[Coco] Re: Coco Digest, Vol 30, Issue 31

Andrew keeper63 at cox.net
Sat Feb 11 20:01:48 EST 2006

> Message: 2
> Date: Fri, 10 Feb 2006 13:04:54 -0800
> From: "Jim Cox" <jimcox at miba51.com>
> Subject: [Coco] CoCo robotics? (Rhetorical test to the list :)
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Message-ID: <web-203065094 at treehouse.forest.net>
> Content-Type: text/plain; charset="ISO-8859-1"; format="flowed"
> To follow up Art's test to the list, I'll ask a rhetorical 
> question just get a resonse;
> Is anyone out there currently doing anything closely 
> related to robotics with the CoCo?
> I have a small robot arm that I was thinking of hooking up 
> one day and playing around with, but as with many of my 
> ideas/plans/goals, it will be some time before it happens.

What kind of robot arm is it? This is very important to know. If it is 
DC motor-based (not DC stepper motors), then you are going to need a 
different approach than if it is stepper based. Furthermore, if it is an 
old Tomy/Radio Shack Armatron arm - then you are in for a real treat (I 
say that sarcasticly).

Regardless, you need a way to interface the motors (and/or any sensors - 
are you wanting a simple open-loop design, or do you envision a 
closed-loop feedback system?). Some people (in the past - there were a 
few Rainbow articles on this back in the day) would interface via the 
cartridge port. This can be tricky to do today, since you would either 
have to cannabalize a drive controller cartridge or etch your own edge 
connector. Then, you need a pinout of the port pins, and information on 
how to properly interface and control them (addressing, hex buffers, etc).

It would be easier to get an RS-232 pack, or somehow hack the bit-banger 
serial port - and connect that (via a cable) to a BASIC Stamp or PIC, or 
to a dedicated serial-port to relay/stepper controller. These 
controllers aren't hugely expensive (still pricey, but not the major 
expense they used to cost - demand for such systems in hobby robotics 
has driven the cost down greatly over the years). Expect to pay around 
$200.00, maybe more, maybe less. If you handy with a soldering iron and 
know your electronics, it would probably be easier and cheaper to build 
something using a BASIC Stamp and/or PIC.

This would then interface to your relays, motors and/or sensors. If you 
are using regular DC motors, then you will need to use either relays, 
power transistors, MOSFETs, etc - to drive the motors in an H-bridge 
fashion (to control direction). You might want to add pulse-width 
modulation (PWM) for speed control, but it isn't critical for a simple 
toy arm (and can be simulated to some degree with software). Remember 
that whatever H-bridge scheme you use, use one where if you drive both 
bits high or low which control the relays/transistors in the H-bridge, 
you won't short the power-supply. This is critical!

If you are using steppers, then you are going to need to set up stepper 
driver circuitry (generally a few darlington drivers or dedicated 
stepper control ICs) properly - to handle the current and voltage load. 
Proper heat-sinking and cooling may be critical here, depending on the 
size of the steppers being used.

Now - if you are using an old Armatron (Tomy or Radio Shack - though I 
implore you - if you have a Tomy arm, please don't take it apart, as 
they are more collectable to collectors as part of the Tomy robot toy 
line - but if it is the later Radio Shack version which Tomy licensed, 
go for it!), there are a few sore spots:

Both Tomy and Radio Shack sold robot arms. Tomy had the Tomy Armatron in 
the early 1980's (despite what you see, the Armatron isn't from the 
1970's), and then licensed the manufacturing to Radio Shack in the 
mid-late 1980's, which Radio Shack sold as the Radio Shack Armatron. 
Later, RS came out with their own model (or licensed it from some other 
company - not Tomy) called the "Super Armatron" which had a controllable 
wheeled base (and looked nothing like the original Armatron). Then, 
still later, RS dropped that model, and released the original model of 
the Tomy Armatron they were licensed, but labeled it the "Super 
Armatron". So, you had the following:

1) Original Tomy Armatron
2) RS-licensed Armatron (identical to 1, above)
3) RS-licensed Super Armatron (wheeled base, no relationship to 1 or 2)
4) RS-licensed Super Armatron (identical to 1 and 2 above, but named 

With this in mind, you need to realize that Armatrons 1, 2 and 4 are 
fundamently different from the Armatron described in 3. The Super 
Armatron that RS released (#3), was based on multiple continuous 
rotation DC motors. Most toy robot arms (OWI and others as well) are 
built and controlled in this manner.

