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R.A.D. the Robot Hack - a.k.a. Project Roland

R.A.D. the Robot is actually a very cool base. It's largish at 12" x 12" square and 23" high, has tracks for mobility, and the original platform is fairly heavy, so the motors are good-sized. The motors are a little noisy. The base also has a 2-speed high-low transmission.

R.A.D. looked like a good base that could be hacked for good mobility around the house. We found several R.A.D. and RAD2.0 at auction on ebay in October 2006, and which sold for between $17 and $44. This thing is a steal.

We actually have a number of gearmotors and wheels and struts and material, that we have acquired over the past several years for building a base of this size, but were always stymied by good ways to mount the motors and wheels, not having access to good machine tools. Finding the right hubs to mount wheels to motors, and the right brackets to mount motors to frames, is always a problem, and many people make them by hand on lathe and milling machine [expensive]. Buying a R.A.D. base solves several problems. The tracks will go over about any surface in the typical home, and the speed is fast enough to go from one end of the house to the other in a reasonable amount of time.


THE GOAL

The original R.A.D. Robot was obviously designed as a Robot Butler with a tray that could carry beer to the guy sitting on the couch drinking Coors-Lite, and watching the many games on TV-sunday. The arms move in and out, and the body bends forward so the arms can touch the floor and pick up things. It can carry the tray in its hands, or inserted in the tray-slot, as shown at right. It also has a built-in speaker and talks in a raspy voice - "system test, opening arms", etc. It has a wireless microphone built into the control unit, that someone in the kitchen can use to broadcast "Hey, wake up Dummy, your beer has arrived". It's really quite cool.

We found at least one other R.A.D. hack on google here, but they lashed a few things on top of the existing platform, while we decided to mothball the top unit for now, and didn't have to mess up any existing hardware or electronics to produce a nice hack. Instead of a grouchy talking bot that actually gets irritating after a short time, we wanted a high-mobility platform for sensor development and testing wireless devices. We also wanted a good platform to experiment with subsumption-based software. For something more serious [than toting beer].

[about 23" tall]

THE HACK

Base Jiggering. After removing the 10 screws holding on the bottom cover of the base, we discovered the bottom and top parts of the robot are held together with just 4 screws and 6 wires. The top [body + head] unit is a totally self-contained unit with a plastic extension that slides into a channel of the bottom unit, clips in with locking tabs, and is held firm by the 4 screws.

By simply removing the 4 screws and cutting the wires, the base motor unit is completely freed of the top unit of the robot without causing any mechanical damage whatsoever to either unit, and can later be re-attached in just a few minutes, if so desired. All in all, this is a rather remarkable modular engineering design, for being a toy.

Motor Electronics. The 6 wires connecting base and top units are simply 2 for the 6-volt NiCad battery, and 2 each for the 2 motors. The motor mechanical drive units are self-contained, and have a simple in-out mechanical linkage that selects high-low gear range (observable in motor detail picture). This should be hackable using a standard R/C servo.

A little bit of playing around showed that each motor draws only about 300 mA or so with just the tracks for load, and under 1-Amp with heavy drag loading on the tracks. We connected the motors to an OricomTech OOBOT40-3 Controller Board, which uses an L298N dual-channel 2-Amp h-bridge chip. It ran great, and the h-bridge chip didn't even get warm. We discovered the relationship between speed and PWM duty-cycle for these motors is much more linear, and therefore controllable, when using a PWM frequency near 1-khz than up at 5-khz.

New Robot Concept. The diagram at the lower-right shows the preliminary concept for the reconfigured R.A.D. Robot base. There is actually plenty of free room inside the base to insert the controller card and batteries, and have a complete robot no more than 6" tall, but we decided to build on top.

The deck is 12" x 12" x 1/4" expanded PVC material, bought from Budget Robotics, and allows plenty of space for adding electronics and sensors. It is attached easily without damaging or even drilling a hole in the base, by use of foam spacers secured with double-sided mounting tape, plus the existing screw-holes in the channel used to mount the top-unit.

We are using a set of 6/ea rechargeable 2500 mA-hr NiMH AA-cells, wired in series, to drive the base. These cells should theoretically last for more than an hour at continuous full-speed on the motors, and 2-4 hours of more nominal operation.

The 6v Nicad battery that comes with the base is several years old, and is not specifically marked, but no doubt is much less than 2500 mA-hr capacity. Given the size of the battery and motors, the original R.A.D. [shown at top] is somewhat too heavy and under-powered. However, "The Hack" loses about 5-6 pounds of weight, and with the larger battery capacity, should be about ideal.

[blow-up] [base - blow-up]
[blow-up] [base innards - blow-up]
(space a plenty)
[blow-up] [motor detail - blow-up]
(the piece between the
motors rotates to change
gear ratios)
[JP1] [conceptual - blow-up]

For a couple of years, we have also been collecting a number of Folger "3-pound" coffee containers [actually 2-lb, 2.5-oz, given how things are marketed these days] for use on robot bases. These are made out of HDPE (high-density polyethylene) plastic material, and are strong and light-weight and easy to drill. An easy way to increase the height of the base, for holding sensors, etc.

See next page for continuation: Project Roland - Zigbee-equipped subsumption robot

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© Oricom Technologies, Oct 2006, updated June 2007