Added Electronics to the Balancing Bot

Last weekend, before getting the sumo bot kit, I spent some time working on the balancing bot.  I added a vertical length of Aluminum and mounted the electronics on it.  The plate is 3/8 thick and about 5 inches long... it not only acts as a place to mount the electronics, but its main purpose is to raise the center of gravity (CG) higher.  Confused??  Which is easier to balance in your hand, a pencil or a broom stick?  (the correct answer is the broom stick).  The greater the distance between your hand and the CG, the easier it will be to control.  

Before ripping the motor controller off to be used on the Sumo Bot, I was able to get all the parts working... I still have a bit of work before I will be able to get that thing balancing.  During initial wiring, I managed to smoke the H-Bridge and fry the PIC Microchip on my PICKit2 Evaluation board.  Too bad really, I used that thing all the time (no, really.)  These motors have a 6 Amp stall current, so I need to buy something a little beefier.

After that fiasco, I spent some time using my USB to Serial breakout board from Sparkfun (DEV-09716).  After a bit of playing around, I managed to send the accelerometer data from one axis to my PC using Hyperterminal, which I think is a standard program installed on every machine... if not, I'm sure you can find it, or an equivalent for free.  The accelerometer is from Pololu (MMA7361L).

Front Isometric View

Side View

Rear Isometric View

Added Electronics to the Sumo Chassis

Last night was a busy night.  From about 7pm to 2am I managed to do the following.

• Design IR sensor bracket and standoffs
• Fabricate the bracket and standoffs
• Modify the ballast plate to mate with razor blade 'scoop'
• Assembly everything to the chassis
• Wire the line sensors on the bread board
• Wire sensors to my makeshift sumo board (reusing my tachometer board)
• Wire motor driver board to sumo board
• Begin rough version of program
• Fix all of my mistakes in wiring
• and finally, actually get it moving in a somewhat logical fashion

The Cobra chassis does come with standoffs and additional hardware for mounting, but they were just a little too high for my taste.  Using small diameter tube, I made my own standoffs which were about 1/4" shorter than the stock ones.  My ultimate goal here is to limit the height in an attempt to reduce the IR signature (i.e. make it harder for other bots to see me).  As you can see from the following images, it's quite low profile.

IR Sensors - Isometric View

Low Profile Front View

Side View

Although the Cobra kit came with the circuit diagram showing how to wire the line sensors, I wanted to make sure everything worked for me as it should. The included instructions are from Lets Make Robots. The image below shows the breadboard set-up  The bottom left pin of the line sensor block is the output pin.

Line Sensor Circuit

The following images show the 'completed' sumo bot.  I say 'completed' because this is only a rough first cut of the Bot.  I plan on playing with the code to get this working well enough to figure out what improvements need to occur.  For example, I can already tell (I think) that the IR sensors have too narrow of a field of view.  This causes the bot to loose sight of it's opponent too easily.  I'll try to include some video showing this on the next post.

Isometric View 1 - 'Completed' Version 1 of my Sumo Bot

Isometric View 2

Side View

Front VIew

Top View

Things left to do.

• Attached line sensors
• Create line sensor circuit
• Wire output of line sensor to board
• Start design and layout of custom Mini Sumo Bot PWB
• Work on scoop mechanism

Review of Fingertech Robotics "Cobra" Mini Sumo Bot

As I mentioned in a previous post, I ordered the Fingertech Robotics Mini Sumo Bot kit.  At $120, I was hoping I would not be disappointed in the quality of the parts and assembly.  In summary, I was not.

• 4 Motors at $20 each          = $80
• 4 Wheels at $10 each          = $40
• 3 Sensors at $1.75 each      = $5.25
• 1 Chassis at ~$10 each       =  $10
• 4 Posts at ~$0.25 each       = $1
• 8 Fasteners at ~$0.25 each = $2
• 1 Scoop at ~$5 each          =  $5
• Glue                                   = Priceless
• Grand Total                       = $143.25

The first thing I though when I opened the box was "it's assembled"!?  Being mechanically inclined, I usually like to put stuff together myself (or in most cases, rip things apart).  But it was nice to see it all together right out of the box... I guess.

The first thing I noticed when I pulled this out of the box was the weight, it seemed very heavy.  Mini sumo bots are allowed to weigh a maximum of 500 grams, per Robogames.net and the RobotRoom.com.  Although I do not have a scale handy to check the weight, Fingertech claims it weighs in at 333 grams.  (3-3-3, come on... what is the likely hood of that number?)

My only area of disappointment was the method of securing the motors down to the chassis.  In this case, they are glued on.  Typically, I am not a fan of glue.  It can be easy to shear a motor off the chassis during handling or worse during a competition.  Lets hope they picked a good glue (Elmers = Bad).  I will probably change this in the near future, stay tuned.

Also, I did notice that one of the motor axes was just a little off from being parallel with the others... again, this is a big drawback when using glue.  Its hard to fix the position once its stuck together... but I'm sure it is not enough to cause any issues.  In fact, it will probably not even be noticeable to most people.  But I know it is there, and I'll probably just HAVE to fix it sooner or later.  If it ain't broke...... make it straight.

Fingertech's images of this kit were lacking, so I figured I would show it off for them.

Isometric View

Side View

Front View

Bottom View

Rear View

Rear Isometric View

Included Hardware and Sensors

Wheel Removal In-Progress

Wheel Removed

Snazzy Isometric View

Project 6 - Balancing Bot

For a while now, I have been gathering all the parts needed for a two wheeled balancing robot.  Finally, I had the motivation (not to mention a few nights) to design and fabricate the chassis.

Balancing Bot CAD Isometric View

Isometric View #1

Isometric View #2

Underside View

Side View

I'm using gear motors and wheels purchased from Pololu.  The unique thing about this design is the o-ring belt drive system.  At work, I am constantly using o-rings in their traditional means... sealing.  However, when I inspected the o-ring bible, published by Parker, they discuss using them as belts.  Odd?  Next time your taking apart that old printer, keep your eyes open... this method is used often when gears are not needed or optimal.

I have a few more parts to make, then the 'fun' begins.... How hard can it be?

Mini Sumo Bot

After getting cyclops up an running, I started to think about alternative chassis.  Sure the Tamiya track version is fine for a test-bed, but I needed something that was a little more robust and competition worthy.  I ended up buying Fingertech's Cobra chassis from Fingertech Robotics.

Fingertech Robotics 'Cobra'  Chassis

It has not yet arrived from Canada, but I'll be sure to transfer all of Cyclops's guts over to this beast.