5v logical vs. 12v motor power for a simple robot

us202000

Joined Jul 5, 2011
25
Hi, I am making a simple 4 wheel robot with two 12v motors and arduino at 5v. Currently I am using two separate batteries: a 5v USB battery bank, and a 12v LiFePo4 battery for the motors, and the two batteries share the same ground.

My question is whether I can just use the 12v battery and use a converter to step down to 5v for the arduino. However, I recall that there may be problems when first power on because for a moment, the arduino isn't quite ready so the motor may run wild. Ideally there should be a power on delay (if such thing exist) between the logical power on vs. the motor power on (driven by H-bridge). However, using two battery systems is a bit hard to maintain. Have to charge each separately etc.

Any recommendations? Thanks.

Papabravo

Joined Feb 24, 2006
19,344
You can do anything you want. The first step is to quantify your power needs. This means knowing how much 12V power the motors and their control circuits require and knowing how much 5V power the Arduino requires. Once you complete this exercise you can make a determination based on weight, cost efficiency or whatever to see if the DC-DC converter is worth the effort. Do it for a reason, not just because it sounds cool or some such bumpf.

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LowQCab

Joined Nov 6, 2012
2,515
You need 2 "ESC's", ( Electronic-Speed-Controller ),
the RC-Hobby scene is loaded with any type of ESC that You can imagine.
Many include what is called a "BEC", or "Battery-Eliminator-Circuit",
which is really nothing more than a standard 5-Volt Linear-Regulator.

When You get into higher Input-Voltages, and heavier Current-Ratings,
the BEC that comes with the ESC will usually be a SMPS, instead of a Linear-Regulator,
this will create slightly higher-efficiency in Voltage-Conversion,
with slightly less Heat-Dissipation.

ESC's are available for "Brushed", or "Brushless"-Motors,
and are available with, or without, a 5-Volt-BEC-Output.

I highly recommend going with Brushless-Motors,
they are superior in every possible way, except for being twice as expensive.

So, with 2-ESC's handling the heavy Motor-Control chores,
You will also get 2- Regulated-5-Volt-Supplies to choose from,
either of which will supply more than enough Current for your Controller.
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MisterBill2

Joined Jan 23, 2018
13,199
While the electronic speed controllers and brushless motors are very good suggestions, and the battery eliminator circuit would be handy. However, this robot will probably be a development project for a while, and that may involve a fair bit of havng the processor active while wanting the motion portion inactive. So from that point of view it will make more sense to stick with separate battery packs. This will also allow you to keep the load-carrying portions of the wiring separated but still having the two supply commons connected at some point.
Unwanted coupling between loads can be a challenging problem to solve, as has been discussed in a few threads already. These get called "ground loop issues", although the common on a mobile device would not really be a "ground".

LowQCab

Joined Nov 6, 2012
2,515
All of the ESC's that I'm aware of must be "turned-on" by the Controller,
and while they certainly are not as efficient as a direct-connection to a smaller Battery,
we are talking about large re-chargeable-Batteries here,
which should , (less efficiently ),
run the Controller for several days, or possibly more, before needing to be Charged.
So "overnight" trickle-Charging of the 12-Volt-Battery
would keep the Controller running indefinitely if so desired,
and this is with the ESC's semi-permanently connected to the Battery.

The heavy-Grounds to the ESC's are normally soldered together,
and then go directly to the heavy-Battery-Connector,
then either one, or both, of the ESC's normally supplies the Ground to the Controller.

Arranging the Grounds,
in a manner other than the way that they were originally designed to be used,
could be potentially problematic.
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djsfantasi

Joined Apr 11, 2010
8,587
And most Arduino models can accept 12V as input. They have on onboard voltage regulator. Connect the 12V supply to the Vin and Gnd pins.

KeithWalker

Joined Jul 10, 2017
2,525
I have experimented with a number of tracked and trackless motorized robots using several different sized motors. I have always used a single battery for the Arduino and motors without any problems. As mentioned above, it is important to connect the negative common of each directly to the battery negative. I usually use a linear regulator for the Arduino 5V supply. The current it uses is insignificant compared to the motor current so it's not worth the extra cost and effort to use a switching supply.
Are you using an H-bridge to drive the motors? If so, I have found that you don't have to worry about the motors going wild while the Arduino wakes up because it takes the right combination of two separate signals to energize the motor. If you are not using an H-bridge, you will have to make a simple R-C time delay circuit to turn on a P-type MOSFET in series with the positive 12V to the motors.

djsfantasi

Joined Apr 11, 2010
8,587
I usually use a linear regulator for the Arduino 5V supply.
Did you have a specific reason not to use the Arduino onboard voltage regulator?

There are four different ways to power an Arduino.
1. The USB port
2. The 5.1 jack, with 7-18V (22V on some models) There is an onboard 5V regulator to create the voltage required by the MCU.
3. The Vin and Gnd pins on the board itself. Same voltage range as the 5.1 jack. There is an onboard 5V regulator to create the voltage required by the MCU.
4. The 5V and Gnd pins on the board. The voltage must be clean and regulated
Which method you use depends on your project.

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KeithWalker

Joined Jul 10, 2017
2,525
Did you have a specific reason not to use the Arduino onboard voltage regulator?

There are four different ways to power an Arduino.
1. The USB port
2. The 5.1 jack, with 7-18V (22V on some models) There is an onboard 5V regulator to create the voltage required by the MCU.
3. The Vin and Gnd pins on the board itself. Same voltage range as the 5.1 jack. There is an onboard 5V regulator to create the voltage required by the MCU.
4. The 5V and Gnd pins on the board. The voltage must be clean and regulated
Which method you use depends on your project.
The spec for the Arduino Uno R3 power input via the 5.1 jack is 7 to 12 volts.
A 12V lead-acid battery can charge to 14.7V. A 12V LiFePo4 can charge to 14,6V. Both exceed the Arduino supply spec..:

https://docs.arduino.cc/hardware/uno-rev3

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Irving

Joined Jan 30, 2016
3,131
The spec for the Arduino Uno R3 power input via the 5.1 jack is 7 to 12 volts.
A 12V lead-acid battery can charge to 14.7V. A 12V LiFePo4 can charge to 14,6V. Both exceed the Arduino supply spec..:

https://docs.arduino.cc/hardware/uno-rev3
The on-board regulator on an Arduino can handle 25v, however its heatsink is very limited. If all you are doing is powering the Arduino itself, 14v may be Ok, but if you use the 5v or 3.3v out to drive peripheral devices you need to limit it to ideally 9v, or use an external TO-220 cased regulator.