Author Topic: Motorshield that can run up to 10 motors from 2 pins (Read 6804 times)

Tamsyn · « **on:** August 22, 2012, 10:35:02 pm »

Just found this:
http://letsmakerobots.com/node/33842

It should be a small and simple shield that allows more than the (at most) 2 motors that the digispark can run now. I would think something along these lines should be good?

sparr · « **Reply #1 on:** August 23, 2012, 10:50:42 am »

Can you get that control IC in a small enough form factor for a digispark shield? AND enough headers for all 10 servo connectors?

MrCruzII · « **Reply #2 on:** August 24, 2012, 07:48:12 am »

You\'re also forgetting about power. Servos, even cheap RC servos, can draw a lot of current, north of 1A and more when taxed. The board would need to fit a regulator able to supply a peak of several amps to be on the safe side, otherwise the Atiny would self-reset.

ericlawshe · « **Reply #3 on:** August 28, 2012, 05:15:04 pm »

with this, could you drive 3 stepper motors? it would be cool to use the Digispark as the brains for a CNC mill.

sparr · « **Reply #4 on:** August 28, 2012, 10:04:33 pm »

A digispark could only be a very rudimentary CNC platform. There\'s a lot of number crunching involved in a good CNC controller, for things like acceleration. The atmega2560 in an arduino mega isn\'t completely up to the task.

ericlawshe · « **Reply #5 on:** August 29, 2012, 09:37:44 am »

@sparr - so then the arduino uno probably couldn\'t manage it either? bummer.

sparr · « **Reply #6 on:** August 30, 2012, 11:58:35 am »

There ARE CNC controllers that run off things as weak as an attiny85, and some that work from an Uno, but they aren\'t nearly as good as the ones that run from a Mega (like RAMPS). And even the ones using an atmega aren\'t as good as dedicated CNC controller hardware using beefy processors. If I was going to build a CNC controller today, it would probably be based on the Raspberry Pi.

Bluebie · « **Reply #7 on:** September 06, 2012, 02:59:53 am »

The digispark is about as powerful as an arduino - the tiny85 runs the same instruction set as the mega328 found in most recent arduinos, including hardware multiplication. The digispark runs at 16.5mhz, most likely autocalibrated off the usb port of a host computer, but by tweaking the OSCAL register in your program you can overclock the AVR as high as 30mhz - though 20mhz is all these chips are specified for. This lets you squeeze in a little more performance than the typical arduino running at 16mhz by an external crystal (so not configurable at runtime). Suggesting the tiny85 is somehow weaker than arduino\'s mega328 is incorrect.

sparr · « **Reply #8 on:** September 06, 2012, 10:35:03 am »

@Bluebie the major differences in the tiny85 and mega328 that are relevant to a CNC controller are as follows:

8kb vs 32kb of Flash, for storing program code. The acceleration logic alone in Marlin (an atmega328-based cnc controller) is more than 8kb.
512b vs 2048b of RAM, for storing variables. With less RAM, a controller won\'t be able to load as many instructions in advance, for look-ahead and pre-parsing.
2 timers with 2 comparisons each vs 3 timers (one 16-bit) with 2 comparisons each, for handling interrupts and acceleration.