Hello, I am somewhat new to vex. I have been designing drivetrains recently to get better at CAD and I am wondering if the 2 inch Omni wheels on 600 rpm are any good.
They have a travel distance of about 60 inches per-second similar to the standard 360 rpm 3.25 or 450 2.75 drivetrains. Another benefit is the drivetrain will be a lot slimmer. Let me know what you think about this.
the linear speed is fine. the problem comes from the fact that the 2inch omnis arent a continouse circle sicne they dont have 2 set of offste rollers so the ride is extremely bumpy leading to robot vibrations and that means lose screws and all kinds of stuff. so unless you are doing 2 wheels that are rotated to act like 1 double roller its not really the best option.
Yes That will be a problem. I was thinking as a solution to do a 8 wheel drive with 4 Omni’s in 1 orientation offset and the rest in the other so that the drivetrain height off the ground does not change.
As Timmy said, due to the weird nature of the shape of 2’’ omnis I would not recommend them for drivetrain purposes (they are commonly used for Odom pods however). They also only have 2 competitive gear ratios, and no top teams from my knowledge use them for drivetrains.
If you’re looking at center of gravity (which is another reason why I assume is why you use 2’’ wheels), I would instead recommend as you said a 450 rpm 2.75’’ omni wheel drive. 2.75’’ wheels have a nice suite of speeds (65, 70, and 80), lower your center of gravity, and allow you to use traction wheels (unlike 2’’ wheels).
If you’re looking forward to future seasons and a wide array of speeds, go for 3.25’’ wheels. They have the most competitive gear ratios of any wheel size and are relevant to any season.
I think this is the main problem with 2" wheels as a drivetrain choice, but if for whatever reason you really, really wanted to make a 2’’ drivetrain, you could offset the wheels by 45 degrees and have a more complete circle; however this comes at the expense of drivetrain width since the two 2" wheels by themselves already make up a good 1.5 inches.
Good suggestions overall, but… Just to clarify about the center of gravity (this is the second time in the past week that I’ve read on the forum about smaller wheels having a “better” center of gravity)…
I think you probably mean rotational inertia as all wheels should have the CG in the center of the axle. Otherwise, the wheel would be unbalanced.
When you switch to a smaller wheel, not only does it get lighter (less inertia), but it also has its mass closer to the axis of rotation. This mass distribution results in a smaller rotational inertia and the wheel is easier to accelerate. A common example that gets the basic idea across is how an ice skater changes their rotational inertia by bringing their arms close to their body. As rotational inertia decreases, angular velocity increases (conservation of momentum)… you see them spin faster and see the effect of rotational inertia.
Please let me know if you meant something else.
I think people just mean that It allows your bot to be lower to the ground, but this is doable with any wheel size depending on build style.
Oh…
Yeah I was more talking about how since you have smaller wheels… theres less distance between the axle and the ground… so your drivetrain will be closer to the ground and hence the entire robot (since the robot is built off of the drivetrain)
I guess that works to though
That makes perfect sense… thanks
Instead do 4 wheel drive but have 2 omnis on each axle offset from each other.
Thank you, that’s what I said in a earlier post.
