29-10-2014 15:18

bkahl

Re: pic: FRC558's modified VEXpro Drive in a Day

I'll be the first to attest that this drivetrain is a BEAST. For reasons I have yet to figure out, it could manhandle almost any bot on the field... Including 2 speeds.

29-10-2014 16:31

AllenGregoryIV

Re: pic: FRC558's modified VEXpro Drive in a Day

Looks good, I like the purple.

Why did you opt for 3/8" solid bolts as dead axles instead of using 1/4"-20 bolts going through 1/2" tube axle?

29-10-2014 17:23

Knufire

Re: pic: FRC558's modified VEXpro Drive in a Day

The dead axle WCP Colson hubs are already bored out for 3/8" bearings.

29-10-2014 17:28

R.C.

Re: pic: FRC558's modified VEXpro Drive in a Day

You can use the 1/2" I'D x 7/8" OD bearings as well. Allowing teams to use tube axle.

29-10-2014 17:54

Mike Marandola

Re: pic: FRC558's modified VEXpro Drive in a Day

Just curious, what is the benefit of that? To save weight? Smaller holes in the frame?

29-10-2014 17:54

BrendanB

Re: pic: FRC558's modified VEXpro Drive in a Day

Truth this setup was a beast.

29-10-2014 18:17

Chris is me

Re: pic: FRC558's modified VEXpro Drive in a Day

I'm curious if anybody has run these for a season. My gut would think the smaller balls of these bearings would reduce their load carrying capacity to the point where I'd be concerned about an ill-timed bearing explosion. But I haven't tested it, run numbers, etc. so I'd love to hear some reports of teams having success with this setup.

29-10-2014 18:44

AllenGregoryIV

Re: pic: FRC558's modified VEXpro Drive in a Day

The tube axle becomes a frame member and dramatically increases the rigidity of that chassis section. When using the 3/8" bolts you can't tighten the bolts since that would bend the frame. With the tube axle setup you preload the bolts to achieve greater chassis strength.

29-10-2014 22:16

AdamHeard

Re: pic: FRC558's modified VEXpro Drive in a Day

Did you guys slit the colson wheels at all? Or run them stock?

29-10-2014 22:36

Ty Tremblay

Re: pic: FRC558's modified VEXpro Drive in a Day

Not to steal any thunder, but they ran them stock. 228 is/was the biggest proponent for slitting Colson wheels and I think Art Dutra might have posted numbers somewhere.

Personally, I don't think the cost of implementation is worth the benefit of the added traction. Colsons are already up there in the traction world. They're just under blue nitrile if I remember correctly and slitting them still doesn't get them to nitrile's level. Their wear characteristics far outplay any wheel I've seen in FRC, though.

30-10-2014 06:39

Gregor

Re: pic: FRC558's modified VEXpro Drive in a Day

If you were to use proper length spacers with the bolts, couldn't you tighten the bolt too?

30-10-2014 07:06

TD78

Re: pic: FRC558's modified VEXpro Drive in a Day

In my past experience, if the bolts were tightened (to the point of them trying to act as a stiffener) with spacers, the spacers would interfere with the bearings and lock them up, making the dead axle wheel hard to rotate.

Ideally in this configuration, you would use standoffs around the axle to provide stiffness. That adds more parts, more weight, etc. Not hard to do, but you are limited to using the mounting holes provided by the DIAD, chain routing, etc.

Anyone have thoughts on using 3/8" steel rod as dead axles? Tap both ends of the axle and it'd be close to using tube axle/bolt. I wouldn't think a 1/4"-20 bolt would work...not enough thickness left in the rod. Something smaller like a #10 or #8...at which point you would have to drill all 4 holes in the DIAD sideplate, rather than using the pre-punched 1/4" hole for the outer wheels (of the 8wd)...but it could work.

30-10-2014 09:27

JesseK

Re: pic: FRC558's modified VEXpro Drive in a Day

We had great success with 1/4" steel rod that was put through a die on either end with locknuts in 2007. 2011-2012 we moved to 3/8" steel rod that was supported similarly. It was quite easy to machine - stick the die into a vice, stick the rod in a cordless 18V drill, use lots of tap magic and BAM 30 seconds later you have an axle. Just make sure the mount hole hits the solid rod and not the threads.

As for maintaining proper wheel alignment & spacing - I'd recommend any solid non-deforming material for standoffs. The dark-grey plastic from Andymark works great (it's why it's in the KOP, or was last time I used a KOP).

I agree that the axle itself should NOT be used to stiffen a frame. The only load you want on a wheel axle is normal to the floor so it rides correctly on the balls inside the bearing.

30-10-2014 09:35

TD78

Re: pic: FRC558's modified VEXpro Drive in a Day

I should clarify. I was not looking to form 3/8"-16 threads (or similar) using a die...I was thinking about drilling and tapping the ends of the steel rod (using a drill and tap). The rod would become a stiffening dead axle.

