Mechanum drives are very different in terms of movement to the X/holonomic/H drive. This is because with mechanums, you can only either go sideways or forward at a time, you can’t do both at the same time. With x/holonomic/H, you will be able to move diagonally, in 2 directions at the same time.
Though, how much faster it will be really depends on the driver of the robot and the power of it. A good driver with mechanums can be faster.
In my opinion, the mecanums will serve a great purpose this year. They are rather bulky, but that’s a sacrifice that some teams have to make. No holonomic drive is free from some form of space sacrifice (X drives need to be exactly 45 degrees, H Drives take up space in the middle, mecanums are really wide). Plus, the added weight of the mecanums (even if it’s not a super large amount) will help teams who want to make a heavier base so they don’t tip.
My team are thinking off a h drive with three wheels on each side and one strafing wheel.
Another issue to consider about mechanum wheels is how much drag they create. During Sack Attack our mecanum wheels where creating so much drag that we over heated and we had to change our gear configuration from high speed to torque. With what I have seen x-drives do not create as much drag and they are generally faster then mechanums. Also during Sack Attack at Worlds one of the champions of the Art Division had an x-drive that spread out making the robot wider durring autonomous.
That was probably 1492A.
I don’t know if mecanums really have more drag. We have used mecanums since gateway and they have worked fine for us. We had a 4-motor high-speed mecanum drive during sack attack, with a heavy robot and lots of beanbags. It did not overheat except with excessive strafing or pushing.
Yes, the mecanum’s worked well for us, not only in driving mode, but in programming auton’s for matches and for the skills runs. Take a look at the strafing used during one of our last programming skills runs from sack attack. Even after loading several bags, it worked well. We have had to design around the width, but have done so successfully the past couple of years. The robot in the video had one motor per wheel in high speed gearing. The only thing we had to watch was to not strafe long distances - we usually limited it to about a foot or 1/2 a tile. If we had to go more than that, the driver or program would turn the robot and drive instead of strafe.
https://www.youtube.com/watch?v=TUmyI8DoeQE
Like every design solution, they have pros and cons and the team needs to weigh all the options and choose what they feel best solves the problem for their specific case and/or robot design.
The problem we are seeing with mecanum wheels is they take 4-6 motor which is to much for what we are thinking of.
Hint hint includes a bar lift.
Mecanum wheels can move diagonally, too.
I mite be wrong but I don’t think they move diagonally.
Mecanums can certainly move diagonally, or any direction for that matter. It all depends upon how much power you apply to each of the wheels. My son’s Gateway robot used mecanums and a gyro with a driver-oriented control setup. One joystick was used to control the direction the robot traveled and one joystick was used to handle rotation. So if the drive joystick was pushed forward the robot moved away from the driver, regardless of where the “front” of the robot was facing. This allowed him to move in any direction and rotate at the same time. With this setup his movement was rarely directly in line with the direction the mecanums where mounted.
Jay
A BIG thing with drive bases and wheels is the amount of weight it can take. A big topic on the forum is tipping. when wheels are set in line, the robot is more prone to tipping specially with a lot of weight. I believe in an X drive, tipping wont be as easy since there are more points of contact on each corner. I still need to prototype this all but i feel X drives are a good way to reduce the chance of tipping.
That’s not how it works. X drives don’t have more points of contact in each corner, and it wouldn’t be relevant if they did.
It’s true that if you made a robot bicycle it would tip very easily, but a tank drive isn’t that. It’s two sets of wheels that are set far apart. Because the wheels are far apart, the base of support is wide. How many points of contact exist at each corner doesn’t matter; it’s the difference between the furthest points of contact that matters.
Also, robots aren’t just objects resting on a stationary base. They have wheels and rollers. If you build a tank drive robot with all omniwheels and then apply a force to the top of the robot to try and tip it over sideways, the robot will just slide sideways on its rollers because there isn’t much resistance between the wheels and the foam.
Robots don’t tend to tip sideways anyway. It’s much more common for them to tip forwards or backwards, because that’s the dimension in which their centre of gravity shifts and in which they accelerate. If you build a tall robot on an X drive base so that you can accelerate sideways, then you will probably fall over sideways occasionally.
An X-drive actually has a slightly smaller polygon of support than a tank drive, since the angled wheels are further inwards than the tank’s straight ones. I do see sideways tipping being an issue on holonomics, particularly if teams don’t anticipate the effects of quickly sliding from post to post horizontally. Especially with the presence of vertical lifts, which don’t shift weight forward or back much, robots will have a more centered COG, so omnidirectional drivetrains will probably wind up tipping equally frequently in any direction.
This is true, and therefore, I expect many tips and/or antitipping solutions. I know that tipping has been a huge topic of discussion at our club, but we should have clever ways to prevent tipping. VERY large, Heavy wheelbase? Gyro with funny programming? A way to get back up?