Easy Build Self Balancing Electric Skateboard

What is it?
Twin wheeled skateboard that works like a Segway. Electric skateboards exist already with powered rear wheels. Plan here was to build something like a Segway but in the form of a skateboard. It knows which way is "up" via a combination of gyroscope and and accelerometer sensors, using a complementary (not complimentary) filter which reads and combines data from both 100 times per second. Steering by a simple rocker switch in hand controller (or a rewired Wii-Nunchuck as in photos if you are more ambitious).
Upper photo is original budget version with two lead-acid batteries and solid wheels. Lower photo is 2013 not-so-easy-build version, with pneumatic tyres and Headway LiFePO4 batteries just to see how far I could push this overall concept. More on the new one is here: https://sites.google.com/site/onewheeledselfbalancing/Home/18-2013superskate

NOTE: All my self balancing projects are now documented on my Youtube channel here: Click

UPDATE regarding IMU's and CODE (December 2014):
This Instructable is a little old now and the IMU used is no longer available. Therefore I have removed the pages that describe the IMU wiring and the code as it is confusing people.

If you use a digital Sparkfun 6dof IMU (which is much more easily available) then for instructions on how to use this with an Arduino, to control a self-balancing skateboard, with code, then look at this new Instructable of mine here:
https://www.instructables.com/id/Arduino-Self-Balance-Controller-using-DIGITAL-IMU-/

Also there is a scooter I have made inspired by the 1970's Raleigh Chopper with updated (December 2014) software using the same easily available digital IMU from Sparkfun: Raleigh Chopper inspired self-balancing scooter.

If you want to build a big unicycle check out this one I built with two friends for the 2014 Hackaday competition, called the MediCycle: http://hackaday.io/project/1156-Medicycle---Urban-...

Can I buy one ready built?
Well, looks as if you now can. The German S-Walker looks strangely familiar!
http://www.s-walker.com/index.php/de/products/board

Also there is the "One-Wheel" single wheeled skateboard which was a recent Kickstarter project: One-Wheel

For a good electric unicycle you can buy check out this very recent Russian one (about US$1000): Russian electric Monocycle

How does it stay level?
It controls the wheel motors so the wheels always stay under your centre of balance, like balancing a broomstick on your fingertip. This is called a "PID" control system and is used for all sorts of control situations. Think of the 363 feet high Apollo rockets used in the moon landings..........
Q: How come they didn't just fall over when they took off? They took off incredibly slowly for the first few seconds, tailfins would have no effect, far slower than Shuttle launches. Watch this video - it takes a full 10 seconds just to get to 100m and clear the launch tower:
http://www.youtube.com/watch?v=_PEGi3k6yNQ
A: They had engines mounted on swivelling mounts hydraulically controlled by a PID control system (lots of analog electronics I think involved too). First stage projected guidance system failure rate was approx. 1 in 256 which was considered an acceptable risk (!)

Background:
In 2008 I saw a YouTube video by Ben Smithers of his one-wheeled self balancing skateboard whizzing around a car park in Norwich UK. http://www.robosys.co.uk/ Video: http://www.youtube.com/watch?v=HGbbag9dklU
It turns out he was a Lotus cars controls system engineer - which makes sense.
Also see Trevor Blackwell's site: http://www.tlb.org/eunicycle.html
Meanwhile I wanted to teach myself microcontroller programming and, totally underestimating the task, thought this would be a great fun way to do this. Advantage of two wheelers is that they turn more easily and can turn and balance even when stationary - which is fun. I (used to) prefer skateboards to segway clones as you just jump off if it goes wrong without tangling in the handlebars.

Why an Instructable?
Having learned lessons the hard way I thought it would be worth redesigning the project around an Arduino microcontroller, then seeing how low-cost and easy-build I could possibly make it. Something like this is not for the complete Arduino beginner, nor is it that "easy" however this is about as easy as a self-balancing machine is realistically ever going to get.

Skills:
Projects like this lend themselves to being built as a team. Some examples below were built as college projects. There are
i) some electronics (not making circuit boards, just wiring and soldering) to master,
ii) some mechanical fabrication; this version is designed to require no welding, just nuts bolts and some woodwork. Wheel/sprockets/axles/bearings come as a unit (electric scooter rear wheel assemblies).
iii) some programming; the programs (Arduino sketches) you need, including those to help debugging, are attached (P43 - 47).
There are; IMU tester, motor tester, balances-nothing-else, rocker switch steered and potentiometer steered code examples.

