## Re: Symet was anemic, now is inert

Expand Messages
• And Eric gets the prize. My hat s off to you. From what Matt is showing, I think you are spot on. ... Connect the capacitor anode (positive) to cathode
Message 1 of 26 , Sep 4, 2005
And Eric gets the prize. My hat's off to you. From what Matt is
showing, I think you are spot on.

Now, on to Matt's questions:

> PS, how the heck do I short the caps?

Connect the capacitor anode (positive) to cathode (negative) with a
wire. This discharges the capacitor, ensuring the circuit is reset
and near 0V. Only short low voltage capacitors.

> I have put the 2.2 resistor back in and the FLED does not flash
> anymore, out the thing still just twitches.

Good. You are moving in the right direction because the FLED should
not flash.

> The three in the bottom seem to be what I am getting out of my
> symet. Not much.

That is similar to how our Symets run.

> Do you think I would get better action by replacing the 1000uf caps
> with 2200uf caps?

Would not hurt to try. The Symet will take longer to charge. When it
fires, the Symet will have a longer "twitch"

> how does one figure the amount of caps needed in a circuit? How
> does uf convert to available voltage?

The amount of storage capacitance one chooses depends on time.
Specifically, time to charge versus time firing. The formula is:

T = (C * V) / I, where

T = Time to charge (Seconds)
V = Voltage to charge
I = Charge current (amps)

For your Symet, with three 2200 uF capacitors and estimating the
voltage and current:

6600 uF = 0.0066 F
10 mA = 0.01 A

1.716 = (0.0066 * 2.6) / 0.01

You can get a rough idea of runtime by measuring the motors current.
I generally use my multimeter's current setting, run the motor from
battery. Battery + to meter -, meter + to motor +, motor - to
battery -. Since the circuit is firing the motor around 3V, use a 3V
battery pack.

The current will be a very rough estimate for several reasons. Motors
use more current when loaded, the circuit itself uses current, and so
on. Still, it gives fairly decent estimate. Let's suppose you find
that the motor consumes 25 mA when free running.

V = Trigger voltage - Reset voltage
1.8 = 2.6 - 0.8

25 mA = 0.025 A

0.475 = (0.0066 * 1.8) / 0.025

Such a setup would take about 2 seconds to charge, then run for about
a half second.

What is right depends largely on what you want. For Photopoppers such
as Jon's Dogbot, you would not want the SE to fire for too long. The
robot would over-shoot the target. For a Symet, you might make it as
long as you can for more action. Gord, one of our members, likes to
use 1F capacitors. He has a Symet called Taz that spins all over the
place. Very active, just takes a very long time to charge.

Regards,

J Wolfgang Goerlich
• Thanks for all the help, guys! My symet is now twitching around on the floor and the cats can t quite figure out what it is. I put the two 2200uf caps back on
Message 2 of 26 , Sep 4, 2005
Thanks for all the help, guys!

My symet is now twitching around on the floor and the cats can't quite
figure out what it is.

I put the two 2200uf caps back on it and that seemed to help out a
bunch. One bored night, I will probably add a third.

On to the next project: Frankenmouse.
Your message has been successfully submitted and would be delivered to recipients shortly.