I built this 'Velocipede' Droid by using parts from existing LEGO® set - "Star War 7748, The Clone Wars Corp Alliance Tank Droid" (2009) and some other LEGO Technic Bricks, Plates.

The original 7748 set (See Photo 4) contains 196 pieces. I used only 76 pieces out of 196 (approximately 38% of the set.) And I added 63 pieces using other LEGO Technic Bricks, Plates, etc.

My intension is to transform the Tank Droid into motorized robot by modified the T Pro SG90 servo to only use its motor (See Step 2 for the instructions.) And then use Palm Arduino Plus to control the motor controller (L293D) that is included on Palm Arduino Plus PCB.
And I use the XBee module to receive the commands from the computer wirelessly.

And here is how I built the 'Velocipede' Droid!

See video and more photos in Step 11.

Disclaimer:
LEGO®, TECHNIC, are property of The LEGO Group of Companies (http://www.lego.com), which does not sponsor, own, authorize or endorse this creation.

Step 1: Parts & Tools

LEGO Parts from "Star War - The Clone Wars Corp. Alliance Tank Droid" (#7748)

(Also shown in Photo 1)

2 nos. - Light Bluish Gray, Dish 10 x 10 Inverted (Radar) with SW Tank Droid Pattern (#4549191)
2 nos. - Light Bluish Gray, Dish 4 x 4 Inverted (Radar) (#4211664)
2 nos. - Dark Bluish Gray, Dish 2 x 2 Inverted (Radar) (#4211010)
3 nos. - Gear 24 Tooth (#4514558), Dark Bluish Gray

2 nos. - Red Technic, Liftarm 1 x 2 Thin (#4186678)
4 nos. - Light Bluish Gray Pneumatic T Piece New Style (T Bar) (#4211508)
2 nos. - Liftarm 3 x 5 L-Shape with Quarter Ellipse Thin (#4234247), Light Bluish Gray

2 nos. - Red Technic, Axle 2 Notched (#4142865)
2 nos. - Light Bluish Gray Technic, Liftarm 1 x 4 Thin with Stud Connector (#4211561)
3 nos. - 2x6 Plate (#4211002)

2 nos. - Light Bluish Gray Lever Small Base with Black Lever (#4221775)
2 nos. - Trans-Yellow Plate, Round 1 x 1 Straight Side (#3005744)
2 nos. - Two Blue Connector Peg/Cross Axle (#4206482)

4 nos. - Light Bluish Gray Arm Mechanical, Battle Droid (#4211658)
1 no. - Black Technic, Axle Connector with Axle Hole (#4107081)
4 nos. - Dark Bluish Gray Minifig, Neck Bracket with Back Stud (#4210469)
2 nos. - Black Brick, Modified 1 x 2 with Studs on 2 Sides (#4253815)
2 nos. - Light Bluish Gray Technic Brick 1 x 2 with Axle Hole - New Style with X Opening (#4233493)

6 nos. - Black, Cone 1 x 1 without Top Groove (#4529236)
4 nos. - Black Technic, Pin Long with Friction Ridges Lengthwise and Stop Bush (#4140801)
4 nos. - Black, Round 2 x 2 with Axle Hole - New Style with X Opening (#403226)
2 nos. - Light Bluish Gray Technic, Pin 1/2 with 2L Bar Extension (Flick Missile) (#4520320)
4 nos. - Dark Bluish Gray Tile 1 x 2 with Groove (#4211052)
2 nos. - 1x2 Plate (#4211398), Light Bluish Gray
2 nos. - 1x4 Technic Brick (#370126), Black

2 nos. - Black Technic, Axle Connector (Smooth with x Hole + Orientation) (#4512363)
2 nos. - Black Bar 6L with Stop Ring (#4538722)
2 nos. - Black Technic, Axle and Pin Connector Perpendicular 3L with 2 Pin Holes (#4173970)
2 nos. - Light Bluish Gray Technic, Axle 3L (#4211815)
1 nos. - Cross Axle 6M (#370526), Black

LEGO Parts

(Also shown in Photo 2)

2 nos. - 1x10 Plate (#4477), White
2 nos. - 1x8 Plate (#3460), White
2 nos. - 1x6 Plate (#3666), Yellow

4 nos. - 1x4 Plate (#3710), White
2 nos. - 1x4 Plate (#3710), Light Bluish Gray
7 nos. - 1x4 Plate (#3710), Yellow

2 nos. - 1x2 Plate (#3023), Light Bluish Gray
2 nos. - 1x2 Plate (#3023), White

4 nos. - 1x1 Round Plate (#6141), Light Grey

4 nos. - 1x8 Technic Brick (#3702), Black
4 nos. - 1x6 Technic Brick (#3894), Black

