Hey guys, my team is about to start planning robots for Starstruck. I made a full-court flywheel shooter for NBN, but build quality was quite shoddy in my opinion, which probably led to another teammate’s non-full-court shooting robot being used as my team’s robot for VEX Worlds. This year, I’m looking to build a better-quality robot for one of the team’s robots. I know for one cantilevered wheels are a no-no at a high competitive level, but what other pointers could you give me in build quality?
To get good build you want to start with designing it in a CAD program or maybe on paper, so you have a very good idea of what you are going to build and how. Also, never take short-cuts, always go almost overboard with making it structural.
If it isn’t suppose to move make sure there is no way it can move. If it is suppose to move make sure it only moves exactly the way you want and not move in any other way. Make sure every screw is tight (locknuts).#303
Make sure metal is aligned and cannot get misaligned. This is especially important when you have axles spinning at high speed (such as a flywheel) because it reduces friction. However, friction between robot parts is always bad, so you want to minimize it on everything. Also, make sure your metal and axles are straight. That will mess up your design if something’s bent.
One thing that I have seen after having been on a team for two years that never won a single award based off of our shoddy build quality is that the saying “It doesent matter if it looks ghetto as long as it works” doesent that often work out. Generally, if something needs to be ziptied, you did something wrong, and dont try to find a quick fix just to test something. Just build it right from the start even if that means not much gets done
I think one of the most important parts of building a quality robot that will outperform other robots doesn’t even take place at the build table. It is pertinent to design a robot with goals in mind, goals which you believe will help you win matches. Furthermore, it is important to look at possible scenarios, and try to find “niche” bots, which are not often built, but are the perfect partner bot - a good example of this would be the Nothing But Net Field Bot, before the point in the season when many teams switched from a mainly preload robot to a field bot.
A huge thing I found in NbN was that it is important that everything on an axle is not squeezed together too much. Basically, without leaving too much room, washers and spacers should be able to spin freely. This helped drastically on our flywheel, and we found that one tight axle (basically, one washer too many) was making our robot not drive quite straight.
Similarly, using bearings right next to motors on an axle will add excess friction but won’t really help to keep the axle aligned. If doing this, be mindful of the next precept:
Keep your motor screws tight.
Make sure the bearings on either side of any axle are lined up so the axle isn’t crooked. Having any crooked metal elsewhere is also laying a poor foundation and will look shoddy.
Use at least two but preferably more screws at points where c-channels meet.
Minimize your use of strips and bent plates. They can look shoddy and they can’t really be relied upon to not bend.
On your chassis, attach the two sides in at least two places (c-channels going across).
Plan how you are going to mount things before you put it together. Often times, build quality is an issue of not the individual pieces, but how they are put together. Make sure nothing can wiggle, shake, or move when it is not supposed to.
A lot of people seem to be suggesting lock nuts over wingnuts, including Cody in is build series, but why? I always prefer wing nuts because of the several advantages they pose. For one, you don’t need a wrench to tighten them, which is awesome. 2, it only gets hard to turn once you start touching the metal, making it much faster to assemble. I’ve also never seen a wing nut ever go loose, well not as bad as a standard nut at least. So, what’s the problem?
One neat trick I’ve learned is that if you are screwing two metal pieces together, put a shoulder screw in one of the holes nearby, just to help you align the square holes.
Yeah, shoulder screws are usually the norm for our structural attachment, because then you can rest assured that the metal won’t shift around even the slightest, since the “shoulder” part of the shoulder screw is exactly the right diameter.
I would argue the “never goes loose part”, it’s just not my experience.
One big advantage of the nylock nut is that you can control the tension on the bolt. Kelps nuts must be tightened or they will fall off, nylock nuts will stay wherever you put them on the bolt, generally at the tension you left them at too.
For example on the scissor lift we’ve been designing, We NEED the ability to have the bolts acting as shafts to be somewhat loose, that way the lift actually moves smoothly and without extra effort.
IDK that’s all I got.
While I agree with your overall statement, in VEX, and really, in engineering in general, if something can get loose during competition, you have to assume that it will. If there is even the slight probability of wing nuts coming loose during a match, wing nuts will compromise the overall build quality of the robot in question. Furthermore, while I won’t argue ease of access, many times, can be designed around - ie. by placing your connections in places where it would be simple to reach the lock nut.
Make sure that all rotating shafts are braced on both sides. Never use pop rivets.
Make sure to use at least one cross-brace on every major part of the robot. Avoid excessively long shafts when the shaft has to bear a lot of force. Don’t use structural zip ties unless it’s not something that needs a lot of strength in that area, for example an intake guard. If something has to pivot on a screw, use a lock nut; tighten the lock nut to the point just before it stops the joint from moving. I know some of these may seem like common knowledge, but that doesn’t mean they shouldn’t be said.
We changed from keps nuts to nylock nuts in Toss Up. At first it was a real pain to get used to having to use a crescent wrench to tighten anything down, but it definitely saved time in the long run since we didn’t have to waste time tightening screws down all the time. They never come loose; that’s the benefit. Keps nuts just came loose in transit to/from tournaments.
As for general build quality tips, make sure to have at least 2 points of contact on all connections. This makes it so that even if one screw comes out, the piece will still be attached and hopefully continues to function. Redundancy is key. Put shafts through bearing flats while screwing them in; it will help keep the bearing lined up.
Keps nuts always end up on the floor of the trunk. They can vibrate loose much easier than nylocks. So they are preferred.
Other build tips
- Ensure free spinning wheels an shafts. A bit harder for driven wheels since you need to pop it out from the motor.
- Don’t over use the nut driver. When in a tight spot, you move the metal over a bit and many times leads to not fully square sections. which then leads to number 1 above.
- Balance an arm rubber bands before adding the motors. This makes sure the motors are not straining too hard.
- Don’t over stress the motors. If you have extra motors, add them to the highest torque required spot. No sense in not using them
- Order of preferred sensors - potentiometer, quad encoders, button, line follower, IME, gyro, light sensor, sonar, accelerometer. Trust a pot reading over and IME on a lift. Buttons are reliable but only give one spot of coverage.
What about tools? I absolutely dread the allen keys! Especially when it comes to tightening nylock nuts. And they strip sooo easily. Honestly at this point I am considering replacing all of my screws will Phillips. But maybe better tools could help. What are your tips on tools?
VEX is switching to star drive (torx) screws. Do not switch to phillips, those will be even worse than hex.
http://www.vexrobotics.com/all-screws.html (Star screws start about halfway down the page.
I’ll second this. I’d also suggest higher end Bondhus products for Allen Wrenches. Just about all the guys at the company my FRC team works at has their own personal tools, and it seems they all use Bondhus. I bought myself a high end set of standard and metric and have been extremely happy with them. Obviously for VEX I wouldn’t buy a full set, just the required sizes.