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Post by Ron Walker on Aug 24, 2022 12:12:26 GMT -7
Posted by: Ron Walker Feb 24 2008, 01:50 PM QUOTE(Owen Phairis @ Feb 24 2008, 12:52 PM) * Hi Ron, I had a question on A3Ps. I see that the diurnal and lattiude motors are under the base plate and gear driven up at the top of the central core. I see a motor under the star globe which must be either annual or presession, where is the 4th motor and how is it coupled in? I have never taken one apart, and will default to your experience. Thanks, Owen The square black motor under the star globe is for precession. The "missing" 4th motor, the drive for annular motion is actually ten separate small synchronous motors which are controlled electronically from a variable frequency power supply inside the console. The only one visible without opening the central core is on the back of the Moon projector. It is the round silver device that sticks out of the small box and runs parallel to the main body of the Moon projector. This motor only drives the Moon phase. At full speed it runs at 2/3 rpm. Opening up the top of the central drive core (removing the plate that attached to the projectors center core, the plate the Moon projector is mounted on, we can see most of the remaining drive motors. The motor in the center is for the Sun and the five motors starting at the six o'clock position and going around to the two o'clock position are for the five naked eye planets. All of these are also 2/3 rpm full speed drives. At the four o'clock position are two motors that drive the Moon analogue. They are 8 rpm motors because the Moon's speed is approximately twelve times faster then the rest of the solar system projectors. They use two because the higher speed of these motors produces a lot less torque and also because of the speed this section of the projector must accelerate and decelerate twelve times faster then the rest of the annular system. The last motor is also a 8 rpm drive which turns the dove prism that keeps the Moon image in proper direction on the dome. I can't seem to find a picture of it handy (I might not have taken one) but it is attached to the part of the Moon projector that normally lives inside the central drive core and is removed with the rest of the Moon projector. As long as power is applied to these various motors there should be no slippage. The problems with maintaining proper synchronization can probably be attributed to age. When this projector was originally designed (late 50's early 60's) is was probably way ahead of its time. The electronics, however, have suffered over the years. To change the speed of the annular drive, variable frequency had to be provided to the motors. The motors ran at the speeds listed above when standard line 60 Hz power was applied. The entire system would slow down as the frequency was lowered. This frequency was derived via mechanical relays which would open and close as many as 60 times each second. This on off voltage was then amplified to provide the voltage and power required to run the ten motors. Synchronization of the system is totally dependent on the changing magnetic fields within the motors and it is easy to see that slippage (especially with the Moon drive) can occur if the speed change and/or reversing of the drives is requested quickly. Some safeguards, such as DC breaking, were designed into the system but it appears everyone who works with this series of projectors learns to live with slippage. It is fairly easy to readjust so no one really complained. As the electronics in these various machines began to fail most found it easier to just replace the electronics with a newer version rather then try and keep the old stuff running. Some of the new designs where not as good as they left out some of the synchronizing safeguards, but the more complex a system is, the more costly, and nobody really wants to put a lot of money into old technology. Now the A3P and following series of projectors are really designed beautifully and now working directly on one I can say they will probably last forever with minimal TLC. The problem is with the drive electronics. This is where the problems and maintenance costs lie. My design is to remove the electronic drive entirely and go with a tried and true mechanical one. The projector can still be adjusted easily but the "slippage" of the various analogs with each other will be eliminated entirely. Ten drive motors will be reduced to one which can be a simple DC device capable of a much larger speed range. The only thing that the old system could do the my variation won't is change the Moon phase while holding the Moon in one place. This could be easily overcome with a simple slip clutch and a small second motor, but at this time I'm not planning on it. You all know about my rather adamant (stupid?) demand for accuracy in how these machines project the heavens and I think that having the Moon go through its phases without its movement about the Earth will confuse some people no matter how well and often it is explained.
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Post by Ron Walker on Aug 24, 2022 12:13:00 GMT -7
Posted by: charles jones Feb 24 2008, 03:31 PM QUOTE(Ron Walker @ Feb 23 2008, 06:24 PM) * Your probably talking about the Bodine 24A-D series motors. I am looking at the model 0196 for the annual motion drive. It runs $240 at the web site.
Is there a special reason why your looking at the Minarik controllers?
