Cody's Crane

[sacherjj]

I used to see some information about this on various robot sites, but I don't have any links handy.  I would search around some of the robotics sites.  Although, most of them will use small processors, like the BasicSTAMP, because that is the easiest way to drive the servos.

[SirElliott]

See "Building a motorized pan/tilt head step 1" in the Cranes section.

[AMelling]

The 555 is not good for our application because it causes large voltage spikes and is notorious for having bad noise.   This causes the servo to jitter.  The + and - voltage spikes could also damage the circuitry inside the servo.

The 555, when used as an astable multivibrator, creates a chain of pulses, just like a regular oscillator.  This pulse train is sent to another 555 acting as a monostable multivibrator, which allows you to vary the length of the individual pulses.  This effectively modulates the duty cycle. Since this requires 2 555s, it is normally done on a 556.  A 558 has 4 multivibrators.

The 555 is also the most produced integrated circuit in history.  This is because it has such a range of uses in simple projects, but for our use it is simply too inaccurate and pervious to noise.

Although learning to use and program a microcontroller does have a steep learning curve, I think it is worth the work.  Discrete digital components are more accurate and controllable than analog equivalents. While the initial investment of time and money is higher, microcontrollers will save you both in the long run.  This is why they have sold $12 billion last year alone.

[AMelling]

I forgot to mention that the 555 is notorious for changing characteristics with heat and voltage changes.  This means that you will have to continually recenter the center frequency, unless you implement some feedback system that automatically calibrates the monostable frequency...  or you could write 35 lines of code.  I've done both, and the latter is way easier.

Edited by: AMelling at: 3/5/05 0:49

[Cody Deegan]

Okay, you people are causing my head to spin.  My jib just uses simple r/c servos.  The information you all are discussing would be very beneficial to advanced builders, but they'll never find it because it's in a forum about my jib.  Keep up the great discussion in the regular Cranes forum.







Cody