I think about this combination alot and wonder where the line is drawn between it being a magical girl show or where it just becomes about the robots. I think about it so much that I sometimes forget what I decided about it a week ago and start second guessing myself XD

So this'll just be a place to organize my thoughts and of course any feedback or input will be quite welcome! So don't be afraid to chime in!
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Early examples magic + machines of course start with Cutey Honey and Miracle Girl Limit

Limit, who was injured in an accident is now rebuilt with robotics.Her new cyborg powers allow her to help people in need for a limited amount of time.


Cutey Honey (in all versions) is about an android (raised as a human) who seeks justice for the death of her father/creator and other victims of the crime syndicate Panther Claw. 

Since both of these shows are classified as magical girls by their creator, and in 1973 the magical girl trope was just getting started - I give them a free pass.

But now its 2014 and magical girls are mixed in with everything from machines, detectives, thieves, fantasy and in the mix of everything. So what counts and what doesn't? 

More on that to come.

interestingly, but I guess not surprising, most Mecha magical girl shows usually are found in work aimed towards boys and men. 
I think this is why I have so much trouble pinning it down because shonen and seinen ideals and tropes speak to a different audience than say "Fushigiboshi no Futagohime".

In the 90's we got Magic Knight Rayearth which combines Magical Girls, RPG Fantasy and mechs.


the show uses the mechs as their trump card so It's not really like it is the defining thing for it. Rayearth gained enough popularity with girls and boys to become sort of gender neutral in terms of demographic.

but aside from that we got lots of little OVAs with high-tech armor, giant mecha swords and space battles.

Moldiver:

Taking cues from more traditional tokusatsu super heroes (Ultraman for example). Mirai accidentally activates her older brothers super-suit and is able to transform into the heroine "Moldiver" 

I haven't seen enough of Moldiver to know why Wiki has it listed as "mecha" but since it plays into alot of sci-fi and superhero tropes I wouldn't be surprised.

Galaxy Fraulein Yuna:

wiki synop: "After winning a "Galactic Bishōjo Contest", she becomes "The Savior of Light", a magical girl charged with defending the universe from evil. After becoming the "The Savior of Light", Yuna gains an impressively powerful armored suit"

An interesting note about her origin is that she was originally designed by Akitaka Mika who designed several Gundams, he did a series titled "Mobile Suit Girls" (MS Girls) which became the groundwork for Yuna.

since the mecha suit (in the context of the show) was made by a strange unexplained source I think its good enough to count as a magical girl.
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Next Up is "Hyper Speed GranDoll"

Hikaru is a girl who discovers that she is really part of a royal lineage of aliens from a distant planet and had strange powers since she was a child. She's given the "GranKnight" to transform and defeat evil.

I haven't seen this one at all, but it seems to fit the bill


Lastly to round-up the 90s, Cyber-team in Akihabara:

Hibari has always wanted the hottest big trend - the PataPi, a little pet/personal assistant who's always got your back. After receiving one from a Prince in her dreams, Hibari's Patapi has the magical ability to transform into a winged mecha warrior to defeat villains. 
Later in the series Hibari is able to transform also using her PataPi's power. 
 
This show feels like such a hodgepodge of other big 90s shows its a little hard to take seriously and also hard to pin down. Sometimes it wants to be a fanservice comedy, sometimes it wants to be a coming of age story, other times it wants to be a philosophical wonderland like Evangelion and Utena. 

but this show is just weird enough to count as "magic" so I think it counts.

I think it has a lot to do with appearances. If the characters act like magical girls, its a mahou shoujo show; likewise if they transform like magical girls it is more than likely to be a magical girl show(or Saint Seiya :p). In Vividred Operation they are unmistakably magical girls because of how they are portrayed and how they act. Take into consideration the first two mechanized magical girls; Limit-chan acts like a typical cute witch and Cutey Honey is the prototypical magical girl warrior. Regardless of the power source or even costume (D4 Princess comes to mind) the thing that makes a magical girl most like a magical girl is acting like a magical girl.