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  #1  
Old Mon 12 February 2007, 03:46
Irfanulla
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CNC Router with Servo motors & belt drives (non-MechMate) - Bangalore, India

Hi all,

I am intending to start a thread pertaining the build of my machine which will use PMDC motors converted to servos using US Digital optical encoders and UHU controllers, so far the controller has been built and awaiting the mounting on the machine.

The machine i am getting together is based on teh mechmate and thats why I want the thread to be on this forum. Yup there are variations to the design but only in areas where i needed the motors to be mounted and so on....

I hope this thread has the right location.

So far I have done my design in Solidworks - only X axis and the y car which I still think are incomplete a few pics for ref.
  #2  
Old Mon 12 February 2007, 04:09
Irfanulla
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  #3  
Old Mon 12 February 2007, 05:05
Gerald_D
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Interesting...
  #4  
Old Mon 12 February 2007, 07:25
Mike Richards
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It took a minute to realize how your design worked. Am I guessing right that you are using a single servo to turn a jack-shaft that has spur gears on each end?
  #5  
Old Mon 12 February 2007, 07:33
Gerald_D
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I thought those "spur-gears" were belt pulleys, with the final pulley and pinion still to be shown?...

I have a scheme for mounting the stepper motors roughly where the "spurs" are now (motors pointing inboard) and then running toothed belts down to the pinions....

How will the y-car drive work? How will the y-car hold-downs work if the x-jackshaft is in the way? Lots of curious questions to take me on a dangerous side-track, but I promise I will resist.
  #6  
Old Mon 12 February 2007, 07:44
Irfanulla
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Mike, Geral is right, i mentioned that these are just incomplete pictures and I am working on them yet, as I am going to get it done at one of the fabrication houses here. The reason I will be posting the images is to get more out of you there so that i correct my mistakes as well...

Let me finish the 3d modelling and then post it so that there is some clarity.

Gerald U have mentioned a scheme with motors running the spur with toothed belts kindly provide me with images or links

the x jack shaft will not come in the way, for the work , its on the same height as the cross member tube for the y car is.

Regards
Irfan
  #7  
Old Mon 12 February 2007, 12:43
Irfanulla
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some more



  #8  
Old Wed 14 February 2007, 11:19
Irfanulla
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My V rollers are in.

  #9  
Old Wed 14 February 2007, 11:39
Ali Ahmad
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Hello Irfanulla
Your design looks interesting.I am just getting started in solidworks myself.Where did you get your V rollers?
thanx Ali
  #10  
Old Wed 14 February 2007, 18:35
Mike Richards
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Irfanulla,

That design is very interesting. It's given me a few new ideas. I am wondering, however, how much effort would be required to replace a wornout or broken belt?
  #11  
Old Wed 14 February 2007, 22:43
Gerald_D
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Mike, the old trick in this situation is to hang one or two spare belts over the through shaft from the beginning. (Tied out of the way with wire or nylon ties). And then 10 years later when you need the first replacement, you find the spare has gone hard through lack of exercise and it breaks in a few days. But, if you don't hang a spare there, the first one only lasts one year...
  #12  
Old Thu 15 February 2007, 11:42
Irfanulla
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Ali,

I got the V rollers turned at a friends place, he got it heat treated and ground too.......

Mike nice Q well initially i did want to go with a gear box, but ruled out due to the costs......U can say that the pain in replacing the belts is a necessary evil......any idea out of it is welcome

Gerald ur idea might work but i am thinking of using gates poly chain belt which i suppose has a long life span....

Thats it for now
CYA
  #13  
Old Thu 01 March 2007, 10:33
Irfanulla
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Hi all,

Finally from Manjeet's idea I got a automotive timing belt from gates for 3.5USD thats INR 165 its length is around 24 inches and a 3/4" wide, I even got the timimg belt pulleys which are from a suzuki car called teh Maruti 800 in India with a idler pulley. the only thing is that both the timing pulleys have a bore of 24mm diameter and my motor has a shaft size of 19 mm dia......but the positive thing I got all the three for a prize of around INR300 thats under 7 USD....well teh smaller pulley does have two threaded holes through thm planning to use thm in some way.


  #14  
Old Thu 01 March 2007, 10:54
Gerald_D
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The only snag with that is your ratio is only 2:1 - you need a much bigger difference in pulley sizes to make it really worthwhile. Looks like the small pulley is about 20 teeth while the big one is 40 teeth? (if it is from a car engine the big one will be exactly double the small one)
  #15  
Old Thu 01 March 2007, 11:41
Irfanulla
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Gerald,

what would be teh correct ratio, the motors are rated at 2000rpm @ 110v, each motor is 625watts.

U are right its 20 and 40, iam planning for a bigger wheel probably 80 teeth at the pinion end...what do you suggest.

Thanks and Regards
Irfan
  #16  
Old Thu 01 March 2007, 11:54
Gerald_D
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Gut feel says around 8:1 in total - if you only have 2:1 at the motor, then you need another 4:1 at the gantry ends. I just mentioned the numbers for a feeling of how it works, you need to do all the calcs yourself.