30-10-2014 09:44

Ty Tremblay

Re: pic: FRC558's modified VEXpro Drive in a Day

You could turn down the ends of the 3/8" rod and thread them for 1/4-20. The major downside of this being that you'd need to remove the outside of the drivetrain if you wanted to change a wheel.

30-10-2014 09:45

JesseK

Re: pic: FRC558's modified VEXpro Drive in a Day

Ah, I see. If you mount through the bolt rather than the axle (i.e. the mount hole is 1/4" rather than 3/8" and the 3/8" axle is the stiffening rod) then I don't know if there would be axial load on the bearings.

I would worry about the 1/4" bolt elongating the mount holes after a rare hit - like one that tips the bot up a bit, then the bot slams back to the floor, or like what happens when coming down off of a ramp/bump. We experienced some of this in 2007. When we went back to this style of dead axle in 2011, we used 3/8" rods and also used 1" angle brackets (1/8" thickness) to mount the wheels below the 1x1 frame. This gave us flexibility to change a mount out if we had problems. The "look" of the drive train where we mounted the wheels was similar to the old IFI KOP frame rails.

30-10-2014 09:51

jwfoss

Re: pic: FRC558's modified VEXpro Drive in a Day

Thanks for the feedback, feel free to keep the questions coming. FRC558 was extremely happy with our drivetrain's performance and reliability in the 2014 season. There is something to be said for being able to assemble during week 2-3 of build and not have to touch the drivetrain for 100+ machines.

I've looked into this, and would likely pursue it if we had the internal resources to machine them. At this time it would require relying on our mentors and sponsors to do work outside of the teams shop.

We run them totally stock, I don't believe the benefit is worth the extra work, however if we need more traction we'll look into it. We have never wanted more traction.

RC, have these bearings been tested for load? I'd love to run these but I have concerns about testing new things in our drives. If these are more then capable, we'll switch over to them and the tube axle material for 2015.

30-10-2014 11:08

puneeth.meruva

Re: pic: FRC558's modified VEXpro Drive in a Day

do you guys think that there's any chance that FIRST will move back to a max of 4 CIMs instead of 6 CIMs?

30-10-2014 11:26

AdamHeard

Re: pic: FRC558's modified VEXpro Drive in a Day

It's a possibility. Or some rule limiting max power in drive.

30-10-2014 13:56

Mr. Van

Re: pic: FRC558's modified VEXpro Drive in a Day

We can only hope! With the introduction of so many powerful motors available, it's simply lead to a drivetrain power "arms race".

- Mr. Van

30-10-2014 15:31

Re: pic: FRC558's modified VEXpro Drive in a Day

To a point. For the majority of games, what matters most is what's on top of the drivetrain, and how it's used.

30-10-2014 15:37

AdamHeard

Re: pic: FRC558's modified VEXpro Drive in a Day

The current level of power allows a team to get going faster, in less distance.

With E= 1/2mv^2, this leads to substantial increase in energy storage in the average FRC robot.

These hits add up over time, and don't really add value to the game.

I would MUCH rather see a drivetrain power limit than a "rough play" rule... The line in the sand the rough play rule introduced was a real bummer.

30-10-2014 20:58

Oblarg

Re: pic: FRC558's modified VEXpro Drive in a Day

6-CIM drives aren't only useful for big hits. The added speed is extremely useful for all sorts of defense.

Our drive strategy last year depended almost entirely on positioning - we had to stay between the opposing robot and where they wanted to go. A little extra agility makes that a lot easier to do. It came with definite tradeoffs, and was not an obvious design choice to make, but in the right situation it was very useful, and not just in a "ROBOT ANGRY, ROBOT SMASH" capacity.

I mean, I wouldn't blame FRC for reducing the motor budget, because there was a lot of damage last year, as many teams were not particularly thoughtful in their willingness to smash into other teams' mechanisms. That said, I don't think it can really be argued that it added nothing to the game, and I wouldn't mind the drive power staying where it is, either. I don't think it was game-breaking.

Full disclosure: I believe we played entirely reasonable (but certainly stiff) defense at the DC regional. At the end of that competition, we discovered a sizeable (but not functionally-damaging) dent in one of our AM14U end-plates. So, yeah, it certainly was rough, but I don't think it was anything I'd be unwilling to deal with in future years. I don't believe we caused any non-superficial damage to another robot at any of our competitions.

Edit: Completely agree that the "rough play rule," as it was worded, was awful. I do think it could be done better than that, though.

30-10-2014 22:11

JesseK

Re: pic: FRC558's modified VEXpro Drive in a Day

I don't know what it "added to the game" for any team on the receiving end. It's the ignorance that makes me hope the GDC changes something.

30-10-2014 22:16

Oblarg

Re: pic: FRC558's modified VEXpro Drive in a Day

By that logic, anything that changes the game in favor of defense ought to be removed, because clearly it doesn't "add to the game" for the robots trying to play offense.

