Multiple power sources

On the robot I’m planning to build, I’ve got the following:

2 arduinos
1 RC reciever
3 servos
8 LEDS and 2 incandescent lamps
multiple motor controllers

The motors are going to be powered by a 12V 7Ah lead dry cell battery. The servos and receiver run on 4.8-6V, and the arduinos are 7-12 volts.

Am I better off powering the servos and reciever with a 6V NiMH pack, and the arduino off a 9V voltage regulator on the drycell? Or should I just use the one battery, and use both a 9V and 5V voltage regulator? Also, since everything has to use a common ground, is it safe to use a common ground between different voltage devices?

And what about 3.3V devices? Use a regulator for that as well, off the dry cell?

Since I’ll only be running the 2 drive motors a majority of the time (2 amp run, 4 amp stall), I figure I should get 30-45 minutes of runtime out of everything.

Am I better off powering the servos and reciever with a 6V NiMH pack, and the arduino off a 9V voltage regulator on the drycell?

Not ideal...ideally you would keep the highest-current devices (motors I'm assuming) on their own power supply. Ideally you'd power the motors and servos off one supply, and the Arduino on another (with common ground).

And what about 3.3V devices? Use a regulator for that as well, off the dry cell?

Any reason not to use the 3.3V output of the Uno?

-- The Rugged Circuits Yellowjacket: 802.11 WiFi module with ATmega328P microcontroller, only 1.6" x 1.2", bootloader

RuggedCircuits:

Am I better off powering the servos and reciever with a 6V NiMH pack, and the arduino off a 9V voltage regulator on the drycell?

Not ideal...ideally you would keep the highest-current devices (motors I'm assuming) on their own power supply. Ideally you'd power the motors and servos off one supply, and the Arduino on another (with common ground).

And what about 3.3V devices? Use a regulator for that as well, off the dry cell?

Any reason not to use the 3.3V output of the Uno?

-- The Rugged Circuits Yellowjacket: 802.11 WiFi module with ATmega328P microcontroller, only 1.6" x 1.2", bootloader

Didn't realize the Arduino had a 3.3 as well. Knew it had a 5.

OK, so if I powered the motors and their controllers with the 12V/7.2Ah lead acid, powered the arduino with a 7.2/2500 NiMH pack, and powered the servos with this 2 amp regulator off the same 7.2 stick, all would be good?

It's worth a shot. Keep the grounds of all 3 components separated all the way to the power supplies and connect the grounds together at a single point, at the power supplies.

-- The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

I'm gonna have everything on one 10" x 5" polypropylene sheet, oriented vertically landscape. Should I add a layer of sheet metal between the electronics and the polypropylene, to reduce the static electricity transfer? I'll be using 4-40 bolts and nuts for standoffs, unless there is a better way (ie, ready-made standoffs with 3/8" of thread showing, to put a nut on the backside of material). The batteries are going to be separate but next to eachother, fastened to the chassis.

The 12V+ lead will go to a chassis-mounted kill switch, and from the kill switch to a 4 row barrier strip (row 1). The 12V- will go straight to the barrier strip, row 2 The 7.2V- will go straight to the barrier strip, row 3 The 7.2V+ will go straight to the barrier strip, row 4.

I will have a shorting bar between rows 2 and 3, to make a common ground

The arduino connection will be the barrel plug coming straight from the 7.2 barrier strip The voltage Regulator will have a 2 pin molex connector connecting it to the 7.2 barrier strip The drive motor controllers will have a 4 pin molex connector connecting them to the 12v barrier strip (outside wires +, inside wires -) The stepper motor controller will have a 2 pin molex, opposite gendering from the regulator plug, connecting it to the 12v strip.

