Hello, I'm in the early stages of designing my plasma table. My question is regarding step and direction signals. I purchased the Acorn plasma package. The table dimensions are 6 X 12. I'm actually repurposing an old Torchmate III table. I intend to use Stepper Online Nema 24 kit including:
4 x CL57T-V41: Closed Loop Stepper Driver V4.1 0-8.0A 24-48VDC for Nema 17, 23, 24 Stepper Motor
4 x 24HS40-5004D-E1000: Nema 24 Closed Loop Stepper Motor 4.0Nm/566.56oz.in Encoder 1000PPR
2 x LE-350-48: 350W 48V 7.3A 115/230V Switching Power Supply Stepper Motor CNC Router Kits
1 x CABLE-PC-1: RS232 Debugging Cable
4 x CE2M: 1.7m(67") Long Encoder Extension Cable for Closed Loop Stepper Motor
4 x CM2M-20: AWG20 1.7m(67") Long Motor Extension Cable with GX16 Aviation Plug
I can't seem to get a straight answer regarding encoder cable length. Obviously, a table of this size will require long cables. My question is should all encoder cables be the same length? Looking at Y as a paired axis and running a 4th axis for rotary. The kit cables are 20 ga. shielded. If cables were "cut to length", one y axis cable would be 18' and the other y axis cable would be 28'. Is this a problem?
Encoder cable length
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Encoder cable length
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Re: Encoder cable length
Encoder cables not being the same length will not cause you any problems at this scale. You'll want to make sure they are shielded the whole length.
Were you worried about the voltage drop or differences in time it takes for the signals to travel from one end to the other?
Encoder cables often do use really thin conductors so the resistance from length does become significant sooner. However, assuming 28 AWG conductors for the encoder cables, you are looking at less than two ohms at 28 feet. If they are 20 AWG then resistance will be even less. The drop will not be significant enough at those lengths to do anything. I'm calculating about 0.04 volt drop assuming the encoder output drivers are basic logic level drivers.
There will be a slight time delay in the signals from the longer encoder cable but it is going to be insignificant by orders of magnitude.
Were you worried about the voltage drop or differences in time it takes for the signals to travel from one end to the other?
Encoder cables often do use really thin conductors so the resistance from length does become significant sooner. However, assuming 28 AWG conductors for the encoder cables, you are looking at less than two ohms at 28 feet. If they are 20 AWG then resistance will be even less. The drop will not be significant enough at those lengths to do anything. I'm calculating about 0.04 volt drop assuming the encoder output drivers are basic logic level drivers.
There will be a slight time delay in the signals from the longer encoder cable but it is going to be insignificant by orders of magnitude.
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Re: Encoder cable length
Thank you very kindly! I have spoken to several "authorities" at Lincoln and Stepper Online and was getting conflicting info. My question was about voltage drop and timing. I wasn't sure if the controller would compensate or the encoder. However, it appears to be a moot point. Thanks again!
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Re: Encoder cable length
No problem! Unfortunately, I got a little distracted and did more math...
In this case, assuming the encoder cable is similar to Cat5 cable, the delay from the encoder to the drive is about 40 nanoseconds for 28 feet and 27 nanoseconds for the 18 foot cable. That difference is about 13 nanoseconds which is a grand total of 0.00078 inches of difference at 1000 inches / minute.
These are simple incremental encoders and on the low end of resolution so they are going to be low speed and moderate rise time signals. The cable length and characteristic impedance etc. aren't going to be that critical.
On drives with high speed serial communications for the encoder, then the length becomes a bit more important. Definitely have to follow the manufacturer's recommendations for cable length. Sometimes they say to use a thicker gauge conductor which I suspect is often for the absolute encoder battery.
In this case, assuming the encoder cable is similar to Cat5 cable, the delay from the encoder to the drive is about 40 nanoseconds for 28 feet and 27 nanoseconds for the 18 foot cable. That difference is about 13 nanoseconds which is a grand total of 0.00078 inches of difference at 1000 inches / minute.
These are simple incremental encoders and on the low end of resolution so they are going to be low speed and moderate rise time signals. The cable length and characteristic impedance etc. aren't going to be that critical.
On drives with high speed serial communications for the encoder, then the length becomes a bit more important. Definitely have to follow the manufacturer's recommendations for cable length. Sometimes they say to use a thicker gauge conductor which I suspect is often for the absolute encoder battery.
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Re: Encoder cable length
I would suggest spending 40 bucks per drive more and getting the A6 400W Servos.
They have more options and are much faster than the steppers.
Uwe
They have more options and are much faster than the steppers.
Uwe
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Re: Encoder cable length
Hello Suntravel,
Thanks for your input. I looked at your suggestion and discovered that the total cost will be almost double. I'm not opposed to servos and I'm open to the suggestion however, I have no experience in the servo realm. I've been back and forth with Stepperonline for weeks regarding my potential order. Having to wait 15 hours after every communication takes a fair amount of time as well as getting my point across is sometimes challenging. I would prefer not to get all of my info from the vendor.
I would need a fair amount of input to consider this direction. Can you suggest a good resource with very specific instructions regarding building a control enclosure for servo operations using the acorn? I'm certainly up for a challenge but will require significant research.
Thanks
DC
Thanks for your input. I looked at your suggestion and discovered that the total cost will be almost double. I'm not opposed to servos and I'm open to the suggestion however, I have no experience in the servo realm. I've been back and forth with Stepperonline for weeks regarding my potential order. Having to wait 15 hours after every communication takes a fair amount of time as well as getting my point across is sometimes challenging. I would prefer not to get all of my info from the vendor.
I would need a fair amount of input to consider this direction. Can you suggest a good resource with very specific instructions regarding building a control enclosure for servo operations using the acorn? I'm certainly up for a challenge but will require significant research.
Thanks
DC
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