Re: What is your drivetrain's top speed?
 

^+1!

This is the key.

Re: What is your drivetrain's top speed?
 

Did your team end up going with shifting gearboxes this year?

Re: What is your drivetrain's top speed?
 

This year, I designed a modular gearbox because I wasn't sure what the drive team would want to use or what would be best for the game. We've got speed ranging from 8 ft/s to 20 ft/s. I started the first config at 15 ft/s and this thing is already burning rubber. Any more than 15 and I think it gets uncontrollable.

Re: What is your drivetrain's top speed?
 

For teams that are looking at doing speeds such as this, I would suggest taking your bot out into an open area (if you dont have a dedicated field that is), and just setting up obstacles such as cones etc, and letting your drivers practice at that speed maneuvering around etc. IMO It shouldn't take a good driver too long to get used to such speed and control without too much practice.

Re: What is your drivetrain's top speed?
 

Yes. We are evaluating two options: DS and EVO. Should have a decision soon.

Re: What is your drivetrain's top speed?
 

Our gearboxes: http://www.vexrobotics.com/vexpro/mot... if anyone cares :P

Re: What is your drivetrain's top speed?
 

It's definitely a second order effect. Essentially, by doubling the torque available at the highest speeds, you are going to be able to get closer to free speed. That is, the "speed loss constant" in JVN's calculator will nudge a bit closer to 100%. (or more likely, move farther away from 100% on the 2 CIM side, because I'm pretty certain that 4-6 CIM geartrains are far more typical of the ones used to determine the 81% value).

Re: What is your drivetrain's top speed?
 

Some empirical speed loss constants based on drivetrains I've built (west coast "belt in tube" style drives):

6 CIM: 90%
4 CIM: 84%

Your mileage absolutely will vary. Measure an old robot's actual speed sometime to get an idea what your team's speed loss constants are.

Re: What is your drivetrain's top speed?
 

Luckily, we have a senior driver that was around for 2014. Our max speed will be 18 fps, low gear will be 7. For anyone curious, we're running the WCP DS gearboxes, with custom standoffs to fit sprockets inside (still smaller than the WCD version of these gearboxes). For any teams that haven't finalized cad yet and have the money to spare, I highly recommend them.

Back in 2014 (or so I've heard) we were extremely fast, looking at actually reaching our 19 fps speed with considerable acceleration.

Re: What is your drivetrain's top speed?
 

The 4272 chassis would theoretically be capable of hitting up to 30ft/s (although the field isn't long enough for that to actually happen. We did the math).

We will realistically be able to hit a top speed of between 17-20 ft/s, (takes about 3-5 seconds to accelerate to that point).

We are using 3-Cim Ball shifters, with low gear at 7.5, and high gear at 2.81. We are using 4" wheels. In order to maximize acceleration, the students are working on some automatic shifting. Low gear hits about 10-ft/s.

I will also say that we have a driver with 3 years of experience, and this chassis has already been built for a little while. Also...we are building a practice bot.

Re: What is your drivetrain's top speed?
 

Everyone is focused on high speed getting across field. Don't forget that there are some very precise movements needed to align with the feeder stations and place the gear. How does your drive train handle precision?

Re: What is your drivetrain's top speed?
 

If I understand you correctly, we're getting across the field faster with single speed 2-CIM gearboxes based on our time trials with a tote full of spare parts to simulate full robot weight. As strange as it sounds, you'd probably get across the field faster with slower gearing; I suggest you do more math.

Re: What is your drivetrain's top speed?
 

A robot with single speed gearboxes and 4 CIMs total each can cross the field in under 4 seconds. Choosing a high-gear of 2.81:1 sounds a little bit much, something around 4-5:1 could be a better option. It also means that you don't to worry about tripping your breaker if you accidentally start off in high gear.

Re: What is your drivetrain's top speed?
 

We are theoretically geared for approximately 15.5 FPS high, and 5 FPS low. Alignment and pushing power both count this year, maybe as much as or more than top theoretical speed.