Mecanum Wheels is it good fin the Pits
 

Dear Friends!
We studded AndyMark Mecanum Wheels it is perfect for us, which can move in any direction, rollers attached to its circumference, these rollers having an axis of rotation at 45° .
But still we have suspicion if any robot will push us what behavior will be.
Second question what size wheels Left 8" Mecanum Wheel or 6" Mecanum Wheel for stabilization is good.
Any help will love to hear
Mohamed
Team 1946

Re: Mecanum Wheels is it good fin the Pits
 

As part of team 1083 we did omni wheels. It was awesome to work with and fun. Loved to watch the bot move around.

BUT you loose major pushing power maybe 45% where a few percentage points of extra push makes the difference.

With 1902 we ended up going to the basic six wheel design that was a strong pusher and turned well plus a lot easier to work with.

There maybe games where mechanism will be an advantage, but pushing seems to be a major issue most years.

Re: Mecanum Wheels is it good fin the Pits
 

You're going to get pushed. On the other hand, you don't have to worry about frying motors due to pushing matches--you'll be spinning your wheels.

Don't try to win any pushing matches; use the extra maneuverability to avoid them.

Re: Mecanum Wheels is it good fin the Pits
 

6" wheels inherently give you more torque over 8" wheels at the same motor power. They also have their mass closer to the axle making them (slightly) easier to spin. In other words, with the 6" wheels, you should see much greater acceleration but a little less maximum speed.

Re: Mecanum Wheels is it good fin the Pits
 

you'll have awsome manuverability, get pushed around alot and very easily, and if you have to climb anything, like last years ramps, you'll have some trouble...

Re: Mecanum Wheels is it good fin the Pits
 

Well.... I'd hope they use the gear ratio to determine torque/speed rather than the wheels. but you are right...

Re: Mecanum Wheels is it good fin the Pits
 

As others have already said, with omni's and mecanum designs, you will get pushed around. BUT what you will have is manueverability AND less stressed components. Since we have started using omnis on the outer wheels on our robots, our motors don't heat, breakers don't trip, less chain breaking/problems. But again we had to remind our driver all to often, not to waste time trying to push others around.

If you want to push folks around, your drive system better be tough.

Re: Mecanum Wheels is it good fin the Pits
 

Perhaps I should have stated "all else equal", does that satisfy it? It was a small statement anyways. In the end, if we say torque/speed needs to be determined and set via the gear ratio then there is no reason to even choose between 2 different size wheels other than possible field components; so why even argue this at all?

The power transmission from motor to rotation against the floor is one great system that should hardly be considered internally modular for the purposes of determining the benefits of acceleration vs speed. As an example, wheels that have most of their mass away from the center can adversely affect either variable just as much as a bad gear ratio. It all has to be considered.

Re: Mecanum Wheels is it good fin the Pits
 

You will be pushed around since your mu is reduced by ~30%. The advantage is manuverability, and your strategy must require manuverability in order to make use of this advantage.
Either is good, depenfing on where you want your axles. Stability is much more a function of center of gravity than wheel size.
Good luck and have fun

Re: Mecanum Wheels is it good fin the Pits
 

We had mecanums on our robot last year, they were great, we were able to play defense (between the other team and the rack so that we didn't have to push), and if we got pushed, we couldn't really push back, but we could easily dodge to the side and go around.

Re: Mecanum Wheels is it good fin the Pits
 

Try stacking 4 on a axle, it will give you more traction. Our design used a set of three at each wheel, it did help, we have not tryed four. We did put a student on a cart and we pushed him all over. I do realise that is different than a powered robot.

Re: Mecanum Wheels is it good fin the Pits
 

I don't think that'll fit... four mecanums would be like eight+ inches thick... I'm surprised you could even fit three on one axle.

Re: Mecanum Wheels is it good fin the Pits
 

As a part of team 357, I have been working with my team on different variations of Mecanum wheels for the past three seasons. One misconception we have found is that mecanum wheels cannot push or will be pushed very easily. However, we have found that mecanum wheels are good for what they are designed for. For example in 2005 we wanted a fast, highly maneuverable robot. We decided to use mecanum wheel with a fast drive train. Our design worked very well for us ad we were very happy with the results. In 2006, we modified our design to accompany a ten inch wheel, up-sized from our six inch wheel in 2005. By enlarging the wheel we got a much larger contact patch with the ground. As a result we found that we could push many robots, in all directions. In one competition we were able to push one robot, then another at the same time, preventing both from scoring in the upper goal. While mecanum wheels are not usually designed for pushing and are well known for their maneuverability, if they are designed right, and for that purpose they can be pushing force to be reckoned with, as well has having the known maneuverability of traditional mecanum wheels. If you want more more information our team is always glad help at www.team357.org or you can PM me.

Re: Mecanum Wheels is it good fin the Pits
 

Contact patch has nothing to do with pushing force.

Coefficient of friction (CoF or Mu) is what gives you your pushing force and maintaining contact with the surface allows you to sustain that pushing force in a shoving match.

More than likely your wheels were made of a different material (better CoF on carpet), you had a better suspension (able to maintain contact with the carpet) or just had more power (more motors or lower losses in the transmission). Because of the accuracy needed to shoot into the upper goal, in 2006, just a small ram (momentum only) was needed to ensure difficulty in shooting.

Mechanums, by nature, do not have the pushing power because the bearings allow for translation from an outside source (IE low CoF when being pushed).

Re: Mecanum Wheels is it good fin the Pits
 

For the past week or so I've been working on a design for a drive system implementing both mecanum and omni wheels

but right now im on the fence as to which way to go,

whether to allow for a complete omni system (ie separate motors for each mecanum wheel),
or to use two motors (one for each side) and then implement a transmission i designed which allows for the two wheels linked to one motor to change direction and stop (ie for the strafing and diagonal movements).

the down side to the second system is i will not be able to code it to drive in relation to the driver completely, but i believe it will still be possible to code it so it drives in reference to a side, (ie if the right side is facing away from the robot, it now becomes the front),
also the fact that if the robot is strafing or going diagonal, that that is the only movement it can do(ie to rotate the robot the driver would have to stop strafing)

the nice thing about the second system is you would have only two motors,
also the transmission seems to work well with the omni wheel set up, because i was able to align the gears so the only time the omni wheels run is when both mecanums on one side are going in the same direction, the omni wheels allow for the robot to climb which seems to be a significant issue with the mecanum wheels

the drive system would look like this
o/m o o/m
O-----O-----O

the first wheels being both an omni and a mecanum
the second being just and omni
and the third being an omni and a mecanum

all of the wheels on each side would be powered by the same motor, and therefore would go at the same speed



just looking for some feedback
thanks