there’s a lot of really valuable build quality information on the forums, although it’s pretty scattered and a bit hard to find once the topics have died. Here are some of the basics in building I think you should know before doing anything.
Friction and Slop
In any moving system, friction is your main enemy. You want to reduce friction as much as possible. Friction can be caused by many things, but the best ways to reduce is are to make everything line up perfectly, use bearings, spacers, and washers properly, and don’t over-tighten joints and pivots.
You want to use bearings wherever an axle goes through a hole, but don’t overuse bearings. each axle really only needs 2 bearings, on either end. if you load an axle with too many bearings, it will actually cause more friction.
When you have axles going through holes you need to take extra care to make sure the holes line up perfectly. Vex holes are square, and larger than the screws, which means they allow for some wiggle of parts. This can misalign holes which in turn puts pressure on axles and causes lots of friction. So make sure things are lined up before locking them down.
Additionally, you should know what kinds of joints you should use and where. using shafts is necessary for many parts of your robot, but screw joints are a much better joint because they have less friction and wobble to them.
good video on the different kinds of joints:
https://www.youtube.com/watch?v=rhfNeMwAKnI
Another cause of friction could be any kind of unwanted perpendicular force on an axle. The best example of this I can think of is in a cantilevered drive. Cantilevered drives are where you have your motors, then a c channel, and then a wheel, with no exterior support. This means that all the force of your robot is direction perpendicular to the axle, which causes it to really dig into the bearing on the c channel, causing tons of friction. This is why you want to always have an inner and outer support on your drive. Cantilevering isn’t always bad though, for lightweight things like sprockets and rollers it can be fine, as well as balanced things like a lift that is cantilevered on both sides of the towers.
Another cause for friction could be over-tightening your joints. This causes unwanted pressing and rubbing between parts, and is just not good for friction. Overspacing an axle also causes this, which is when you put more spacers or washers than you should. I like to leave at least a washers worth of empty space in the spacing on my axles to keep it nice and loose, but not too sloppy.
Another thing you have to consider with moving parts is slop.
Slop is the amount of free wiggling a part can do that isn’t intended. For example, it’s the amount of free spin your wheels might have before the motor engages. Or it could be the amount of wobble something has on a possibly loose axle
Typically you want slop to be as low as possible as well as friction, but often times you have to trade one for the other, and slop usually is less of a concern than friction. Depending on the subsystem, slop may or may not be an important factor.
For example, in a drive you want as little slop as possible, because you don’t want your robot to be able to move without the motors. But in a system like an intake, slop usually isn’t very important, because these systems often spin rapidly without needing much precision, so you should be more worried about friction that slop.
Rigidity
The next super important factor of building a quality robot is to have rigidity and strength in your structure. To put it as plainly as possible, you don’t want your robot to be able to move at all unless it’s supposed to. That means preventing wobbling, flexing, and bending of the structure.
The first thing about the structure of your robot is that c channels are really the best structural piece. They have the most strength and versatility, making them the superior structural component. I use almost exclusively C channels when building the important structure of a robot. (there are of course exceptions when an angle or a U channel can be useful.)
The next important thing is learning how to properly connect pieces. You should use multiple screws, and really lock them down tight so they don’t come loose or allow for any slop in the connections. Lock nuts are really great for making sure your screws don’t come loose. Using star drive (torx) screws also helps in preventing strips and being able to really tighten them hard.
Using box bolting is a really powerful technique that makes the connection of pieces incredibly rigid for very little added weight.
in the above image, you can see how box bolts work, basically its just putting a long screw all the way through the c channel and filling it with spacers. This should be used wherever you can tbh, it’s such an effective building technique.
In general, just make sure to brace all the parts of your robot together in a way that the whole thing may as well be one solid piece. If you find that it’s floppy, flexy, bendy, or even a bit wobbly then something isn’t build right.
This topic isn’t really specific to one area of build quality, but it has a lot of really good information in it, so probably should check it out:
DR4B Tutorial by 333A
Design
all well build robots need to start with a well made design. This can be as little as much conceptualizing the concepts with prototypes, sketches, and mental images, but really I would recommend using CAD software to fully model your robot before even building. its a steep learning curve, but it’s well worth it. After starting to use CAD in my designs, my build quality and overall success in vex skyrocketed. And once you get proficient at it, it will end up saving you time because you’ve essentially just created instructions for how to build your robot without touching a part. It helps you avoid technical oversights, and saves you from being able to make unforeseen decisions on the spot while building.
here is a post I made about designing a quality drive that might give you some guidance when going about designing a robot.
Designing a Quality Drive
Another thing that might be helpful/inspiring is to look at CAD models of other robots. I’ve learned a lot of good things just by exploring other robots in CAD.
here’s some places you can acquire models of good robots:
Remembering the best
SCA: Tower Takeover CAD Reveal
And here is a generally decent place to look for information, although it contains far more than just building info
Wiki - #2 by technik3k
And lastly, don’t be afraid to ask questions. This is a very very broad topic, and there’s no way to tell you everything you need to know about building in one post. But there are people here that can help you with any question you might have regarding building, and asking for help is one of the best ways to learn.
I hope this post helps, good luck with building!