In the scene reintroducing Alpha in "Once A Ranger," Alpha implies he hadn't been in working order for a while. Who's been working on him to get him up and running? Adam, who had experience with Morphin' era tech, and Andrew Hartford. Who created an Artificial Human. Who better?
The Morphin Grid is some sort of energy formed from the battle between good and evil, and the run-off energy tends to form in explosions. With multiple bad guys (and later in the team-up episodes, multiple good guys), the Grid must've been overloaded and gone crazy with the explosions.
Considering RPM's explanation for these explosions, perhaps the equivalent of RPM's "bio-channels" got clogged up because of all that.
The seemingly fridge-logical aspect of Andrew making his robot son a young adult in appearance shifts to brilliance because when he finally dies, Mack can live on his own and not be discovered by an adoptive parent.
The final battle between the rangers and the powered up Flurious makes very little sense, there's no reason Mack not being human should have allowed him to overpower the Corona Aurora, UNLESS Flurious' wish on the Corona has actually been that no human could defeat him? Mack defeating him suddenly makes more sense, the Corona Aurora played Jackass Genie and gave Flurious exactly what he wished for and ONLY what he wished for. Fate then threw the ONE ranger who could beat him at Flurious.
Of course Fireheart's scale would become a mini-Battlizer. Fireheart is technically one himself.
Andrew creating an artificial son that was physically a young adult, although it's likely that this is a preferable alternative to making new bodies for him to simulate growing up.
If Andrew is skilled enough to create a robot sophisticated enough to perfectly pass for human as much as Mack does, why doesn't he use that technology to create a team of Power Rangers?
He probably would have used up a lot of time and energy for it.
Plus as noted by Linkara, he could have built Mack as a prototype for a team/army of robot rangers to protect the Corona Aurora, but they would develop sentience like Mack. and considering how resilient Andrew was against letting Mack become a ranger and being put in harm's way, would be a good enough reason to put an end to it.
Regarding "Once A Ranger": In the original MMPR series, Rita Repulsa replies on two occasions to Lord Zedd's idea of having children with utter disgust. So, what changed her mind enough to conceive Thrax?
One would expect much alcohol was involved, hence why we never hear of it before now, what with this being a kids show...
So Thrax is the son of Lord Zedd and Rita. Okay, stretch, but we'll go with it. But that makes him only ten years old, tops. And yet he was sealed away by the Sentinel Knight, who was, at the start of the season, incorporeal. So WHEN, exactly, did this happen?
There is a simple answer here that is this Troper's personal headcanon: Thrax... was... lying. About what? All of it. Thrax is some two-bit villain who discovered that the Sentinel Knight once defeated a warrior named 'Thrax'. He takes the name as his own and then decides to go one step further and claim he is the son of two powerful evildoers... who aren't around to deny such things. Suddenly makes Thrax's actions make more sense.
Rita and Zedd only got married ten years prior. Prior to being sealed in the dumpster, Rita was a minion of Zedd's. While they didn't get along when Zedd came to Earth and banished her, what happened between thousands of years ago is unknown.
Perhaps the idea of the combination of their powers was too tempting and they created Thrax by non-sexual means.
There is the possibility of some timey-wimey thing happening to Thrax that would get him sent back in time 10,000 years or whatever.
This troper finds this likely; during Zeo and Turbo they gave birth to Thrax and probably sent him back in time for his safety until they attempt to conquer the universe as shown in "Countdown to Destruction". But they didn't count on being purified by the Z-Wave. Either they have forgotten or decided he's better off.
Since Mack is a robot, he won't age like those around him. If Andrew had died before telling him who he really was, Mack would never know why this was happening. Not every day you see a teenager filling up the fridge like this...
Kind of rectified in the end, since Mack found out, and he eventually became human.