The original Tomy Armatron (and the two licensed RS arms as noted) are 
unique in toy history (actually, many of Tomy's devices, especially the 
various 1980's table-top "arcade" games, are like this). These devices 
are what some consider "wonders of mechanical engineering", which is why 
the original Tomy stuff is so collectable to those in the know. This is 
also why the Tomy Armatron (and others) are so difficult to convert to 
computer control, unfortunately.

You see, these arms use a *single* motor to control all functions of the 
arm!!! Via a complex transmission system, all motions of the arm are 
controlled and powered by a single DC motor. These motions are 
controlled by the user via the two joysticks on the base of the arm, 
which have eight directions each (although, IIRC, only 6 of these 
directions control independent functions), along with rotation of the 
joystick handles (one controls wrist rotation, the other gripper 
movement), to control all 5 axes of the arm, along with the gripper 
function. The joysticks operate levers which shift the transmission 
(similar to an automobile), which is powered by the single motor, to 
transmit power from it to a variety of shafts which are connected to the 
arm via a series of ring gears in the base, which then transfer the 
power via a complex arrangement of bevel and spur gears up and through 
the arm, all the way to the gripper (it is a VERY ingenious design, 
coupled with a nice cam-based clutch system that prevents the arm from 
being destroyed when the motions are at their limits).

Tomy did similar systems like this for most of their toys (especially 
the games, as noted) - they were marvels of complex mechanical 
ingenuity, which is what makes the original Tomy toys so collectible. 
You will not find similar engineering in toys today. They are really 
something to marvel at, especially if you like to take things apart (and 
put back together, of course). Tomy toys are like the world's most 
complex mechanical jigsaw puzzly. I swear, they are the 1980's version 
of 15th and 16th century doll automata.

The problem with this system, while being very ingenious, is that it is 
very difficult to control the Armatron with a computer. A few approached 
can be used in this endevour, though, to various levels of success.

The simplest method involves controlling the joysticks directly, 
typically with motors or solenoid actuators. This has been desribed in a 
few texts over the years, and some have tried it to varying levels of 
success. The biggest issues with this approach the the amount of current 
used by the actuators, as well as proper control the rotation of the 
joysticks to control the wrist rotation and gripper function, while 
still being able to control everything else. The best way to approach 
this is to arrange four solenoids (minus the return spring, or with a 
weaker return spring) around the joystick, opposing pairs in a push-pull 
arrangement, connected mechanically to the joystick via springs (to 
allow diagonal movement). If you arrange the pairs properly, you can 
stagger them in such a way so that opposing pairs, when both are 
actuated, actually "twist" the joystick in one direction, while the 
other pair twist in the other. Otherwise, you will need a rotary 
solenoid or motor to perform this function.

The next hardest method involves connecting the input levers (controlled 
by the joysticks) to actuators like solenoids and such. In effect, you 
are replacing the joysticks. This is a more difficult approach, as it 
involves dismantling the base to get to the levers, but it is a possible 

The final method is to replace the transmission system altogether with 6 
independent motors, then control the motors as usual. Depending on your 
level of skill, this can be the best option to persue. It was originally 
described in an issue of Radio-Electronics (now defunct?) in the 1980's, 
where the author described modifying the arm to allow this, and then 
building an interface board to allow hookup of the arm to a C-64 or 
Vic-20 computer (so it should be possible to hook it up to a CoCo via 
the cartridge port or a serial interface system). The methods described 
in the article can be used as is, or as a guide for the other methods 
described above.

Fortunately for you, if you are using an Armatron and want to explore 
these routes - I have scanned the article in and have it on my website 
for download here:


It is a ZIP file which you can unzip and then view the scans with your 
browser or another viewer. Please note that in the future the above link 
may not work. In that case, just go to my website directly, and browse 
around or email me, as I will always host the file somewhere because I 
like the article so much (unless the publisher tells me to remove it, of 

I hope this information helps you, and good luck with your project, 
whenever you decide to pursue it (and if you get it working - please, by 
all means, show us the pictures!)...

-- Andrew

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