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Author Topic: Motors and AstroEQ  (Read 98 times)

AradoKYSky

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Motors and AstroEQ
« on: June 10, 2020, 21:33:25 »

Hello,

I am using a custom motor to run a telescope using RPI 3 B+ and Astroberry. I recently had a problem with a driver. It would get very hot at 1.8A. Then it quit. I am reviewing my wiring to make sure I have it setup correctly.

My table from my motor, NEMA 17, is as follows


Step  A          B         A'          B'
1       +         +         -           -
2       -          +         +          -
3       -          -          +          +
4       +         -          -           +
CW is walks down
CCW walks up.

Both NEMA 17 are paired from the same specs.

Per the AstroEQ scematic, both RA and DEC are pinned the same way.
Table 1
2 = B1
3 = A2
4 = B2
5 = A1

A motor is geared as in diagram 1 of 4 where:
Table 3
Black = A
Green = A'
Red  = B
Blue = B'

At the motor to the AstroEQ, I should have the following

Table 4
Red = B1 = 2
Green = A2 = 3
Blue = B2 = 4
Black = A1 = 5

Here is my problem. At 128x forward works, reverse stutters. 600x, 700x, and 800x forward and reverse works. I am looking for the optimal configuration. I have been attempting different settings. The image supplied works as described.





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TCWORLD

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Re: Motors and AstroEQ
« Reply #1 on: June 12, 2020, 00:12:02 »

Hi,

You've got your connections crossed. The drivers and motors all use different naming schemes. In the A1/A2/B1/B2 scheme, A1/B1 are the first coil, and A2/B2 are the second coil.

As your motors are labelled A and B, where A is one coil, and B is the other coil. then the RJ11 cables should be wired as A B B A per the FAQ. It doesn't matter which coil you use for A, and which coil you use for B, nor which end of each coil is which, as long as you are consistent on both RA and DEC wiring.

In your case, the simplest way to correct your wiring is to swap the red and green wires, so:

  • N/C
  • Green
  • Red
  • Blue
  • Black
  • N/C
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Tom Carpenter (AstroEQ)

AradoKYSky

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Re: Motors and AstroEQ
« Reply #2 on: June 12, 2020, 02:37:13 »

Hello Tom,

Thank you. I must have goofed then.

I should have provided this schematic first. The schematic for both motors is as follows.

A ----
       ||
A'----

B ----
       ||
B'----

Per the Motor table I provided.

AB  = Step 1
BA' = Step 2
A'B'  = Step 3
AB' = Step 4

Then, I would have
A1/A2 = First coil, and B1/B2 = Second Coil.

Given the FAQ, the ABBA schematic then is as you describe. But A' is the lead. To me, the pattern is flipped depending on which pin gets the pulse first. The table says A is the first step. Given the logic was yours, which pin fires first step, 2 or 5, to match the table? 

Going backards is the same table but starting at A. Both forward and backwards have A as the first step.

Should this be the sequence if pin 2 gets energized first.

2 = A = Black
3 = B' = Blue
4 = B = Red
5 = A' = Green

or


The Schematic shows this sequence with supplied charge

1B = 2 = +
2A = 3 = -
2B = 4 = -
1A = 5 = +

The motor is expecting and using FAQ ABBA. Leading variable is always positive.

A + B = 2 + 4 = Step 1
B + A' = 4 + 5 = Step 2
A' + B' = 5 + 3 = Step 3
A + A' = 2 + 5 = Step 4

For Reverse, the motor is epecting and using FAQ ABBA

A' + A = 5 + 2 = Step 1'
B' + A' = 3 + 5 = Step 2'
A' + B = 5 + 4 = Step 3'
B + A = 4 + 2 = Step 4'

This assumes that the FAQ ABBA is good and the motor likes the setup. However, the schematic is different. What does AstroEQ bring to the motor?

Ok. I used my Fluke to test what is at the AstroEQ. Starting from the Driver, North is pin 1.  has Given the pins in the RJ11 where 2 3 4 5 and the driver, they each tap out to be as follows.

2 = A1 = A = Black = +
3 = B2 = B' = Blue  = -
4 = B1 = B = Red = +
5 = A2 = A' = Green = -.

Therefore the PDF is not correct for the DRV8825. The FAQ is correct for the DRV8825.  Thank you for your assistance.

T
 
« Last Edit: June 12, 2020, 15:26:16 by AradoKYSky »
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TCWORLD

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Re: Motors and AstroEQ
« Reply #3 on: June 12, 2020, 09:26:37 »

Different motor drivers have different naming conventions for the pins. The net labels on the AstroEQ are following the A498x driver naming where 2x is one coil, and 1x is the other coil. The DRV882x and several other drivers are named differently, with Ax is one coil and Bx is the other coil.

Your suggested pinout has each coil being driven by both drivers (e.g. + of one driver - of the other), this is wrong. It will prevent the motors spinning properly, and will cause overheating of the drivers and motors due to inability to current regulate.



Follow the ABBA wiring scheme, it is correct for all of the 16-pin Pololu driver modules.

For your motor A/A' are one coil, and B/B' are the other coil. Any of the following are valid wirings:

Code: [Select]
Option 1:
x  A   B   B'  A'  x

Option 2:
x  A   B'  B   A'  x

Option 3:
x  A'  B   B'  A   x

Option 4:
x  A'  B'  B   A   x

Option 5:
x  B   A   A'  B'  x

Option 6:
x  B   A'  A   B'  x

Option 7:
x  B'  A   A'  B   x

Option 4:
x  B'  A'  A   B   x

If the motors rotate in the wrong direction (i.e. sidereal tracking spins east not west), you select the "Reverse" option in the configuration utility to correct for it.
« Last Edit: June 12, 2020, 09:35:55 by TCWORLD »
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Tom Carpenter (AstroEQ)