accuracy and low speed qualities.

 

On the though of going closed loop and needing an encoder.  I just saw this product announcement on a competing website.

 

http://www.eeweb.com/news/high-accuracy-magnetic-position-sensors

 

 

Aeroengineer
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Re: Acceleration and nozzles
Aeroengineer   6/24/2014 12:15:14 AM
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I had never heard of that type of transducer.  It seems to be a variant of a resolver.  Learn something new each day.

 

As to the wire drive vs belt drive.  The nice thing about the wire drive is that the design space is a lot smaller than for a belt.  There is the issue of ensuring sufficient tension is maintained to control for slippage, but I like it because it is a very space efficient design.  There is another aspect in that it could be set up to carry current.  This is something that would have to be looked at very closely, but could offer some interesting possibilities in that it would be easy to shield this so that you would not have to worry about it being open (unlike carrying power through the slides (which I think is an interesting idea, but hard to shield).

 

The advantage to using a belt is that you can get grooved belts, but they are more prone to stretching and hence might lack in precission.  The would also not have the ability to carry power if necessary. 

Aeroengineer
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Re: Trading speed for size and accuracy
Aeroengineer   6/24/2014 12:02:43 AM
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I have it on good authority that his mighty lordship, Lord Mannion would not consider such an act an act of treason, but would laude such a valient effort to bring forth this mighty, yet mystical machine.

Max The Magnificent
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Re: Trading speed for size and accuracy
Max The Magnificent   6/23/2014 11:32:41 AM
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@Aerospaceengineer: I think that this may be a good thing to do a poll on.  What do you think about that Max?

Let me ask those who don the undergarments of authority and stride the corridors of power -- those magnificient creatures whose names I am not fit to utter...

Aeroengineer
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Re: Trading speed for size and accuracy
Aeroengineer   6/23/2014 11:05:46 AM
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I think that this may be a good thing to do a poll on.  What do you think about that Max?

Max The Magnificent
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Re: Trading speed for size and accuracy
Max The Magnificent   6/23/2014 11:01:53 AM
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@Aeroengineer: What size work area are you thinking of Max?  It seems that we are talking as low as 4"x 6" up to 8"x 10".

Oooh -- that's a hard one -- obviously I would like to have the capability of going as big as possible -- on the other hand most of my boards would be quite small -- it would be rade indeed for me to be making an 8 x 10" board ... and then I think about making an 8x8x8 LED cube...

How about going up to 6" x 8"?

Aeroengineer
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Re: Counterweights ??
Aeroengineer   6/23/2014 10:48:38 AM
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I like the thoughts that you have going on this.  This is one of the reasons that I have not rules out stepper motors and a belt system either as with the belt system, it would be very easy to do the counter balance approach by mounting the weight right onto the belt.  I have not looked into the steel wire method, though doable, usually for higher load parts.

 

The dual heads moving in different directions could be an interesting idea, and could make it very useful in that you would not have to dock heads.  Have to give this one some thought on a general methodology to integrate it.

 

Aeroengineer
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Re: Acceleration and nozzles
Aeroengineer   6/23/2014 10:44:34 AM
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I see that you found more than my twitter page ;)  Yeah, I am an engineer because if I were anything else, I am not sure what I would do.  I love it. 

 

My back of the envelop crazy calcs are just that, crazy, trying to help me understand the absolute limits.  I did a quick calc with a whole sequence last night, including a trap accel.  The accel definitely will play into the time on this machine as the travel distance is so short.

 

The other thing that I need to look into is the PV capacity of the nuts.  Usually they are not just rated for a linear speed, but a value that is proportional to the load times the speed.  This will bring some more reality into this effort.

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