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velocity
« on: June 27, 2008, 10:07:03 AM »
I need to speed up my machine.  The only way I can seem to up my max speed is to change my steps per.  Any suggestions?  My steps per is set at 15245 and I can only go up to about 98imp.  I need to move at about twice that.

Thanks

Offline jimpinder

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Re: velocity
« Reply #1 on: June 27, 2008, 10:27:39 AM »
I cannot see how changing your steps per unit will affect your velocity, one is a distance, the other a speed.

The only way to change your velocity is, either get the motors to turn faster, or reduce or introduce step up gearing between the motors and the table (or cutter).

If you increase the gear ratio between the motor and table (or cutter) then your accuracy will suffer, in that each step will mean a move of greater distance. Your steps per unit seem an odd number anyhow at 15,245 how do you arrive at that.

As far as the motors turning faster is concerned, I take it you have altered the distance per minuter upwards and your motors are now complaining and will not turn any faster - are they steppers or servo's. I recently increased my steppers by a factor of 10 by rewiring, and you can also increase the voltage to get them to turn faster. Servos I don't know much about.

I don't know what you are trying to move - is it a gantry? Is it smooth enough to move at that speed. There will be a physical limit to the weight your motors can accelerate (and decelerate) - and it may be that your motors have reached their limit, and to move faster, larger motors will be necessary to get over the inertia.

Not me driving the engine - I'm better looking.
Re: velocity
« Reply #2 on: June 27, 2008, 10:36:50 AM »
In motor tuning when I change the steps per  then it changes my max velocity that I can set.  I set my steps per by distance traveled and compared that to what the 'axis calibration" came up with.   The problem I'm having is that the max setting for velocity in motor tuning is 98 with steps per at 15245.  It is a cantilever gantry used for waterjet work.  It is very smooth at 130 ipm.  The only way I can seem to get it to that speed is to boost my feed rate to 200%

Thanks
Re: velocity
« Reply #3 on: June 27, 2008, 10:38:32 AM »
I am using servos  thanks

Offline Hood

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Re: velocity
« Reply #4 on: June 27, 2008, 10:45:52 AM »
The Steps per cant be changed or your machine will not be accurate, you need to work out what steps you need to move 1 unit then stick to that. If you need to get faster then you can increase the kernel speed on the Ports and Pins page, this will determine how fast you can set for your given Steps per setting. You are probably at the default 25KHz kernel and you should try at 45KHz and see if things run fine.
Hood
Re: velocity
« Reply #5 on: June 27, 2008, 11:13:02 AM »
THANK YOU!!!

Taking it to 45 got me to 175 ipm, which is close enough.  Runs great thanks again

Offline Hood

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Re: velocity
« Reply #6 on: June 27, 2008, 11:15:46 AM »
You could try the kernel  faster if you wanted but some computers wont put out more than 45KHz smoothly enough while others can run 100MHz no problem. Some computers wont even run the 45KHz and struggle at 25KHz, its all trial and error I suppose
Hood

Offline jimpinder

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Re: velocity
« Reply #7 on: June 27, 2008, 01:30:48 PM »
That was simple -

But you now, if you want to be accurate, need to set your steps per unit (inch) to an accuurate figure, instead of just setting them at a figure to suit a speed that you want to achieve - otherwise how are you going to draw out what you need to cut.

This means calculating the number of steps.
How many steps do your motors need per revolution (A) is there any gearing to your leadscrew (B) {1 for direct drive}: how many turns does your leadscrew make to move 1 inch (C).
Multiply A x B x C = number of steps per inch.
Set this in your motor configuration and then adjust the speed upwards to what you need to achieve. Increase the speed first til it complains then back off til it runs smoothly, then increase your acceleration until it complains then back off.
Not me driving the engine - I'm better looking.
Re: velocity
« Reply #8 on: June 28, 2008, 09:30:26 AM »
I appreciate the help.  That's why I couldn't change my steps per.  My accuracy is fine.  I just needed to gain speed. 

thanks