Re: Power drop with R/C servos and PIC form same battery


Thanks for all the help from the NG. So putting it all together, I got it
checked in the skope and working! Yeah!

So here's a summay:

Problems:
- regulating 6V down to 5V is a bad idea, because of voltage drop.
- running up to 24 servos simultanously on a walker robot puts huge strain
on the battery, each servo sucking up to 1Amp!
- noise!

Limitations:
- due to space and simplicity in the charging unit, it is not possible to
have a second battery

Solutions:
- the voltage regulator runs through a filter, then a low drop diaode, then
a cap, then the regulator, then two more caps
- Connect the regulator as close to the battery as possible, don't run the
lines by a few motors first (stop thinking digital! Wire is always a
resistor and a cpacitor!). Clean up the layout!
- Worst case, use a switching regulator that even pumps 3V up to 5V if need.
- a 300Ohm resistor on every servo data line in series keeps the noise from
the servos to the PIC low (not neede for digital servos)
- 3k pullup on the servo data line keeps the servos from jerking all at
onece when power is switched on
- I change the software to send pulses to the servos in groups of 4 with 2ms
delay from group to group, so that there is only on high load (leg) servo
per group. This spreads battery load over the 20ms cycle.
- with digital servos, the load on the battery is even greater. On the other
hand, they are happy with 3.2V pulses. So in that case, I use a 3.2V
regulator which runs more stable on 6V battery anyways.

Problem solved! Thanks for all the help!!

20uH +---+
Bat ---UUUU---|>|--o--|reg|--o---o--> pic
| +---+ | |
=== | === ===
470uF| | 10u| |.1uF
GND ---------------o----o----o---o--> GND



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