Arduino Segway

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Introduction: Arduino Segway

Hello!

More than 3 years ago I started to tinker a homemade segway. Though it's still not really finished (I have to replace the 250W Motors by 500W-models) my children are able to drive around.

If you're going to build one you will Need the following parts:

* wheelset: In my case I use 12 1/2 x 2.75 tires usually taken for dirt bikes (f.e. www.amazon.de/HMParts-REIFEN-MIT-SCHLAUCH-12/dp/B0038X9ODA; http://www.ebay.com/itm/Tire-Rear-Wheel-Mini-Pocket-Dirt-Bike-47cc-49cc-50cc-COOLSTER-QG-50-RX1-Traxxis-/182346539856?hash=item2a74b36350:g:BxUAAOSwh6xTtmwX&vxp=mtr)

* batteries: I use two 12V/12Ah lead accumulators to get 24V for the Motors

* Motors: At the moment two 24V/250W models but the 500W-motors are already waiting for their use

* for the axle I asked a local welder and some of my bicycle-parts (bar, stem) fit perfect too.

Step 1: The Motor Driver

First I tried a homemade full-bridge. To control it I used the analog-out (pwm) of the arduino. But with this variant I didn't succeed. Therefore I bought a commercial product, a 2x60A Motor Driver from sabertooth (www.dimensionengineering.com/products/sabertooth2x60).

The arduino is able to communicate with the sabertooth via a simplified serial code.

Step 2: The Angle Determination

To determinate the current angle I first used a separate accelerometer (ADXL335) and gyroscope (LY530AL). Last week I changed this Setup and the two boards have been replaced by the MPU6050.sensor, which combines the two elements.

The advantage of the gyroscope is, that accelerations don't influence the measurements. The disadvantage is, that the gyro has a drift and after a while the angle goes higher and higher.

The Advantage of the accelerometer is, that it doesn't show any drift like the gyro. But it's being influenced by accelerations, which change the Output.

A filter combines both pro's so the calculated angle is near the real value. This filter can be a simple complementary-filter (like in the Picture) or the more complicated kalman-filter. The Input of the kalman-filter is the actual angle measured by the accelerometer, the angular Speed measured by the gyroscope and the time-step between two measurements. With these Parameters the kalman-filter is able to calculate an angle, which follows the gyro in times of high accelerations and in times of less accelerations it approaches the value of the accelerometer. In the Picture you can see the drift of the gyro and the good Job of the filter.

Step 3: The PID-controller

The segway tries to get the angle down to 0°. If the angle is positive, the segway brakes or accelerates backwards. If it's negative the segway accelerates forward.

But which signal get the motors? This is exactly the task of the pid-Controller.

The proportional-part: The angle should be 0°. So the greater the angle, the higher the speed of the motors.

Mathematically you can write:

angle_error = angle_should - angle_is

p-Motor-value = k_p * angle_error

The integral-part: When the current angle isn't zero, the Controller tries to get the segway horizontally again. But this approach shouldn't be slow and the smaller the angle-values, the slower the changes. Therefore the Controller allows a faster approach with the disadvantage, that the movement doesn't stop at 0° and goes a bit to the other side. This behaviour is guaranteed by the integral-part. All the angles are added (integrated) and this integral over time should be Zero. So if the angle is f.e. positive for a while, the Controller tries to get the seqway into the negative area. This guaranteeds faster approaches...

Mathematically you can write:

error_sum_new = error_sum_old + error

i-motor-value = k_i * (error_sum_new)

error_sum_old = error_sum_new

The derivative-part: Not just the current angle is important but also the changes of the angle. Let me explain: If the angle is f.e. 10° and it doesn't Change a lot, the Motors don't need to correct this shift very fast. But if the angle is 10° and it changes very fast (high derivative), than the motors have to correct this also very fast.

