Introduction: What's Inside My RC Lego BB8?

About: I studied Electrical Engineering and a lot of other things. I'm always driven by my passions. Please visit also my Youtube channel.

I entered the contest: "Sensors" as I've used 4 tilt switches (SW-520D), to control BB8 using the movement of my arm. Please vote for me!

Hi there,

last year I made a fully working RC version of BB8 using Lego Star Wars parts, so I thought it was time to show my "calvary"... ehm, better to say the process I went through, to make this cute droid.

At that time there were a lot of similar projects around, but no one of them had a "reasonable" size of the droid for me. I don't have too much space at home, therefore I have to shrink everything I want to make.

As you can see from my previous projects, I've created a lot of mini/micro/nano stuff

(R2M8N, K/\steroid, Starkiller Base Game and my V.E.P. Very Easy Plane).

Anyway, going back to BB8, you need the Lego parts listed in my Instructable...

Mainly you have to buy the planet and 4 corner/pieces for the head (4586275 - 88293 white)

1x 360 Degree Spin Spins RC Remote Radio Control Wheelie Stunt Car (White or Orange)

1x Connector Micro JST 1.25 2 Pin (Female)

1x Lipo Battery 3.7V 300mah 25C (Always use all the precautions when you handle these batteries)

1x DC motor 7x16mm

2x Magnets 10x2mm (please don't keep these magnets at hand if you have little kids)

8x Magnets 5x3mm (please don't keep these magnets at hand if you have little kids)

1x Lego Bush for Cross Axle

1x Lego Axle Extension 2M

1x Lego Axle 4

1x Lego Axle 6

4x Washers 6x25mm M5

2x Washers 4x25mm M3

3x Sinkers (lead) 50g

1x Popsicle Stick

1x Cork

2 pieces of self-adhesive velcro

For the sounds unit

1x DFPlayer

2 pushbutton

1 3.7V Lipo Battery 300mah 25c

Glue UHU Por

Step 1: Transforming a RC Stunt Car in a Motor Unit That Moves BB8

There is a very good "tutorial/teardown" about this RC stunt car on Instructables, that I recommend to watch.

Basically you should start to disassemble it, removing the body of the car (there are 3 small screws).

Between the receiver and the chassis of the car there is exactly the space required to insert the Lego axle 6, that you can join to the axle 4, using the axle extension 2M. I did some tests with the axle 10 but it flexes, because of the weight, so the lead/sinkers rub against the inner surface of the planet. It's a matter of millimeters.

When you finish to join the axles, you should glue to the body the bush for cross axle and the extension (like shown in the pictures).

Now the body of the car won't fit anymore because of the Lego axle, therefore you should cut 2 notches that allow to re-position it as it was, and also you should shorten the part close to the anterior spinning axle, because otherwise, adding the washers they will rub against the body of the car.

Secure the body to the chassis using 2 rubber bands.

Now detach the anterior wheels and start to insert 2x washers M5 and 1x M3 per side.

Using (very carefully) a cutter, remove the rims, leaving just the spokes of the anterior wheels.

You basically have replaced the original wheels, with a bunch of washers.

At this stage the unit should work already (using just the planet). so you can start to have some fun with the RC ball you've just made.

Please be aware that in order to have grip inside the Lego planet, the distance between the wheels should be around 6cm.

Step 2: Installing the 7x16mm DC Motor That Spins the Posterior Wheels of the Car and the Battery

From now on this transformation will be a bit tricky.

The 6x14mm motor is not powerful enough to spin the planet and the head (with the magnets), therefore it has to be replaced with a 7x16mm one.

You should remove the 6mm motor and the gear box, enlarging the cylinder/support of the motor.

To do that I used my soldering on iron (using a tip that wasn't retaining the tinning anymore).

Please be aware that if you use your usual tip to do this job, you'll ruin it, therefore use a very cheap one/spare one.

Don't rush doing this process, otherwise you'll melt the holes of the gear box, making it unusable.

Now you should remove the 2.4V battery that normally powers the stunt car.

Just disconnect the cables and attach the female JST connector double checking the polarity using a multi-meter.

If you don't do that there are chances you'll fry the receiver of your stunt car, therefore please check it.

Attach the battery using some velcro to the posterior part of the chassis of the car.

To be sure that the motor doesn't move you can cut some pieces of cork (or you can use a piece of the Popsicle stick), gluing them to the exposed part of the motor.

Step 3: Attach the Sinkers to the Spinning Axle and Painting the Body

I cut the sinkers in small pieces and I've glued them together, being sure they do not rub against the inner part of the Lego planet.

When you are gluing them, you can use some sell-o-tape to keep all the pieces together.

When the glue is dry, you can remove slowly the tape.

Warning!!! Be sure the sinkers are firmly glued together before you spin the axle.

That's why you should use the sell-o-tape (it helps to keep them together).

Please be aware that you have to put 150g of weight, to overcome the inertia generated by the rolling motion.

To give to the BB8 Unit a better look, I have painted the body of the RC car in black.

P.S. Use the weight of the battery to counter balance the inertia generated by the head of BB8.

aka I've moved the battery forward.

Step 4: Assembling BB8 Head

Following the instructions of my previous Lego BB8 Instructables, assemble the head of the droid.

If you want to be sure that the head will stay in one piece, you can add a drop of glue on each side of the 4 Lego corners. (well, this tutorial is not for Lego purists :)

Now you should stick at least 3x5mm magnets inside each corners, having one side positive and the other one negative (possibly as shown in the picture).

In this way BB8 head will be slightly twisted to the left.

Step 5: Attaching the 10x2mm Magnets to the Body

Even in this case, attach to the body of the car one side of the magnet positive and the other one negative

(possibly as shown in the previous picture). I separated the magnets using some pieces of the Popsicle stick.

In this way they will not drive you crazy when you are gluing them.

Apply also a piece of sell-o-tape to make sure the magnets will stay in place all the time.

If they move, they will start to produce friction and the planet will not roll.

Try to attach the head to the planet, (after you put the motor unit inside) and test it.
If 3 magnets per pole (+/-) are not enough, add 2 more.

To tilt the head of BB8 slightly forward, I've added a little strip (1cm) of foam at the bottom of the body of the car,

gluing it with UHU Por (foam friendly).

In this way the position of the head remains slightly inclined.

Step 6: Charger

I used the USB charger of an old micro drone in order to make the recharging cable for the 3.7V Lipo battery.

Please be aware that every time you recharge the Lipo battery, you should supervise it all of the time.

The other connector shown in the picture is for the Lipo battery of the sounds unit you'll find in the next step.

Step 7: The Sounds Unit

Now that BB8 moves he has to make some noise! :-)

I bought a DFPlayer Mini MP3 Module and following the diagram I've connected the push buttons and another Lipo battery, making a mini black box out of foam.

You can record some sounds in mp3 format, renaming them 0001, 0002, 0003 and placing the files under the root directory MP3 of your sd card.

Once I completed the sounds unit, I've attached it to the transmitter using some self-adhesive velcro.

Step 8: Add-on... Gesture Control!

I saw how cool it was the Force Band and I thought: "Ok, I can easily make a cheaper version of it."

I bought 4x SW520D tilt switches and I've soldered them to other side of the the buttons of another transmitter (same frequency),

Now I can control BB8 using the buttons and by the movements of my arm.

Step 9: Tool to Insert the RC Motor Unit Inside the Lego Planet

Last but not least, I made a mini tool (out of the paper clip) that helps me to align the Lego axle to the hole of the Lego planet. When I don't need it, 2 magnets keep it in place, inside the transmitter.

Sensors Contest 2017

Participated in the
Sensors Contest 2017