Re: FRC Blogged-Kit of Parts Drive System Option
 

Maybe AM made it easier to attach super structures because teams typically need to attach super structures? Nothing can be implied with these kit frame details other than the robots will most likely be allowed to have wheels.

We loved the kit frame last year, it's great to see some improvements are being implemented. I'm hoping the transmissions are easier to get into than they were on the previous iteration, that's what gave us the biggest setbacks.

Re: FRC Blogged-Kit of Parts Drive System Option
 

but...but...reality without wild suppositions is so much less convivial! ;)

This is silly. Obviously, the point is that all robots will have to be both long- and wide- simultaneously. In fact, they'll have to be entirely symmetrical, because we're landing on the field like this* [/sarcastic wild supposition]


*Mars Pathfinder 40g "bounce" landing, if you don't want to click.

Re: FRC Blogged-Kit of Parts Drive System Option
 

If its 6" wheels, with the 10.71:1 ratio configuration, JVN's calculator drops out 10.51fps as the max speed.

Re: FRC Blogged-Kit of Parts Drive System Option
 

How do you know what "Speed Loss Constant" to use?

Re: FRC Blogged-Kit of Parts Drive System Option
 

I don't. I just assumed the 81% isn't wildly out to lunch. I'm also guessing that HQ/AM in saying "10.5fps" did some kind of calculation using commonly available tools -- likely JVN's calculator.

Re: FRC Blogged-Kit of Parts Drive System Option
 

Does anyone know where the 81% number came from?

Re: FRC Blogged-Kit of Parts Drive System Option
 

Two stages of gearing, each 90% efficient -- .90 * .90 = .81

Re: FRC Blogged-Kit of Parts Drive System Option
 

Are you sure that's not just a coincidence?

The "Speed Loss Constant" in cell I5 is independent of the gearing in cells C12 thru D15, or the Drivetrain Efficiency in cell J5.

.

Re: FRC Blogged-Kit of Parts Drive System Option
 

Looking at the blog again, I see that they're calling that an "estimated final drive speed," so I shouldn't have been looking at maximum theoretical speeds.

As an extra piece of information, last year they said this about the 2013 kit drive:
That drive had a 42:39 timing belt reduction, so the ratio was 11.53:1. If they used the 0.81 factor last year, they'd get around 9.75 ft/s, which they might have rounded up to 10 ft/s. Based on that I'd agree that they're very likely doing 6" wheels with 10.71:1 gearboxes. If not, they're estimating the speed differently this year.

Re: FRC Blogged-Kit of Parts Drive System Option
 

Also worth noting: in the real world, the % of "speed loss" is not constant when changing gear ratios either:

Team 1678 did some testing earlier this year on a bot with a 2-speed gearbox. The "Speed Loss Constant" was 92% in low gear and 72% in high gear.

Re: FRC Blogged-Kit of Parts Drive System Option
 

Ether is correct on most accounts. Keep in mind that JVN's "speed loss constant" comes after a "drivetrain efficiency" (i.e. losses from gearing), therefore the 81% number cannot be attributed to gearbox losses. The testing we did earlier this year found the overall speed loss from the theoretical free speed of the motors. The numbers we found make intuitive sense, given that motor resistance, friction, rolling resistance, and air drag all tend to increase as speed increases.

My conclusion now is the same as it was then: test your drivetrain instead of blowing smoke from your behind about the theoretical speed you think you'll get.

Re: FRC Blogged-Kit of Parts Drive System Option
 

The Speed Loss Constant does not come "after" the drivetrain efficiency (at least not in the 2013 version). It is completely independent. See below:

^^This is exactly what the "Speed Loss Constant" in the JVN spreadsheet is.


I love test data too.

But I still think it may be possible to develop a physics-based model that will reasonably predict overall drivetrain performance -- including not only top speed but also time to reach a desired speed, time to reach a desired distance, and accel, speed, distance, motor amps, motor volts, and Coulomb consumption versus time -- based on a priori estimates of a limited number of parameters .

Re: FRC Blogged-Kit of Parts Drive System Option
 

What if the water is only 1" deep?

Re: FRC Blogged-Kit of Parts Drive System Option
 

Then that drastically reduces the coefficient of friction between the wheels and the playing surface, reducing the robot's ability to accelerate to the maximum drive speed, and possibly making it impossible to accelerate to 10 ft/s within the length of the playing field. However, they never said that the robot would be able to achieve that speed on the field. That was just the estimated speed. ::rtm::

Re: FRC Blogged-Kit of Parts Drive System Option
 

I'm hoping that the dimensions are increased this year. The dimensions last year severely limited what teams could design (although it meant less clutter on the field). The fact that they somehow fit 6 wheels in a wide configuration makes me hopeful the dimensions are increased this year.

Has anyone tried modifying last year's wide 4-wheel KOP drive base in a 6 wheel base, keeping the same dimensions? This could answer the question of dimensions; if it's unfeasible or useless, then chances are that the dimensions could have been increased for next year.