6 nos. - 1x2 Technic Brick with Ø4.9 hole (#3700), Light Bluish Gray
4 nos. - 1x2 Technic Brick with Ø4.9 hole (#3700), Yellow
2 nos. - 1X2 Technic Brick with 2 holes Ø4,87 (#32000), Dark Bluish Grey

1 no. - 2x2 Plate (#3022), Dark Bluish Gray

2 nos. - Cross Axle 3L with Stud (#6587), Light Bluish Gray
2 nos. - Cross Axle 6M (#3706), Black
1 no. - Cross Axle 8M (#3707), Black

1 no. - Axle 2 Notched (#32062), Red

2 nos. - 1-1/2 Connector Peg (#32002)

2 nos. - Bush for Cross Axle (#6590)

2 nos. - Two 8-Tooth Gear (#3647), Light Gray

1 no. - Pin Connector Round (#75535), Black

1 no. - Yellow, Panel Fairing # 1 Large Short, Large Holes, Side A (#32190)
1 no. - Yellow, Panel Fairing # 2 Large Short, Large Holes, Side B (#32191)

Servo

Servo horn glued to LEGO Cross Axle 3L with Stud (#6587)
2 nos. - 9g Micro Servo modified to be continuous rotational (Tower Pro SG92R, or T Pro SG90)
2 nos. - 3D Printed Servo Mount
(NOTE: The STL file for the servo mount (V01) is available for download here, for latest version (V06) that I used with this Wireless R/C Race Car. You can view the model or have it made at Shapeways, here.)

Others

3.7V Rechargeable LiPo battery or similar
7.4V 500mAh Rechargeable LiPo battery or similar

L293D (or SN754410) motors driver IC

Arduino or Arduino compatible
NOTE: I used Palm Arduino Plus in this project, since it has Motor Controller (L293D/SN754410) slot added on the PCB.

Wireless Radios
Palm Arduino Plus has three options of wireless radio modules,

XBee module,
RN-XV WiFly module,
Bluetooth module.

I chose to use XBee module in this project, since I already have a couple of them in my possession.
In order to use Xbee module or RN-XV WiFly module with Palm Arduino Plus we need extra breakout board, I used XB-Buddy Basic Kit (Jameco's Part no. 2163680) or similar.

Tools

The tools that I used in this project are:

Super Glue
Sand paper
Files
Solder iron and Solder station
Hookup Wire
Diagonal Cutter
Pliers
X-Acto Knife
Wire Stripper
SolderSucker

Step 2: Servo to Motor Conversion

Following are the photos show how to convert servo to be used as the motor and assembling them to the 3D Printed Servo Mounts:

Photo 1 9g Servo.

Photo 2 Remove all four screws from the servo.

Photo 3 The PCB was broken! Not the motor.

Photo 4, 5 Close up look at the servo and it wiring.

Photo 6 I disconnected the wires from the potentiometer.

Photo 7 Then removed the wiring from the motor.

Photo 8 And I removed the three wires with 3-pin female connector at the other end from the Servo PCB9

Photo 9 Removed the cap.

Photo 10, 11 Look for the notch below the topmost gear. I used X-acto knife to slice these two notches out of the top gear to make the top gear 360 degrees rotatable.

Photo 12 Put the cover back into it place.

Photo 13 I soldered the power supply wire (red) and ground (brown) wires to motor.

Photo 14 Close the bottom with four screws.

Photo 15, 16, 17 At the other end of the connector, I used the X-acto knife tip to open the lock, then pull out the orange jumper.

Photo 18 I got all of my three broken servos converted to usable motors and ready to be used in my next project. (I will only used two of them in this project.)

Video
- Test the motor.

Photo 19 Prepare my 3D Printed Servo Mounts (2)

Photo 20 Insert the cable into the top opening (As shown)

Photo 21 Slide the bottom of the servo into the servo mount.

Photo 22 Push the servo to the end.

Photo 23 Now the assembled servos (actually motors!) are ready!

Step 3: Assemble the Motor Axles

Following are the photos show how to modify the servo horns to be used as the motor axles:

Photo 1 We needed two LEGO Cross Axle 3L with Stud (#6587) and two servo horns that came with the 9g servos.

Photo 2 Glue the servo horn and Cross Axle together with SuperGlue.

Photo 3 Wait for the glue to dry (probably 24 hours) before proceed to the next step.

Photo 4, 5, 6 Use the diagonal cutter to clip off servo horn arm.

