| Motor currents |
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12.02.15 21:50
bbdn00 
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Motor currents
I have several questions regarding the tuning of the motor current.
I know the motors in the complete kit (42BYGHW811) are max rated above average for nema17 motors, so 2.5A instead of 1.7A. According to my research this gives the motor an above average acceleration. This current level means that they can handle the maximum current of the pololu drivers, only when operating 4 motors at full current I really get worried about the heat, those pololu boards heat up incredibly fast. I already applied small heatsinks on the boards and planning to put a fan above the board. Now for the questions:
1. When cooled, is it safe to work at maximum current for a couple of hours?
2.1 Is it wise(r) to buy replacement Pololu boards which are rated for higher currents?
2.2 Any suggestions for such boards?
2.3 Do these boards fit on the GRBL shield?
Thanks!
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17.02.15 09:57
bbdn00
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Re: Motor currents
Thanks! I guess that is what I was looking for. It can handle 0.2 amps more max and 0.5 more without excessive heating. However, is this just a "plug and play" replacement board? I read something about the DRV8825 having 1/32 microstepping instead of 1/16. Any changes I have to make within GRBL controller?
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23.02.15 20:04
bbdn00
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Re: Motor currents
Thanks again. I ordered them and post my findings as soon as I get them working.
Another question:
I have been trying out GRBL 0.9g but I can't get the probe function to work. I know the GRBL shield is not designed for 0.9 but should have most of the pins broken out. The probing pin on the arduino is A5 which as far as I can trace goes to the pin on the lower left next to VCC (and above STOP http://myhobby-cnc.de/wiki/lib/exe/fetch...:img_0850_t.jpg)
So when trying the auto-level function in Chilipeppr which usis thing probing function and this pin connect to ground it says the probing failed and I have to reset. Any idea what I am doing wrong?
Also, I cannot get the CoolEn function running on the shield. I am using a chinese 2 channel relay with a normally closed connection. As soon as I plug in the USB the fan starts running and does not stop nor can be controlled. I am connecting VCC to 5v on the shield, GND to GND and signal to the left pin next to CoolEn on the shield, also any suggenstions?
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26.02.15 14:37
bbdn00
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Re: Motor currents
Allright the probing works just soldered a wire to the A5 pin and ground on the arduino. Still haven't figured out the relay
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26.02.15 14:54
Ronald  Moderator
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Re: Motor currents
Hi bbdn00,
the pinout of the shield is independend of the version you are using. If you are not sure what signal goes to what pin, look at the schematics on the product page in the shop at the bottom.
I assume that the relay must be switched with a transistor or FET. The processor pin likely do not have enough power.
LG
Ronald
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13.03.15 14:14
bbdn00
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Re: Motor currents
Allright the DRV8825 arrived in the mail yesterday and I tried them out. Carefully measured and set currents using Vref and all seemed to be fine until I started cutting. It made an oval shape as if the X axis made different size steps than the Y axis.
Is there anything else I have to adjust? Such as the jumpers on the shield or the GRBL settings? These are my current GRBL 0.9g settings:
$0=30 (step pulse, usec)
$1=255 (step idle delay, msec)
$2=192 (step port invert mask:11000000)
$3=5 (dir port invert mask:00000101)
$4=0 (step enable invert, bool)
$5=0 (limit pins invert, bool)
$6=0 (probe pin invert, bool)
$10=3 (status report mask:00000011)
$11=0.050 (junction deviation, mm)
$12=0.002 (arc tolerance, mm)
$13=0 (report inches, bool)
$14=1 (auto start, bool)
$20=0 (soft limits, bool)
$21=0 (hard limits, bool)
$22=0 (homing cycle, bool)
$23=0 (homing dir invert mask:00000000)
$24=25.000 (homing feed, mm/min)
$25=250.000 (homing seek, mm/min)
$26=100 (homing debounce, msec)
$27=1.000 (homing pull-off, mm)
$100=33.330 (x, step/mm)
$101=33.330 (y, step/mm)
$102=320.000 (z, step/mm)
$110=2000.000 (x max rate, mm/min)
$111=2000.000 (y max rate, mm/min)
$112=250.000 (z max rate, mm/min)
$120=100.000 (x accel, mm/sec^2)
$121=100.000 (y accel, mm/sec^2)
$122=15.000 (z accel, mm/sec^2)
$130=700.000 (x max travel, mm)
$131=1000.000 (y max travel, mm)
$132=54.000 (z max travel, mm)
thanks
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14.03.15 11:53
bbdn00
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Re: Motor currents
I wasn't aware that there would be a change in step sizes so I guess I will have to play around with these settings.
Thanks Muggi you have been a great help again
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