maximum speed
05 Nov 2013 04:26 #40541
by yoavmil
maximum speed was created by yoavmil
Hi, Im trying to make a really fast and strong machine, about 500 mm/sec and 10000 mm/sec^2 accelartion (about 'G'). I am currnetly using arduino as the motion controller, and I think its not fast enought, so I considiring checking linuxCNC.
can you please think of any bottle-neck, that will limit my speed? the serial port? the 'realtime linux'? the CPU?
can you please think of any bottle-neck, that will limit my speed? the serial port? the 'realtime linux'? the CPU?
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06 Nov 2013 00:58 #40556
by andypugh
Maybe the motors. What type of motor do you intend to use? What sort of drive?
CPU might be a problem depending on how frequently you want to update the position calculations. At 500mm/sec and 1kHz servo-thread you will only be able to issue a position update every 0.5mm. If you require a more accurate trajectory than that (at that speed) then you will need to find a CPU/board combo that can handle a faster-than-usual servo thread rate.
Are you thinking in terms of steppers or servos?
Replied by andypugh on topic maximum speed
can you please think of any bottle-neck, that will limit my speed? the serial port? the 'realtime linux'? the CPU?
Maybe the motors. What type of motor do you intend to use? What sort of drive?
CPU might be a problem depending on how frequently you want to update the position calculations. At 500mm/sec and 1kHz servo-thread you will only be able to issue a position update every 0.5mm. If you require a more accurate trajectory than that (at that speed) then you will need to find a CPU/board combo that can handle a faster-than-usual servo thread rate.
Are you thinking in terms of steppers or servos?
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06 Nov 2013 02:25 #40560
by yoavmil
Replied by yoavmil on topic maximum speed
I currnetly have
very large steppers
and drivers, Im pretty sure they wont be the bottle neck.
any ways, we will probably change to servos soon.
Im am not familiar with how to work with servos, so I don't understand
If I'll buy a strong intel I7 computer, that has about 2.4GHz, wont it solve any problems of that sort?
Im sorry if I am a little clueless.
any ways, we will probably change to servos soon.
Im am not familiar with how to work with servos, so I don't understand
CPU might be a problem depending on how frequently you want to update the position calculations. At 500mm/sec and 1kHz servo-thread you will only be able to issue a position update every 0.5mm
If I'll buy a strong intel I7 computer, that has about 2.4GHz, wont it solve any problems of that sort?
Im sorry if I am a little clueless.
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06 Nov 2013 02:42 #40562
by andypugh
Unfortunately it isn't as simple as getting a PC with a very fast CPU, as the limiting factor is the latency, how fast (and how reliably) the system can switch to the real-time task.
www.linuxcnc.org/index.php/english/forum...-the-latency-problem
Explains some of the factors.
You also need to consider the maximum step rate you require. It is hard to get above 20kHz step rate with software stepping. This is probably slower than your Arduino was managing, which may be a disappointment to you.
For very fast step generation I think you need to look at one of the hardware-based step generators. The main options supported by LinuxCNC (and from vendors that support LinuxCNC) are the Pico-systems USC ( www.pico-systems.com/univstep.html ) ($250) which connects to the Parallel port (but uses the p-port as a communications bus) or various combinations of hardware from Mesa (www.mesanet.com). The popular Mesa combination at the moment is the 5i25 + 7i76 combination ($200). Both can generate steps faster than any stepper can follow, so the choice would be on bus type or the onboard hardware extras.
You will get a much better result with a $100 Atom motherboard and a $200 FPGA card than with a $1000 PC and no FPGA card.
Replied by andypugh on topic maximum speed
If I'll buy a strong intel I7 computer, that has about 2.4GHz, wont it solve any problems of that sort?.CPU might be a problem depending on how frequently you want to update the position calculations. At 500mm/sec and 1kHz servo-thread you will only be able to issue a position update every 0.5mm
Unfortunately it isn't as simple as getting a PC with a very fast CPU, as the limiting factor is the latency, how fast (and how reliably) the system can switch to the real-time task.
www.linuxcnc.org/index.php/english/forum...-the-latency-problem
Explains some of the factors.
You also need to consider the maximum step rate you require. It is hard to get above 20kHz step rate with software stepping. This is probably slower than your Arduino was managing, which may be a disappointment to you.
For very fast step generation I think you need to look at one of the hardware-based step generators. The main options supported by LinuxCNC (and from vendors that support LinuxCNC) are the Pico-systems USC ( www.pico-systems.com/univstep.html ) ($250) which connects to the Parallel port (but uses the p-port as a communications bus) or various combinations of hardware from Mesa (www.mesanet.com). The popular Mesa combination at the moment is the 5i25 + 7i76 combination ($200). Both can generate steps faster than any stepper can follow, so the choice would be on bus type or the onboard hardware extras.
You will get a much better result with a $100 Atom motherboard and a $200 FPGA card than with a $1000 PC and no FPGA card.
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