At an industrial site in the capital Kyiv, Musa and his team were busy building the frame of a buggy from metal pipes.
He revved up another finished vehicle for a hair-raising ride.
Driving it up and down steps, it accelerated powerfully before braking just as it seemed about to crash into a wall.
The buggies weigh 650 kilos (0.65 tonnes) -- about half the weight of a normal car -- and sell for $6,500 each.
Musa has named the company Dracarys, a nod to the fire-breathing dragons in "Game of Thrones".
They have made "a few" of the vehicles since last summer, he said.
The buggies are assembled from a hodgepodge of engines and other parts from old secondhand cars, such as Audis and Volkswagens, without complicated electronics, making them easy to repair in the field.
"These cars, there are so many of them in Ukraine and they're cheap," Musa told AFP.
The buggy he drove has added features such as plastic roll-up side windows to guard against rain and mud and a heater.
Once the finished vehicle is test-driven, it will go to a battalion called Crimea for use in reconnaissance missions.
Musa has given up medicine for now and feels he can help the war effort more through the buggies.
He is a Crimean Tatar, a Muslim group from the peninsula that largely opposed Russia's annexation and has been harshly punished.
Russians "hate freedom," he said.
"I want to (go) back to my home. I want to meet my family and it's my internal motivation to do this."
'Frankenstein vehicle'
In another workshop in Kyiv's outskirts, mechanics are also at work for the war effort -- on armoured vehicles for medical use.
The project is spearheaded by Romanian volunteer Radu Hossu, who raised funds among Romanians and Moldovans via his Facebook page.
It will provide state-of-the-art transportation for a medical battalion in the war-hit eastern Donetsk region.
Hossu hopes it will then be reproduced more widely.
His team is creating a complex of different-use vehicles to work in tandem, costing around $165,000.
They include a hybrid of a Ford truck and a Soviet Gaz chassis that will become an extraction vehicle to remove wounded soldiers from frontline areas even under fire.
It will be heavily armoured, with huge wheels.
"This is basically a Frankenstein vehicle -- it doesn't exist on the planet," Hossu said.
A Polish bus has been rebuilt as a mobile hospital where medics can immediately do complex operations.
Next, a former food truck is being converted into a medics' sleep and wash area.
And a towable boat will be able to evacuate the wounded by water.
Hossu, a former political consultant, has named the project after Oleg Gubal, a Ukrainian soldier who died en route to hospital.
He knew Gubal personally and wants to stop other families experiencing such grief.
"If something like this would have existed... I'm not saying Oleg would be alive, but it would have been a chance for him to survive," Hossu said.
