Synchronizing motors - two motors turning one shaft

Discussion in 'General Electronics Chat' started by RogueRose, Apr 28, 2017.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
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    I need to know what the best way would be to go about using 2 motors to turn a single shaft - basically like a lathe where at least one side can be moved back/forth along the turning axis as well as allowing one side to slow down (user controlled) and then come back up to the synchronized speed.

    The shaft will need to turn from 5-100 rpm and the weight of the shaft (each end mounted on 2 bearings - 4 total) and material will be from 4 - 25 lbs - but probably 6-12lbs on average.

    IDK if a direct drive setup could be used where the motor is attached directly to the shaft or an alternative could be chain or belt driven. If belt driven, a spring tensioner could be used when the one side needs to be slowed temporarily.

    What I most need to know is if motors can be this accurate as to synchronize, maybe by using the same power source feeding both motors but IDK if minuet differences in the motors would make them turn at slightly different speeds?

    Assuming that 2 identical motors are used, what type of motor would be best suited for this application? As for the power supply, what would I need to look for, something like a PWM or a simple DC drive controller?
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Again, this sounds like you are asking us to solve your solution to a problem rather than letting us solve your problem. What is the core issue that you think needs two motors to drive one shaft?

    A hint that you may have other (better) solutions is that no drive tools or common design tools exist for this "problem" (driving one shaft with two motors).

    Also, "cogging" issues will cause the load to be moved between each motor (and alternating inductive kick from each driven motor) but those issues depend on the type of motors you are planning to use.
     
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  3. Alec_t

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    Sep 17, 2013
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    If the two motors drive the same shaft, how can one be slowed down without affecting the speed of the other? In other words, doesn't the shaft automatically keep the motors synchronised?
     
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  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There is a stepper motor solution where they can be fed with the same step pulse rate.
    If precise synchronization is needed, I have done this in the past with servo motion control cards such as Galil Motion that have electronic gearing feature, where one motor encoder is geared off of the other, but it is not cheap.
    I believe they can go up to 8 slaved axis.
    Max.
     
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  5. shortbus

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    We had machines that cut and placed wire. Slow speed to pull the wire out from a large spool and fast speed to return to grab the next wire. Both speeds were off of one motor. The actual drive used two different size pulleys that were free turning on the shaft, with a dog clutch that was keyed to the shaft. For one speed the clutch engaged one pulley, for the other it shifted over to engage the other pulley. Neutral was in the center. The dog clutch had a shift fork that moved it where it was needed.

    A similar idea is used in the lower drive of an outboard motor, but there it is used to get forward and reverse. This happens because both are driven by a single gear not separate pulleys. But it is the same shifting principle.
     
  6. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    I'm with Alec on this one. If I have a lathe and am turning a piece of wood (from both ends for whatever reason) and want to slow one side down - wouldn't that twist the heck out of my wood stock? Or metal stock? Unless that's precisely what you're trying to do.

    Now, if you're using some sort of differential and having both motors synchronized (but in opposite directions) then the output on the differential would be zero RPM. If one motor was to slow or speed up it would cause a difference in rotations and the differential would rotate one way or the other.

    To be perfectly honest, at least to me, your question doesn't make sense. But I'm always open to learning new things.
     
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  7. RogueRose

    Thread Starter Member

    Oct 10, 2014
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    This setup is basically exactly like a lathe in design but has some non-lathe like requirements (wood/metal lathes that is). There are two "pillars/blocks" that are 10" cubed - aligned with a shaft mounted on the top of each mounting block. Each block has 2 bearings with the shaft rolling inside. One block is fixed and another needs to be able to move along the axis of the shaft - getting closer or further away fro the stationary block. This "shaft" is 2 pieces, one on each mounting block & each shaft has a threaded terminal that can accept different hardware - kind of like a chuck. These 2 terminals/chucks face each other mounted at the end of the shaft in the space between the mounting blocks.

    There will be various materials placed in these terminals/chucks that will connect the two sides of the shaft, making it a "single" shaft. This will need to be able to turn at a constant speed of 5-100 rpm and as said total weight of entire shaft/coupler material/terminal/check will be 4-25lbs - so I don't think a lot of power will be needed to turn this & the bearings are all identical and have very low resistance.

    At times, while the shaft is turning, one 1o"^3 block may need to slide N/S along the shaft axis (this can be controlled by an hand crank or maybe another motor, TBD). The block will also need to slide when not running to adust for different size work pieces.

    It would be GREAT if I could slow the rotation of one side of the shaft, either the one mounted on the movable block or the permanent block - it really doesn't matter as either way can be made to work. When this happens, the material that is between the terminals/chucks WILL get twisted up and maybe stretched (if one axis is moved while doing this as well) and this is DESIRED. The material is meant to be flexible at this point and it will give a unique effect to it. The thing is, that I'm not sure I'll need power to turn the side that is slowing and maybe just a way to "let off the clutch" so that it drops power - slows down - and then re-engage the clutch and get it back to speed. I just think this will have a number of problems and I know that being able to slow the motor would not have these problems.

    Now, I've considered using a drive shaft the length of the base with something like bicycle gears fixed to it and then other gears on the shaft then use a chain to link them - there would need to be a set for each 10"^3 block mount. Also I thought about using something like a 21 spd that has 7 gears on the back that could give 7 different speeds. Actually a CVT transmission would be ideal - with 2 opposing cones with a belt in the middle - giving infinite speed options. The problem with using a single drive shaft is IDK how I could get one mounting block to be able to slide along it when I need to move it while it is turning. This is why I thought 2 identical direct drive motors that are screwed onto the 10" ^3 mount would allow for the movement along the axis.

