Thanks guys.
I hadn't even thought in terms of using electrolytics to prevent V drop during high I drain during servo operation. Thanks for raising that issue. I had thought only in terms of using a V reg. with plenty of margin. I am familiar with using a low ESR electrolytic in this role because a GSM module I did lot of work with required it to prevent V level slump and hence module auto shut down during burst data txing at max. power.
I didn't even know what what star distribution was for pcb layout. Thanks Dippy. I found this doc helpful. Also thank you for pointing out the fact there are different quality/grades of caps., I wasn't thinking of that. I will specify the high grade caps you suggest.
http://focus.ti.com/lit/an/szza009/szza009.pdf
I propose to use this line of capacitors for decoupling Dippy.
http://www.mouser.com/catalog/specsheets/x8r.pdf
I have decoupling on the picaxe supply pins and on the reset.
I am going to do as has been suggested and use a separate reg. for the servos and the mcu.
I am using 2 X Hitec HS-311 servos to operate a pan-tilt on which the pcb is mounted.
relevant Hitec HS-311 specs.
Operating Voltage: 4.8-6.0 Volts
Current Drain (4.8V): 7.4mA/idle, 160mA no load operating
Current Drain (6.0V): 7.7mA/idle, 180mA no load operating
At 5V the servos pull 630mA stalled according to my trusty bench top power supply.
The deal is I have a hardware engineer doing the pcb layout. He has come back to me with a partial schematic and a lot of questions. Some things he is very knowledgeable about, others not so good, I know more and my BA degree is in humanities. His specialty is DSP (digital signal processing) which I would of thought would be highly sensitive to just the sort of design issues we are trying to ameliorate here so I'll point out to him the issues.
The upside is the development costs for the pcb are low enough that I can afford a bit of hit and miss. I know that good design should obviate the need for "a have stab at it and see what happens approach" but I have the margin there to do just that if need be.