Cartridges & Accessories — The RTC / RTA Ecosystem

Why a cartridge at all

The HERO Jr was sold to a buyer who was not expected to own a soldering iron, an EPROM programmer, or a logic probe. That single assumption — the consumer, not the classroom (Vol 1) — shapes the whole expansion model. On the HERO 1, growing the robot’s repertoire meant working at the level of the silicon: programs lived in ROM, and an owner who wanted new behaviour either typed machine code into the hexadecimal monitor or physically swapped accessory ROM chips into the board. That is a fine model for a teaching machine whose owner is supposed to learn the hardware. It is a poor one for someone who bought a robot to have it sing, guard a room, and carry a drink across the living room.

The HERO Jr answers that with the RTC program cartridge: a snap-in module the owner inserts to give the robot a new body of programs, with no chips to handle and no code to enter (theoldrobots.com). The robot already carries an unusually large 32 KB ROM holding the monitor and the built-in personality programs (Vol 2); a cartridge extends that library outward through the same memory-mapped path the built-in firmware uses, so a “Games” cartridge or the BASIC cartridge becomes, from the owner’s side, just another thing the robot now knows how to do. The act of expansion is reduced to inserting a card — the consumer inversion of the HERO 1’s chip-and-monitor approach (Vol 6 covers what the BASIC cartridge in particular unlocks for those who did want to program).

Alongside the program cartridges sits a second, parallel line: the RTA accessory catalogue — hardware add-ons (a motion detector, extra batteries, a memory adapter) rather than program modules. Together the RTC and RTA numbers form the documented expansion ecosystem of the machine.

The RTC program cartridges

The program cartridges are catalogued under the prefix RTC (“Robot Cartridge”), numbered RTC-1-1 through RTC-1-11 (theoldrobots.com). As a family they spanned several kinds of content: games, educational material, fitness routines, and — the one cartridge whose number the record fixes precisely — BASIC, which is RTC-1-8 (theoldrobots.com; and the factory HERO Jr BASIC manual is itself titled for the RTC-1-8 cartridge). Beyond those categories, and beyond the single fixed BASIC number, the public record does not pin a specific title to each of the eleven slots. The honest position is therefore that the range and the categories are documented while most of the individual titles are not, and this volume does not invent them.

Table 1 — The RTC program cartridges

Part #	Type	Source
RTC-1-1	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-2	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-3	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-4	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-5	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-6	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-7	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-8	BASIC cartridge (programming, over RS-232 — Vol 6)	theoldrobots.com; HERO Jr BASIC manual
RTC-1-9	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-10	Program cartridge — specific title undocumented	theoldrobots.com (range)
RTC-1-11	Program cartridge — specific title undocumented	theoldrobots.com (range)

The discipline in that table matters. The record gives a contiguous range (RTC-1-1 … RTC-1-11) and a set of content categories (games, educational, fitness, BASIC), but only one number-to-title binding that can be stated as fact: RTC-1-8 = BASIC. Every other row is therefore marked “specific title undocumented” rather than guessed at — there is no documented mapping that says, for example, which number is a chess game or which is an exercise routine. A reader rebuilding a cartridge collection should treat any number other than RTC-1-8 as a slot whose exact title needs primary confirmation (a label, a catalogue page, or the cartridge itself) before it is asserted.

What a cartridge does for the owner

Functionally, an RTC cartridge is the consumer-facing equivalent of the HERO 1’s accessory ROMs, but it is handled like a console game cartridge: insert it, and the robot gains the programs it carries. The categories the record names give a clear sense of the intended use:

• Games — interactive play, the cartridge supplying the program the robot runs while the owner interacts through the keypad and the robot’s speech and sensors.
• Educational — content cartridges in the home-learning idiom of the mid-1980s, consistent with HERO Jr’s marketing as a family product.
• Fitness routines — the robot leading or timing exercise, an unusual use that fits a machine designed to be a presence in the home rather than a lab instrument.
• BASIC (RTC-1-8) — the outlier: not a packaged behaviour but a toolchain. It turns the robot into a target you can program in BASIC over the RS-232 serial link (Vol 6), which is why it, alone of the eleven, has a dedicated factory manual.

The crucial point for this volume is the delivery mechanism, not the catalogue: in every case the owner expands the robot by inserting a card, and the robot’s existing firmware and memory map (Vol 2) absorb the new code. The cartridge is the bridge between a sealed consumer appliance and a genuinely extensible computer.

The RTA accessories

The hardware add-ons are catalogued under the prefix RTA, numbered RTA-1-1 through RTA-1-5 (theoldrobots.com). Three of the five are documented in function; the remaining two numbers are part of the stated range but their specific products are not fixed by the record, and are left unclaimed here rather than invented.

