Good luck with this season!
Use proper c chanels instead of rails for your chassi space out your wheels and add bracing for your chassi
Another thing is that your indexer and arms are made of steel c channel I think that if you change them to aluminum you will lower the center of gravity of your bot and mitigate tipping
Thats a great point, although would it change the center of gravity by much because id have to buy aluminum parts
aluminum is always much better than steel, but it’s also more expensive, so if you are on a tight budget steel is ok.
My thoughts on steel
so a couple questions. obviously I would want to use all aluminum if I had the choice, but what it be smart to use steel for the base and aluminum for everything above it? (To help with the center of gravity) Next question is if I am using steel does that mean I have to box bolt?
First answer. Yes you can make your whole base steel to lower the center of gravity which might help a lot with your tipping. You still might want to move the cortex. Then yes you can make everything else aluminum. And no, you don’t have to box bolt anything. It just makes the connections stronger.
Typically, no. That’s overkill, and you’d be increasing the mass without that many gains. I still would box bolt a few connection points for aesthetic purposes. And for areas with very high loads, I would box bolt it even if the steel can handle it. Better to be safe than sorry.
If I was in your situation (with limited aluminum parts), that is what’d I do. Steel not only helps your center of gravity, but it also gives you more traction because of mass. Traction is defined as
coefficient of traction x normal force (this is also referred to as static friction). Traction is needed to transfer the energy from the motors to the ground. You can’t move without traction (unless you have some sort of chemical exhaust which is illegal).
Normal force is directly proportional to weight. So in essence, you gain traction by having more mass (weight is
mass * force of gravity) or increasing the coefficient of friction of the wheel material you’re using. Omni-wheels tend to have enough friction for most applications. A set of traction wheels can’t hurt you (but don’t use all traction wheels on a drive).
In general, think of how different mechanisms will logically function. I understand it can be difficult without having taken a higher level physics course. That being said, I highly encourage everyone to take a course such as AP physics as these concepts apply to all aspects of robotics (even software).
Even with a lower center of gravity, you have to account for the balls the robot will store. I’d say a competitive robot can store at least three balls which is a significant amount of mass for a robot. Especially very fast robots. (This is because of momentum which is
mass*velocity). Speed is key in this game (imo). So, back to the original topic of this thread. An anti-tip will probably be very helpful.
Well actually I do agree with you but I don’t agree because these balls are extremely light.
I’ve taken ap physics so I understand what you are saying (and this is the first time what i’ve learned is useful wow). anyways I understand what you are saying is true, but then you don’t want it to be too heavy because that would put too much strain on the drive base motors right? This is why I made the switch from 2 to 4 motors for the drive base
Yes exactly. Understanding the limitations of the motors while also optimizing their functionality through physics is what I’m trying to get at. Friction between axles and bearings and traction are the biggest bottle necks for drive trains. In short, finding a balance is very important. And a 4 motor drive is almost a pre requisite to be competitive,
Also I want to make my robot hard to push from the sides… I am thinking locking an additional pair of omni wheels centered in the middle of the chasis, or maybe the same thing except with traction wheels. What would be the best way to go about making a robot that won’t be pushed around?
Yes, but there are also multiple options to fix you tipping with having your whole bot aluminum. It is just one solution I gave. Anyways I don’t think you should worry too much about stain on the motors because of how powerful and plus just by looking at your robot from that first pic it is very light.
Even though they are “light” to you, they aren’t light on a robot. Momentum primarily and many other factors impact the performance of the robot substantially. You need to take careful consideration of this when making a design. I’m not saying the v5 motor can’t handle it, but I am saying that it is important to consider everything in order to optimize performance.
You should not think like this when designing anything. Just because the v5 motors can handle some friction and various other forces does not mean you should lack on basic design principles. That is just bad engineering (imo).
thanks for saying that a 4 motor drive is a pre requisite in order to be competitive lol. My school team is very new… I am the senior member and don’t even know that much lol. Anyways are there any other almost pre requisites that I should know about? I’ve learned to always use c channels and never rails… lock bolt aluminum… two c channels should go across entire robot… anything else worthwhile?
It kind of depends on the robot. Try and look for various other kinks in the robot and try to solve them. Your robot is never “Finished” you should always be able to find a way to make your robot better. If you can’t find one, then you aren’t looking hard enough.
I really like this chassis set up (skip to around 5:30). It prevents pushing from the side while also maintaining maneuverability. This is because it maximizes traction.
Also what are your guys thoughts about using stand offs for essential parts of the robot? I find that they lossen pretty easily and I am trying not to use them too much but it’s hard
as you can see from the photo my lift is being elevated by stand offs and I am wondering if this is a janky building practice