Lord knows I'm terrible at these writeups, so I'd recommend glancing at the attached CAD screenshots to get a quick idea of what this project is about-- on that note, most of this post will be copy/pasted stuff from the design docs, mainly stuff that won't change, so apologies in advance.
Long story short, I've talked to a bunch of guys, both on the chans and elsewhere, who have some great ideas but aren't sure where/how to get started. My hope is that a (comparatively) simple, modular base that provides power, movement, and basic sensor data will let them get started on their own project without having to re-invent the wheel (and get nerd-sniped in the process.)
The purpose of this platform is to establish a generalized "blueprint" of a (comparatively) cheap, human-scale "modular base platform" that can be built by a capable layman and maintained by a hobo, while supporting and powering any "robo payload" <= 75lbs, 5kW. Emphasis is placed on all parts being readily available or substitutable, and could conceivably be built from salvage at near zero cost (or in the face of malicious sales restriction), excepting digital controllers. Durability has also been prioritized, with over-engineered tolerances and (optional) bilateral redundancy for everything but the drive motors. Sacrifices have been made to accommodate this vision (primarily weight, though to a lesser extent, performance), and Builders with access to specialized tools or a higher budget will likely want to tweak the design (ex. using aluminum T-Slot instead of right-angle stock, welds in place of frame bolts, etc.)
The design is purposefully made to resemble (and, if necessary, function as) a wheelchair (see reasoning below.)
## Project Budget
Target Cost: $2,500 USD-2023 with new, mid-grade parts, excepting computer/processor.
(realistically, I expect this to be closer to $3,500 in the short term, until people more clever than I improve some of the design's weaknesses/sacrifices)
## Prototype Info
- Prototype Budget: $10,000 USD-2023
- (I have access to specialized equipment and labor (at a price), including a commercial 3D printer, 5-axis mill, welding, lifts, etc.)
- First design revision expected by the new year (2024). Physical construction to begin Spring 2024. Basic electronic control system, motor/BMS interface to be somewhat complete between January and (Spring) 2024.
# Requirements & Purpose
- At bare minimum, the Robo shall be physically capable of navigating any ADA-compliant environment.
- Robo shall be capable of interacting with standard human features-- counter-tops, tables, eventually doors, etc.
- This necessitates vertical mobility, as many counters expect a human's "waist height" to be @36in
- Should be constructible from either imperial or metric materials as available, with the standard being 25mm/1in framing stock.
- Tolerances should be excessive, and all components that cannot be handmade (sprockets, chains, gears, wheels, batteries, etc.) should be interchangeable with off-the-shell parts (ex. bike/car parts)
- The "baseline model" should require no specialized tools or skills beyond the grasp of a determined autist.
- It will, however, require basic tools like a drill with specialized bits, soldering iron, an appropriate saw, angle grinder, and a lot of time.
- Should be movable, even when inactive/broken, by a single adult of reasonable fitness.
- Assumes novice male deadlift of ~173lbs (up to 220lb would be reasonable with minimal training), and the ability to raise+carry 75lbs (Payload) near shoulder level.
- Should be transportable within compact vehicles, not to require more than 1 minute to restore to a mobile configuration, with no tools.
- We assume a back-seat forward distance of at least 18in (upper minimum 20in), and two non-occupied passenger seats total (front or back, need not be adjacent).
- Should attempt to (technically) remain within the legal bounds of a plausible "mobility aid device", "prosthetic", etc.
- Not a particular stretch, as the design's default configuration looks quite similar to a wheelchair, can be occupied by replacing the Mount with a seat, and is big enough to carry a human (and powerful enough, though expect significantly decreased speed and runtime)
- An added, if unlikely benefit is that in may help public acceptance due to a less-threatening, more harmless appearance.
- A fully capable model (to spec), with a complete payload (~75lbs), should not exceed 250lbs, ie, the lower end of (architectural) transient load limits.
- Note that static weight is an entirely different measure, and "parking" your Robo should NOT be done just anywhere. Find somewhere made to carry a static load (kitchens, baths, bedrooms with a safe mount, etc.) And, of course, check building codes in your area, obey laws, etc.
- Has space and hardpoints for (optional) safety mechanisms (for now, I'm simply designing with this "in mind")
- Ideally, this would include something to avoid running over unseen objects, be it LIDAR, ultrasonic, electrostatic, etc.
- Lower-hanging fruit to prevent easily-avoidable accidents, such as bumpers and chain/gear shrouds, shall be included in the initial design.
- In case of catastrophic failures, the Platform should be designed to sacrifice itself to prevent the Payload being damaged.
- Non-catastrophic failures should ideally not impact Robo capabilities (immediately) in the case of a system with redundancy, or engage the fail-safes otherwise.
# Final Remarks
> Career engineers will probably cringe at the... /misuse/ of materials, such as bolts in a force-transfer or structural role (Bridgehead Rotation and Payload Locking Clips, respectively). (PS don't look a the scrap Bridge Clutch schematic)
This entire project is built on the idea that "Something real that theoretically works is better than something theoretical that really (might) work." The goal is a design that can realistically be built by anyone capable, out of parts they save up for and salvage, so they can build something to improve their own lives.