Monty McGraw's R2D2 Blog

Monty and his R2D2 at Starwars Celebration 4

2008-01-08T00:45:00.000-06:00

The Droid Races were a lot of fun at Celebration IV. In this photo, I'm trying to get my R2 to press a button behind the dataport in the pedestal. Kelly Krider's bright yellow and blue droid is barely visible to the right and behind the pedestal trying to do the same thing.

Then I turn R2 back to the right and use the rear probe with a magnet and try to grab an R2 head and drag it across the finish line. I'm dressed in my Obi-Wan Jedi outfit including lightsaber and boots.

I had no time to paint my R2 before this show so he is raw aluminum!

Photo courtesy Robert Ross

This blog covers some information about my Version 2 foot drive design. Below are also drawings and parts list - courtesy Mark Mullen - of Marks original design that I incorporated heavily in my V1 foot drive design - with adjustments done by Alan Wolfson and Scott Powers to accomodate the EV Warrior motors instead of Mark's original scooter motor.

Thanks to Mark, Alan and Scott

Mark Mullen's Parts List Page 1

2008-01-08T00:40:00.001-06:00

Mark Mullen's Parts List Page 2

2008-01-08T00:39:00.000-06:00

Mark Mullen's Parts List Page 3

2008-01-08T00:38:00.001-06:00

Mark Mullen's outside foot plate design

2008-01-08T00:29:00.001-06:00

In Mark's design, the outer foot plate is not the same as the inner and has additional mounting holes.

Mark Mullen's motor mount dimensions

2008-01-08T00:21:00.000-06:00

This wheel drive assembly drawing shows Mark's foot plate design.

One difference between this and my version 1 foot plate is Mark includes the ankle pivot in the top of his foot plate. My V1 side plates came from Scott Powers, based on his changes for using the EV Warrior motors. I use an aluminum "U" bracket to attach to the ankle - this bracket is bolted to two spacers at the top of my side plates. The "U" bracket will be epoxy bonded to the foot shell, so the two bolts allow the whole foot mechanism to be detached from the foot for maintenance - which I have now done a couple of times :)

You can see from Mark's drawing that the length of the foot plate could be as long as 12.75".

Mark Mullen's Foot Drive Design - Mechanical Overview

2008-01-08T00:08:00.000-06:00

This drawing is Mark's overview of his original R2D2 Foot Drive design. He used a scooter motor and a rear omniwheel.

My first generation foot drive design at Celebration 4 was a variation of this with the rear 4" diameter omniwheel replaced by a 4" diameter Omniball - see my description at http://www.astromechbuilder.com/mechloader/v/bluejedi/modifiedBallCaster

Foot Drive V2.0 - my side plate design sketch

2008-01-07T23:59:00.000-06:00

This picture is my sketch of my R2D2 Foot Drive version 2.0

There are two identical plates for each foot. I marked three holes to "match previous plate" in my V1 design. These three holes are where the spacer blocks are installed to ensure 2.5" separation between the side plates.

Offset holes allow the shaft bushings to be moved forward/backward slightly to adjust for smooth parallel operation. Offset hole for motor allows slight adjustment of drive motor gear to 4" gear.

Not pictures in this sketch are the additional two holes immediately above the lower "match" hole and immediately to the right which secure the EV Warrior motor mount.

R2D2 Wiring

2008-01-07T23:11:00.000-06:00

My wiring is kind of messy right now, but this was done in haste to allow me to drive my R2 at the May 2007 Starwars Celebration IV convention in Los Angeles (see driving picture above).

Basically, the motor, battery and thermocouple cables from each foot enter the body through the shoulder motors. The Vantec RFDR23 dual channel speed controller is located above the Power Analyzer Pro. I've got a 70A DC circuit breaker above the charging connector to the right of the analyzer. Above that is the Futaba RC receiver and above that is a Pitman gearmotor used to rotate R2's dome.

Almost all the aluminum parts in this view are from JAG!

Left Battery Box

2008-01-07T23:00:00.000-06:00

This close up of the left battery box shows another thermocouple cable, the end of the battery and the red/brown battery cable. There is an unused charging cable tucked under the battery. This charging cable has a series overtemp switch which I don't want operating with my quick charger so I charge using the same cable as discharge.

The battery and thermocouple cables are routed through a large slot in the ankle bracket and ankle and up through the leg to the shoulder.

The Power Analyzer Pro "blue box" in this photo is in series with the 24V battery pack and logs Volts, Amps, Amp-Hours, Temp for both charge and discharge.

The center foot is shown in this photo and contains two 4" Omniball casters with my modifications to dramatically reduce the height of these casters to match the height of the 4" Colson wheels in the outer foot drive assemblies.

Monty's R2D2 Foot Drive V2 Design

2008-01-07T22:51:00.001-06:00

View of right foot from the rear. Battery box with cover removed is fastened to inside of foot shell using keyway slots and bolts. Battery is 12V 10AH NiMH - one in each battery box for total of 24V 10AH for my droid. White cable in battery box is telephone cord used to connect thermocouple sensor - used by smart charger to stop charging when battery temp indicates battery is charged.

I used 10AWG stranded wire for battery connections with Anderson connectors and same gauge wires for the EV Warrior motor - soldered to the motor (see the Yellow/Brown twisted pair of wires).

Bottom View of Left Foot Drive

2008-01-07T22:38:00.000-06:00

This is the bottom view of my foot drive. You see the new outer chain drive on the left side. The top shaft is the driven shaft supported by two bronze bushings. The spacer and the Colson caster wheel keep the shaft centered. The EV Warrior motor is below this shaft with a small gear seen on the right side. This small gear meshes with the 4" gear below to drive the 1/4" shaft below the motor. That shaft is supported by small bronze bushings. A sprocket on that shaft drives the small chain and a bigger sprocket on the lower shaft which is the main drive shaft.

Primary change between my V1 and V2 design is moving one of the two Colson wheels from the front shaft to a new rear shaft - driven from a #35 chain and pair of sprockets. The bronze bushings on the front and rear shafts are mounted inside the side plate to allow the sprockets to squeeze in on the outside just clearing the inside of the foot shell. I also moved the two drive wheels to be centered under the foot pivot to minimize twisting torque on the ankle.