pic: Coaxial Swerve Drive Module with 2-speed Ball Drive and Nitrile Tread

[Kevin Ainsworth]

loading photo ...

[fb39ca4]

Fancy. How much does each module weigh?

[Oblarg]

Great-looking design. With just 1 CIM per wheel, though, isn't that top speed a bit high, unless you're planning to use autoshift code?

[Tyler2517]

What is the benefits in running this one over the last design? 2 speed shifting is nice but you have decreed mechanical efficacy and a higher center of gravity.

Still like the design though really smart roundabout thinking.

[Tyler2517]

Originally Posted by fb39ca4

Fancy. How much does each module weigh?

7lb 3" it says it in the post.

[nathannfm]

Are you planning on building a drive with these before the season?
I really like the bevel gear embedded in the drive wheel eliminating an extra stage.
What kind of module rotation speeds are you looking at (rps)?
Did you design your own ball shifter? From the cutaway it looks different then the VexPro one.

I think we would all appreciate you posting the CAD or a few more views, you can hardly see the rotation motor.
Very nice work!

[Kevin Ainsworth]

Complete CAD file can be downloaded here.

https://drive.google.com/open?id=0B6...Qzg&authuser=0

After our successful 1st year using our "In wheel" swerve we learned a few things and applied those lessons to our 2nd swerve design.

-Swerves can usually out maneuver other robots when there is an open field
-A single speed swerve is not good in a scrum with multiple defending robots
-Slip rings add weight, complexity, point of failure and the legality of the best Mercotac slip rings is being debated currently
-Colson tires get good traction and have a low rolling resistance but are more traction limited than Nitrile treaded tires

Therefore we developed a 2-speed coaxial swerve so we have speed and the ability to get out of a jam. We switched from Colson wheels to custom aluminum nitrile treaded wheels to gain added traction. We reduced the weight per module by 1lb each and the area is 33% of the "In Wheel" swerve.

[Scott Kozutsky]

Looks pretty great, I would have personally repackaged it similar to 1717 and sacrificed some of the bellypan area just to get that CIM out of the air and lower the COG but I really like this evolution of swerve. When are we going to see a manufactured unit?

[Kevin Ainsworth]

Originally Posted by fb39ca4

Fancy. How much does each module weigh?

This module is approximately 7lbs.
A little under in Solidworks, a little over with fasteners in the real world.

Originally Posted by Oblarg

Great-looking design. With just 1 CIM per wheel, though, isn't that top speed a bit high, unless you're planning to use autoshift code?

My apologies, I stated the wrong speeds. The speeds listed on the description are for a 3.25" wheel, with a 3" wheel the speeds would be around 4.55/5.55 fps in low and 14.47/17.65 fps in high (actual speed/theoretical).
It was easier to chance the wheel diameter than the gearing.

Originally Posted by Tyler2517

What is the benefits in running this one over the last design? 2 speed shifting is nice but you have decreed mechanical efficacy and a higher center of gravity.

I posted what we feel the benefits are on my other reply with the CAD link.
We will loose around 4% efficiency due to the 3rd gear stage but should gain efficiency by using roller bearings over the delrin rollers on the cim end caps like the "In Wheel" module. Should be close to the same efficiency.
We were just talking about the higher center of gravity last night during our Mechanical Team meeting and this is a trade off. We have another version of this unit where the CIM comes out to the side but for that version there are two more stages of gearing and the extra weight and loss of efficiency didn't seem like a fair trade off. Ground clearance is an issue if the CIM is tucked under the robot. But if being low to the ground or having a low center of gravity is valuable than we can modify the design. The "In Wheel" modules center of gravity is 3.25" off the floor and the coaxial unit is 5.75" off the floor. This version puts 20% of the robots total weight 2.5" higher, not really enough for concern with the center of mass.

Originally Posted by nathannfm

Are you planning on building a drive with these before the season?
I really like the bevel gear embedded in the drive wheel eliminating an extra stage.
What kind of module rotation speeds are you looking at (rps)?
Did you design your own ball shifter? From the cutaway it looks different then the VexPro one.

I think we would all appreciate you posting the CAD or a few more views, you can hardly see the rotation motor.
Very nice work!

We are starting machining of the prototypes at our next off-season team meeting. All purchased components are on order.
The rotational speed is 48 RPM at peak steering motor power, "In Wheel" module was 40 RPM. They can spin faster during driving with no pushing.
The ball drive is the 217-2792 unit from VexPro with a modified output shaft.
CAD link is posted in my other reply.

[Ether]

Originally Posted by Kevin Ainsworth

the speeds would be around 4.55/5.55 fps in low and 14.47/17.65 fps in high (actual speed/theoretical)

Where did you get the "actual" numbers from?

[asid61]

Crazy! This is definitely the most advanced/ best swerve I have ever seen. Dual speed at a weight of 7bs per module rivals that of WCD; it's like having torquey holonomic motion at the cost of 4-5 lbs.

I have a couple of application questions:
1. Why did you not flip the cim? It look like you have the room to do so. Flipping it and adding a belt drive to the first stage of the gearbox would add half a pound or so, but would alloy you to add another cim or a minicim to the drivetrain if you wished.
2. Why the small banebots motors over something powerful like the RS-775 18v?
3. Why did you choost to have a seperate pair of gears for the absolute encoder instead of simply having an encoder on the versaplanetary output?
4. Tons and tons of machined parts (the most notable to me being the miter gears). What do you expect the turnaround time to be for these?
5. How are you planning on fixing anything if a module breaks? It seems very compact and complex and hard to repair.

Again, very nice swerve drive. It's a bit beyond my team's capabilities, but I hope that you can use this this year and improve this further next year.

[page2067]

This looks beautiful. PWNAGE has been advancing swerve to new levels of elegance.

I do not see the steering motor in the views I have seen (or am blind) - I see the steering encoder, pneumatic cylinder and CIM - what are you using for steering motors/transmissions?

Also are you planning to be field-centric steering next year (of course with game dependency disclaimers)?

[asid61]

Originally Posted by page2067

This looks beautiful. PWNAGE has been advancing swerve to new levels of elegance.

I do not see the steering motor in the views I have seen (or am blind) - I see the steering encoder, pneumatic cylinder and CIM - what are you using for steering motors/transmissions?

Also are you planning to be field-centric steering next year (of course with game dependency disclaimers)?

The steering motor is hidden behind the main shaft. It's an RS550 on a 100:1 versaplanetary plus the final stage with teh big orange gear.

[avanboekel]

Originally Posted by Ether

Where did you get the "actual" numbers from?

Looks like its ~82% of the theoretical speed. Maybe based on the number of gear reductions?


Really cool design by the way. Cant wait to see this in action!

[Jared Russell]

Originally Posted by Tyler2517

2 speed shifting is nice but you have decreed mechanical efficacy and a higher center of gravity.

If 2451 truly gets about 82% of the theoretical free speed out of these transmissions, that's in the efficiency ballpark of most FRC skid-steer drive trains. Some teams can hit the low 90s, but that is the exception rather than the rule.

Also, the intuition of "what's too fast for high gear" is somewhat different for an independently steered/driven swerve than for a skid-steer drive train. Your wheels never need to fight each other, so you are asking less of your drive motors than in a 6/8WD where you need to force wheels to slip sideways in order to turn.