The Beancat
The Beancat is an all-wheel drive, battery powered bean bag chair, controlled by a Wii nunchuk. Getting a drink from the fridge has never been so much fun. The low profile drive, frame and controlling hardware are completely concealed so at first glance it’s just a simple bean bag.
Quick Facts
Budget: $400
Weight: 50 lbs
Top speed: 6 mph
Concept
A quick look at the conceptualization stage…
Imagine a bean bag chair that you could drive around, in or outdoors. A commuting vehicle, entertainment device and relaxation enabler all in one.
Why, you ask? Because we wanted to.
(Drive system concept sketch, one side)
The real challenge here was fitting everything into such an envelope that would not be obvious when looking at the bean bag. We didn’t want a bean bag that was simply sitting on top of a big, ugly frame. There should be some degree of mystery as to what exactly is going on here- as a matter of fact, how is that person driving around on a bean bag chair?
(Internal bean bag frame)
The bean bag itself would also need a little structural reinforcement so that it was fit to hold its shape and enable comfortable (and safe) riding.
(Prototype platform)
This was the first test of concept to see how small of a motor we could use. We actually hooked up a cordless drill to the front wheel and used it to pull one of us on the platform. The power wasn’t quite there so we switched to testing with a corded drill. Let it be noted that this was not the strong point in our decision making process. It resulted in my (Ed) jeans, underwear and right buttocks being sliced open.
CAD Models
Using Solidworks, we designed our parts for frame and drive train in what we deemed a pretty efficient manner.
(The overall drive frame)
The frame is aluminum. Each driving side is three inch square tubing and the front and back are three inch, ninety degree angle stock. The bottom has a screw on plate to keep dirt out of the innards.
(Wheel and sprocket assembly, exploded view)
(Wheel and sprocket assembly)
Each of the four assemblies has a hub which is pressed into the stock wheel. A bearing is pressed into each side of this hub, and then the protruding end of the hub is then pressed into the chain sprocket. In this way, each wheel idles on a stationary shaft attached to the frame and is chain driven by its motor.
(Entire drive assembly, one wheel)
Here is a close up of the way in which one wheel is driven. In the upper left-hand corner, the motor is directly coupled to a small sprocket, which is connected by chain to the next larger sprocket to the right. This is then directly coupled to a smaller sprocket that drives the wheel’s sprocket. The step down in gearing is necessary, as the motors we got were rated at 5000 RPM. (It works out well for this application though, for after the reduction we get a speed of about 300 RPM at the wheels and a load more torque.)
(Side assembly, with motors)
Here you can now see specifically how each side is driven, assembled and why the tubing was chosen as such. We designed the hub so that each wheel and sprocket assembly was restricted from side to side movement, and each shaft was also retained so that it could not move either. By drilling all shaft holes through both sides of the tubing in the same operation, we eliminated all needs for alignment of different plates. In the case of designing, making, and welding your own frame, this was invaluable.
(Circuit Board Schematic)
The controlling circuit board uses a microprocessor programmed in c to adjust the speed of each wheel. This keeps the chair on a straight path by default. When the joystick is turned to one side or the other, it adjusts the speed on each side of the vehicle accordingly for a turn radius based on how far the joystick is pushed. It can also drive and turn in reverse when the joystick is pressed backwards.
In Process Photos
(Hole spacing test piece)
The first thing to check was that the shaft spacing was correct before doing anything to the final piece. We used a scrap piece of aluminum and then assembled the motor, sprockets, chains and all to make sure that nothing was too tight or loose.
(Wheel hubs)
These hubs were turned out of aluminum on a lathe and then pressed into each wheel.
(Frame minus batteries)
Unfortunately we got so caught up in making the actual thing that we neglected to take any pictures from that test piece until this point. Let us fill in the blanks here to catch you up to the above picture.
- 3” tubing was cut to length, then faced and shaft holes drilled on the mill
- Top cutouts were then done on the mill as well
- Angled aluminum was cut to length and faced on the mill
- The rectangular frame was welded together
- Bottom plate was cut and sides were tapped for screws
- Wheels, sprockets, shafts and motors were assembled to frame
- Controlling circuitry was attached to frame
(Assembly, with one battery)
(Drive close up with battery)
Here’s a close up shot to show you how it all really looks assembled. You can see the clearance in the frame for each component and how compact the drive is. This is essential to the very last build step of the Beancat- the supporting frame.
(Walk the Dog)
The first run was a walking, rather than riding, test to double check all controls and functions. Note: You cannot run fast enough to catch it if you crank it on. You will rip your wii remote off and have to repair it. COOOOOOOOOOOOOOOOOOOOOOOOOL.
(In process shots of frame)
(Completed frame)
So the last part! The bean bag support frame was built entirely out of scrap wood, hardware and $2 worth of foam from the “House of Foam” in Palo Alto, CA. As you can see, it changed a bit from the rough sketch above. This was the least planned part of the project, as it was simple enough to just do as a last step. The back of the frame is tensioned with a steel cable that runs from one corner up to the top center of the backrest and down the opposite corner. In this way, we were able to keep the backrest super strong, flexible and lightweight.
The bean bag was then stretched over this, refilled with beans, and we were driving!
