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bitraf / bitraf-cnc

CNC-related research and projects at Bitraf
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Stepper drivers #3

Open Jaknil opened 6 years ago

Jaknil commented 6 years ago

What does the pins on the driver do? Check these:

What is the pin spacing on the card? (To be able to design a connector)

What does the second pin do for each pin? Is it to be able to pull it HIGH/LOW permanently?

How many steps per mm does the shopbot take? Is it compatible with the standard GRBL pulse length?

Bonus: Is there any settings we want to tweak on the stepper driver like closed loop error tolerance?

JensDyvik commented 6 years ago

I have committed the manual here. See page 29.

In default shopbot settings the X and Y motors have 97.748705 steps per mm. Z has 117,298445 steps per mm. It might be that these values need to be multiplied by 5. Also note that the interface pins on the driver allows for microstepping to be changed on the fly. The oriental motors have 1000steps per resolution and a 1;7.2 gear box.

So default is 7200 steps per resolution. Exact pinion circumference is unknown, by estimate rough 130mm for X and Y. Pinion comparison with a 45mm circumference pinion here

I think default pin spacing is the very common 2.54mm on the ribbon cable connector on the old card. The new card does not have cable but plugs right into the drivers. It might be handy for us to source rady made ribbon cables with the driver connector. See page 34 of the manual.

about the second pin for each pin, I think this is a separate GND for each signal. Not sure about permant high/low.

About bonus alarm tweaking, I think the driver and alarm settings are quite ok the way they are. These can later be tweaked without changing our HRBL card

Jaknil commented 6 years ago

I ran the numbers and the setting for 1000 steps / revolution should work fine. We will get a max speed of 542mm/s (32,5m/min) at 30kHz. The smallest movement will then be 0,02mm (/ step) which isn't fantastic but should absolutely be good enough. (Calculated for 130mm pinon).

What I couldn't calculate my way to is the value of 97.748705 steps per mm. Were did that come from? Is it a shopbot setting? Odd if so.

Value Unit Comment
1000 puls/rot pre gearbox Stepper driver setting
7,2 gearbox ShopBot PRSalpha
7200 steps per rot,  
0,05 deg per pulse ink gearbox  
130 cicumference ca?  
0,018 mm/pulse Min movement, ok
55,38 steps/mm with these settings  
97,748705 steps per mm Shopbot vaule from jens?
30000 puls per sec max from arduinno  
4,17 rotations per sec max  
541,67 mm/s Max travel speed, more than needed
32,5 m/min  
45,7 m/min shopbot stock max speed, never used

https://docs.google.com/spreadsheets/d/1Y3MvswSqBQ8RFYrYUnVyuyF4CHkhxUoRPI-_O0XpTAo/edit?usp=sharing

JensDyvik commented 6 years ago

I am puzzled as well by the default values in the shopbot firmware.

The shopbot drivers are capable of microptepping x5 and x10. They can also do half steps. I am not sure what stepping level shopbot3 uses. Default shopbot3 settings do use different step levels for jog and and cut commands. If our current setting is 500steps (before gearing) for jogs and 1000 (before gearing) during cuts, we are all good with the GRBL firmware.

If what we are accustomed to today is 5,000 or 10,000 steps (before gearing) during cuts, we need to do some testing to verify that the reduction in motion smoothness and precision is acceptable.

Jaknil commented 6 years ago

Notes: Connector to connect to stepper driver is 3M 10136 (IEZ? ) https://no.farnell.com/3m/10136-3000pe/plug-mdr-solder-36way/dp/9292659