pic: FRC558's modified VEXpro Drive in a Day

[Gregor]

Originally Posted by AllenGregoryIV

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.

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

[TD78]

Originally Posted by Gregor

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

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.

[JesseK]

Originally Posted by TD78

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.

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.

[TD78]

Originally Posted by JesseK

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.

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.

[Ty Tremblay]

Originally Posted by TD78

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.

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.

[JesseK]

Originally Posted by TD78

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 (although you don't advocate that practice).

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.

[jwfoss]

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.

Originally Posted by TD78

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.

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.

Originally Posted by AdamHeard

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

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.

Originally Posted by R.C.

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

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.

[puneeth.meruva]

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

[AdamHeard]

Originally Posted by puneeth.meruva

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

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

[Mr. Van]

Originally Posted by AdamHeard

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

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

Originally Posted by Mr. Van

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

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

[AdamHeard]

Originally Posted by Andrew Lawrence

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

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.

[Oblarg]

Originally Posted by AdamHeard

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

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.

[JesseK]

Originally Posted by Oblarg

...

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.

[Oblarg]

Originally Posted by JesseK

I don't know what it "added to the game" for any team on the receiving end.

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.