How much does it cost?
I realised when costing them up that the cost of a self balancing robot would only be a little lower than that of a ride on machine, therefore I went for a ride-on machine! For me the cost was about $300 equivalent PLUS whatever batteries you choose to use. I recommend starting with lead-acid batteries then make improvements later once you have a working machine.

Why do it?
i) For the challenge of doing something original. Segway skateboards have been invented in principle BUT there is huge room for improvement.
ii) Making something that is practical and intuitive to ride is quite a challenge in terms of both electronics/software and fabrication/packaging. Cannot all be done on a computer. Eventually you have to actually build something then incrementally improve it. Despite the myth of "Eureka" moments, the truth is that this is how most innovations come about, by slow incremental development and hard work. Edison did not invent the lightbulb. He developed the first practical lightbulb.
iii) To educate yourself, you might become a world expert, there are no textbooks so you are genuinely pushing into the unknown with each machine you make. Few things as an individual hobbyist allow you to truly do this.
iv) These machines are really good fun to ride!

This instructable:
There are a large number of pages in this. This is deliberate, if you are serious about building one then you need every single step documented.

Additional information:
I have documented all my machines both good and bad on another website here:
http://sites.google.com/site/onewheeledselfbalancing/

Can I do this as a beginnner?
The fabrication has been deliberately kept really simple.
The soldering between sensors and arduino board needs to be good quality!
If you are new to Arduino I would recommend buying an Arduino starter kit. These come with some ancillary sensors etc. and a set of about 12 tutorials. Work through them all (about 2 days work) and read a beginners book to Arduino. You will then be ready.

Can I build a SegwayTM clone?
Yes. Australian SciTech group have built a very low cost machine using a version of the Arduino code from this Instructable: https://www.instructables.com/id/Self-Balancing-Scooter-Ver-20/
Here also is the Thatch No-Way Segway using my code almost unaltered: http://www.youtube.com/watch?v=R4ax3N0UW38 and more recently the Jackal: Jackal

Has anyone else built one?
Ages currently range from 12yrs to 81yrs.
This Instructable is over a year old now, so yes indeed, people have. Here are a few I know of:
1) Skateboard: http://www.youtube.com/watch?v=kSW7YXLCjqk
2) Skateboard: http://www.youtube.com/watch?v=u-uUidBZEnM
3) The Velociryder: http://www.youtube.com/watch?v=xvfUIxusPZw&feature=player_embedded
4) Great board video - Buffalo State College senior project: http://www.youtube.com/watch?v=FEaTxahyQxc
5) Another board based on this Instructable: http://www.youtube.com/watch?v=vhbH_AmIKZA&feature=related
6) A board based on old FIRST robotics parts + code from this instructable (FIRST robotics was started by Dean Kamen who also invented the Segway, to encourage youth to get interested in engineering): http://www.youtube.com/watch?v=Vh9LpNQ_S0k&feature=related
7) Carbon fiber racing car seat with 2 - the SciChair: http://www.youtube.com/watch?feature=player_embedded&v=HtivH7INpZ4
8) Carey's self-balancing platform, good video: http://www.youtube.com/watch?v=ngMJcxeB7og
9) Really cool video (on clifftop path by the sea): Skate auto-balancé http://www.youtube.com/watch?
10) The KSLURP board from Malaysia: http://www.youtube.com/watch?v=x3O2NkjJOlg
11) The MIT Seboard, video clip: http://www.youtube.com/watch?v=zZQb-w_wyhM
12) The SITWAY sit-on machine by the 81year old gentleman above, with video: https://www.instructables.com/id/SITWAY/
13) This one has nothing to do with me but is such a really cool inspirational project I include it here, the TILTER skateboard, with hub motors and a suspension system: http://www.youtube.com/watch?v=WsYukdSO64A&feature=player_embedded
14) New one wheeler from team cosmos with some technical information and video here: http://teamcosmos.com/skateone/index.shtml

Potential areas of improvement
It would be cool if people took this design and improved upon it.
The only way I can envisage further improvements in terms of weight reduction and compactness on my 2013 design with Headway cells and pneumatic tyres would be as follows:
a) Make frame from welded alloy.
b) The cheap scooter motors are quite heavy so use equally powerful but lighter, smaller combat robot motors.
c) To reduce length and make even more compact, someone, say a mech eng student, could design a neat hub motor for each wheel using epicyclic reduction gears.


