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Author Topic: MOTOR LOCK-UP ON RAPID MOVEMENT  (Read 15090 times)

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Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #10 on: April 25, 2006, 06:40:58 AM »
taking it down to 25KHz will take a little stress of the computer... If you don't need it up that high then why not :) Please be sure to set the step to 5us long.
Thanks
Brian

Bryan, I will give your suggestion a try in the morning.  Can you explain how kernel speed cause a motor to stall?  I appreciate all your input.

Steve
Fixing problems one post at a time ;)

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Offline fdos

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Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #11 on: April 25, 2006, 07:50:43 AM »

I attached the specs on the stepper motors. I have size 34 P/N PF4913A-05 on all three axis.

Steve...

Looking at that there are two 1280 oz/in motors.   Looks like you have been wise and bought the lower inductance one.   Although they dont mention it at all.   But my guess is the lower current version 34 P/N PF4913A-11 is the higher inductance versoin.

It may be that you are just not driving them with enough voltage.   I know nothing of the drives you are using..

I personally wouldnt of had the 2:1 reduction with steppers.   It generally makes matters worse, and they need to spin faster with it.

I'm currently retrofitting a small vertical machining centre and have 920oz/in steppers driving 5mm pitch ballscrews 1:1 through compliant couplings.   I get over 5000mm/min rapids with no stalling.  I'm using 72v supply through Parker drives.  Motors rated at 4.2A.

The same motors struggled to spin at an equivilent of 3000mm/min on the bench.

Anyway you can try it without the reduction?

I really dont think this is a signal jitter problem..


Wayne...
Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #12 on: April 25, 2006, 08:42:54 AM »
Wayne,  I believe that the package I bought has Prodrive 2000 drives but they don't advertize or publish this in their documentation.  They stated that the power supply is a 48V DC 13.8 amp unit.  They recommended using a 2:1 ratio based on their past experience with this combination on larger routers.  My router has a fairly large working area of 48" x 96" x 24".  To remove the gear redcution I would need to buy some more parts. Your speeds are much higher than anything I have ever seen with my machine.  That might be because of the gear ratio setup requiring the motors to spin faster to turn the screw.  Does this new info give you any other ideas?

Brian,  It might be hard for me to reproduce the problem since it only occurs once in a while.  I will give your suggestions a try and get back to you on what I find.

I really appreciate all the feed back.  This forum has really help me achieve things that I could never of imagined or figured out on my own. I am in debted to you guys.

Steve
Regards,
Steve

"Caution: Cape does not enable user to fly."

- Batman costume warning label, Wal-Mart, 1995

Offline fdos

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Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #13 on: April 25, 2006, 09:08:25 AM »
I believe that the package I bought has Prodrive 2000 drives but they don't advertize or publish this in their documentation.  They stated that the power supply is a 48V DC 13.8 amp unit.  They recommended using a 2:1 ratio based on their past experience with this combination on larger routers.  My router has a fairly large working area of 48" x 96" x 24".  To remove the gear redcution I would need to buy some more parts. Your speeds are much higher than anything I have ever seen with my machine.  That might be because of the gear ratio setup requiring the motors to spin faster to turn the screw.

Steve.   Well if it does have Prodrives in there, they are ripoff's of the Gecko G201.  The Gecko's at least are rated to 80v.

Re: reductions.   It's all about tradeoff's, with 2:1 reduction you probably more than half the torque at your target rapid speeds, as the stepper looses torque most at higher speeds.  I dont quite get their logic!   If it's a wood router then it needs much less torque than my machine cutting metals.  You will be wanting to cut at higher speeds than me.   If you were using servo's I'd understand it.

My vmc yesterday was cutting Al-alloy during testing at 1000mm/min (40"/min) 3/4" endmill 40% stepover and 3mm (1/8") deep cuts, no problem with it at all.  and thats direct drive steppers with lower holding torque than yours.  No idea of their torque when actually moving though.  These are chinese square body motors.

Steppers can be  a pain to get right, but very possible!  Doesnt help that there's so much duff information out there!

Offline fdos

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Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #14 on: April 25, 2006, 09:34:14 AM »
Steve....

Just had an idea for something you can try..

Take the motors off the machine, and run them one at a time on the bench.

Increase your max velocity in mach until they will stall on the bench, the motor will just stop turning an squeal.

They probably wont all behave the same, but that soesnt matter.

Now lower velocity until they no longer stall on long rapids.

Now the figure you get will be LOWER than what you SHOULD be able to achieve loaded by the machine.

In my case I was able to increase max velocity by over 50% when loaded by the machines mass and friction..

Let us know what you find..

Wayne....
Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #15 on: April 25, 2006, 11:04:09 AM »
Wayne,

Once I establisht the maximum speed on the bench are you suggesting that I increase the velocity after I put them back on?

Steve
Regards,
Steve

"Caution: Cape does not enable user to fly."

- Batman costume warning label, Wal-Mart, 1995

Offline fdos

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Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #16 on: April 25, 2006, 11:18:51 AM »
Steve..

You should be able to!   They should go faster than the speed at which they stalled on the bench.

If they dont, then I'd expect that they are not seeing enough load.  Or if they stall at a lower speed you got some serious friction, but I very much doubt that will happen.

I still reckon you might be better off at 1:1.    You have some big motors there.

What are you intending to cut?

Wayne...
Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #17 on: April 25, 2006, 11:25:32 AM »
Wayne,

I just order the new pulleys and belts to give the 1:1 ratio a try.  I am cutting hard maple blocks, thin gage aluminum sheet, and fiberglass. We make aircraft composite and sheet metal parts for general aviation aircraft.

Steve
Regards,
Steve

"Caution: Cape does not enable user to fly."

- Batman costume warning label, Wal-Mart, 1995
Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #18 on: April 26, 2006, 06:44:57 PM »
Hi Guys,

I ran a binch of bench level tests with the motors removed from the machine and here is what I found:

Started with a basic motor tuning / mach 2 setup of:
Units / sec^2 = 5
Steps per unit = 20000
Kernel speed set at 25000 Hz

Checked effect of Velocity Variations:
Max = immediate stall
1.0 = immediate stall
0.95 = runs a little then stalls
0.90 = runs with missed steps every 2 or 3 seconds (sputters and jerks motor)
0.85 = runs with less missed steps (counted 7 or 8 sputters and less of a jerk)
0.80 = runs a little better than 0.85 but still misses steps (counted 6 sputters)
0.75 = even better but still sputters (jerking is gone)
0.70 = even better but still misses once in a while
0.65 = only misses a couple times on a long run
0.60 = runs without missing steps but still a little loud
0.55 = runs smoother and less noisey
0.5 = runs quietly and smooth

The sputter or missed step is basically a change in the noise emmited from the motor and sudden vibration. At higher velocities it is visible but at lower velocities it is not visible (can only feel and hear it). The best way I can describe it is like its about to stall but keeps on going.  My original setup used a velocity of 0.5 when I had a motor stall for five to ten seconds (still mounted to the machine).

Does this provide you any insight that could lead to a solution or do you have any other suggestions?

Steve




Regards,
Steve

"Caution: Cape does not enable user to fly."

- Batman costume warning label, Wal-Mart, 1995
Re: MOTOR LOCK-UP ON RAPID MOVEMENT
« Reply #19 on: April 26, 2006, 07:59:22 PM »
As a test try Sherline mode and tell us if that makes it better.
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com