[Kevin Ainsworth]

Thanks for all the great feedback, some of these questions were already answered so sorry if I repeat them. Also, sorry for the long posts but we would like to make sure the students questions are given an educational answer. I would like to thank Aren Hill for his inspiration for our "In Wheel" swerve as well as this unit.

Originally Posted by Ether

Where did you get the "actual" numbers from?

We have been recording our theoretical to actual numbers for a few years now and 82% is our average actual speed to theoretical. So the working of "actual" should be changed to "expected".

Originally Posted by 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.

1) We considered flipping the CIM due to reasons already explained and a guess that since the field has been flat for the last few years we are expecting a field obstruction this year. We can always reconfigure later. A second motor on each wheel was considered also, see our previous discussion on using 8 MiniCIM's. The 3" OD wheels would probably be overpowered in a pushing match but the extra motors would be helpful for acceleration. You might just see dual motors from us in the future if it fits the game and if something like current monitoring is effective enough against blown fuses.

2) Already answered, but no need for a RS775. Aren Hill used a RS395 on the first "In Wheel" swerve. We have been wondering what happens when our 2014 swerve bot gets pushed up on two wheels and the wheels are not pointed in the direction of the push. Do the steering motors have enough power to change direction? It seems like the edges of the wheels could be digging into the carpet and requiring extra force to rotate. On our off-season list of tests to perform.

3) The ratio between the Vex Versa gear isn't 1:1 to the modules steering gear so a 360 degree absolute encoder can't be used. The two plastic gears are 1:1 so a 360 degree absolute encoder can be used. An incremental encoder could be used but adds another place for human error. We like the robot to not depend on a human to set the wheels at the beginning of a match.

4) Miter gears are purchased from Vex and are 4140.

5) If designed properly the units should last a full season without repair.
If repair is needed they will be bolted onto the chassis and can be changed in ten minutes. We bring at least one extra unit to competition in case a swap is needed. Last year our mechanic Jose and I changed out a steering box on our robot between rounds in finals on Curie. We had previously swapped in a Banebots gearbox from our practice bot at Chicago. During our debugging of our first swerve drive ever we burned up about a dozen steering motors. Mainly due to the rotation stops we used so as not to pull CIM motor wires out. We reused the pinion gears and this particular pinion had been installed/removed one too many times. The motor shaft spun inside the pinion and we lost one wheel of steering. Took about ten minutes for Jose to install a new one while I ran around grabbing the replacement parts. We had students dedicated to our swerves from the very beginning of last year to clean, inspect, repair, etc.

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)?

Steering box question was already answered correctly, hidden in view shown.
We had field centric software installed by IRI last year with the successful integration of the Kauai Labs gyro. There was a great thread on this a little while ago. "Best gyro for frc." Big props to our students Bennett and Duffy. Bennett for coding the entire swerve software, about 10 iterations, and to Duffy for spending the better part of the season fine tuning our teams first gyro ever used.

Originally Posted by Jared Russell

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.

Great point, I never thought of it that way. I think that being able to overdrive the outside wheel is important because in a high speed strafing turn the fastest wheel is the limiting factor. If just one wheel is traveling the outside radius it will limit overall speed. The other three wheels can power you through the turn.

Originally Posted by Bryce2471

I really love this design overall. I've wanted to design a swerve with a single reduction ball-shifter for quite some time. I do have some questions and concerns though.

1. It looks like there is no thrust bearing above the vertical miter gear. This is not a big deal by its self, (We used thrust washers last year) but it will increase the speed of deterioration on the gears, and decrease efficiency in that gear-set. It also looks like you're planning on using the VEX Pro aluminum Miter gears. This is also not a big deal, lots of team use them, but I suspect the fact that they are aluminum will increase wear speed. With those two things combined, your drive performance may not suffer, but you will probably find yourselves replacing the miter gears pretty often. What is the process for replacing a miter gear? How long will it take?
2. How many man-hours will you spend to machine all the parts? How about to assemble the modules? I feel like you could have designed a module with the same performance, that would have been much less resource demanding to build.
3. What kind of bearing are you using to move the robot's weight from the red base plate to the top of the castor? In the cross section, it looks very thin.
4. Not sure if it is a problem or not, but I couldn't help but notice that your pneumatic cylinder is mounted to a plate, that has standoffs to a plate, that has standoffs to a plate, that is stood off from a plate, that has standoffs to a plate, that is mounted to your frame. Not sure why, but that makes me cringe a little.
5. What gears are you using on the ball-shifter shaft, and as the CIM pinions?

1) Vex 4140 pre-hard steel miter gears
Not sure I fully agree with the needle bearing vs radial bearing arguement
The radial bearing can take over 100lbs of thrust force.
I get nervous when the balls are too small in diameter
2) Easier said than done, especially with the two speed design
3) Silverthin 4 point contact bearing with 1100lbs of dynamic thrust load
Only 1/4" cross section but should hold up, we are supporting completely.
We were going to use a cross roller bearing but Aren Hill informed us of these lower cost bearings
4) Lower standoffs support plates, upper standoffs support shifter. Non support the weight of the robot
5) 12:60 (low) or 28:44 (high) CIM to ball shifter, with 12:30 for 2nd stage, to 1:1 miter to wheel

Originally Posted by magnets

This is a fantastic design. There have been many designs of two speed swerves posted over the years, but nothing has come close to what you've put together.
I know from looking at your swerve design from last year that you guys shouldn't have trouble machining the parts in this design, but I've got to ask, how do you guys even have time to make these parts and finish the robot on time? What sort of tools do you have, and how many people do you have working?

There was a tear in my eye last year when on a Saturday we had two lathes, two CNC's and six Bridgeport Prototrak's (2D CNC) going at the same time. All students except for the CNC machines. Our program is unique in that we teach machining to all students that want to learn and we have enough machines for kids to use at the same time.

Originally Posted by Tyler2517

I can confirm what Bryce2471 is saying we saw reduced life and over time reduced efficiency due to us not having the thrust bearings between the mitter gear and the radial bearing.

Radial bearing will not hold up as long as a thrust bearing, true.
The OD of a needle thrust bearing being too large to fit is the reason we went with a radial bearing. Sometimes you have to make sacrifices.

Originally Posted by nathannfm

Now I have a few questions:

Why the hollow drive axle?

According to the CAD the shifter gears are steel but reference aluminium VexPro gears, what's up with that?

Amazing looking drive, great work, I hope I get to check it out in person at champs!

The axle is hollow for weight. It needs to be steel since the axle runs through needle bearings (with thrust bearings). An aluminum axle on needle bearings would wear too much.

The two ball shifter gears are aluminum in our model. The two CIM gears are steel to reduce wear. We like to run a steel against an aluminum gear, we keep the smaller gear steel for weight. This greatly reduces the wear and therefore efficiency loss of the gears over the season. We've found the aluminum on aluminum ceramic coated gears will destroy each other over time.