So my team has had a big debate between Mecanum and 6WD. 6WD is ideal for transporting tubes from one side of the field to the other because of the potential speed, while Mecanum is ideal for placing tubes on the scoring grid due to the lateral movement. We are allowed to “throw” the tubes to the center. This ability supports Mecanum because it shortens the distance of travel. However, this will cause an increase in robot to robot contact to which mecanum wheels are not well equipped for due to low traction. We have heard a lot of hype about the 6WD on the forums.
Questions:
6WD or Mecanum? Which do you prefer and why?
What is the turn radius of 6WD?
Do you predict the game to be high contact or not? Why?
I think Mecanum seeing as it brought success for us last year, the turn radius can’t be that good for 6WD not to mention the extra power expended in turning those two extra wheels. Then again Mecanum requires four motors. I predict we will see robots shatter. I liked that at the kickoff.
6WD - higher traction, less weight, simplicity, comes in the KoP!
Turning radius - of a properly designed 6WD should be zero, it should turn around the center point of the robot the weight should be relatively centered on the robot.
Yes - after seeing 2007
Edit:
Simplicity because of less gearboxes, another plus is less weight because of that same reason.
Turning radius - see above
Extra power - this is a misnomer. The same amount of power would be going to the ground, in fact in mecanum, there is wasted power because the force vectors work to cancel another wheel’s. A 6WD should also require 4 CIMs.
It would be helpful if you could explain some of your assumptions:
Why do you assume Mecanum slower? Atleast, it isn’t slower in forward and reverse.
Also, why would “throwing tubes” to the center give the advantage to mecanum? Assuming that you would go pick them up again, which is what I think you mean, how is it quicker?
To answer your question, a dropped center 6wd can turn with 0 turn radius.
To those above, can you cite a rule that says you can only use four motors?
Mecanum has less traction, which will be key in this game. A good defender should be able to lock down the scoring zones–unless there are two robots attacking at once.
What would you say is a properly designed 6WD? With the middle wheel lower than the others in West Coast style?
“throwing tubes to the center” is an advantage to mecanum because it is a shorter distance from where the tubes are picked up to where the grid is. Thus, more time is spent placing tubes on pegs and less time is spent traveling. The forums have stated again and again that 6WD is faster in a forward, reverse direction than mecanum.
You can have a max of 4 cims plus the motors included in the kop.
I would go with 6wd over mecanum in a heartbeat. Mecanums as mentioned have no pushing power and you won’t be driving as fast around the field either. One problem with throwing the tubes to the center is you are increasing the chance for your opponents to grab it especially if you are the weaker drive. Yes there is some advantages with the lateral movement in front of the rack, but I’d take speed and pushing power over that.
A properly built 6wd and 8wd will have a turn radius of zero and waste no power.
A little definition: West coast drive means that the wheels are cantilevered (unsupported on one end). 6WD is usually implied that the middle wheel is lowered (usually between 1/8" and 3/16"). A way around this is to have equal diameter omni wheels on the outer wheels.
You can use 4 CIMs <R45c> plus the rest of the motors in the kit of parts <R45a>, there’s a special section about the RS motors (you can use up to four in any combo, even duplicates) <R45d)
If i were on the other team, I would be stealing those tubes that are “in the open”.
As per speed, in the forward direction, mecanums, (for the most part) act as any other wheel with lower traction would. Therefore, if it were geared the same way and the wheels are the same size, and your wheels do not slip on acceleration, a 6wd, 8wd and mecanum drive will be the same speed forwards and back.
6wd is the best because, not only is it faster and has more power, it can even be considered more manuverable than a mecanum. We tested this with our previous robots it takes 4 seconds with 6wd and 11 seconds with mecanum.
Speed: Equal
Maneuverability: Mecanum
Traction: 6WD
Difficulty in Design: Mecanum
Power Consumption: equal
I disagree with difficulty in design. The programming, as well as driver training is a much greater requirement for a good mecanum system (I have built an omnidirectional system before, and I say this even considering the availability of example code). The maneouvrability is also a lot tighter than you would think (strafing is not as much of an advantage as most people think). In the end, with a well designed system, it is driver skill, either way.
If I recall, 80%+ of championship Einstein robots have been tank drive over the years.
First: I think he was saying difficulty in design is greater for mecanums.
Second, I think that when the safe zone is only seven feet long (minus the 16" pegs for <6 feet), strafing could actually be really useful, especially since an effective defender will just body block in front of where they know you’re going to put the tube. With a mecanum you can sort of get in from anywhere and sidle over, with tank that takes quite a bit longer.
Third, I agree that while each system is stronger than the other in certain respects neither is inherently superior.
<R45> Motors specifically permitted on 2011 FRC ROBOTS include:
A. all motors, actuators, and servos listed in the 2011 KOP Checklist,
B. an unlimited number of COTS servos with a maximum power rating of 4W ,
C. one or two CIM motors in addition to
those provided in the KOP. This means up to four CIM motors and no more can be used on the robot