What is your drivetrain's top speed?
 

What is your drivetrains top speed in FT/S (FPS)? If you are doing a shifting drivetrain please comment with your low speed too! I would love to hear any other comments about what you think is "best" and why!

Re: What is your drivetrain's top speed?
 

Your poll has an issue; we clock the stock AM14U3 at 10.0 feet per second in the user guide (PDF link). (That uses 75% of free speed for calculations, to account for losses to friction.) If you meant it to be 10-13 (since the previous option is "less than 10"), you'd be correct.

As for Iron Kings, we'll be around 15 theoretical or about 13 in practice. 5.95:1 gearing, 4" HiGrip wheels.

(Full disclosure of the painfully obvious: I work at AndyMark.)

Re: What is your drivetrain's top speed?
 

Yes, that was meant to be 10-13. I did see that the kitbot was listed at but also thought (or hope) that most kitbot teams will elect to use two CIM motors rather than just one that the 10 is derived from.

Re: What is your drivetrain's top speed?
 

If you use two CIMs or one, your top speed will not increase--simply how fast you get to it (and how much current a motor will draw). To go faster, you would have to change the gearing or start integrating motors with a higher free speed (like a Mini CIM, whose free speed is about 500 RPM faster).

Re: What is your drivetrain's top speed?
 

The number of CIMs does not affect the top speed of the kitbot, just the acceleration and some other stuff.

Re: What is your drivetrain's top speed?
 

Using multiple motors won't change the top speed significantly, though they will decrease the time it takes to get to top speed.



3946 is geared for 12.7 ft/s per AM's calculations - 2015 gearing, 2016-17 wheels. We're using 4 drive CIMs and keeping the weight down by only using four wheels and two belts on a "half-long" chassis to keep the current draw reasonable.

OBTW, thanks to the folks at AM for putting those churro holes 4-1/4" either side of the drive bearing! So far, the only drilling we've done to the chassis were to accommodate rivets and rivnuts rather tan 10-32 and nylocks.

Re: What is your drivetrain's top speed?
 

I'm having a really hard time with the idea that 17+ fps is ever a good idea for most teams. I'm also having a hard time with the polling results that seem to show most respondents disagree. YIKES

Re: What is your drivetrain's top speed?
 

Our robot will be zippy. Cruising ratio will be less than 5.7:1. Not saying exactly how much less.

More critical questions might be, how many seconds will your driver need to move the robot from a retrieval zone to an elevator, or the other way 'round? How many seconds will a defender be able to delay that?

Re: What is your drivetrain's top speed?
 

EEP. Okay.

My question to you, oh CD Community, is this: do you have any students who have driven a robot that travels 17 fps or faster? 14-15 fps is on the edge of control for most drive teams, and the last two years had games in which something between 7-11 fps was usually ideal, so unless your drivers are seniors with experience in Aerial Assault as freshman, this will be a significant challenge.

My question to myself is: which do I think is likely; that those responding to this poll don't realize that their Toughbox Mini only goes at 10fps, or, that my team will be struck by a careening, out-of-control alliance parter while lining up to receive a gear or a load of fuel? I think I will prepare for the worst, and add extra thickness to our gussets. 2014 is still a raw memory.

Re: What is your drivetrain's top speed?
 

The answer is to your question is: It doesn't matter.

If you have alliance partners in quals that bump into you while loading for gears, so will other people. Make your gear pickup more reliable so it doesn't matter. Don't pick teams that can't drive, and you being careful of overgearing your robot will be more desirable as you will be able to control your robot.

Rather than trying to change other people's designs over a message board, count yourself lucky that you have thought of this potential issue and come up with one of the several solutions to the issue. You will be a more attractive pick for it.

Other teams can do what they want, maybe they have the ability to make the drivetrain work better than a lower geared one. I don't know if they can, you don't know if they can, I bet some of the teams attempting don't even know if they can. The concerns are valid, but it's not for us to judge them this early in the season.

Re: What is your drivetrain's top speed?
 

Who's judging? This early in the season, when teams have some time left to work on their designs, CD is about the best place there is to get advice from people with experience. Teams have their own ideas and they will do what they want, but now is the time to give and receive advice.

Re: What is your drivetrain's top speed?
 

Absolutely! Advice is a good thing. Just no need to freak out about the poll results of only around 100 respondents say that the majority are gearing their robot fast on a flat field.

Teams should heed the advice in this thread, though I would hope most teams have their drive train worked out by now.

Re: What is your drivetrain's top speed?
 

We're running the same setup with wheels from 2015's kit since we used 6" wheels that year.

I understand the theoretical max speed won't increase with additional CIMs since they all have the same free speed, but won't the effective speed you can reach change because of the additional torque available at the same point on the motor torque/speed curve? If the kitbot is rated at 75% of free speed due to friction losses on one CIM per side, then I would think the additional CIM per side would add enough extra power to run at a higher percentage of free speed before friction becomes the limiting factor again. Is there a significant amount of friction added from the extra gear for the second CIM?

Re: What is your drivetrain's top speed?
 

228's going 4 CIM, 14 / 6 ballshifters. For packaging more than anything else - the 2 CIM model is a really compact gearbox, but the 3 CIM is huge.

Re: What is your drivetrain's top speed?
 

14+ fps is drivable if your drivers get a LOT of practice. I would never gear a bot that fast without a practice bot.

Our fastest bot ever was 17.3 free speed but our driver had more than 50 hours of drive time before our first event.

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.