I’ve seen many robots painted and some look great, but others are all chipped and ugly. What is the best way to get paint to stick to aluminum pieces so that it lasts and looks good? I know anodizing is far superior to paint, but it’s not in the budget right now.
Dipping can be really nice and durable, but it can be just as expensive as anodizing though if you’re wanting textures(if you want to order it to be done). But if you do it yourself, it’s fairly cheap but not as cheap as spray painting. One issue with this is that it can have filled holes so you have to poke them out, as well as make sure the desired holes stay un-painted to ensure no friction loss.
EDIT//: [BELOW] is most recommended. If you want to make your robot look more professional, have lexan cut to the edges of the sides of your robot, add paper behind, then use a knife to trim the paper to the edges of the lexan. 
I’ve painted my robot before. Looks cool but I honestly felt like it was a waste of time. The paint eventually chipped off like crazy because of rebuilds and insane practice hours. Just have good build quality and your robot will look clean :D.
An inexpensive method to paint aluminum in a way that’s not likely to chip:
- Clean the aluminum thoroughly with very warm degreasing detergent water, made up using something like Dawn or Palmolive dishwashing liquid.
- Rinse with clear water.
- Follow that with 50/50 bath of white vinegar and water. Blow dry.
- Spray on a self-etching primer, like this one: http://www.rustoleum.com/product-catalog/consumer-brands/auto/primers/self-etching-primer/ That’s about $4-$5 US per can; you’ll only need one. Keep the first primer coat at a light dusting; don’t make a wet-looking surface with it. In a couple of minutes, spray another light dusting. Two “dust coats” are usually enough, but you shouldn’t need more than 4. It’s not going to look pretty at this stage.
- Now, topcoat it with a nice paint. (If you used Rustoleum primer, it’s probably worth using Rustoleum topcoat, though you’re not likely to have issues with most any high quality rattle-can paint.) You might want to put on a couple of coats, but you probably can get by with just one.
This is a pretty cheap way to go. You can add more complex and expensive steps, like an alodine wash after the acid dip, but alodine is kinda expensive unless you have a lot of aluminum you need to paint. Also, you can use a phosphoric acid prep instead of vinegar. It costs a lot more than vinegar, (which costs less than water in most cases), but it’s readily available at any paint or hardware store. Here’s some from home depot:
Note that this isn’t actually much better than using vinegar for our purpose of painting new, clean aluminum.
Alodining actually is an improvement, but it’ll add a bit to the cost. Alodine treatment turns the aluminum copper/gold, and bonds a chromate layer to the aluminum. The chromate layer resists corrosion, primarily. But it also takes primer very well, which is why you’d use it here.
Here’s a link to buy a pre-diluted quart from Aircraft Spruce and Specialty Company, a place that supplies parts for homebuilding experimental airplanes. (Yes, I’ve done that too. EAA chapter 186: http://eaa186.org) Even wooden and fiberglass planes use aluminum, so almost everybody ends up needing to treat and paint aluminum.
That quart bottle is $25.85 plus shipping, but it’s good for 100 square feet of surface. Maybe a couple of teams or programs that want to paint could go in together. Note that Alodining only works on aluminum; it won’t help prep any steel parts.
Also, note that you can get alodine treatment from Amazon, but it costs yet more.
[edit: fixed typo of “we-” to “wet’”]
@kypyro Thats very helpful. Thank you!
I’m currently halfway through doing it and am starting to regret it
I would suggest using plasti dip. It peels off a whole lot easier then spray paint and looks nicer