Servo startup

Archiver

Hi All,

Whenever I am controlling servos they jolt a little when powering up.
I'm pretty sure this is no fault of the Stamp, but I'm wondering if
it's possible to dampen this effect with a capacitor or something so
my robots don't jerk when I turn them on. Any ideas? Thanks.

-Dave

Archiver

From: "nuclearspin2000" <nuclearspin2000@y...>
>
> Whenever I am controlling servos they jolt a little when powering up.
> I'm pretty sure this is no fault of the Stamp, but I'm wondering if
> it's possible to dampen this effect with a capacitor or something so
> my robots don't jerk when I turn them on. Any ideas? Thanks.
>
I'd be interested if anyone has other ideas, but this is what I think is
going on. We have a nominal first position for each servo. Call that center,
though it is sometimes otherwise. When the robot is powered off, any
movement tends to displace one or more servos from center. And of course,
when we powered down, it might have been elsewhere unless we program a
specific shut-down sequence that centers all the servos. (Or moves them to a
default start-up position if "center" is not the right term.)

Now when we power up and send the first pulse to any servo, it will jerk to
reach "center" position unless it happens to be there already.

I don't know for sure this is what's happening, because it hasn't been
annoying enough to instrument; but it is consistent with the symptoms I see.
Preventing it is tough. I try to mechanically position the articulated
elements before applying power, and the fact that the jerking is greatly
reduced that way supports that guess about the cause.

Otherwise? Only one thought, and I haven't tested it yet.

The next big version change on my design will be position sensing for the
limbs. I'm putting pots on each limb. Now if I read the position before
sending any pulses to a servo, I can make the first pulses consistent with
the wake-up position and gradually move the servo to the desired initial
position -- the "center" position -- instead of letting it jerk into
position. Best I can offer. I'll be interested to see if anyone has solved
this.

Gary

Archiver

--- In basicstamps@yahoogroups.com, "nuclearspin2000"
<nuclearspin2000@y...> wrote:
> Hi All,
>
> Whenever I am controlling servos they jolt a little when powering up.
> I'm pretty sure this is no fault of the Stamp, but I'm wondering if
> it's possible to dampen this effect with a capacitor or something so
> my robots don't jerk when I turn them on. Any ideas? Thanks.
>
> -Dave

Dave,

You can cushion you starts and stop buy putting a small cap (10uf?)
from your control pot output to ground. If your voltage is 0-5v then
in the middle it is 2.5 when the motor is stopped. The cap will slow
down the change in voltage thus the start up. BUT. Usually it is the
motor that is the problem. Most normal motors have a break free
point. So the motor may not be able to go 5 rpm. It's minimum speed
may be 300 rpm.
The slowest start up motors are coreless ones made companys like maxon.
Instead of the armature turning, the winding turns. Check them out
at www.maxonmotorusa.com

Lou