I feel if you made the legs short enough for bumpers and added rubber spheres to the feet to avoid field damage this should be legal?
My main concern when doing a re-read of section 8 is R502, the “four propulsion motors” rule. But I think if all movement was at the knee joint, and the legs turned like swerve modules, this could work.
I have prepared a scientific diagram to present my idea in full.
So, I think after plenty of explaining to an inspector, this should be legal. Can anyone highlight any glaring issues I may have missed? Also, don’t take this seriously, just a fun little idea I had.
Of course it is legal for you to have a walker, if you’re old enough and you really need it. But then you probably wouldn’t be a pre-college student so it would not be legal for you to drive in an FRC match.
I mean, one of the most legendary robots in FRC was a walker for most of the match… but would NOT be legal these days, mostly due to the lack of carpet after it walked through an area.
I would be cautious of any extension limits re: number of items that can simultaneously extend beyond the frame perimeter horizontally. I might be concerned about articulated Frame Perimeter as well, depending on how the bumpers are kept in the bumper zone, but don’t think that’s as big of an issue.
I was curious about this as well. If you could attach larger diameter feet (think AT-AT shaped feet) you could massively increase pushing power. But at the same time, tank treads would be easier to pull off and have an even larger amount of friction on the floor. two capstan drives on the front legs and two passive wheels would definitely legal provided bumper rules are followed, and I would love to see it.
I played around with a concept like this in CAD during the off-season after Charged Up, I think walkers are a little too complicated for FRC robots, Shufflers could be viable if you can figure out how to not tear up the carpets
Your pushing power is limited to uN (coefficient of friction * mass). If your motors can deliver more than this — that excess is “wasted”. Also once your contact patch gets larger than what is required to transfer that force to the floor, that excess is also “wasted”. The larger your contact area with the floor, the less pressure (eg psi) you exert on the floor. 150 lbs, 5 sq inches, 30 psi; with 50 sq in, 3 psi for example.
This is why fat robots push best. And why 71’s robot was so unstoppable — file cards hooking into carpet have in insanely high coefficient of friction.
wasn’t that a shuffler? anyway, I see very little point in making a purposefully slower less reliable drivetrain in a game/sport that hugely revolves around being agile and reliable.
This is true for physics class, this is not true for rough surfaces on carpet.
Against carpet you can have interlocking interactions that can provide far greater than the normal coefficient of friction should allow.
Physics says a roughtop treaded robot with a 5 square inch contact patch will be exactly as hard to push sideways across some carpet as a robot that just has a 24x24 inch patch of roughtop on the bottom. Reality will show you that is incorrect. Sure it won’t be 100 times harder but you DO get benefit in this game from more contact, arguing otherwise is disingenuous. Reality is complicated.
Clarifying with respect to @Richard_Wallace’s post : wouldn’t be a legality issue. Of course, a great many years the average roller skater is taller than a legal robot, and if you lean forward so your controller [brain] is outside of the frame perimeter, any damage is at least partly on you.
Assuming R502 (only 4 propulsion motors) doesn’t change much from 2024, it doesn’t matter rules-wise how many articulated axes (or sliding dimensions, or non-motor sources of propulsion energy such as pneumatics (R608A), springs (R608C)) or intermediate storage such as vacuum) there are, just how many motors are driving propulsion. With 4-bars, universal/CV joints, and other such mechanisms, a single motor [or other energy transducer] can drive multiple axes of articulation.
The initial storage part is likely not competitively useful unless you find a seam in the game, or figure out a way to [safely] store spring energy with a suitably high density of energy storage to spring+mechanism mass.
Good point. Just to follow on.
Physics class gives a nod, but doesn’t fully explain. It will give a “dynamic” and “Static” coefficient of friction value, but that is just because those are relatively good, but more importantly relatively simple math models.
As you referenced, tire interaction with surfaces can also be modeled as a “Static and Dynamic” friction, and it will get you very close… but if close isn’t close enough, then you tend to go into a Slip based model like this one: https://www.researchgate.net/figure/Typical-tire-longitudinal-friction-slip-curves_fig1_3333088
If you assume the Peak of one of the curves is “Static” and the tail around 50% slip is the dynamic… Your calculations will likely be within 90% using that two case model as opposed to the slip curve.
This too is just a simplified math model that is good for slip in purely 1 direction. If you are needing slide slip too… then something like a traction circle becomes a better math model.
This too is a simplified model vs. reality. You talk with Racing folks, and then will add in tire and surface temperature relationship. IE, there is a curve when the tires are at regular temperature, then there are other curves when the tires are at “operating temperature”, but once they get too hot, then they start loosing grip. This behavior is often heard as “becoming greasy” is often due to both behaviors of the compounds at elevated temperature, but also how the air in the tire gets hotter which increases the pressure, which reduces the contact area, which increases the friction energy per square inch in the tire contact area, which increases the temperature effect which…
Often all these little effects aren’t that important… but sometimes they are. People have literally earned PHDs and lucrative careers in tire and racing industry making more accurate models to try to gain a less than 1% advantage. 1% may not sound like much, but for a race that has 100 laps, 1% difference is literally the difference from winning to being a lap down. The difference between 1st and 2nd in racing is often a very small fraction of 1%.
(50 feet is about 1% of a mile, so a 100 lap race, of a track that is 1 mile long would be a 0.01% lead… which would appear as a 1-2 car-length win). A photo-finish at Indy 500 where the cars are within 5 feet of each other would be a (5/5280)/500 * 100% or .0002% advantage to the winner… Just being on the lead lap at the Indy 500 means you were within .2% of victory.
: wouldn’t be a legality issue. Of course, a great many years the average roller skater is taller than a legal robot, and if you lean forward so your controller [brain] is outside of the frame perimeter, any damage is at least partly on you.