Servo Speed

Mykal1999

Hello all.

I am working on a little project. Basically, I am trying to launch ping pong balls with a standard servo. I have my BasicStamp wired with two triggers (buttons). One trigger releases the ball (servo arm·flys forward) and the other brings the servo arm back·for reloading. The only problem is that I cannot get the servo to move fast enough to actual throw the ping pong ball.

"IN3" is the line of code that throws the servo arm forward. I started out with "duration = duration - 10" and changed in increments until I got to "duration = duration - 50" because the higher the number the faster the servo moved. Unfortunately, the servo seems to have maxed out at 50 because it·does not go any faster after that.

Have I reached the servo's top speed or is there something else I can do???

Much appreciated!

SRLM

The Parallax servo has a maximum rotational speed of 60 degrees per second (if I remember right). At the (high) risk of ruining your servo, you can use higher voltages to make it go faster. However, you still won't get too much of an increase. Alternatively, You could make a long, counter balanced arm that is like a catapult. This might work, at the cost of space. What you need is some other sort of launching mechanism. Might I suggest the un-patented Spinning Arm^tm technique? I haven't had a use for this yet, but sometime I would like to try it out. Anyway, you attach a arm to a standard motor. You then have a half circle wall that goes around on the outside, with a floor on bottom (and maybe a partial roof) Anyway, you drop the ball in, the arm swings it though half a rotation, then the wall that was holding it in ends, and the ball flies out. If you want to make it automatic, you could probably use your servo to do feed control.

Back on to servos: the RC-Hobby industry has some pretty fast servos for use in helicopter and the like. Take a look there if you're interested in the same route.

agfa

just an idea.

use a servo to compress (stretch or twist) a spring then a trigger mechanism to release it.

Bruce Bates

Mykal -

Have you considered the use of "Muscle Wire"? If you need more information, just let me know. "Muscle Wire" IS made in spring configurations! Just an alternative thought. You WILL need some heavy duty batteries on the BOT. "Muscle Wire" (by its very nature) is power HUNGRY!

Regards,

Bruce Bates

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When all else fails, try inserting a new battery.

Carl Hayes

If I were doing this I would build a trebuchet, which is a neat project in itself. Then I might use a servo to reset the trebuchet after each launch, and perhaps another to release the trigger.

A trebuchet can achieve much higher launch velocities (because of the slinging action) than most other devices of similar size (excepting firearms, of course), and the distance through which a force must be exerted to reset it is rather small, although the force required is relatively large (a trebuchet is powered by a dead weight on the non-throwing end of the arm).

With a little experimentation you could even build some tables from which a Stamp could calculate settings for various ranges.

Scientific American magazine had an article on trebuchets, along with many photos, a couple years ago. Your local library may have that issue. One of the photos showed a large trebuchet (built by an group in the UK) throwing a full-sized upright piano several hundred yards. Imagine the sound when it hit!

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· -- Carl, nn5i@arrl.net

allanlane5

Lego Mindstorms do this sort of thing all the time.

The key is to use a rubber-band powered lever, and put a 'cam' or something on the servo horn. Then, when the servo rotates, through part of its cycle it 'loads' the lever by pulling it down against the force of the rubber band. Then, at one point in the servo rotation, it 'releases' its end of the lever. The rubber band "snaps" the lever forward against the back of the ping-pong ball, and the ball flies.

Trying to have the servo accellerate and decellerate fast enough to 'snap' the ball is usually the thing people first think of, but it's almost entirely impractical. Using a spring (or rubber band) powered lever to 'snap' the ball, and using the servo to "pull it back, then release", works really well.

Mykal1999

Thank you all very much for the suggestions. I have alot to work with now. I will get to work on these other ideas and let you know how it turns out. Thanks again for all the help!!!