NOTE:
You build these at your own risk. If tilted they WILL accelerate to correct the tilt. If you are not on the board, this means it can fly across a room or into your head. This is why you have to have an emergency hand switch that cuts the power if you let go of it. If it develops a fault it does not have multiple redundant systems like a real segway, most likely you will fall off! The code is not guaranteed against any bugs. If you don't believe me here is a video of Clint Rutkas developing a similar machine, also featuring some holes it punched in the walls of his apartment! http://vimeo.com/2013773

Have fun. Treat it as an adventure. Once you get it to balance there are many ways to improve it.

John

This is a Sabertooth 2 x 25Amp (40Amp peak) robot motor controller for medium sized robots with 2 motors.
Each motor has to be able to go forward and reverse, and switch direction frequently and rapidly without mishap.

The ones I have are 250 Watt 13.7 Amp peak (that is what it says on them). Watts = Amps x Volts and I have 24 Volts so that makes 10.4 Amps using that calculation. Anyhow, well within limits of the Sabertooth.

NOTE: It will handle most forms of abuse and will shut down rather than burn out and so on. It will NOT tolerate having the power supply leads conncted up back to front however - be warned.

Also it has to be able to handle a lot of power as if falling over, motors have to be big enough to allow machine to accelerate fast to bring itself beneath you once again.

Therefore unless you really know what you are doing, designing your own is out of the question.

The sabertooth can handle many types of misuse but you mustn't connect the batteries to it back to front!

The Arduino can send control data to it in several ways but I have chosen a mode called simplified serial mode. The Sabertooth website has a lot of downloadable information on all this.

It isn't exactly low cost but worth the money.

My "de-luxe" self balancing skateboard has a wireless Wii Nunchuck as the control system.

However here we are interested in reducing cost.

Therefore we have a cable with a hand controller on the end.

This has a dead-man switch (cuts motors if you let go i.e. fall off)
Also has steering left and steering right plus a switch to fine-tune the balance point of the platform.

See links on first page to my newer Instructables desribing how to wire up newer IMU's to an Arduino and the Sabertooth, with code.

Arduino analog inputs all used apart from one for balancing etc.

All handcontroller inputs go in through the digital input pins on other side of the Arduino board.

The cable is fixed to the deck using simple cable ties again so the wires are not stressed where they are soldered to Arduino input pins. The cable itself is screened cable with 6 or more wires inside it.

You can also see the 10K potentiometer used to control the "overall gain" function. This allows simple user adjustment of the machine between feeling "squishy" and "tight" as you ride it.
NOTE: See my links on page 1 to my newer Instructables describing how to wire up newer IMU's to an Arduino and use it to control the skateboard, with code.
These newer versions do not use the potentiometer any more.

 

I fixed the IMU with blu tack to start with as you always end up with it back to front or the wrong way around!

When you get it working then fix it properly. Protect it from debris from the wheels and keep it near to centre of the deck by the way - it works best there.
NOTE:  If you hold the IMU with Blu-tack initially, make sure it is a decent sized blob - if IMU is wobbly the board will bahave erratically and oscillate wildly.

One example of how you might mount an IMU and an Arduino on a board.

There are many ways to potentially improve this project, here are just a few

Powering the Arduino
Using a 9V battery to power the Arduino is quick and simple. However it won't actually last that long and when it runs out you may fall off!

A better option therefore is to use a commonly available voltage regulator to convert the 24V from main batteries to a little over the 7V the Arduino needs and run it that way.

The problem is that to go from a big voltage to a much lower one means the voltage regulator generates a lot of heat and may need a heat sink. My batteries are already a little on the small side so I looked for a more efficient way to do this.

A solution does exist; it is called a Tracopower TSR 1-2490. This particular one puts out 9V which is fine for the Arduino. The way it works is very clever but it is very efficient and generates almost no heat.

Similar devices exist to power radio receivers in R/C aircraft from the main batteries, but the one I have used is small and reasonably priced.