You’re mad.

That’s what father Ben Ryan of North Wales said he would have told anyone who suggested he become an engineer.

But when his son Sol developed a blood clot that caused him to lose the use of his left arm, Ryan said he wouldn’t accept that.

“When he came home from the hospital his left arm was no longer moving at all. That wasn’t good enough for my son. So I decided to do something about it myself.”

In a moving YouTube video, Ryan describes his journey from elation at finding out he was going to be a dad, to using an Xbox Kinect scanner to create digital scans of his son’s residual limb, to fitting his son, Sol, with a prosthetic arm.

When he actually got a perfect fit, the reaction of Sol, now 2 1/2, was this:

“He actually said the words ‘it fits properly’ and he just wanted to go to school and show it off to all his friends. That’s when I knew I had done it right.”

Ryan is learning product design and engineering skills with the support of the Bangor University Engineering Department in the United Kingdom and said he would love to go back in time and become an engineer.

Ryan, a teacher in psychology and applied science, said he can make a prosthetic arm system for between $150-$250, according to CNN.

Ryan says he’s currently making 20, 3D limbs for other families around the world. Find out more on Ryan’s website, Ambionics.

The YouTube video is produced by borntoengineer.com.

“If you have an idea and you have the motivation to do it, you can do it,” he said. “You can change the world.”