People really like to say that you can’t do 6 week swerve without the swerve turning out janky or it having a large negative impact on the rest of your robot, so naturally my team is trying it.
Just to get all the basic questions/warnings out of the way:we know that it’s kinda risky so we do have hard deadlines that if we miss swerve is dead. In the past we’ve had one programmer who programs all robot function, this year we had a 4th year frc programmer transfer to our team. His only job this build season is to program and tune the swerve on a seperate test bed. None of our strategy revolves entiely around the swerve, if we get locked into crab drive due to full swerve being too much of a problem to program that wouldn’t be a big hit on robot function. My only job this build season was to design the swerve, and get it finished mechanically, once that’s all done i’ll head off and help another sub-team.
soooo yea 6 week swerve it’ll work or it won’t but i’m excited to see what happens
None, programmer made some swerve code for fun and I had been toying around with the idea in the offseason but everything was started fresh on everything when the season started
Out of curiosity (if you don’t mind me asking) - what was the thought process behind deciding to choose swerve for the first time in-season this year?
I want everyone moving this season
[spoiler]Do you wanna build a swerve drive?
That doesn’t move at all
I know that tank drive is a bore
But you won’t score
Stuck up against the wall
It’s best to test pre-season
But you did not
So please ask your-self why!
Do you need to build a swerve drive?
It’s not too late to not do swerve drive.
(please just drive…)[/spoiler]
I wonder if the game this year is at all conducive to taking these sorts of risks. We’ve been able to spare some individual team members for tackling quite a few of these “don’t try this during build season” projects. For some reason, it seems like a more favorable risk/reward scenario compared to previous years in case we don’t end up checking off all the boxes.
Looking forward to seeing how this turns out for you guys!
more lyrics
[spoiler]
Luke, please, I know you’re in there
People are asking how the drive has been
They say do tank drive
And I’m trying to
The design is right here for you
Let’s just change it…
We only have this one 'bot
Just this one season
What are we going to do?
Do you wanna build a swerve drive?
[/spoiler]
Like a lot of other people we thought omnidirectional drive would be useful, swerve was best for our method of dropping off stacks of totes, and we honestly just thought it would be fun.
Something important I forgot to mention is that we have a set day in week 4 where we will consider if we have actually made it to a point where we think our swerve gives us any benefit over a traditional tank drive. When subsystem integration is fully cadded it will include a fully fledged tank drive configuration so if we decide to ditch swerve we should be able to have a running tank a few days later.
If that bottom is a single piece, you will want to add a radius on the inner edges on the top.
How thick is the bottom plate? It looks pretty thin right now.
How are you constrianing the bevel gears on that shaft? How are you constraining the other gears?
Your top plates are too thin. It looks like it’s 1/8" at most. Make it 1/4" to be really safe.
I LOL’d at that gear on the top. I assume that’s a versakey gear with 3/8" hex bore like I ised on my drill press verson.
You need some thrust bearings on the module to support the vertical loads. This year more than ever it’s going to be turning under a lot of load.
All things considered I would not do a swerve drive fresh out of the box. Please consider buying something like a premade team 221 revolution module and just belting some motors to it.
Probably should have posted cad cause it would clear up a lot of your questions/considerations but my naming on some parts is embarrassingly bad (I blame sleep deprivation) but this should definitely help http://imgur.com/QfTX6i1
The bottom is being milled out of a single piece of 4x6x.25" 6061 channel
the plates are .125, but this is designed to use the chassis to beef up the outer edges and the gray squares are actually bearing blocks holding 1" ID 2"OD bearings. these are bolted straight through, counterbored on the top bearing block, with nut clearance on the bottom. We think this should be fine for preventing the plates from warping.
I didnt see your drill press swerve but yea it’s a 3/8 bore 44 tooth versakey gear. Great minds think alike (and fools seldom differ)
there is a 1" ID thrust bearing and accompanying washers in there.
Put your module into the CAD of the field right at the transition between the carpet and the scoring platform. Rotate the module as it would if the steering motor was rotating it, will that low ground clearance gear run into the ramp in any orientation? Looks to me like it will.
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
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.
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.
