Question For Experts: Robot Power Supply

[reefat]

Hi everybody,

I got some very important questions which are required for building a robot from scratch. Suppose you are designing a robot with MCU, some TTL devices and servos (i.e.: HS-311 analog). Additionally you can think about having options for Stepper Motor (optional), which could be 6-12V. What will you use as battery?

1) A LiPo - Lithium Polymar Pack (7.4V)
2) NiMH. If so, 4 cells (4.8V) or 5 cells (6.0V)?
3) NiCad. If so, 4 cells (4.8V) or 5 cells (6.0V)?

7.4V or 4.8V or 6.0V. Whatever you use, can you draw a schematic for me specifying different voltages for Servo and MCU/TTL devices.


Consider the 2 schematic as follows:



Which one will you prefer for your robot? Schema - A, or B? And why? Please describe your explanation briefly. If you don't prefer any of these two, please prove your preferred design.

Note: In "Schema - A", the last extra cell will be discharged fast. Because motors/servos requires more power than MCU or any other circuitry.

[Razor Concepts]

I'm not an expert but know a bit about batteries coming from the RC world. Schem A as you said would have one cell discharging faster, so that will have to be separate from the main 4-cell pack. That would mean separate and difficult charging. Dont know much about which schematic is better, but A will give you some charging hassle.

[Webbot]

You are far better off keeping the TTL and Motor supplies as different power sources sharing a common ground. Motors/Servos have high start up currents - and will quickly drain any large capacitors. Hence the $50 Robot 'preferred' supplies are:
- a 9v battery via a voltage regulator for TTL
- another battery pack for driving motors/servos.

[Rebelgium]

nothing expert level about this question

The best option is (as webbot said) two different batteries. One for the motors and servo's, and one for logic, and ofcourse commen ground.

The B schematics is also a good solution, the A schematic is not good at all.
In schematic A the cell on the bottom will discharge LESS (not more, the four cells would power the motors and the logic, the cell on the bottom only the motors...) and thus the four cells and the separate cell would have to be charged separatly.

[TrickyNekro]

If you wonna go with logic and heavy duty electronics on same source I recommend LiPo batteries...

But LiPo batteries need extra electronics for preventing extensive voltage drop which leads to battery damage and annihilation after reaching these voltages.

So... for the beginning get some 7V2 NiMh and then play with other batteries...

Also... power whatever from 7V2 as said before cells which have been separately discharge (almost) won't, at least, benefit the whole pack...



Best Regards, Lefteris
Greece

[Admin]

Reefat, funny how schema B on your website looks just like the schematic I custom made

http://www.societyofrobots.com/schematics_powerregulation.shtml

[reefat]

@Admin. Schematic-B isn't in my website. I just attached it to Schematic-A and published it in this forum only. Sorry to mention that, I just copied your schematic for comparing reason. Anyway, some people are preferring to use 2 different power sources (2 batteries). But you used a single source in Schematic-B. Could you please tell me, which one do you like better? And why?

[Admin]

Depends on what you're powering, how sensitive your sensors are, etc