pic: ABS-122, shifter-in-tube chassis

[Monochron]

Originally Posted by chrisfl

Looking at the size of those tubes, would you be able to put the wheels inside them to maximize space used in the tubes? That would also allow you to move your side rails out more to create more space in the center of the frame.

You know, now that you have the gearbox AND the wheels in that tube . . . you could probably get the RoboRio and the VRM in there if you get creative . . .

[Chak]

Originally Posted by Monochron

You know, now that you have the gearbox AND the wheels in that tube . . . you could probably get the RoboRio and the VRM in there if you get creative . . .

How to Give Electrical a Heart Attack, part 3

[frcguy]

Originally Posted by Chak

How to Give Electrical a Heart Attack, part 3

I do electrical, +10000000000

[GeeTwo]

Originally Posted by GeeTwo

On the other hand, if 60% of my robot's weight were on the front wheels in a static configuration (and presuming I had at least six wheels), I would be VERY worried about the robot falling on its face in a braking maneuver.

Originally Posted by MichaelBick

That is completely dependent on CG height and, given 4587's short robot, probably not a major risk.

I know it sounds strange, but if this is the case, I would seriously consider not driving the back wheels at all -- save the chain and sprockets and heartache. I might even consider skipping the back wheels and putting some pegs or furniture gliders. Here's why: If 60% of the weight is on the front wheels, the CoG is closer to the front wheels than the middle wheels. If the CoG is low enough that you are "not at major risk" of braking hard enough to tip forward, you are probably "at minimal risk" of ever needing to put weight on the rear wheels, and at "fuggetaboudit" for need to drive those rear wheels.

[Cothron Theiss]

Originally Posted by GeeTwo

I know it sounds strange, but if this is the case, I would seriously consider not driving the back wheels at all -- save the chain and sprockets and heartache. I might even consider skipping the back wheels and putting some pegs or furniture gliders. Here's why: If 60% of the weight is on the front wheels, the CoG is closer to the front wheels than the middle wheels. If the CoG is low enough that you are "not at major risk" of braking hard enough to tip forward, you are probably "at minimal risk" of ever needing to put weight on the rear wheels, and at "fuggetaboudit" for need to drive those rear wheels.

Interesting idea. From what I can tell, unpowered wheels used to be more common on early FRC drivetrains, but have fallen out of style in the past several years. It would probably work well in this case, but I do see one thing that might be a concern. In a six-wheel drop center (which might or might not be what we're talking about, I don't know 4587's robot), doesn't the robot tip backwards onto the back four wheels when driving forwards? Now I know that the position of the center of gravity affects the tilting of the chassis, but this would be on a case by case basis. If the chassis DOES tilt backwards when driving forwards, not powering the back wheels may make acceleration quite slow.

[MichaelBick]

Originally Posted by GeeTwo

I know it sounds strange, but if this is the case, I would seriously consider not driving the back wheels at all -- save the chain and sprockets and heartache. I might even consider skipping the back wheels and putting some pegs or furniture gliders. Here's why: If 60% of the weight is on the front wheels, the CoG is closer to the front wheels than the middle wheels. If the CoG is low enough that you are "not at major risk" of braking hard enough to tip forward, you are probably "at minimal risk" of ever needing to put weight on the rear wheels, and at "fuggetaboudit" for need to drive those rear wheels.

The major issue with this (for my team) is pushing matches: for example, during forward pushing you can easily have 100% weight on the back two wheels.

[Clayton Summerall]

The back wheels are solely used on defenses. Happy we didn't go 4 wheel.

[Cash4587]

Having un-powered wheels in your drive train is generally not a good idea. They create friction and make it really, really hard to turn. Replacing them with a caster or some low friction nylon for example, is also not a great idea because this year our back wheels help us get over defenses, and when you put something in place of a wheel that doesn't roll, and hit defenses as hard as we do, it won't turn out so well. Removing wheels and just replacing them would not be as good as just designing a drive train with 4 wheels only. In cases like this year, we needed 6 wheels to not get stuck on defenses so that's what we went with.

When it comes to drive trains we go with something we are confident with. 6wd and 8wd are types we've worked with before and have given great repeatable results. Adding furniture sliders or caster wheels to our drivetrain is probably something we will never consider doing on our drivetrain.

[Bryce2471]

To OP:

I recognize that this is a mostly theoretical drive train but have you thought about how you would remove a CIM, if it were necessary?

[Cash4587]

Originally Posted by Bryce2471

To OP:

I recognize that this is a mostly theoretical drive train but have you thought about how you would remove a CIM, if it were necessary?

It looks like he oriented the motors in a way that you can access the bolts around the gears. But I am just assuming so I could be wrong.

[asid61]

Originally Posted by Bryce2471

To OP:

I recognize that this is a mostly theoretical drive train but have you thought about how you would remove a CIM, if it were necessary?

I actually added a lightening pattern later such that a ball end allen key can access the bolts to remove the CIMs. As it stands right now, removing the gear in between the two CIMs would suffice to remove them.

[Bryce2471]

Originally Posted by asid61

I actually added a lightening pattern later such that a ball end allen key can access the bolts to remove the CIMs. As it stands right now, removing the gear in between the two CIMs would suffice to remove them.

I guess the question I was trying to get at is: How would you remove the idler gear with the bearing flanges to the inside of the tube?

[asid61]

Originally Posted by Bryce2471

I guess the question I was trying to get at is: How would you remove the idler gear with the bearing flanges to the inside of the tube?

...
Good point. That raises the other question: how would the shaft get in there to begin with?
The lightening holes might let you get away with not removing the gear. But IRL if I made this, all bearing flanges would be on the outside and/or I would use riveted bearing blocks to save space inside the tube. That particular spot is actually easy to put at least one of the bearings on the outside because I have space in there.