Ron, the only reason I was looking at the Minarik controllers is there is a location close to home and I can drive 50 miles and pick up the Bodine Motor and controller (Minarik) in person (and ask more questions). Also, the Minarik controller I was looking at will work two motors. Not sure if Bodine has one that will do that. The motors in the 24 series were planned for diurnal and latitude motion. I really wanted something smaller for annual motion but haven’t found anything yet as I am currently on a cruise ship and my planetarium construction has been
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Post by Ron Walker on Aug 24, 2022 12:13:35 GMT -7
Posted by: charles jones Feb 24 2008, 03:33 PM QUOTE(Ron Walker @ Feb 23 2008, 06:46 PM) * Another thing that I'm incorporating into this system is some fairly accurate readouts so I can have a fairly good idea as to that time the planetarium is set for.
Ron, how is this synchronized to the annual motion motor. I can understand if the motor is a syncronous motor in both places, but weren't you planning on using a DC variable speed?
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Post by Ron Walker on Aug 24, 2022 12:14:08 GMT -7
Posted by: charles jones Feb 24 2008, 04:09 PM QUOTE(Ron Walker @ Feb 23 2008, 06:46 PM) * Another thing that I'm incorporating into this system is some fairly accurate readouts so I can have a fairly good idea as to that time the planetarium is set for.
Ron, will the clock readout be on the projector and connected directly to annual motion motor, or on your console?
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Post by Ron Walker on Aug 24, 2022 12:14:33 GMT -7
Posted by: Owen Phairis Feb 24 2008, 04:37 PM QUOTE(Ron Walker @ Feb 24 2008, 12:50 PM) * The square black motor under the star globe is for precession. The "missing" 4th motor, the drive for annular motion is actually ten separate small synchronous motors which are controlled electronically from a variable frequency power supply inside the console. The only one visable without opening the central core is on the back of the Moon projector.
It is the round silver device that sticks out of the small box and runs parallel to the main body of the Moon projector. This motor only drives the Moon phase. At full speed it runs at 2/3 rpm.
Opening up the top of the central drive core (removing the plate that attached to the projectors center core, the plate the Moon projector is mounted on, we can see most of the remaining drive motors.
THANKS RON,
That answers my question, I guess there is no need to take into account the (93 million * 2 + sun diameter) annual parallax views in the planetarium projection of the stars. Light years are comparitevly fairly distant...
Thanks again, Owen
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Post by Ron Walker on Aug 24, 2022 12:15:06 GMT -7
Posted by: Ron Walker Feb 25 2008, 09:16 AM QUOTE(charles jones @ Feb 24 2008, 03:31 PM) * Ron, the only reason I was looking at the Minarik controllers is there is a location close to home and I can drive 50 miles and pick up the Bodine Motor and controller (Minarik) in person (and ask more questions). Also, the Minarik controller I was looking at will work two motors. Not sure if Bodine has one that will do that. The motors in the 24 series were planned for diurnal and latitude motion. I really wanted something smaller for annual motion but haven’t found anything yet as I am currently on a cruise ship and my planetarium construction has been
If the exsisting motors on the A3P had not worked as well as they are, I would have replaced them with these as well.
As far as I can tell, all of the Bodine controllers are for one motor only.
I won't know the exact load until I have all of the proper timing belts and gears finalized. I'm guessing that the entire annular drive requirements will be only two or three inch pounds. I'm sure someplace there has to be a smaller motor out there but I'm not sure it would be as controllable. I'm really liking the great range of speeds. I might eventually replace the diurnal drive motor as well, just to get a larger range on that drive as well. However I will wait until I have the entire projector working and see if I really need it.
I'm also not worried about the weight of the motor as there is a large counter balance weight attached to the annular drive core just below the Moon projector. This motor can probably replace it for balance.
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Post by Ron Walker on Aug 24, 2022 12:15:42 GMT -7
Posted by: Ron Walker Feb 25 2008, 09:43 AM QUOTE(charles jones @ Feb 24 2008, 03:33 PM) * Ron, how is this synchronized to the annual motion motor. I can understand if the motor is a syncronous motor in both places, but weren't you planning on using a DC variable speed?
