6 motor mechanum drive

[Yolkedgravy69]

Hi there Our programmer needs help with the program when our robot base looks like this.

. She doesn’t know how to program a drive like that and I was wondering if anyone else has a program for that drive.

[teresajude]

Does she know how to program a normal mecanum drive?

The easiest way to handle that drivetrain would be to simply configure motor groups for the two double-motor wheels. One of the motors in that group would have to be reversed, due to the gearing.

You can then use that motor group as if it was just another motor.

Due to handling quirks, I would recommend calculating the velocity for all of the wheels and storing them in variables, then set the motor speeds in adjacent lines (don’t set motor 1 speed, do a bunch of calculations, set motor 2 speed, etc).

Good luck! I will be curious to hear how that drive base design works. I don’t think I have seen that motor layout used before.

[Yolkedgravy69]

Yeah we are a shopping cart and needed more strength to get the mobile goals up the platform. Thank you so much

[langchen]

where are the other two wheels?

[Foster]

Looks like they go on that slanted bar. To me that was a pretty helpful picture to show more of the inside setup.

@teresajude

I will be curious to hear how that drive base design works. I don’t think I have seen that motor layout used before.

Me too. For some reason I had mechanum locked into a 4 wheel / 4 motor design, so using 6 motors is an interesting concept.

[Hudsonville_Robotics]

Using VexCodePro with a basic Robot Configuration

Then referencing @Codec’s example here but transformed to use motor groups in the rear:

Vexcode Mecanum Wheel Program

When programming a drive the general ideas is to add up all the values for the wheels, this may incude forward, sideways, left, right and/or turn. This picture shows the direction each wheel should go for mecanum wheels… Using this your code should look something like this… int forward = /*your value*/; int sideways = /*your value*/; int turn = /*your value*/; frontRight.spin(vex::forward, forward - sideways + turn, vex::percent); frontLeft.spin(vex::forward, forward + sideways - turn, vex:…

void usercontrol(void) {
  // User control code here, inside the loop
  while (1) {
    int forward = Controller1.Axis3.position(vex::percent);
    int sideways = Controller1.Axis4.position(vex::percent);
    int turn = Controller1.Axis1.position(vex::percent);

    RF.spin(vex::forward, forward - sideways + turn, vex::percent);
    LF.spin(vex::forward,  forward + sideways - turn, vex::percent);
    RRGroup.spin(vex::forward,  forward + sideways + turn, vex::percent);
    LRGroup.spin(vex::forward,   forward - sideways - turn, vex::percent);

    wait(20, msec); 
  }
}

[Eli_63303]

Hey! I might be able to help, I’m on team 63303V. One big factor that allows us to clime so easily up the platforms is the fact that we used high strength shafts on our drive base, also after much testing mecanum wheels are not very viable for climbing. We’ve found that four inch omnis work best…

[Yolkedgravy69]

How many motors were on your drive?

[Eli_63303]

@Yolkedgravy69
It was a six motor drive, although with the HS shafts we could have easily done a four motor drive.

[Xenon27]

@Eli_63303

It was a six motor drive, although with the HS shafts we could have easily done a four motor drive.

why would HS shafts make your drive better suited for climbing with fewer motors? they don’t add any torque or power to your drive, and in fact might work to reduce it considering the higher friction inherent in HS shafts compared to low strength or screw joints.

[langchen]

Why the HS has higher fraction? Is the any theory or experiment or data to support this? Really curious.

[Xenon27]

the HS shafts don’t spin quite as freely inside HS bearings compared to LS shafts or screw joints.

You can always drill out the bearings ever so slightly to mitigate this, but it still won’t provide any benefits to the power of your drive. And built properly, HS shafts should be completely unnecessary for a drive. LS shafts or screws should be plenty strong to support the weight of a typical robot.

[langchen]

@Xenon27

the HS shafts don’t spin quite as freely inside HS bearings compared to LS shafts or screw joints.

I respectfully disagree.

[Xenon27]

I mean agree or not, that’s just my experience with HS shafts and bearings.

[Eli_63303]

They are much stronger, and when in the motor, they have much more contact with the motor versus low strength shafts.

[muradmalik]

i would put a omni in the middle of the chassis instead of putting 2m on 1 wheel, might cause strafing issues (1m per wheel

[Xenon27]

@Eli_63303

and when in the motor, they have much more contact with the motor versus low strength shafts.

that is a good point, however you can get the same thing by putting a metal gear insert into the motor to stabilize the shaft.

[Eli_63303]

Here is a old picture of our drivetrain… It can easily climb with all the goals in the shopping cart…

[teresajude]

Is this picture looking down from the top or up from the bottom?

If it is up from the bottom you have the rollers aligned incorrectly (the robot can be spun in place without any motors turning).

[langchen]

I agree with all your points here. But I am puzzle how it translates into more fraction.