On the output side: The wires running to the cargo box (6 stepper wires, 6 servo wires, 2 lighting wires) will be spread across two DB-9 connectors (because i'm not trusting of myself with a DB-15 plug...) The wires for the drive motors (4 wires) will be on another DB-9 connector, with 2 pins per physical wire (for amperage reasons) The wires for the winching motors (4 wires) will be on a fourth DB9 connector (the actual winch motor will have 2 pins per wire for amperage reasons)

The DB9's will be mounted to the electronics tray, then DB9 patches will go to the connectors mounted to the frame. Extra connection, yes, but they will be reliable connections that will be easily undo-able if necessary, and allow for quick removal of the electronics tray if were necessary.

You might be able to power everything off the 12V SLA:

Run the Arduino's each off a single 7809 regulator (or give each one a 7809) - be sure to add the capacitors and heatsinks.

Run the servos each off of their own regulator (simple solution would be a single 7806 - plus capacitors - per servo - this would drive the servo's at 6 volts each, with up to an amp of current - be sure to put a heatsink on each 7806).

Run the gearmotors off the batteries straight.

For the 3.3 volt devices, as noted you can use the Arduino's 3.3 regulated output (as long as the devices won't exceed the current capacity). Alternatively, you can use a 7803 or LM317 (again, with the extra components - you may or may not need a heatsink, though).

Be sure you have fuses from each positive voltage bus to the components, and a single larger fuse (for your max current needs) or breaker near the positive terminal of the battery (keep the run from the battery to the fuse as short as possible).

cr0sh: You might be able to power everything off the 12V SLA:

Run the Arduino's each off a single 7809 regulator (or give each one a 7809) - be sure to add the capacitors and heatsinks.

Run the servos each off of their own regulator (simple solution would be a single 7806 - plus capacitors - per servo - this would drive the servo's at 6 volts each, with up to an amp of current - be sure to put a heatsink on each 7806).

Run the gearmotors off the batteries straight.

For the 3.3 volt devices, as noted you can use the Arduino's 3.3 regulated output (as long as the devices won't exceed the current capacity). Alternatively, you can use a 7803 or LM317 (again, with the extra components - you may or may not need a heatsink, though).

Be sure you have fuses from each positive voltage bus to the components, and a single larger fuse (for your max current needs) or breaker near the positive terminal of the battery (keep the run from the battery to the fuse as short as possible).

Great information, thanks. I needed the fuse reminder..not sure how that skipped my mind. Any information on if I need to shield the polypropylene?

Should I add a layer of sheet metal between the electronics and the polypropylene, to reduce the static electricity transfer?

I would not think that is not necessary. Nor particularly effective.

Is there a specific reason you chose the lead-acid and NiMH batteries? The rest of your design sounds well thought-out. Just curious as to the reason those types of batteries are going to be used.

Waruma: Is there a specific reason you chose the lead-acid and NiMH batteries? The rest of your design sounds well thought-out. Just curious as to the reason those types of batteries are going to be used.

The lead acid is 7Ah @ 12V, which will give me plenty of runtime, running 2 high-amp (2 amp run, 4 amp stall) motors. While it does have a significant weight influx on the robot design, it was going to be cheaper and easier than putting multiple 7.2 packs in parrallel. Also, it is lighter than a motorcycle or lawnmower battery, and is a drycell, which means i can operate it at any orientation.

Theoretically, I should go to a Li-pack rather than a 7.2 NiMH pack, but that's the easiest place for me to save budget. It's common, easily replacable, and can be quickly charged. Since it will only be powering a few things, a 2500 pack should have the same runtime as the lead acid battery.

Okay. That makes sense. I was going to assume that the batteries would be heavy, and maybe try and use a Li-Po or a Li-Fe battery pack, as they are tiny and don't cost too much. But I don't know how quickly they can be charged. I haven't started experimenting down that road yet. I know with the technology out now, they have some battery packs that are upwards of 10Ah which are used for RC applications. Just a thought...

I honestly have paid no attention to Li-packs.... This is the battery I have: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXL370&P=ML

Yes, something like this would be nice, but the price cannot be justified. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390289586256&fromMakeTrack=true&ssPageName=VIP: