As an avid maker of "things that Seg" this one is inspired by the 1970's Raleigh Chopper bicycle.
I was recently involved in the Hackaday competition with the MediCycle: MediCycle This was a big one wheeled electric motorbike styled machine. Impressive looking maybe but quite difficult to ride and if you fell off it really hurt:
I have also built all sorts of other self-balancers after starting in 2008 with a skateboard design: self-balancers site
Having learned the lessons, for this machine the objectives became clear:
- Lightweight, fun, more like a bicycle in construction.
- It is strictly not a unicycle but is a di-wheel or di-cycle.
NOTE: I have other instructables describing self-balancers that would be easier to build than this one. This one does require some tools, fabrication skill and a welded frame. The self-balancing electronics described here could be used in other projects with slight modification, such as a Segway, and are up to date using an easily obtained digital IMU.
Extra features 01/01/2015:
- Twist grip speed control on left handlebar.
- Uses a gyro to resist sudden spins when going straight, for example if one wheel hits stone.
- Brake levers each side are actually to steer left or right.
- Overspeed "lean back" automatically stops you going too fast and falling off the front if motor power >70%.
- If you pull both steering levers simultaneously, they act as a handbrake and machine will lean back and slow down.
NOTE: 27/05/2015An error in the wiring diagram has been corrected. "Deadman" switch is wired to digital pin 4.
NOTE 23/6/2015:One person building this found that the IMU "locked up" and stopped talking to the Arduino. He solved it by making sure he used the SAME GND PIN on the Arduino for both the IMU GND wire and also the 0V wire from the Sabertooth. There are several GND pins on an Arduino Mega and they are connected to each other on the board, however he found it was more reliable if you use the same one for all your GND connections to the Arduino.
Main parts list, not everything, but the main key parts:
- Sparkfun 6dof digital inertial measurement unit (IMU). (Part No. SEN10121). Most of my previous projects used analog output IMU's which were useful as you read the voltages from the gyro and accelerometer sensors using the analog ports of an Arduino. For this project I am reading the tilt angles using the FreeSix IMU code of Varaseno. $39.95
- Arduino Mega 1280 (same price online as an Uno, but has hard wired serial ports which are useful). As low as $16
- Dimension engineering Sabertooth 2 x 25 Amp motor power controller. Not the cheapest but has self-protection features which reduce risk of it burning out, so can be used in all your other similar projects. $124.99
- LED battery voltage indicator. Incredibly cheap on ebay. Example: $1.65 inc. shipping! LED voltage indicator
- Serial LCD display module. Example: 4 x 20 Serial LCD display NOTE: Some cheaper ones on ebay don't always work. Get one from a supplier that also sells Arduino's. Not essential to have this but useful for status updates as you ride the machine. Approx $29.95
- MY1016Z3-24V brushed gearmotor x 2. Has 6:1 reduction gear built in and sprocket for a chain already fitted. Designed for electric bikes. Comes with sprocket that fits 410 standard bike chain. $76.49 x 2
- 410 standard bike chain. NOTE: In the photos I am using belt drive but to be honest if doing it again I would stick with chains.
- Two big sprockets to fit to wheels. Needs to have between 4 to 6 times as many teeth as on the motor sprocket. Make sure they are for 410 bike chain. Get cheaper solid steel ones possibly, as easier to drill the 6 holes that will allow it to be fitted to the disc brake mounts of the wheel hubs.
- Mountain bike front wheel hub (with 6 threaded holes for mounting a brake disc) x 2.
- BMX bike rim x 2, fitted to the above hubs for me by a bike shop. The reason I did not use a BMX wheel and hub off the shelf with disc brake mounts is because apparently very uncool to have a BMX bike with disc brakes so disc-brake BMX wheels are not made. Need tubes and tires too.
- Same bike shop fitted a spacer tube between inner and outer bearings of each hub. This means they can be compressed sideways by a bolt later on without huge side-loads being placed on the bearing internal rollers.
- Rally car emergency power-off switch. For safety (stops small children turning it on when you are not with it), can handle 100 Amps, and looks a bit like the Raleigh Chopper gear-shift from a distance.
