Re: pic: 6 week swerve
 

Unless we want to do any sort of rotation on the step, that could cause the gear to hit the step and that would obviously be bad. The solution was to go from a 30:50 gear reduction to a 40:40 which increased the max fps from 11.5ish to 15ish but since pushing isn't an issue the lost torque from turning down wheel speed in programming shouldn't be an issue

Re: pic: 6 week swerve
 

The lost torque will be manifested as a loss of low-speed control, loss of acceleration (especially when loaded with game pieces), increased current draw from your drive motors, and a general loss of 'responsiveness' from your drive.

Do not dismiss such gearing changes so flippantly.

Re: pic: 6 week swerve
 

Which is why we're playing around with last years robot in high gear with max motor speed turned down in code.

Re: pic: 6 week swerve
 

Good.

However, the principle of limiting power-train speed in code, typically done via limiting the maximum voltage from each motor controller, is very bad. This artificially cripples the drive train, which is likely the most important sub-system on your robot. You might consider using chain, belts, or another lower-profile means of getting the gear reduction you should have inside of the envelope you're limited to.

Re: pic: 6 week swerve
 

http://www.chiefdelphi.com/forums/sh...d.php?t=132640

Re: pic: 6 week swerve
 

I understand that it isn't a perfect idea, but what it does allow us to do is get 4 modules made and starting testing on 4 modules. If we want to change the top gear reduction to something that will give us a more reasonable top speed we can go back and change the belt reduction to #25 chain. We'd have to redo the actual gearbox plates but those are relatively cheap. 4 module testing will be the make it or break it for the swerve so I see continuing on and limiting motor speed in code to be the best option.

Will come back and edit so this makes sense

Realized I forgot to add other important info but the gist of it is 3d printed preliminary pods and having the gears for this gearing change in shop

latest post covers everything

Re: pic: 6 week swerve
 

Just to be clear: The point James was making is that your testing will not be representative of the fine control you could get by reducing the speed via gearing.

Re: pic: 6 week swerve
 

Yup.

I can appreciate that you have a hard deadline and you want to prove the drive works before then.

However, consider this: you can make the gearing change, the drive is sluggish and does not perform well when you demo it, but by gosh it never gets hung up on the ramp (which is the whole reason to change gearing, right?) Or, you can leave in a more robust gear ratio, and show that the drive accelerates well, is very controllable, and behaves nicely; and though the gears might contact the playing field under certain rare circumstances, you can solve that problem by making any of the changes mentioned in this thread.

If you're going to argue for swerve drive, which of those situations gives you a firmer position to argue from?

Edit: In the spirit of full disclosure, my team is setting up a chassis with a free speed of around 14 ft/s. We made this decision based upon easily available gear ratios, easily available wheels, and ability to neatly integrate it into our chassis. We are, however, planning on using 4 CIMs and 4 mini-CIMs, which will help offset the losses in acceleration and low-speed control at the expense of weight.

Re: pic: 6 week swerve
 

Fine control through appropriate reduction gearing is a huge benefit. In past years, this has been a big reason we have used a 2-speed robot. Typically, people focus on "low gear" for pushing power, but a "low gear" is awesome for fine-control situations.

In 2012 we optimized the drive base design for bridge balancing. We knew we needed very fine control and designed the drive base around that. Teams all year wondered how our driver could balance with nearly any other robot so quickly and efficiently. The real key was the fine control of the drive base. If our driver wanted to move the robot forward a half-inch to finish the balance, she could easily do that - no problem. Our gearing in low gear that year was 2.35fps (after efficiency losses). The real benefit of the low gearing wasn't the power in low gear (although that didn't hurt) but was the fine control for bridge balancing.

Does stacking totes seem like a high-precision task?

Re: pic: 6 week swerve
 

I'm back on a computer and actually have some time so hopefully I can write a response that will make me seem less willfully ignorant

First of, the change in gearing is an admittedly quick and dirty fix, but what I believe to be the best fix just to get some pods printed up and working together. We are 3d printing the first iteration of the pods in the next few nights so that we can have something together and working so our programmer has the maximum amount of time to work on getting the pods working together nicely and field oriented control working nicely. The gearing change is by no means a final fix which is something I something I don't think I ever mentioned (serious mistake on my part), it is just a quick fix to get the test bed together and running.

What i'm leaning towards as a final fix is a cim face mounted to the lower plate with a cim gear going to a gear on some .5 hex shaft. That shaft will have the pulley that was previously on the cim with the same gear reduction. If I do this right that means the wheel pod reduction could actually end up being something like 50:30 (as opposed to the previous 30:50) which should leave more than enough ramp clearance for the wheel gear.

The testing we're going to do tonight is only to see if last years robot (roughly 15 fps) with motor speed limited will give us fine enough control for our collector (In my mind our robot design is split into collector and indexer, collector is the only part that needs fine control). If it is it leaves the current quick and dirty gear change fix as a semi viable option if for some reason everything goes to crap. All of the downsides (motor speed being limited as opposed to proper gearing, barely scraping by on ramp clearance, etc.) will all be taken into account in the final decision matrix that decides if our swerve is actually worth it or if we should throw in the tank drive.

Re: pic: 6 week swerve
 

updates http://imgur.com/a/MYNGL