High Current steppers.

Recently, I have become more active in the firmware department as I progress to getting my 20year old desktop CNC prepared for use as a Repstrap.

I took the old control box apart to replace the fans. Inside I found a bog standard system, which is controlled by step/dir signals. I upgraded the dos program to the demo version of Mach3.

The lead screws are 1mm pitch. There is a 45:24 tooth timing belt on the X axis.

My steppers are big monsters which are about 120CM in diameter, and require 3.5 amps. I just refurbished the control box, which uses standard step/dir signals. At issue is these only move the MM screw at a rate of 8 inches per minute. Yes I know I am mixing units. The DOS program only did inches. The calculated step rate is 27091/3 which the old program gave as 2.716

The reason I bring this up, is I was considering a firmware solution for micro-stepping based on the AtTiny25, Most of the solutions only go to 2 amps,

Probably the long term solution is to get some of the Gecko drivers, which seemed to be priced at about what the parts would cost for a DYI build.

The AtTiny25 ( 8 pin version of the chips used in the Arduino ) can directly PWM drive an H-Bridge through the 4 phased high speed PWM pins. This should handle micro-stepping. Communications is through serial interface. There is also an on die temperature sensor.

Any suggestions as if there is an cheap and easy to obtain discreet 4 amp H-Bridge design out there somewhere?

-julie

Is there a way you could stack or connect in parallel the parts that limit you to 2 amps? Or what if you just built 2 2-amp drivers and connected them together?

To be clear: this is just brainstorming. I am by no means an electronics expert.

There is an option to parallel the L298 outputs, At least when configured for a BLDC motor.

Connecting together silicon devices to increase power is a black art. This is why I am looking for a more proven implementation.

4 Amps is a lot of power. Unlike low current high voltage, High current low voltage can do some pretty serious damage.

-julie

It may be worth considering using something low current off the shelf like the A4983 as stepper controller/gate driver and driving higher power FET's from it to cope with the higher current steppers.

If you google gate drivers they look remarkably similar to the lower current output stages.

There may be something I am missing though.....

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Necessity hopefully becomes the absentee parent of successfully invented children.

the internal dead time and fast/slow decay modes, and the PWM too will not drive external fets properly. They will spend lots of time with floating gates and probably explode from being in linear zone while carrying current, or sending themselves into destructive oscillation from feedback effects.

Allegro do make a stepper controller that uses external fets, however reading about it on cnczone tells me that it is speed limited especially at low duty cycles because of the fixed dead-time logic. read up, make your own decision on this chip.

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Wooden Mendel
Teacup Firmware

Yup already have done and ordered some toshiba stepper driver chips (3A) and a better package to heatsink

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Necessity hopefully becomes the absentee parent of successfully invented children.

Tosh stepper chips have arrived now.

Hopefully I will get to have a play with them some time soon.

TB6560AHAHQ 3.5A 40v peak

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Necessity hopefully becomes the absentee parent of successfully invented children.