All of the readouts will be at the control console. In my boxes of "good junk" I have two sets of small selsyn drive motors. They came from surplus some time ago and were basically designed to run remote readouts on old military equipment. They will just be connected into the two drive systems via timing belts and then electronically drive their counterparts on the console. Since this projector will be at a permanent location I doubt that they will slip at all when not energized. One would have to physically turn the drive by hand to get it off. I originally thought about doing this when I looked at the original indicator on the A3P console. It shows only a seven year shift forward and backward from an arbitrary zero point and is driven by an eleventh small sync motor tied in with the others electronically. There is no indicator for the diurnal drive and I thought it would be kind of nice to have something so I would have an idea as to when sunrise was coming.
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Post by Ron Walker on Aug 24, 2022 12:19:35 GMT -7
Posted by: charles jones Feb 25 2008, 10:23 AM QUOTE(Ron Walker @ Feb 25 2008, 08:43 AM) * Since this projector will be at a permanent location I doubt that they will slip at all when not energized. One would have to physically turn the drive by hand to get it off.
I sure like what I am hearing. It's a great idea. I don't know anything about selsyn motors, except that if you turn one, the other turns the same amount.
Can they vary when the current is turned off?
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Post by Ron Walker on Aug 24, 2022 12:20:46 GMT -7
Posted by: Ron Walker Feb 25 2008, 03:10 PM QUOTE(charles jones @ Feb 25 2008, 10:23 AM) * I sure like what I am hearing. It's a great idea. I don't know anything about selsyn motors, except that if you turn one, the other turns the same amount.
Can they vary when the current is turned off?
Your absolutely correct. When the are energized it takes a fair amount of torque to make the repeater slip one of the magnetic teeth. Since they are only turning a small clock (I will remove all the other old gearing and just retain the hour, minute, and perhaps second hands) there should be no problem in this department. With the power off they won't vary but one could conceivably move a dial or turn a drive and the reading would be off. When turned back on the units will lock to the nearest magnetic tooth and thus stay off by whatever amount they could have been knocked off. The drive unit would be timing belt connected with the rest of the system so it could never get out of sync. This could only happen at the console and once enclosed I would doubt there would be any chance of accidental misadjustment. I tend to worry about things that shouldn't be worried about.
In a portable system that was transported around in a car, vibration from the road could possibly "vibrate" the readout to a new setting. Again this would not really be a problem in that a note could be made of exactly what date the projector was left at and then if the readout is off at all it would be easy to manually adjust it back to that point before the unit was turned back on.
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Post by Ron Walker on Aug 24, 2022 13:00:12 GMT -7
Posted by: Ron Walker Feb 25 2008, 03:46 PM The next stage or reconstruction moves me over to the Moon projector. This is by far the most complicated unit for me of all the analogs as it is driven by four separate motors. True, two do the same thing and are just used for added torque. They are the drive for the main Moon analog. This is the unit that looks very much like one of the planet analogs and drives the final mirror that reflects the moon's image out to the dome. The drive system at this point rotates twelve times faster then the rest of the analogs and it is here that I plan to attach the new DC drive motor. A 12 to 1 reduction via timing belt will connect this drive to the central Sun drive which will then connect 1:1 to the Mercury analog. Here is the new drive shaft for the Moon analog. Moving along the shaft from left to right we first come to a 40 tooth timing gear that will provide power for the dove prism (more on that later). Next we come to the original plate that held the two 8 rpm motors that originally drove the Moon analog. A set of my "poor mans bearings" hold the system in place. the shaft continues through a small ten tooth timing gear and ends in one of the original gears that once attached to one of the 8 rpm motors. It drives the second large gear that was once attached to the second 8 rpm motor and run together in reverse direction for added torque. This entire arrangement was kept to keep everything going in the proper direction as the set of gears to the far right and adjacent to the Moon analog are necessary to change the rotational speed from one revolution every month to the proper lunar month. Since this is accomplished with just one gear reduction, driving it directly would result in the Moon moving in the opposite direction from normal as the annular drive is set in motion. This angle provides a better view of the original motor support and the replacement bearing and shaft. Also note the timing belt that is driven from the 10 tooth Moon shaft and turns the large 120 tooth Sun gear. We now have monthly rotation at the Moon shaft and a proper year at the Sun shaft. Another angle of the 12 to 1 drive reduction.
