pic: Swerve^2 Prototype

[CD47-Bot]

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[Skabana159]

Are you using potentiometers or digital encoders to track the orientation of your wheels?
Also, can I get a close-up shot of your drill's gearbox? It looks neat.

[Stormhammer]

k, now THAT is interesting... though... hm

[Greg Needel]

very nice system....have you had any problems with drawing too much current or stalling the drill motor since you are only using 1 to power all 4 wheels?

[WakeZero]

We use two pots on both steering chains to determine position, so four total. As for the one drill motor issues, we have noticed that problem to a small extent... but they will go away once we install the second drill

[WakeZero]

We lovingly refer to this little contraption as the X-Box, since it's chains form an X that go out to drive each wheel. What it allows is for two drill motors to be mounted horizontally on the robot to drive the wheels. It also has a nice feature in that it makes the drill motors spin in the same direction (Clockwise and Clockwise, or CCW and CCW)

We may be taking out the four shafts around the middle one and just putting four or two sprockets on the top of the middle shaft... we would only do this if we thought it was too inefficient, or we were hurting for weight

[Madison]

Originally Posted by WakeZero

We lovingly refer to this little contraption as the X-Box, since it's chains form an X that go out to drive each wheel. What it allows is for two drill motors to be mounted horizontally on the robot to drive the wheels. It also has a nice feature in that it makes the drill motors spin in the same direction (Clockwise and Clockwise, or CCW and CCW)

We may be taking out the four shafts around the middle one and just putting four or two sprockets on the top of the middle shaft... we would only do this if we thought it was too inefficient, or we were hurting for weight

It's clear that it can translate along the ground -- but how does it turn? With two motors powering a single gearbox that drives all four wheels, is differential steering possible?

[edomus]

Originally Posted by M. Krass

It's clear that it can translate along the ground -- but how does it turn? With two motors powering a single gearbox that drives all four wheels, is differential steering possible?

looks like they also are using crab drive with different motors powering the turning

[WakeZero]

Here is what we use to turn ONE set of wheels. We have one of these on the back two wheels, and one on the front. You can't see them in the picture because they are mounted upward, and hidden by the frame

I explained it in the picture description, but that doesn't show up in the discussion. So here it is again

Yes, it does drive on it's own power up the small steps. Right now we have one drill motor driving all four motors, this will eventually be two. To steer we use two globe motors, one for the front wheels and one for the back. This allows us to do two things:

A) Tank-turn by turning the front wheels 180 degrees from the back wheels. This allows us to change the robots orientation easily.

and

B) Change to a car drive mode where only the front wheels turn.

To drive the swerve, right now we have one joystick. In programming we convert the x and y coordinates to polar by using lookup tables. This gives us the angle we want the wheels to face, and then the magnitude for how fast we want to drive.

[Travis Covington]

From what I can tell, it looks like there is no support on the other side of the globe motor shaft. It may just be the picture you showed, but in that configuration there is a significant side load that (typically) results in the globe motor releasing its magic smoke

If I am incorrect, sorry about that... Just thought I would note that... its an easy fix.

Otherwise it is VERY original! Looks good!

[WizardOfAz]

Originally Posted by Travis Covington

From what I can tell, it looks like there is no support on the other side of the globe motor shaft. It may just be the picture you showed, but in that configuration there is a significant side load that (typically) results in the globe motor releasing its magic smoke

If I am incorrect, sorry about that... Just thought I would note that... its an easy fix.

Otherwise it is VERY original! Looks good!

Well, you're right about that. I've worried about it some, but since steering is such light duty cycle, I don't think we'll have a problem. Also, the side load is very close to the motor - it would be much worse with a longer shaft. I'd guess in a typical game we'll turn the wheels an aggregate of a few revolutions, maybe a few tens at the upper bound. In our setup, the globe motors rotate 2.8x as fast as you steer the wheels, so maybe we'll get on the order of 100 total turns of rotation in a game. I'm thinking the motor won't suffer much with that much use. Does this disagree with your intutition or experience?

Bill

[Travis Covington]

Your assumption would be correct for almost all motors in the kit except the globe motor (in my honest opinion).

For some reason (maybe someone knows specifically) the globe motor is VERY sensitive to side loads. In past years when my team used these motors, if the shaft was not supported on both ends we would ruin the motor, even if it was used rarely.

If it is possible (it looks failry easy) you might want to try and put a bearing supporting the shaft on the other end... even though you might not really need it... it seems like it serves an important enough function to deem the extra work beneficial... even if it only gives you peace of mind.

Hope that helps

[WakeZero]

Thanks Travis, we will surely be looking into this now

[Paul Copioli]

I am going to have to back up Travis on this one. We used the globe motors for swerve steering in 2002 and we hade to add a bearing to support the load. We ruined 3 globe motors on our prototype unitl we figured it out. Once we added the bearing, we did not fail any globe motors.


-Paul

[WizardOfAz]

Originally Posted by Paul Copioli

I am going to have to back up Travis on this one. We used the globe motors for swerve steering in 2002 and we hade to add a bearing to support the load. We ruined 3 globe motors on our prototype unitl we figured it out. Once we added the bearing, we did not fail any globe motors.
-Paul

OK, I hear the growing concensus. Our original design had a top plate and a bearing. Just "simplified" it to a single plate to the the prototype going quick, and it worked pretty well, so I was hoping to leave it that way. The prototype in the photo will be getting some road time in the next few days, so we'll see how that goes. What are the first symptoms of impending failure? Noise? Smoke? Just locks up?