Power mangment

[MikeMihailov]

Introduction:

There are 3 servo motors in Niryo one: 2 XL430 and 1 XL320 by DYNAMIXEL. XL430 needs 6.5V to 12V as source voltage (11.1V is recommended - it is the voltage of 3S LiPo battery). XL320 needs 6V to 8.4V as source voltage (7.4V is recommended - it is the voltage of 2S LiPo battery). And it is necessary to have the source of 5v power for Raspberry pi. The main input source of power is 12v.

Of course 11.1V and 7.4V aren’t very common voltage in schematechnic. There may be temptation to use 12V instead 11.1V. But it is the border voltage and it can cause servo damage. Niryo One declares 11.1V for XL430. Team of ZHAW School of Engineering have got the information that it isn’t true.

Power calculation:

• XL430: 11.1V * 1.3A * 2 = 28.86W (30W) => 2.5A@12V
• XL320: 7.4V * 1.1A = 8.14W(9W) => 0.75A@12V
• Raspberry: 5V * 2.5A =12.5W(13W) => 1A@12V

Full current of 12V power supply = 4.25A (without steppers).

Voltage source selection:

In my opinion it is necessary to use step-down voltage regulators in order to have good efficiency. The scheme is more difficult than LDO, but the temperature of components will be lower. The most popular regulator with 3A output current is LM2596-ADJ (IMHO, of course). This component is in TO220-5 case. Besides, it is necessary to have big input capacitor and coil. 470uF x 50V capacitor is recommended (see datasheet). This type of capacitor is not popular in SMD case. 50V may be too much. In my opinion, Х2 reserve is enough (about 24V). I think we can use 3 LM2596 for all kinds of voltage. For 7.4v we can use some other component, but universalization is more important.

The problem of this idea is size. I have made a sketch and the result is bad. I think to change from SMD to THT case of LM2596.