Re: pic: 3 wheel omni drive concept
 

Um... what about high centering??

Re: pic: 3 wheel omni drive concept
 

I wasn't saying that wood robots won't work. I've seen a few of them and they often work well. All I was saying was if there is a gap in the bumpers large enough for another robot to hit inside, you could see legal wood on metal contact (with a manipulator outside the hitting robot's frame perimeter) and that scares me.

As for not wanting to hit that robot because of the possibility of tipping it: if I were a ref and I saw a robot play defense on yours resulting in a tip, I would be hesitant to call that an intentional tip. When you build a robot like that, you should expect heavy defense and make very sure your anti-tipping mechanism work as well as the inherent anti-tipping properties of a normal robot. Teams should not penalized because they were defending against a robot that isn't well build to play the game (which includes defense).

Re: pic: 3 wheel omni drive concept
 

I think the tipping thing was moreso I don't want a robot to land on top of my own, rather than the tipping penalty thing.

Re: pic: 3 wheel omni drive concept
 

Why not use larger omnis for the sides? You could get your CG below the axles and then you wouldn't need nearly as complex mechanisms or software.

Re: pic: 3 wheel omni drive concept
 

There isn't enough of a lever arm to a CG below the axles (even w/ 8" wheels) to keep the robot stable when accelerating.

It also just isn't nearly as cool.

Re: pic: 3 wheel omni drive concept
 

Can you post a picture of the CAD for the strafe wheel module?

Re: pic: 3 wheel omni drive concept
 

These look like they need a tweak - unless there's a real perspective issue, they'll stick about half an inch outside the frame perimeter at the start of the match (presuming a 1/2" hex shaft on those wheels).

Did you plan some sort of end caps (possibly semicircular) to serve as frame perimeter behind the bumpers on the short end?

Re: pic: 3 wheel omni drive concept
 

Click for larger:


Lots of small details would need to be tweaked to make sure all of the rules are met. This is one of those ones I'd put on the list of "things to fix before bagging". It's usually a very long list.

There would need to be some added support structure to satisfy the bumper rules (at least, if the rules stay the same next year). It wouldn't actually make the frame any stronger; the plywood portion of the bumper could easily handle all of the load from an impact.... but rules are rules. Bumpers seem to be one of those things where the letter of the rule is more important than the intent.

Re: pic: 3 wheel omni drive concept
 

Understood. The point is, I can actually think of a few times when this might have been a decent robot strategy/architecture, making these real questions. I don't recall the 2012 (Rebound Rumble) rules all that well, but as I recall it was not a highly defensive game. If you could easily switch back and forth from a vertical to horizontal orientation, drive in both, have a ball pickup and dispenser of modest speed at the "top" end that filled a "stack" of four balls, then you could have done great pickup, goal scoring, bridge tipping, and (obviously) bridge balancing with multiple partners. (I'm not actually sure you would have needed the strafe wheel.) Pretty much the same robot (sized for a single larger ball) could have also done well at STRONGHOLD, flopping and driving over most of the defenses, including the cheval de frise if you could figure out how to navigate the bumper rules.

Re: pic: 3 wheel omni drive concept
 

Nice work; looks like it will score at least 301 points!

I'd love to see a little more about the self-righting works and how damage is avoided when the robot tips over (that's a lot of energy that has to be dissipated). How will this avoid problems with the rule about extending more than 15" beyond the frame perimeter?

A minor plywood suggestion: offset the screws in the tabs and slots so that one side of the nut is flush with the plate that it's pressed into. The change is insignificant structurally, but speeds up assembly, as a hammer can be used to install and align the nuts, rather than each having to be inserted and precisely centered with pliers.

Re: pic: 3 wheel omni drive concept
 

But does it go under the low-bar? :confused:

Re: pic: 3 wheel omni drive concept
 

Re: pic: 3 wheel omni drive concept
 

I think you'll find the directional performance of that strafe wheel will be quite aggressive in one direction, and lackluster in the other.

Having the pivot off to one side results in the wheel trying to "drive under" the pivot when going towards it, and it lifting itself up when driving away from it.

I've seen this effect mitigated via using a linear up/down motion, or the fancy strafe module 148 used in 2014 that used this action to it's benefit.

Actuating it is another option, but has it's own downsides.

-Aren

Re: pic: 3 wheel omni drive concept
 

The battery will be mounted at the top, correct? There can be no other way.

Re: pic: 3 wheel omni drive concept
 

Self righting would be done using a versaplanetary winding a strap to move an arm, one on each side of the robot. The arm would return to it's original position when the strap is let back out, using the magic of springs (more latex).



A damper to lessen the shock when falling over is a really good idea. I'm not sure where the best place to source parts for something like that would be. Some mountain bike spring/damper sets could be used, since they are lightweight by design. Maybe a simple low force gas strut could work, too.

The offset bolt position is a neat idea. You could probably accomplish something similar using centered bolt positions but putting a spacer under the plywood when you hammer in the nuts in.

That's a really good point. Using the toggling style of strafing mechanism is probably a much better application for this, since when it's not in use it leaves the full weight of the robot on the two outside wheels. (I believe this was first used on 148's 2014 robot?) You could probably spend a lot of time playing with the geometry to get it to work just right for a strafing segway robot, since the downforce is dependent on the geometry and how much torque the motor is applying. Would be a fun project!

I make a point to ensure that the battery is always impossible to get to. It might be at the top of the robot, but you will need to unbolt a mechanism to change it.