pic: Swerve^2 Prototype

[Paul Copioli]

The first indications on our robot were that the wheels were not getting to the position we commanded. At first, we thought it was the potentiometer going bad, but it was actually the motor not having enough torque at the lower gains (as it gets closer to the commanded position). The motor slowely loses torque capacity as you fail the front bushing. The planetary gears inside the globe transmission start to wear and bind up, thus losing torque capacity. The motor will eventually lock up, but the swerve steering will suffer long before lock up.

-Paul

[Joe Johnson]

The main reason the Globes need support is that they have only one bearing if you don't. The second bearing becomes the planetary gears on the last stage if you don't give it an external one. This is very bad for efficiency of the gearbox.

Joe J.

[ajlapp]

i noticed you have clearance for the steps....any thoughts about going up the sides of the platform. there isn't much room around that goal once you go up the steps.

[WizardOfAz]

Originally Posted by ajlapp

i noticed you have clearance for the steps....any thoughts about going up the sides of the platform. there isn't much room around that goal once you go up the steps.

Yes, we're working on that. Essentially raising the body bottom for more clearance and putting front and mid-body skids. Will post another picture soon.

Bill

[Paul H]

How much does that prototype weigh?

[WizardOfAz]

Originally Posted by Paul H

How much does that prototype weigh?

It's about 100 pounds, but about half of that is the wood base which will be aluminum for the competition guy. But it is heavy. Lot of hardware in each wheel. We're a tad concerned about it...

Bill

[FotoPlasma]

Do you think you might be able to post a CAD or two of the wheel modules? I am very interested in how you implemented the coaxial swerve system.

[WizardOfAz]

Originally Posted by FotoPlasma

Do you think you might be able to post a CAD or two of the wheel modules? I am very interested in how you implemented the coaxial swerve system.

Here's a photo of a pre-season prototype wheel, #0 as it were. Though the new ones have minor improvements (e.g. better spacers), they are essentially like this one.

http://crush1011.wookus.net/pix/2003...lPrototype.jpg

The motive drive comes down the center shaft, through the miter gear pair, then by chain to the wheel. The ratio is 1-1 all the way from the S-B motor up to the last sprocket, where it gets geared down by 1-2.8 (10 to 28 tooth sprocket). The vertical shaft is spinning in and supported by a half inch bore in the large teflon bushing.

The steering drive comes in the big sprocket on top. That sprocket is bolted through the large teflon bushing to the top plate of the yoke. Steering is accomplished by turning the teflon bushing in the top plate. The top plate mounts to the robot frame. The steering drive is also a 1-2.8 geardown, using the globe motor.

For size reference, the top plate is 6"x6". The large teflon bushing is 3" OD with a 3/8" groove where it rides in the top plate. The teflon splits in two pieces within this groove in order to make assembly possible.

We have some CAD drawings, but a few changes were made to the design post-CAD. Hopefully this picture makes it all reasonably clear. If not, please ask.

This system is not without its challenges, but we're working through them. First, it's a lot of gears and chain, and resulting end-to-end losses. Second, there is some coupling from the motive drive to the steering drive, which makes good steering tracking code more important.

It's very fun working on it though [;-)

Bill

[bjammin64]

hey, i was just wondering how exactly the driver will control all of this. would it mbe one person, or would both drivers have to work together to achieve topmost maneuveurability

[WizardOfAz]

Originally Posted by bjammin64

hey, i was just wondering how exactly the driver will control all of this. would it mbe one person, or would both drivers have to work together to achieve topmost maneuveurability

We have a few different driver control options in the works, but all are single driver, at least for the "driving" part. Another operator will probably manage other gadgets on the 'bot.

We think the "preferred" driving mode will be a single joystick, where the joystick displacement from center is speed, and joystick angle is the drive direction. All four wheels steer in tandem to the same angle and always roll the same direction (never have to run the drill motor backwards).

We'll also be able to lock the back wheels and steer just the front, which makes it drive like a car more or less. This is one way we could rotate the body of the 'bot. Notice that in the "preferred" mode above there's no way for the driver to rotate the body. In "car" mode we'll enable the motors to go backwards for more maneuverability.

Another variation will be to steer the wheels in opposite directions and do a turn-in-place (a tank turn), then return to swerve for moving around the field. This gives a quick way to turn the body to a needed orientation.

Bill