a weekend robot project with a max 14 square mobile robot base
here is an example of a max mobile robot base used to prototype a project.
this project uses the following components:
max 14 square mobile robot base w/ double speed upgrade and a power distribution board.
before mounting any of the electronics, i do all of the work i plan on the bottom of the robot. this includes dealing with the motors power leads and the mounting of the qrb based wheel encoders.
i pulled the max motor leads through to what will be the top side of the robot.
abs is very easy to drill, the through holes can be placed anywhere you like. i was able to use existing holes in the max 14 square.
next i mount one of the qrb reflex photoeyes on each of the drive motors. i have found the easiest way to mount the photoeyes is as follows:
first, use a �” nut as a spacer.
next, i use electrical tape to attach the photoeye to the wheels.
next, i use electrical tape to attach the photoeye to the wheels then you can attach the encoder pattern to your drive wheels.
tip – i normally use a cd as a reflector, this greatly improved performance over using just a paper pattern alone. i also use a hole saw (1”) to enlarge the center hole so it will fit onto the drive wheel.
next i cutout and attach the paper pattern to the cd and the cd to the wheel.
i usually leave a space in the paper pattern for the wheel set screw. you will probably want to have access to the set screw to remove or tighten the wheels.
now we are ready to start wiring the robot up. the first thing i like to wire up is the motor driver. if i wire this up first, i know that the leads from the drive motors will reach the motor driver. if you want to locate the motor driver in a position to far away for the leads to reach, just add an 8 position terminal strip and then wire from there to the desired location of the motor driver.
if using the mc motor driver, connect the backplane power to the motor driver also. do not connect power to any other board in the backplane.
once the motor driver is wired up, i slip it into the backplane. for the robot i have also installed the hc11 and encoder/sonar driver boards.
next i add the power supply. for the project, i will start out with ‘d’ battery holders. i take two 4 ‘d’ battery holders and connect them in series. (i connect the positive (red) lead of one battery holder to the negative (black) lead of the other. then between the remaining two leads, you should get a little more then 12 vdc.
next i wire everything up and see how it fits on the base. i installed a power distribution board on the base also. this board will provide multiple 12vdc and 5vdc power supplies, along with fuse protection. this will come in handy later as i add sensors and actuators to the robot.
after the layout and wiring is complete, it is time to test run the robot. if everything is set up correctly, you should be able to run the current program loaded on the hc11.
next i check the motors controller work correctly. sometimes, the motor leads need to be reversed so the forward is forward, back is back, etc…
after everything seemed to work correctly, i used double sided tape to temporarily hold each board board in place and the ‘d’ battery holders. i plan to make some changes in the near future and didn’t want to permanently mount any of the components just yet.
next, i mounted the upper decks on the robot to see how it looked…
the controller laptop fits nicely on top of the robot.
now it's time to add some sensors to our robot so it can avoid obstacles and maybe determine it's heading. many of the sensors available today use the i2c bus. the hc11 core software includes a routine to drive this bus (pd4 - pin 24 scl and pd5 - pin 23 sda).
i used a 4 position bus for the i2c sensors bus. you can solder the wires directly into the bus, or use pins and connectors - as pictured. four conductor telephone cable was used for the wring to each srf08.
small bus strip
i mounted two srf08 range finders on the front of the robot to avoid running into things. i also used two zagros robotics sensor mounting brackets and double sided tape. i used the double sided tape because i will probably want to move things around depending how thing perform.
next, i plugged a devantech compass module into a solderless breadboard. i also connected 5vdc from the power distribution board and finally inserted a 10k resistor between both the scl and sda lines of the i2c bus and the 5vdc supply. these pull up resistors are required for the bus to work correctly.
a bluetooth modem was installed to allow wireless control of the robot. this is much safer for the laptop, especially during the first trial runs!
finally, i installed a large mushroom push/pull power button. this is will allow the robot to be stopped quickly if required. this is a good idea if you plan to allow your robot to roam around freely. a robot this size can cause some real damage to walls and other valuables in the room.
once the basic robot was up and running, i decided to add another deck to hold more stuff....
like a laptop computer and camera...
this past week, i decided to upgrade the 'd' battery holders to sealed rechargeable battery. the 'd' batteries are great to start with because they are much more forgiving than a 12 amp-hr, 12 vdc battery. usually, with the 'd' battery holders if you making a wiring mistake things will get warm and allow a little time to find the mistake and kill the power. with he rechargeable, you will be able to find you mistake much faster, just follow the smoke. of course, you will then need to replace some parts (usually electronics). there are several advantages to upgrading the power supply of the robot. first, it is better for the environment. second, this new battery provides more power to the robot. finally, over time the rechargeable is cheaper. 'd' batteries are expense! i also always install a fast acting fuse between the robot and the battery. remember, only you can prevent robot fires.
tip: i usually use velcro to secure the battery to the robot. this allows me to quickly remove it, but also holds it securely in place while the robot is in motion. attach the velcro to the battery first, then position the battery on the robot. this way the battery will actually match up to the velcro on the robot. i also used female spade connectors to attach the lead wires to the battery spades. these are easy to unhook when you want to remove the battery for charging (or replacing).
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