Mathematically you can write:

d-motor-value = k_d * angular Speed

Finally you get: motor-value = p-motor-value + i-motor-value + d-motor-value

Step 4: The Complete Setup

Now it's time to start the segway. To drive not only straight ahead you have to mount two buttons. When you push f.e. the right one, the left Motor increases Speed and the right Motor slows down. To ensure smooth transitions the added and deducted value starts at zero and increases step by step (+0.5 every loop) until he reaches the maximum value (f.e. 30).

To try out your own segway I 've attached the simple program for you. Good luck and don't follow the segway-inventor James Heselden down a cliff ;-)

Maybe you want to take a look at my YouTube-channel: www.youtube.com/user/stopperl16/Videos

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    30 Discussions

    Nice to meet you
    Your research is very good
    I am a teacher of an industrial high school in Japan.
    I have a request
    I referred to ”Step 4: The Complete Setup”, but the motor does not work.
    ”FXLSYHKIW6PNEU6.ino” could also be compiled.

    I'm sorry.I still need to study more.
    It would be greatly appreciated if you could explain the details.

    0
    None
    AirraB

    8 months ago

    Can i use another motor driver? i would like to use your project as reference in my project but the driver that you used is not available in our country and the cost was too high heheh... can you give me some advice about the motor driver? thanks ^_^

    thank you for sharing, you have making the best project for me ..you're actually a professional engineer.!

    very good, am making a robot with that code, and its working!

    Way too advanced for me but i know some people in stockholm that made one at maker space. Was very impressed!

    Cool project and nicely documented!

    How much weight does the current setup (250W motors) carry around?
    and do you have some kind of encoders or odometry for the wheels?

    My question, too: why did the Arduino PWM O/P and a bridge cct not work? What does the commercial controller do that a basic DIY set-up not do?

    1 reply

    Take a look at my YouTube-Video "segway - first Version" ;-)

    Hi. What problems did you encounter with Arduino PWM control and H-bridge?

    1 reply

    Hi!

    Take a look at my YouTube-Video: Segway-first Version...

    Then you'll clearly see the Problems I had with the first Setup ;-)

    Yes, you'll need a second button (voltage-divider with the 10 kOhm-resistor)... Pin 12 and 13 are low, if the button isn't pushed. If you push the button for steering, the signal goes high...

    Therefore I ask in the program: if (steering-button-right or left) = high then ...

    I've changed the Picture of the circuit, because in the first version the status was low if the button was pressed ;-)

    Do you have a cost estimate? What are its safety features? I'm a senior, hoping to move to a walkable community where I still might have a need for speed. This looks better than an electric bike. Could a double kick-stand be added to the front edge of the platform to make it stand upright while parked, if it doesn't do that already?

    1 reply

    Concerning the costs:

    * Motors 100 Euro

    * Sabertooth motor driver 150 Euro

    * complete wheelset: 120 Euro

    * chain, pinion: 30 Euro

    * arduino, MPU6050 sensor and other electronics: 15 Euro

    * lead batteries (used): 30 Euro

    The safety Features are, that in the program the maximum-angle is limited with 30 degrees. But I don't have a redundant-System like in the original segways. So it's just a bit for stunt-Drivers ;-)

    If you let the segway alone, it keeps standing horizontally. If you incline it Forwards or backwards the Motors will stop.

    Did you already try the 500W motors ? I think that maybe your 250W motors aren't driven properly, or maybe they are old and have lost some power. 500W is about 0.7 hp, which is one fourth of the average power of a 50cm3 gas engine. Such an engine can carry a load of 200kg at a speed of 100km/h (62 mph) !

    4 replies

    It s because their children are in the nitro circus team. They dont have enough power to pass the triple backflip yet ;)

    I could be wrong, but it seems to me that even a couple of 50W motors would be more than sufficient for this application.

    I don't think so. 100 W is 1/7 horse power and you need a lot of power, especially at low angles. But that is difficult to manage, maybe with a higher threshold, from which the Motors start at low angles...