- Battery holder for 6 AA batteries. To power the Arduino separately from the motors. I prefer to do it this way so Arduino gets stable ripple free voltage no matter what punishment you are giving to the main battery.
- 24V battery. I used a "Headway" kit of 8 LiFePO4 cells. You could also use 2 x 12V 7Ah (or above) lead-acid batteries to save money which would be fine but would not run for as long. I mounted mine in a box in a holder which allows the pack to be easily removed and inserted in another project so may save money in the long run. $273 from China.
- "Ape hanger" handlebars for a chopper style bicycle. Real Raleigh Chopper ones are stupidly expensive so I used generic copy. $30
- Long saddle. Again a real Raleigh Chopper one would be very expensive even in poor condition. However in the US there are loads of companies making low priced "banana seats" which look nice, are long, and I think are made for retro styled Schwinn bikes. Mine came with a rear chromed "sissy bar." $30 with chrome bar.
- I mounted my motors and wheels on two thick alloy plates. You could weld up a frame to do the same job but make sure you measure everything lots of times.
- 40mm spacers (also sold as "stand-offs"). 8mm thread one end and 8mm socket the other end. These were important to get the geometry of everything correct. Correct name is: "M8 Stainless Threaded Stand off Pillar Bolt Extender Extension Fitting" About $9 each but worth it. Example from UK ebay
- Box section steel. 1 inch for seat mount etc and some 40mm wide so it exactly fits between the two plates that have been bolted together using the 40mm stand-offs.
- Big fuse say 75 Amp and holder for it.
- Twist-grip 5K Ohm potentiometer. In reality there is only one make of these, used as throttles for electric scooters, made by Magura. Example US link: Magura US example Link to a UK seller: UK example seller$60
They also sell a matching regular handlebar grip for the other side that matches.
- Children's electric scooter brake lever x 2. Search and you can find them very cheaply. Approx $5. They have an electric switch in them which means we can use two of them to steer left and right. Example link: E scooter brake lever
Raleigh built a copy of chopper-like Schwinn Sting-Ray, launched it in 1966 in the US, but it was not a success. They sent their chief designer, Alan Oakley, to the US to look into the youth market. On the flight home he drew the basic design on the back of an envelope. At around this time drag racing was becoming popular in the UK after some US cars had come over for exhibitions. The 1972 Raleigh Chopper was a hit and is now a cult classic bike. It had the wide large rear tire with the small front and these had red lines on the sidewalls. The "ape-hanger" handlebars, long saddle and plenty of chrome completed the look. The final touch was the chunky gear-shifter dangerously placed in front of the seat, connected to a 3 speed gearbox. It had some stability problems, two people could fit onto the Mk1 saddle at the same time, it was heavy and hard to ride long distances. However to a 12 year old it was just the height of 70's cool.
I am basing the latest self-balancer loosely on the Chopper for several reasons.
- The previous machine (MediCycle) for the Hackaday competition was big, heavy and like a one-wheeled motorbike, designed for maximum visual impact. It needed to be treated with respect and if you fell off you would be likely to get hurt, as I know from personal experience.
- This new machine is to be built with lightness in mind, more like an electric pedal bike in design.
- It needs a long saddle so you can position yourself back and forth along it so that you have your weight at the correct balance point to make it work. Clearly a Chopper-style saddle would be very convenient for this compared to a regular bike or unicycle saddle.
- The "ape hanger" handlebars also conveniently can be mounted so they stick forwards in front of the wheel to get the weight distribution of the rider correct, while using the least metal tubing to do it.
- It gives me an excuse to put some chrome at the back of the seat and on the handlebars for a bit of "bling."
Other experimental features being tested out:
- Toothed belt drive to avoid any slackness in chain when moving from forwards to backwards. It works fine but to be honest I might just use chain drive if doing it again, they would probably have been fine.
- Aircraft grade alloy mounting plates for the entire drive mechanism each side.
- DiWheel design (2 wheels one next to the other) BUT not like a Segway, the legs of the rider will go OUTSIDE the wheels. This should make it relatively easy to learn to ride, stable even when stationary, capable of turning on the spot.
- Could even be seen as a radically different "take" on the concept of a disability scooter.
- Lowish seat height so feet can easily be put onto the ground if any malfunction.