user29519: I am looking for a cheap and not so space consuming motor shield for my Arduino Nano ATmega328. I would like to charge the whole thing with a 9V battery. The shield must have at least 2.1A of output current so I can run 3 brushed DC motors on it. There will also have to be some pins left for a Bluetooth card and 3 analog pins for sensors. 
Do you know any shields that meet my requirements?

user27157: In short:
Nano + Shield = no possible


[...] 9V battery. The shield must have at least 2.1A of output [...]

You can't invent power out of nowhere.

Options for the shield
Option 1:
Use an other Arduino. It will simplify everything.
Option 2:
Use a Nano to Uno adapter.
Option 3:
By an Uno shield and connect it pin by pin to the Nano.
Option 4:
Use MOSFETs. They'll work fine for what you are trying to do.

Options for powering
Option 1:
Use a 2s lipo. Voltage is above 5V so you have to reduce it with a down converter, but you should have enough juice for the motors.
Option 2:
Use a lot of AA, some in series to augment the voltage and then in parallel to augment the current.
Option 3: (just the the crazy minded)
Use a lead-acid battery (aka car battery).

29519: <p>I am looking for a cheap and not so space consuming motor shield for my Arduino Nano ATmega328. I would like to charge the whole thing with a 9V battery. The shield must have at least 2.1A of output current so I can run 3 brushed DC motors on it. There will also have to be some pins left for a Bluetooth card and 3 analog pins for sensors. </p>

<p>Do you know any shields that meet my requirements?</p>
 27157: <p><strong>In short:</strong></p>

<p>Nano + Shield = no possible</p>

<hr>

<blockquote>
  <p>[...] 9V battery. The shield must have at least 2.1A of output [...]</p>
</blockquote>

<p>You can't invent power out of nowhere.</p>

<hr>

<p><strong>Options for the shield</strong></p>

<p><strong>Option 1:</strong></p>

<p>Use an other Arduino. It will simplify everything.</p>

<p><strong>Option 2:</strong></p>

<p>Use a Nano to Uno adapter.</p>

<p><strong>Option 3:</strong></p>

<p>By an Uno shield and connect it pin by pin to the Nano.</p>

<p><strong>Option 4:</strong></p>

<p>Use MOSFETs. They'll work fine for what you are trying to do.</p>

<hr>

<p><strong>Options for powering</strong></p>

<p><strong>Option 1:</strong></p>

<p>Use a 2s lipo. Voltage is above 5V so you have to reduce it with a down converter, but you should have enough juice for the motors.</p>

<p><strong>Option 2:</strong></p>

<p>Use a <em>lot</em> of AA, some in series to augment the voltage and then in parallel to augment the current.</p>

<p><strong>Option 3: (just the the crazy minded)</strong></p>

<p>Use a lead-acid battery (aka car battery).</p>