Photo 7 File or sand to smooth the cut area.

Now we got Motor Axles ready to be used!

Step 4: Motor Encasement

Following are the photos show the assembly sequence of the Motor (Servo) Encasement.

Photo 1, 2 Two White 1x8 Plate (#3460) and two black 1x8 Technic Brick (#3702)

Photo 3, 4, 5 Two Yellow 1x6 Plate (#3666), and two black 1x6 Technic Brick (#3894)

Photo 6, 7 Two Light Bluish Gray 1x4 Plate (#3710)

Photo 8, 9, 10 Two Light Bluish 1x2 Technic Brick with Ø4.9 hole (#3700) and Light Bluish Gray 1x2 Plate (#3023)

Photo 11, 12 Two Black 1x6 Technic Brick (#3894)

Photo 13, 14 Two Light Bluish Grey1x2 Plate (#4211398)

Photo 15, 16 Dark Bluish Gray 2x2 Plate (#3022)

Photo 17, 18 Two Assembled Motor and Servo Mount from Step 2.

Photo 19, 20, 21, 22 Two 1x2 Technic Brick with 2 holes Ø4,87 (#32000), Light Bluish Gray, and two Assembled Motor Axles from Step 3.

Photo 23, 24 Two Dark Bruish Gray Technic, Gear 24 Tooth (#4514558)

Step 5: Motor Encasement (Cont.)

Following are the photos show the assembly sequence of the Motor (Servo) Encasement.

Photo 1, 2 Cross Axle 6M (#3706), Black and Two Light Gray 8-Tooth Gear (#3647)

Photo 3, 4 Four White 1x4 Plate (#3710)

Photo 5, 6 Two Bush for Cross Axle (#6590)

Photo 7, 8, 9 Black Pin Connector Round (#75535)

Photo 10, 11 Two White 1x2 Plate (#3023)

Photo 12, 13, 14 Two White 1x2 Plate (#3023) and White 1x4 Plate (#3710)

Photo 15, 16 Light Bluish Grey 2x6 Plate (#4211002)

Photo 17, 18 Two Light Bluish Grey 2x6 Plate (#4211002) and Two Yellow 1x4 Plate (#3710)

Photo 19, 20, 21 Two White 1x10 Plate (#4477)

Step 6: Batteries Compartment & Palm Arduino Plus

Following are the photos show the assembly sequence of the Batteries Compartment and Palm Arduino Plus.

Photo 1 Continue from previous Step.

Photo 2, 3, 4 Two Blue Connector Peg/Cross Axle (#4206482), and Two Black 1x8 Technic Brick (#3702), Black

Photo 5, 6 Four Yellow 1x2 Technic Brick 1X2, Ø4.9 (#3700)

Photo 7, 8 Light Gray 1x2 Technic Brick with Axle Hole (#4233493)

Photo 9, 10 Yellow 1x4 Plate (#3710)

Photo 11, 12, 13 Cross Axle 8M (#3707), Black and Two Light Gray 1x2 Technic Brick with Axle Hole (#4233493)

Photo 14, 15, 16 Yellow 1x4 Plate (#3710)

Photo 17, 18, 19 Two Tan 1-1/2 Connector Peg (#32002) and Two 1x4 Technic Brick (#370126)

Photo 20, 21 Two Dark Bluish Grey 1X2 Technic Brick with 2 holes Ø4,87 (#32000)

Photo 22, 23 Four Light Grey 1x1 Round Plate (#6141)

Photo 24, 25 3.7V Rechargeable LiPo battery or similar

Photo 26, 27 7.4V 500mAh Rechargeable LiPo Battery or similar

Photo 28, 29, 30, 31 XBee module, Xbee breakout board, and Palm Arduino Plus

Step 7: Front Caster

Following are the photos show the assembly sequence of the Front Caster.

Photo 1, 2 Black Technic, Axle Connector with Axle Hole (#4107081) and Red Technic, Axle 2 Notched (#4142865)

Photo 3, 4 Light Bluish Gray Technic, Liftarm 3 x 5 L-Shape with Quarter Ellipse Thin (#4234247)

Photo 5, 6, 7 Two Red Technic, Liftarm 1 x 2 Thin (#4186678) and Red Technic, Axle 2 Notched (#4142865)

Photo 8, 9, 10 Dark Bluish Gray Technic, Gear 24 Tooth (New Style with Single Axle Hole) (#4514558) and Cross Axle 6M (#3706)

Photo 11, 12 Light Bluish Gray Technic, Liftarm 3 x 5 L-Shape with Quarter Ellipse Thin (#4234247)

Photo 13, 14, 15 Two Light Bluish Gray, Plate Round 4 x 4 with Hole (#4515351) and Two Light Bluish Gray, Dish 4 x 4 Inverted (Radar) (#4211664)

Photo 16, 17 Two Dark Bluish Gray, Dish 2 x 2 Inverted (Radar) (#4211010)

Photo 18, 19 Red Technic, Axle 2 Notched (#4142865)

Photo 20, 21 Angle Element [5], 112.5 Degrees (#32015)

Photo 22, 23, 24 Cross Axle 3M (#4519)

Step 8: Wheels and Accessories

Following are the photos show the assembly sequence of the Wheels and Accessories.

