Re: Calculating Linear Force from Motor Torque?
 

You won't ever need to do math like the above examples to succeed in FRC.

That said, understanding physics principles (like the ones above) can be helpful and are often a part of the engineering process, which is one of the key parts of FRC.

Keep in mind that the goal of FIRST is to inspire future engineers. You aren't expected to know anything coming in. Learning engineering principles is also a part of the process.

Re: Calculating Linear Force from Motor Torque?
 

You ABSOLUTELY need to do math like this to succeed in FRC.

Re: Calculating Linear Force from Motor Torque?
 

Designing your systems to operate at peak effectiveness* is not absolutely needed, but it sure makes the most of what you've got.

For example: for our gathering system in 2012, the conveyer to lift the balls only needed to hoist 3 balls at a time max, and we used a AndyMark motor in its gearbox, massively overpowered for what we needed. We had it geared (post gearbox) 1:1, and it worked just snazzy. If we had done the math, we would have realized it could have lifted the balls 25x faster with ease


*not necessarily efficiency - remember: your robot only has to last 2.25 minutes, pull every last amp/hr you can as long as they are doing something. Why not?

Re: Calculating Linear Force from Motor Torque?
 

That depends how you are defining success. Yes, in the grand scheme of things, students can be inspired and they can develop life skills without ever being asked to do a motor calculation.

However, challenging our students to learn about motor curves and apply that knowledge to designing a component on the robot can inspire them, give them a real world experience and result in a more competitive design. They can learn more and be inspired more. Of course there are plenty of competitive robots each year that are built without applying motor curves or math, but the ones that do use these calculations do some pretty inspiring things.

If success is defined more narrowly in terms of specific design objectives for a robot and its subsystems, it is very possible to fail if motor curves or calculations are not used.

We are also aiming to change culture to celebrate STEM. We should encourage doing the math so everyone can strive for greater achievements, rather than look for reason to justify not doing it because we can be successful that way.

Re: Calculating Linear Force from Motor Torque?
 

I'll agree with Madison and Carl in refuting this statement. Torque equations are relatively basic compared to other types of math used in FRC, yet are extremely helpful. I'd argue that a basic knowledge of trigonometry, for example, would have been quite appropriate in Ultimate Ascent.

This is not even to mention higher-level math. Offensive Power Rankings have been, despite their controversy, an important part of scouting for many years. Today, most teams pull the numbers off of ChiefDelphi rather than do the linear algebra themselves, but I bet 1114 enjoyed a healthy advantage in doing their own calculations before the method became well-known to the public. Another example is the drivetrain testing my own team did earlier this year. Using a graphing calculator and some basic differential calculus, I produced a reasonably accurate equations of velocity and acceleration based on distance-versus-time data. We've been able to use that model to choose gear ratios for our next drivetrain.

Re: Calculating Linear Force from Motor Torque?
 

You could build a regional winning FRC bot this year with no one in your team having more than a 8th grade math education, given a few people on the team fairly familiar with FRC rules of thumb. Frankly, I think you might even be able to get away with a 4th grade math education.

However, this fact completely misses the point of FRC. FRC is one of the few places where students are actually asked to challenge themselves and apply what they've learned. It's been awesome for me to see how different things I've learned in math class (trig, differential equations, etc) apply to robot design, and it's motivated me to continue to do well in the classroom.

If you want to build a well engineered robot (which isn't necessary to win a regional), these types of calculations are extremely important. In fact, you can argue that this discussion of DC motors only scratches the surface in terms of design for DC motors (current draw, changes in performance at different voltages, factoring in acceleration of the motor under load, etc are all great things to look into). Without this type of basic knowledge, you're flying blind. If you don't want to rebuild gearboxes a few times each season because you're cooking motors, do your homework, and actually look at torque requirements and safety factors. It looks like Adam's presenting the math a bit formally (which is really the right way to do it), but don't get scared by a few equations. It's honestly not that hard.

Adam, although I've never built an elevator, a FOS of 4 sounds a bit conservative. I'd assume a FOS of 2 would work well from just general FRC experience. Of course, I'm sure you've had a lot more experience with elevators than me.

Re: Calculating Linear Force from Motor Torque?
 

You are correct, I assumed it was 80 on drum.

Re: Calculating Linear Force from Motor Torque?
 

I didn't recommend any specific factor of safety, and I generally do these calculations without them as they are kind of meaningless in this case.

For example, why design for 25% motor load with a FOS of 2, when you can call that 12.5% motor load.

It's a style preference, I just don't use FOS here (Although I use it a lot elsewhere).

AS for what % stall is okay, that's tough to say and depends on how often it's used and what motor you're using.

Re: Calculating Linear Force from Motor Torque?
 

To be quite honest, I think most folks who managed to pass high school algebra could do engineering math quite easily. But if you asked them what they were doing, or how the equation they're dealing with is derived, they'd be totally lost--which is why engineering is a 4-year (or more) curriculum with math through about 4 semesters worth of calculus and differential equations.


As far as safety factor, what a "good" one is varies by what you're dealing with, and other similar things. If I'm designing something to carry people, I'll use a higher safety factor than if people aren't involved, for example. For an FRC robot, the more critical the system, the higher the FoS should be--to a point. (You probably want somewhere between 1 and overkill, but where overkill is depends a lot on your design, where in the design you're working, what material shape you're using, and how well you made your bumpers this year.)

Re: Calculating Linear Force from Motor Torque?
 

You have to be careful with safety factors. Otherwise you start with a mouse built to government specification---A elephant.

Airplanes are another example of competing safety factors. You don't want wings falling off, but you want your lift to weight ratio much greater than 1.

Re: Calculating Linear Force from Motor Torque?
 

What Madison said.

A perfect example of where math like this was extremely helpful was the Mini-bot race in 2011. By the halfway point in the season, sub 2 seconds mini-bots began to become the standard for teams playing in the last few matches of any events, with 'traditional' mini-bots becoming almost useless by the championship. The secret* behind them was so simple, and once explained was easy to understand, but it's not something that most people would have come to without understanding the concepts in this thread. (IIRC, 973 - Adam's Team - Had the fastest mini-bot at the championship (or at least their division) that year.)

With that being said, this is an awesome thread. I think I'm going to borrow some of these equations for later. :D

*The 'secret' was to remove the transmissions, and use a really small diameter roller/wheel - 3/8" OD or so, IIRC.