[Coco] Robotic Arm from the MegaHoby store...

[Andrew]

 > 
https://www.megahobby.com/products/robotic-arm-edge-wireless-control-kit-owikit.html

I think I have three of these (older yellow version) in my pile-o-junk 
out in my shop (plus more than a few Armatrons...sigh). Anyhoo...

So, John, there are potentially a few relatively easy ways to interface 
this arm to the CoCo:

1) Bit banger -> Controller -> Arm
2) RS-232 Pak -> Controller -> Arm

Whether using the bit banger or the RS-232 Pak, you'd need to convert 
the levels from RS-232 voltages to TTL levels - there are plenty of 
options out there to do so, such as these modules:

https://www.amazon.com/MAX3232-Connector-Converter-Equipment-Upgrades/dp/B07PFB4MHR

The bit banger, of course, is more difficult to code for, versus the 
RS-232 Pak - but that also all depends on how you plan to approach that 
part.

The TTL output could then go to your favorite micro-controller of 
choice, from which you could (attempt) to use the OWI Edge USB interface:

https://www.amazon.com/OWI-USB-Interface-Robotic-Arm/dp/B0028MBWS2

NOTE: All links are for examples only - I do not endorse any of them...

You'd need to figure out that protocol, of course, and your 
micro-controller would need to be able to support being a USB master...

Or - and probably easier and cheaper - and is really all the USB 
interface probably does (more or less), would be to interface either 
some relay modules or small h-bridge drivers (-not- L293 or L298 based!) 
to control the direction of the motors. Most relay modules are SPDT relays:

https://www.amazon.com/MCIGICM-Channel-Raspberry-Optocoupler-Expansion/dp/B072BY3KJF/

...so two relays would be needed per motor for an h-bridge, like the 
example modules above. You could certainly use another solution, or 
design your own.

...or, if you go solid state h-bridges using modules, one bridge per 
motor (if a module can support two motors, which many can, then only 3 
modules are needed) - something like these could work fine:

https://www.amazon.com/Aideepen-Driver-H-Bridge-Replace-Stepper/dp/B075S368Y2/

Note that there are such things as "RS-232 Relay Boards" - so that is 
another option which could eliminate the micro-controller and level 
conversion potentially - but you'd need to implement whatever command 
protocol used by the board, of course (versus needing to implement it 
yourself in some fashion).

Last, I want to note here that I showed how to do everything with 
pre-built modules, but you could build most all of them from "discrete" 
parts, if you so choose.

As far as feedback is concerned, that's tricky - but it is somewhat doable:

https://www.instructables.com/Intro-and-what-youll-need/

As a bonus, this link shows how to hook it up to an Arduino (albeit 
using L293 based motor drivers); feedback is accomplished using 
potentiometers - ugly to hack in place, but doable if you don't care 
about looks.

Or - go with opto-reflective encoders that can fit inside each motor module:

https://www.instructables.com/Modifications-to-Robot-Arm-for-Opto-Coupler-Feedba/

More difficult to put in place, but should result in a neater 
appearance, though programming may be tricky (you'd need to make the arm 
move each joint while counting the "slots" until you hit the travel 
limit - determining that limit using various means; if the motor drivers 
have some kind of current detector, you could use a sharp rise in 
current, sustained, as the indicator - or some micro-switches, or 
something of that nature).

 > Also, didn't Tony DiStefano make a controller for a robotic arm 
(Tomy?) in Hot Coco?  IIRC, he used an extra 6821 as a PIA.  That may be 
a starting point to get this arm working.  All my gear is packed up now 
so I can't go check.

If TonyD did such a thing, it's probably in the "Full Turn of the Screw" 
Book:

https://colorcomputerarchive.com/repo/Documents/Books/Full%20Turn%20of%20the%20Screw.pdf

But what you might be looking for is the CoCoROS project - which I think 
starts with the December 1986 issue of the Rainbow (there are 3 parts, 
Dec 86, Jan 87, Feb 87).

I hope this all helps - and good luck with your project!

Andrew L. Ayers
Glendale, Arizona
phoenixgarage.org
github.com/andrew-ayers