Table 2 — The RTA accessories

Part #	Type	Source
RTA-1-1	Accessory — specific product undocumented	theoldrobots.com (range)
RTA-1-2	IR motion detector (field ~35 ft long × 20 ft wide)	theoldrobots.com
RTA-1-3	Accessory — specific product undocumented	theoldrobots.com (range)
RTA-1-4	Extra batteries — doubles battery capacity	theoldrobots.com
RTA-1-5	Cartridge / RAM adapter — adds 8 KB	theoldrobots.com

RTA-1-2 — the infrared motion detector

The RTA-1-2 is the optional infrared motion detector, the one HERO Jr sensor that is an add-on rather than a built-in (the sonar, light, and sound sensors are standard — Vol 4). Its documented coverage is a field roughly 35 feet long by 20 feet wide (theoldrobots.com), a detection zone sized for a room rather than a benchtop. With the head fixed (Vol 3), the robot cannot sweep the detector by turning its head, so the field is aimed by the body — the detector watches the wedge of room the robot is pointed at. This is the accessory that most directly upgrades the robot’s signature Guard behaviour (Vol 5): a HERO Jr standing watch with an RTA-1-2 fitted has a far larger and more sensitive zone of awareness than one relying on sonar and sound alone. Note that the robot’s front panel carries an “I.R. MOTION DETECTOR” label regardless (visible in the unit photos, Vol 1/Vol 4), reflecting that the function is a designed-in option rather than a third-party hack.

RTA-1-4 — the extra battery pack

The RTA-1-4 adds extra batteries that double the robot’s battery capacity (theoldrobots.com). The HERO Jr ships with two 6 V 4.0 Ah rechargeable batteries and runs about four hours on a charge during normal exploring (Vol 2); the RTA-1-4 adds a second pair, extending endurance toward roughly twice that figure. For a robot whose whole appeal is being switched on and left to roam, react, and guard, doubled runtime is a meaningful upgrade rather than a niche one — and it is purely additive hardware, requiring no change to the firmware or the program model. (The robot’s sealed-lead- acid batteries and their charging cautions are taken up in Vol 8.)

RTA-1-5 — the cartridge / RAM adapter (+8 KB)

The RTA-1-5 is the most architecturally interesting accessory: a cartridge / RAM adapter that adds 8 KB of memory (theoldrobots.com). It sits at the junction of the two expansion lines — it is itself a hardware accessory (RTA), but what it does is extend the robot’s cartridge and memory capability. The base HERO Jr carries 2 KB of RAM (a 6116), and the architecture is documented as expandable to 24 KB (Vol 2); the RTA-1-5’s +8 KB is one documented step along that expansion path. The added RAM is what gives larger cartridge programs — and BASIC programs entered over the serial link (Vol 6) — room to run, since a BASIC interpreter and a user’s program both need working memory beyond the 2 KB the robot ships with. In effect, RTA-1-5 is the accessory that makes the deeper, programmable side of the HERO Jr (Vol 6) practical, which is why it pairs naturally with the RTC-1-8 BASIC cartridge.

How the two lines fit together

Read together, the RTC and RTA catalogues describe a deliberately layered upgrade path for a non-technical owner:

• Out of the box, the robot already does a great deal — the one-touch personality keys driven from the 32 KB ROM (Vols 1, 5).
• RTC program cartridges add software behaviour with nothing more than an insertion — games, educational and fitness content, and (RTC-1-8) BASIC.
• RTA accessories add hardware capability — wider sensing (RTA-1-2), longer endurance (RTA-1-4), and more memory (RTA-1-5) for the programs the cartridges and the serial link bring.

The design intent is consistent across both lines: every documented step is something the owner installs or inserts, never something they have to engineer. That is the through-line from Vol 1’s “capable by default, with a path deeper.” The cartridge slot and the accessory catalogue are how that path is paved — and the RTA-1-5 adapter, by adding both cartridge/RAM capacity and the 8 KB those larger programs need, is the single accessory that ties the software path (cartridges, BASIC) back to the hardware it runs on.

What the record does and does not fix

Because part numbers are exactly the kind of hard fact this series gates strictly, it is worth stating the boundary plainly:

• Documented as fact: the RTC range RTC-1-1 … RTC-1-11; the RTC content categories (games, educational, fitness, BASIC); RTC-1-8 = BASIC; the RTA range RTA-1-1 … RTA-1-5; RTA-1-2 = IR motion detector with a ~35 × 20 ft field; RTA-1-4 = extra batteries doubling capacity; RTA-1-5 = cartridge/RAM adapter adding 8 KB (all theoldrobots.com, with the BASIC manual confirming RTC-1-8).
• Not documented, and therefore left unclaimed here: the specific title of any RTC number other than RTC-1-8; the specific product behind RTA-1-1 and RTA-1-3; and the exact internal contents, capacities, or in-use details of the unnamed cartridges. None of these gaps is filled by guesswork in this volume.

A collector or restorer reconstructing the ecosystem should take the tables above as the documented skeleton and confirm any individual unnamed title against a primary artifact — a cartridge label, a Heathkit catalogue page, or the BASIC manual — before treating it as settled. Vol 8 covers acquisition, where the completeness of a unit’s cartridges and accessories is one of the things that most affects its value.