Remember, if you only do 2:1 at the motor, then your long shaft and heavy couplings turn relatively fast. You might get flywheel effects - lots of torque needed to accelerate the inertias.
  #17  
Old Thu 01 March 2007, 11:56
Mike Richards
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If we assume that you want a top jog speed of 1500-inches per minute (25-inches per second) and that your final pinion gear is 30 tooth (20-pitch, 20-degree rack), then each revolution of the pinion gear will move the axis 4.71 inches. The formula to compute the gear ratio is (RPM * distance traveled per RPM) / inches per minute; therefore, (2000 * 4.71) / 1,500 = 6.28. A ratio of about 6:1 would be a good starting point.

(Edited: Gerald, you posted while I was thinking, but it looks like we're generally in agreement.)
  #18  
Old Thu 01 March 2007, 11:59
Gerald_D
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Mike, my mental calcs also said about 6:1 but I didn't trust the torque from that single motor to budge the gantry, so I inflated it a bit.
  #19  
Old Thu 01 March 2007, 12:10
Irfanulla
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Mike and Gerald,

The torque on my motors is 3Nm, and if the ratio is 6:1 then the torque gets multiplied right, thats 3x8=21 Nm, probably a lot of torque......right?

Regards
Irfan
  #20  
Old Thu 01 March 2007, 12:28
Gerald_D
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Multiplying the torque by the ratio is right. But, if 21Nm is a lot, is like like asking me how long is a piece of string....

Have a look at what the recommended stepper motors can do for torque.
  #21  
Old Thu 01 March 2007, 12:37
Irfanulla
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Gerald I got my multiplication wrong its 6x3=18Nm,a bit of confusion, i think the lot i might spend on the belts and pulleys may as well get me new steppers...........and their drivers what say....let me try the costs involved first, tomorrow i am gonna find the costs.

Good night....
  #22  
Old Thu 01 March 2007, 12:40
Mike Richards
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Gerald, you're right. I saw the 625-watt figure for the servo (slightly higher than the 560-watts that a Gecko can produce at full current and full voltage (7A at 80VDC) and didn't stop to think that the 625-watt rating is probably the PEAK rating and not the continuous rating.

I'm just guessing, but the continuous rating for a motor that size is probably between 50 and 75 watts, which would make an 8:1 or 10:1 ratio more practical. Using the figures from my post above, a 10:1 ratio would still give you about 940 inches per minute - or over 15-ips. That's faster than I jog my Alpha. (Although the Alpha can jog at 30-ips, I have mine set at 12-ips.)

(Edited: Boy you guys are fast. It takes a white-haired old man like me forever to run computations.)
  #23  
Old Thu 01 March 2007, 12:46
Gerald_D
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Mike, I'm cheating, I'm just sucking my thumb and sending Irfan to do the legwork.
  #24  
Old Thu 01 March 2007, 13:02
Mike Richards
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Conversion utilities on the web show that 1 Nm = ~140 oz*in. So 3Nm X 140 = 420 oz*in. Then, with an 8:1 gearbox, you'd get 8 X 420 = 3360 oz*in, which is roughly what the holding torque rating is for the TWO Oriental Motor Alpha steppers geared 3:1 that I have running my X-axis on my Alpha.

However, I'm still concerned whether the servo's rating is PEAK or CONTINUOUS.
  #25  
Old Thu 01 March 2007, 13:03
Irfanulla
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Gerald Mike having a nice time on my expense LOL...

Well teh motors are rated 625Watts contineous, they are huge PMDC motors with US Digital Encoders.....huge in my sence.......and are rated at 3Nm continuous...and powered by UHU servo controllers..

Now what say........

I do know my motors are a overkill already...




  #26  
Old Thu 01 March 2007, 13:06
Gerald_D
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A motor shaft of 19mm (mentioned in the pulley photo post) indicates more than a 625Watt peak motor? Lot's of vague guessing in the absence of real specs.

Edit: Oh, I thought you had gone to bed! Didn't see the last two posts before I did this one.
  #27  
Old Thu 01 March 2007, 13:14
Mike Richards
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It looks like we're posting on top of each other - which is good. It shows lots of interest.

If I were doing the project, and had those motors, my only real concern would be whether I could build a practical gear reduction unit. Using the jack-shaft approach gives two places that you could easily add gears. Two 3:1 reducers would give you 9:1 overall.

You know, it just might work.
  #28  
Old Thu 01 March 2007, 13:16
Gerald_D
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With these HUGE motors, you might get away with a 4:1 ratio total. Go and break up two more Maruti 800's and you are done! Go and get some sleep now.
  #29  
Old Thu 01 March 2007, 13:20
Irfanulla
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Gerald

check the specs of these motors here on the cnc zone link
http://www.cnczone.com/forums/showpo...&postcount=572
  #30  
Old Fri 02 March 2007, 00:23
Gerald_D
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Out of curiousity, how do you plan to use the other two motors on the other axes? Belts, pulleys, shafts, screws....?
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