30-10-2014 22:22

JesseK

Re: pic: FRC558's modified VEXpro Drive in a Day

Sorry, should have specified it was directed at your glorification of linebacker-style hits.

30-10-2014 22:23

Oblarg

Re: pic: FRC558's modified VEXpro Drive in a Day

Where did I glorify linebacker-style hits? I explicitly stated that we avoided them last year, and my entire post was about the value of a 6-CIM drive in contexts other than forceful collisions.

30-10-2014 22:30

JesseK

Re: pic: FRC558's modified VEXpro Drive in a Day

Damage to your own robot, stating 6 CIMs are useful for hits and other things, saying 6 CIM agility plays well into a SMASH (...) strategy, you don't think you did non-superficial damage (pretty rude statement in multiple aspects, IMO).

It's like you state one thing, but the tone of how you word it makes a completely different statement, particularly in context of witnessing 4464 do hit, after hit, after hit, after hit in DC. All in the name of supposed "positioning".

30-10-2014 22:39

Oblarg

Re: pic: FRC558's modified VEXpro Drive in a Day

How is that a rude statement? Could you honestly claim any better than "I don't believe we did any serious damage to other robots" if you were playing any sort of defense this year, unless you specifically went to the pit of every team you faced after every match and checked, and had perfect memory to boot? Robot-to-robot contact of any sort has the potential to cause damage. To pretend this is not the case would be dishonest. Acknowledging this is not rude - to the contrary, I think it'd be rather rude to not hedge my claim in that way.

You are reading what you want to, not what I am saying - I did not say "6 CIM agility plays well into a SMASH strategy." I said that 6-CIM agility allowed us to be successful in a defensive strategy that did not involve serious collisions. "ROBOT ANGRY, ROBOT SMASH" is obvious caricature, and was presented as an example of precisely what we were not doing.

You stated in a previous thread (and I quote) "I don't fault 4464 for its defense this year since it was actually pretty clean relative to other matches I've watched." Where is this "hit after hit after hit" coming from, now? Where were we unreasonable in our defense this year? We made a point of not gaining much speed before contacting other robots this year, both because it was likely to cause damage (to their robot and ours) and because it is not particularly effective defense (unless, of course, you've got no class and are trying to disable the other robot - I think we're all better than that here) - sustained pushing is far more effective for interrupting an opponent's play.

I think you are reading it in a tone you want to read given your experience this year. I am in no way a proponent of NFL linebacker-type play in FRC, nor was my post indicating such.

30-10-2014 23:18

JesseK

Re: pic: FRC558's modified VEXpro Drive in a Day

The videos of the finals show how positional based defense actually works. Watch 2537. A couple of incidental hits while jockeying for position, some hits to turn 225 out of position, but very rarely a back-off-and-hit-again maneuver. It's why we picked them over you.

Eli I'm not aggravated at the defense 4464 played relative to other defense played in 2014. I'm irritated that you think it's appropriate and fun for all involved. There were 4 major hits that broke something non-trivial on other robots caused by 4464, not including damage 4464 did to itself that 1885 helped fix during quals on Friday (though I'm admittedly going off of 2nd-hand info from your driver there). I'm irritated that even when damage from 2 of the hits were pretty obvious to anyone with eyes on the match due to disabled robots, you claim the damage was superficial. I know of 4 because they're a few of the ones that 1885 helped fix during Quals.

30-10-2014 23:22

Oblarg

Re: pic: FRC558's modified VEXpro Drive in a Day

Probably best to take it to PM at this point, but I'd like to know what these were.

This was damage to our roller arm incurred while playing offense, not defense, and was the result of another robot impacting us while we were lowering our roller arm in pursuit of the ball. 1885 was extremely helpful in fixing it, though, and I am grateful for it.

I certainly have eyes, and I try my best to be aware of any robots that become disabled in matches we play in so that I can offer help. I was not aware of any significant damage we caused at DC.

Aside from this, I wish you'd be a bit less hostile. No one here wants to see damaged robots, including myself. I find it upsetting that you'd call a post specifically about avoiding hefty impacts with 6-CIM drives "glorifying linebacker-style hits" and "ignorant." I care as much as you do about this game being fun and fair for everyone involved, and I even admitted in my post that I would not be surprised or upset if the motor budget were reduced. Please don't treat me as a strawman for your frustrations about the nature of the game this year.

31-10-2014 07:37

jwfoss

Re: pic: FRC558's modified VEXpro Drive in a Day

It would have been best 8+ posts ago.
Please keep the comments value added to the thread, this was meant to be a discussion about COTS and drivetrain development.

31-10-2014 12:37

Oblarg

Re: pic: FRC558's modified VEXpro Drive in a Day

Fair enough, that did get out of hand. I'll ask a mod to remove my posts to clean up the thread, since the discussion is now in PM.