At home he practises from about 2m, focusing purely on form and technique, but at weekends he gets out to his club, on the Mt Albert summit, and can let fly from 60m. Naturally, he agrees that archery is part technical, part mental.
"When you go back to full draw, it's easy to get put off, by a clicking noise or someone talking behind you. Aiming can also put you off sometimes. Your form could collapse," he says, though that is rarely a problem for this sharpshooter. Archers can step away and start again but there is time pressure in competition.
He won the JAMA champs in March, but qualifying for the Commonwealth Youth Games only came on to his radar earlier this year and he reached the target mark of 1220 (he totalled 1221) by chance in April in a competition after missing out on the youth worlds at the same time.
There will be no competition in Samoa from the top Australians or Canadians, as they are not sending archers, but Martin-Roberts has set his sights on a score of 650.
"I want to rank high. Your rank or place will be judged off that 720 score," says Martin-Roberts.
Coach Rob Turner, an Australian, irons out any kinks in his technique, and Martin-Roberts attributes much of his big improvement over the last 12 months to his coach and his ability to straighten up his posture.
"He teaches the way I want to shoot, which is the NSS, national shooting system."
St Peter's has about 40 archers, so it is a popular sport at the school, and it even has a small range.