perhaps it works like a phase inhibiter, all of the junk would take enemy ships longer to phase jump.  or...junk could be a discovery only available to junk planets...with the same effect as the phase inihib.

honestly, i havent played Mass Effect (but i want to)

ehhh.......

While new races are fun, the game doesn't really need it. There is also a huge amount of work in setting it up and balancing it with the existing races. However.... if there were any races added, I agree a robot type of race would be quite a good addition. If there was a 5th race, some super organic race would fit as well.

For the robots, you really have to stick with the theme metal, metal, metal and also consider that some concepts of civilization would notbe practiced by them.

Origins: I'd suggest TEC instead of Vasari if you're wanting to go to the junk/salvage sort of feel. The Vasari have very high tech and the nanobots so a slight difference there would be ideal (Though on that subject, the unknown thing following the Vasari could be nanobots gone wrong, think grey goop theory... not really playable, just all devouring). Anyway, robots would originate as a result of faulty programming as suggested on the TEC worlds where automation has been used heavily for ships, resources and other trade items or even as a result of tampering by another race. A nice touch would be to introduce the robots in a mini expansion as a different type of pirate and then as a fully fledged playable faction.

Appearance: given robots have no need of personal comforts and are completely practical in ideaology, ships would be more hodge podge than the TEC but based on the TEC designs. So an ungainly and patchy look but dedicated to it's purpose.

Civilization theme: Repair, recycle, reuse.

• Weapon systems would be more ballistic than energy, being based on the TEC designs. 
• Better at collecting metal than crystal.
• Highly efficient at construction, repair and rebuilding.
• Scrapping or salvaging a structure or ship is more efficient.
• Attacks that transfer hull points from an enemy ship as per the magnetic idea.
• A repair option that transfer hull points from your own ship to another as per the magnetic idea.
• If you want to get really creative then salvaging one ship to create smaller ones is another possibility, this could also work in reverse where smaller ships can be combined to make a larger one.
• For planetary attacks, nuke from orbit does make sense but if you want them to be a bit more original, what about some sort of invasion.
• The race has no concept of trade but neither does it rely as heavily on money.. as robots don't need to be paid.
• Refineries are of more use and have more function.
• Culture... bit of a tough one but I'd suggest that they actually are devoid of culture and therefore it's more of a white noise approach leading to the suggested blackouts on planets and delays after phase jumping.

Just to add some thoughts to it all.....

Depends on the style of robot envisioned really.

hmmm....

Honestly, It's a DECENT Idea... Sounds a bit borglike... but, Hey.

You have to remember, these things HAVE to be balanced. Start off basic, you know, the SoaSE research styled ship advancement. You have the...

Trade and Military oriented TEC

Psionics and Religious Advent

Oppressive and forceful Vasari

and the Logical and Brutal (robots)

As such, the Robots culture would be more based on logical, easy thinking. As your culture improved on an enemy world, their population would start to drop - after all, if automation is the culture, jobs get cut, and people get fired! Their refineries and such would slowly have their 'fuctions' decay, and at 0% Population/Effectiveness, the planet is forcibly abandoned - The same was as the allegiences work.

Their war machines, while based on junk, wouldn't have armor - instead, their hull upgrades would increase 'Cohesion' - Increasing how much damage they could take - and their armor upgrades would increase the 'miss chance' ships had while attacking them, up to a max of like 20%.

As the ships took damage, they would expand and become uglier piles of junk, and then finally explode, dealing 5% damage to ALL nearby ships - thus enabling world destroying junk blasts. But energy weaponry (Lasers and the like) Acctually have the opposite effect - They lower the damage these ships do when they explode, because a laser burns the metal and junk away. So basically...

The Race would be STRONG against fighters and frigates that used Solid Weaponry - TEC and Vasari - But the Advent would mop them up quickly...

But their Capital Ships would be sleek, elegant designs that were pretty much flying glass cannons. Lots of damage, low survivability. THey wouldn't be able to 'death scuttle' like the lower classes of their ships...

Basically, their whole fleet is a Suicide Fleet. They make one hundred ships, fly them in, and pray you don't use a lot of energy weapons.

Their shields wouldn't be shields - after all, their fleet's goal is to die...

They would instead get %chances to reflect an attack every few seconds - maybe 10? It would balance out nicely, because the damage they deal on death is 5% of their max hp - which on frigates and the like will be horribly low, maybe 3-4 hundred, and their cruisers could max out at 7 or so. Their cap ships would be pushing the limits at 1700.

Cheap. Expendable. Effective.

The balance is preserved. If you've got a group of ships flying right on you, it's gonna HURT when you get blasted by the debris - But if your fleet is bigger, the death damage will be spread out.

Basically? Their whole war machine would be 'Shock troopers' - Go in, hit hard, and darn the consequences.  Their planet bombing would be anhilating the populations, blotting out the sun, poluting the surface - basically, making it a 'machine only' world.

Just my two cents.

If you don't like the idea, don't reply.

i had this idea, as well as having the 3 basic tech trees, the robots would also have bonus one, it would be a "or" tree: there would be 3 additional trees, but you could only pick one to research.

so the 3 bonus ones would be:

Combat: things like weapons, armor, and shields would be boosted

Economy: they would get a bonus to metal/crystal production as well as a bonus to culture spreading and culture's effects

Empire: this would enhance the build times of ships and buildings, it would also increase the population of the planets as well as the survivability of those planets...

(but these "bonus" tech trees only enhance the power of the normal tech trees remember)

bump

Correction, last MICRO expansion

But if a fourth race is added, it's most likely whatever is chasing the Vasari. Perhaps something like the Seraphim in Supreme Commander:Forged Alliance.

one of their Capital ships can be a Mobile Factory. To keep things fair one of its other Capital ships would have the ability to disable the Capital Ships of other races. Then another one could unleash a swarm of converted nanobites that would infest the inhabitants of the vessels leaving the ship dead in space. the Mobile Factory would then breakdown the Capital ships and use their scraps to build themselves cruisers and frigates. Now crewed by the assimilated crews of the enemy. Any Capital ships created by this repicator/borg race would have to be created at a larger stationary factory. All ships smaller then Capitals (remember the Capitals are crewed by the brightest and best of the races. making them the biggest target of any enemy race) would be considered obsolete and destroyed where they stood.

nano bots are robots.... 

I like the "replicators/vasari" race idea.  Its a good twist, but will the race be different enought in look and function... i don't know.