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Post by Ron Walker on Aug 24, 2022 13:17:15 GMT -7
Posted by: Ron Walker Feb 25 2008, 04:06 PM I need to place another order for parts (what else is new) but there will be an additional 120 tooth gear that will transfer power from the Sun drive up to the Mercury shaft as seen below. The projector end of the Moon projector resides on the outside of the upper plate of the annular motor housing. It contains two motors. One, an 8 rpm drive for the dove prism, and a second 2/3 rpm one that drives the phasing device. The dove prism drive worked out quite nicely. The motor has been replaced with a new bearing set to hold the original drive gear for the dove prism and the new timing belt gear. The original gearing once again reverses the direction of rotation which is no problem for the original motor. Luckily this drive is mounted "up side down" with respect to the rest of the drives since it is mounted to the top plate rather then the bottom plate of the motor housing. This reverse mounting also reverses the direction of the prism allowing for a direct timing belt connection.
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Post by Ron Walker on Aug 24, 2022 13:29:38 GMT -7
Posted by: Ron Walker Feb 25 2008, 04:26 PM When we put the whole thing together we can see the dove prism tube within the motor core and the two 40 tooth drive gears for power transfer. I need to measure and get the proper belt on my next order. I am not sure at this point in time that I will add an extra bearing on the top plate. It is actually the one at the bottom of the picture above. I'm thinking it is probably a good idea as the motor will attach to this shaft on the opposite side. This shows the top of the top plate. The motor for the entire annular motion will connect to this drive shaft. To the left and below are the end of the drive shaft for the dove prism and the end of the dove prism respectively. The last and final hurtle (other then the instillation of the motor itself) will be the drive for the phase. It was run by a 2/3 rpm motor and is at right angles to the plane of the rest of the drive system. I could use beveled gears but I believe the alignment would be painful. I could use a timing belt, but it would need to make two 90 degree bends which would also be painful. Since the amount of torque to rotate this device is virtually nonexistent, I'm thinking this would be the perfect place for a flexible shaft. I will do some more thinking and post more later.
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Post by Ron Walker on Aug 24, 2022 13:30:08 GMT -7
Posted by: charles jones Feb 26 2008, 10:40 PM Ron, thanks for detailing all of this. I for one have been taking notes as your experimenting will save me a lot of time.
Curious: Did you use 6mm belts or 9mm? If you didn’t use 6mm, do you think 6mm is too narrow?
Also, what did you find as the best source? Boston, Sterling? Small Parts even had a few in their catalog as I recall.
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Post by Ron Walker on Aug 24, 2022 13:30:28 GMT -7
Posted by: Ron Walker Feb 27 2008, 09:10 AM QUOTE(charles jones @ Feb 26 2008, 10:40 PM) * Ron, thanks for detailing all of this. I for one have been taking notes as your experimenting will save me a lot of time. Curious: Did you use 6mm belts or 9mm? If you didn’t use 6mm, do you think 6mm is too narrow? Also, what did you find as the best source? Boston, Sterling? Small Parts even had a few in their catalog as I recall. For all the timing belts and gears I went to Sterling: www.sdp-si.com/They had all of the various sizes I needed. I used the 1/4 inch or 6mm size belt. At the speeds required for this instrumentation they are more then enough. You could probably get away with the 1/8 inch or 3mm but I don't believe you can get the gears less then 1/4 inch in the plastic variety which are a lot less expensive then the metal ones. Also the 1/8 inch gears are not available in as large a selection as the 1/4 inch. Since the MXL 0.080 pitch is the same for the 1/8 and 1/4 inch belts I went with the 1/4 as a slightly over engineered system. So little extra space for so much piece of mind. I did get my shafting from small parts but was not impressed with their selection of timing parts.
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Post by Ron Walker on Aug 24, 2022 13:31:04 GMT -7
Posted by: charles jones Mar 2 2008, 05:05 PM Do you think a small motor could be attached to the shaft for the planet adjustment in each analog? Do you think it would require more torque to move them than a small motor similiar to the ones that are built into the A3P can provide (the little Bristol synchronous motors)?
As I recall several of the analogs I have were hard to move. This may only be because they need a little loosening with lubricant. I remember the Mercury and Venus analogs are adjusted from outside the plastic containers, using a worm gear and were easily moved. Several of the other analogs were harder to move.
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