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Tap into the sum of allhumanknowledge and get your questions answered here!
From software algorithms to material selection, Mr. Roboto strives to meet you
where you are — and what more would you expect from a complex service droid?
This has been a light month for questions, so I’ll
answer one that I got and continue on with the saga of
the Digilent MAX32 board. I’ve decided that I like this
controller and PIC32 combination, and will be updating my
Critter Crunch entry Silver Surfer with a new brain. My old
controller board was one of my own from way back that
was based on the Atmel ATMEGA8535 with a 754410 dual
DC motor driver. I’ll need a new motor driver, and these
days there are a LOT more to choose from that are more
robust than the venerable 754410 dual H-bridge (which
dovetails nicely into one of the questions that I got this
month). This is a BIG upgrade for Silver Surfer to an 80
MHz 32-bit micro from a 16 MHz eight-bit micro. I can
hardly wait! My critter has to compete against humans in
this competition (which is a bit of a challenge, let me tell
you!). Anyway, on with the questions ...
Q. I am interested in the motorization of a 600 g robot (two wheels + rolling ball); max speed 20 cm/sec. I am looking for the following: a set of
brushless motors, wheels, and an I2C driven motor controller.
— F. Saguez
10 SERVO 07.2012
A. The answer to your question is, “It depends.” A 600 g robot will run handily on any motors that are in the torque range of about 2 Kg-cm to 3. 5 Kg-cm. I’m
assuming an indoor robot running on mostly flat surfaces
like a floor or table. If you’re going to be climbing steep
inclines, then you’ll want to use the higher torque motors;
for flat surfaces, the lower end is fine. Now, about speed ...
again, “It depends.” This time, it depends on the wheel
diameter as to how fast you will be moving. You can
calculate the speed of your robot pretty simply by
multiplying the wheel roll-out by the motor rotational
velocity. Wheel roll-out is the distance that the wheel will
cover in one revolution which is the perimeter of a circle, or
πd, where d is the diameter of the wheel. So, if you want
20 cm/sec velocity and you have 5 cm wheels, then your
motor will need to spin at 1.27 RPS (Rotations Per Second),
which is about 76 RPM (Rotations Per Minute).
At all of these sites, the price is under US$100 for a
dual motor controller; some are quite a bit under. There are
no doubt more out there.
Q. (Reprise, part 33 and a third ... of the original question) I would like to see some of the more basic stuff with the chipKIT MAX32 such as
utilizing the ADC with sensors, basic timer/interrupts, and
the like. Also, I would like to see it interfaced with MPLAB
utilizing C, instead of the Arduino processing structure.
A. Here is yet another installment of the continuing saga of the Digilent MAX32 board using the PIC32 microcontroller. I’m off and running ... we’ll see how
much I get done in the time that I have. This month, we’re
going to look at measuring distance with a sonar range
finder. I’ve chosen an extremely inexpensive sonar unit: the