Photo 1, 2 Two Black Brick, Modified 1 x 2 with Studs on 2 Sides (#4253815) and Two Dark Bluish Gray Tile 1 x 2 with Groove (#4211052)

Photo 3, 4 Four Dark Bluish Gray Minifig, Neck Bracket with Back Stud (#4210469)

Photo 5, 6 Two Dark Bluish Gray Tile 1 x 2 with Groove (#4211052)

Photo 7, 8 Two Trans-Yellow Plate, Round 1 x 1 Straight Side (#3005744)

Photo 9, 10 Two Light Bluish Gray Lever Small Base with Black Lever (#4221775)

Photo 11, 12 Two Light Bluish Gray Pneumatic T Piece New Style (T Bar) (#4211508)

Photo 13, 14 Four Light Bluish Gray Arm Mechanical, Battle Droid (#4211658)

Photo 15, 16 Two Light Bluish Gray Pneumatic T Piece New Style (T Bar) (#4211508)

Photo 17, 18, 19 Two Light Bluish Gray Technic, Liftarm 1 x 4 Thin with Stud Connector (#4211561) and two Light Bluish Gray, Dish 10 x 10 Inverted (Radar) with SW Tank Droid Pattern (#4549191)

Continue on to Two main wheels

Photo 20, 21 Two Black, Round 2 x 2 with Axle Hole - New Style with + Opening (#403226)

Photo 22 Turn both wheels upside down.

Photo 23, 24, 25 Two Black, Round 2 x 2 with Axle Hole - New Style with + Opening (#403226)

Step 9: Weapons

Following are the photos show the assembly sequence of the Weapons.

Photo 1, 2 Two Black Bar 6L with Stop Ring (#4538722) and Two Black, Cone 1 x 1 without Top Groove (#4529236)

Photo 3, 4 Two Black, Cone 1 x 1 without Top Groove (#4529236)

Photo 5, 6 Two Black Technic, Axle Connector (Smooth with x Hole Orientation) (#4512363)

Photo 7, 8 Two Light Bluish Gray Technic, Axle 3L (#4211815)

Photo 9, 10 Two Black Technic, Axle and Pin Connector Perpendicular 3L with 2 Pin Holes (#4173970)

Photo 11, 12 Two Black Technic, Pin Long with Friction Ridges Lengthwise and Stop Bush (#4140801)

Photo 13, 14, 15 Two Light Bluish Gray Technic, Pin 1/2 with 2L Bar Extension (Flick Missile) (#4520320)

Step 10: Tail Wings

Following are the photos show the assembly sequence of the Tail Wings.

Photo 1, 2 Four Connector Peg (#3673)

Photo 3, 4 Two Black Bar 6L with Stop Ring (#4538722) and Two Black, Cone 1 x 1 without Top Groove (#4529236)

Photo 5, 6, 7 Two Connector Peg with Knob (#4274) and Panel Fairing # 2 Large Short, Large Holes, Side B (#32191) and Panel Fairing # 1 Large Short, Large Holes, Side A (#32190)

Photo 8, 9, 10 Insert the inner slots of the rear wings into the connectors.

The robot is completed!

Step 11: Summary

That was really fun to make something new out of something that is already exist.

The project could be extended further by adding some sensors to make the Droid to be line following robot, or adding light sensor to detect light, or some other stuffs to make the Droid doing things you want it to do.

Following are the photos of the finished 'Velocipede' Droid, and video shows 'Velocipede' Droid in Action.
Note: I tried the Droid on different surfaces. It seems to me that the smooth hard surface work best. The carpet is the worst the wheels did rotate freely, and the droid could not move on this surface at all. The rough concrete surface didn't work well either.
Also I did not used any of the Radio Controlled module in this video. I did program the Palm Arduino Plus to drive the motors by itself.

Thanks for reading.
And if you are building the Droid, I would love to see picture of your 'Velocipede' Droid.

Video
- 'Velocipede' Droid in Action!