    I had seen some similar setups where a toothed (???) drive shaft/tie-rod (has teeth around circumference the length of rod allowing for a gear to slide along its length) This runs end to end - the length of the device and is turned by a single motor. Then a gear can be mounted to the movable mount and as it slides along the toothed rod, it continues to spin as it moves long the shaft axis. When I saw the price for something like this my jaw dropped as it was about $200-400 for a 36"-54" .75 or 1" diameter toothed shaft! (plush cutting cost, special grooving fee and shipping - another almost $65-100) This is why I looked into synchronised motors. Then with this process there was the problem of slowing one side when the shaft was running at the same rate. I think this could be worked out but it was a lot more work if a dual motor setup could work.

    The reason I thought this might be possible is because I was thinking of servo motors (as someone had mentioned above) and if they could be controlled by a single controller for then they are synchronous and then separate controllers for when one side needs to slow down - then switch back to them being run from the same controller for synchronizing.

    Now I know if a motor faces an opposite direction as another, they turn in opposite directions. IDK if this could be overcome by reversing the wiring, but IDK if that would mess up their perfect syncing. I could setup a system where they face the same way and use pullies to turn the shaft, so they aren't attached directly - but this would allow both motors to face the same way - I guess gears could also be used - this isn't as major a deal from what I can see.

    I would think that since we are talking about fairly low rpm's and power needs, this would be less difficult than trying to sync something running at 1K - 15K rpm as any slight difference at those speeds would be catastrophic.

    I'm sorry I didn't explain this better at the beginning but I was trying to keep the post from being long rambling- I thought I had enough info to get my question across. I get agitated when posts have tons of impertinent info (often repeated over and over) that is a waste of time - so I apologize for not being clearer about needs and why I needed what.

    If anyone can help with the info I have now provided, I would so greatly appreciate it! I hope I have explained what I'm looking for a little better and you have a clearer idea of what I am looking for. Thank you.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I did a retrofit on a double ended railway axle lathe once, where the (400lb) axle was held between chucks each end, I used a single VFD for each AC induction motor, but they had to turn at exactly the same rate, just one reversed obviously.
    To do various electronic gearing on the fly, the Galil motion controllers using electronic gearing excel at this, using servo motors, geared in this case, but they are not cheap.
    You would need to know the required torque when one is electronically geared down compared to the other when they are mechanically coupled.
    The other way is to actuate a brake on one end and turn the other end.
    Max.
     
    Last edited: May 4, 2017
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  9. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    The only place I've ever seen two motors on a machine was on a Swiss Screw Machine. You have a piece of work-stock being turned and bored. The boring process is straight forward - hold a stationary drill bit at the end you want to drill the hole. Drive it in at a given speed to accomplish the hole. Then back the bit out. Now, here's where different speeds on both ends come into play. The work-stock is turning at - oh, lets say 500 RPM. You need to thread (tap) the hole. You bring a tap into the hole spinning the same direction but spinning at 550 RPM. The difference in speed drives the tap into the hole. You then slow down the tap to 450 RPM and the tap backs out of the hole. All the while both the work-stock and the tool were spinning in the same direction.

    From what you said about your goal - deliberately twisting your work-stock. OK. I think if I wanted to do something similar I would still use a single driven system and deliberately lock one end so that the work-stock can be twisted by the motor and the driven end. Instead of having two motors, one at each end, why not build a brake assembly whereby you can create drag, and twist your work? True, I can't imagine what exactly you're after, but perhaps this might spark a new idea - a new direction to consider. Then again, maybe this is entirely wrong.
     
  10. DNA Robotics

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    Jun 13, 2014
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  11. shortbus

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    Sep 30, 2009
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    I may be way off base on your "job", but as it seems you only need one motor driving at one end, just like a regular lathe. The other 'adjustable end' just needs a brake,or even a ratchet type stop, for when you want to 'twist' the work. When not twisting the work the adjustable end would turn freely.

    When working, we did something similar to make twisted pair wire. Wire was spooled off through a spindle to the required length, and cut. Then the spindle would grip the two wires and start rotating, while the far end didn't rotate. This end would then move toward the spindle (rotating end) as the wire twisted and got shorter due to the twisting.
     
    Last edited: May 5, 2017
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  12. RogueRose

    Thread Starter Member

    Oct 10, 2014
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    Thanks for all the suggestions on this problem. I think I found out a way to use one motor, allow for axial movement of one side of the shaft as well as de-linking the moveable side from the main drive shaft so that side can be slowed or stopped if needed.

    For those wondering why this is needed, working with heated plastics, glass, and some wires/bundles (in a mix of the plastics and glass) need these functions of movement and slowing/stopping while one side remains turning. I can show the end result when it is finished.

    My idea is to use a single drive shaft to turn the one fixed side - pulley on drive shaft and pulley on material axis. the moveable side will have the same pulleys but will have 4 other pulleys which will re-direct the directions to allow for the pulley belt to run the length of the drive shaft and material axis. One pulley will be either mounted on a spring or will have a tensioner pulley to take up/give slack to allow for movement of the material axis. As the material moves closer to the other side, the tensioner pulley gets pulled closer and to move further away, the tensioner pulls out, taking up the extra slack from the movement of the material axis. This is compeletly difficult to explain so I'll post a drawing of it once I get a minute ot two.

    Thanks again for the help!
     
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