Dear all,
I have an aluminum tube (30mm outer diameter) which is the bottom part of a flashlight.

BUCK DIMENSIONS:
The inside diameter is 24.5mm, inside which I want to install a buck converter to run a motor.
(This of course allows a 17mm square to just about fit - see diagram).
The height available inside the tube is 15mm max (ideally).

DEVICE COMPONENTS:
Below the buck lies a flashlight driver and below that an 18650 battery supplying the driver.
The driver in turn will supply the buck converter with the full voltage of the 18650, and up to 3A current.
The driver was initially running a 3W LED ( 3.3V @ 0.9A (2.97W) ), but was recently tested running my motor ( 2.5V @ 2.5A (6.25W) ).

BUCK POWER REQUIREMENTS:
My motor (which will get powered by the buck) normally runs off a 1.5V AA battery.
Tests with an 1.2V AA NiMH show 2.1A (@1.0V) continuous and 2.39A (@1.0V) peak at starup (could be higher).
( Manufacturer max recommendation: 1.5V max. x 2A (3W) )
Therefore input should be between 2.8V and 4.2V (18650 voltages). (no battery safeguards needed as they are handled by the LED driver)
Output should be between 1.2V and 1.5V, 2A continuous, 3A peak.

PREVIOUS EFFORTS:
I previously acquired for 5 Euro, the buck converter below, (1.5V 2A max), but it proved unable to start the motor.
Given a manual spin, it would begin turning, but would stall again given enough load.
I thought of ordering a second identical buck in order to join their outputs for more power, but I was advised against it in this forum.

https://www.aliexpress.com/item/1005006096221803.html


Conclusion:
This is a hobby project. I could just go get a resistor and burn the excess energy away. Hopefully this can be avoided.
I am not capable of designing such a circuit. I am only able to solder parts together.

1. Is there such a circuit publicly available that I could build dead bug style?
2. Could someone design such a buck converter for a beer or a coffee maybe?

 

2. Could someone design such a buck converter for a beer or a coffee maybe?

Page out of a data sheet. 5V to 3.3V 4A. Change R2 to reduce the output voltage. It can be programmed to stop working when the battery is low.

 

Page out of a data sheet. 5V to 3.3V 4A. Change R2 to reduce the output voltage. It can be programmed to stop working when the battery is low.

ST1S32PUR STMicroelectronics Switching Regulator, Surface Mount,
Minimum of 0.8V dc Output Voltage, 4A, 1.5MHz
2.8 → 5.5V dc Input

Looks promising thanks!

 

Looks promising

I did a search of parts that might work. Here is a list.
Digikey

 

I think the best candidate is your initial ST1S32PUR since it is simpler with only 8 pins and can do the job.
What I am now worried about are
1. the 5.5 Layout considerations on page 20. (I have no idea)
2. why so many inputs/outputs/GNDs
3. will everything fit in my available space?

 

Pgood pin (PG) can be not connected and remove the resistor.
There are many connectors and options on the PCB that you do not need.
I don't have time today to look at the layout today.

 

Pgood pin (PG) can be not connected and remove the resistor.
There are many connectors and options on the PCB that you do not need.
I don't have time today to look at the layout today.

That's ok. I will have wait for someone knowledgeable such as yourself to simplify this for me, according to the Layout considerations, so that it will hopefully fit in the space available.
I know that this will take some time before it materializes.