pic: MOEnarch Swerve Drive

[nathannfm]

Originally Posted by Andrew Lawrence

10 - 20 ft/s is a pretty big gap there, Nathan

We can use any size up to 44 teeth, flexibility man. Through our testing and based on the game we will determine our optimal speed.

[billbo911]

Is it a fair assumption that you will be using 8 CIM drive with this.
If so, how are you planning to keep from popping your main breaker?
Are you using current monitoring to keep yourself in a safe zone?

[Tom Line]

I would consider changing the location of your digital encoder for a couple reasons.

First, as you tension the belt by moving your cim, it will change the engagement on the Digital encoder.
Secondly, generally speaking those things don't appreciate a lot of side-loading.
Third, if your belt slips, your wheel will no longer be aligned with the encoder reading.

I'd consider a small lightweight bracket that places it directly over the primary shaft of the module itself, so you'll always know the true position of the module. This also relieves any side-pressure on it, and it can be coupled with something as simple as surgical tubing. It will probably be a wash weight-wise.

[nathannfm]

Originally Posted by billbo911

Is it a fair assumption that you will be using 8 CIM drive with this.
If so, how are you planning to keep from popping your main breaker?
Are you using current monitoring to keep yourself in a safe zone?

4 CIM + 4 MiniCIM (assuming the motor count rules stay the same) but yes, current monitoring is the plan, I know there are a few teams this year who had this many CIMs on the drive without problem, but they did not have the additional draw of the 4 rotation motors so we may be forced down to 4 CIMs. We will be testing with 4 CIMs to start then if we can scrounge up enough Jags, all 8. The new control system should make this much easier. We are also concerned about weight, so no guarantees but we wanted to include all 8 mounting positions to cover our bases.

Originally Posted by Tom Line

I would consider changing the location of your digital encoder...

I am not sure if you can tell but the encoder is also on a slot so we can adjust it along with the CIM and make it just kiss the belt so there is almost no side loading. If the belt skips im pretty sure we are just gonna go to chain, we had enough headaches dealing with skipping belts this year

We did consider a bracket like you describe but it was just another part to manufacture and would also put the encoder in a more vulnerable location. If there is some unforeseen mechanical problem with it's current location we may go this route.

[lynca]

Originally Posted by nathannfm

I know there are a few teams this year who had this many CIMs on the drive without problem, but they did not have the additional draw of the 4 rotation motors so we may be forced down to 4 CIMs.

Team 2587 ran 4 CIMs + 4 Mini-CIMs all year for around 70 matches + lots of practice time. Here are details about our drive system.
We did not experience breaker issues while also running an intake motor & compressor.

We also did not perform any type of current sensing.

[nathannfm]

Originally Posted by lynca

Team 2587 ran 4 CIMs + 4 Mini-CIMs all year for around 70 matches + lots of practice time. Here are details about our drive system.
We did not experience breaker issues while also running an intake motor & compressor.

We also did not perform any type of current sensing.

Good to know, depending on the final speed we pick I suspect it will be fine, we shouldn't be trying to pivot the module while stalling the CIMs anyway. Also, nice video, I'm surprised more teams didn't use a pneumatic shooter like you guys, looks quite effective. I couldn't help but notice in the close ups, are you guys using Churros for drive axles? Did you have any problems with that?

[lynca]

Originally Posted by nathannfm

I couldn't help but notice in the close ups, are you guys using Churros for drive axles? Did you have any problems with that?

Many of the pictures are from the 6-week build period. Eventually during the event we changed to black hex VEXpro shafts.

Churros are not recommended drive axles, but they work well for a quick prototype. We did have enough black hex VEXpro shafts on hand at the time.

[Ether]

Originally Posted by lynca

We did not experience breaker issues...

Here's why:

4" Versa Wheels at 12:72 gear * 18:40 sprocket

[asid61]

Originally Posted by Ether

Here's why:

+1. That kind of reduction will result in an extremely low speed, around 5 fps according to JVN design calc. Not really worth a 4 cim 4 minicim drive IMO, as even in high gear mecanum you're only running 12fps...

[Ether]

Free speed of CIM+MiniCIM motor combination geared 1:1

= (343 + 198) / (343/5310 + 198/6200)

~ 5604 rpm


vehicle speed (with traction wheels) @ motor combo free speed =

(pi*4*5604) / (720*12.75*40/18)

~ 3.45 feet/sec

[nathannfm]

Getting there!
https://www.facebook.com/video.php?v...04577359603811

[AdamHeard]

Originally Posted by nathannfm

Getting there!
https://www.facebook.com/video.php?v...04577359603811

The diagonal cut roughtop is killing me! Straight cut (for maximum cleat effect) is the only way to go in my mind.

Congrats on getting to the movement milestone though!

[nathannfm]

Originally Posted by AdamHeard

The diagonal cut roughtop is killing me! Straight cut (for maximum cleat effect) is the only way to go in my mind.!

You noticed that ehh?
We actually tested this last year with a force gauge, it takes ~15% more force to pull/push the robot side to side or front to back (with locked wheels) because when you put it on a diagonal more nubs are touching the carpet per contact patch area.

[Gdeaver]

Looks like a happy happy joy joy moment. Some thing does not sound right when the module was rotating and driven. Those are wide wheels and may cause problems with amp draw on both drive motors and steering. Pay close attention to the tuning of the steering pid. You can have to much traction. For a fall back you might want to consider 1-1/2 or 1-1/4" Colsons. Next, get 4 of them on a frame and get programming. Then you will be half way there. Driver training is the last half. If you get it going before kick off, do you want to meet and do some swerve on swerve driving?

Note for the drive encoder, Do you really need quadrature? Wouldn't a tachometer solution be good enough? I do not now what the under side of the coaxial pulley looks like but, could you put some reflective tape strips on it and use a optical reflective sensor? We used a magnet solution last year and will use optical this year.

[nathannfm]

Originally Posted by Gdeaver

Looks like a happy happy joy joy moment. Some thing does not sound right when the module was rotating and driven. Those are wide wheels and may cause problems with amp draw on both drive motors and steering. Pay close attention to the tuning of the steering pid. You can have to much traction. For a fall back you might want to consider 1-1/2 or 1-1/4" Colsons. Next, get 4 of them on a frame and get programming. Then you will be half way there. Driver training is the last half. If you get it going before kick off, do you want to meet and do some swerve on swerve driving?

Note for the drive encoder, Do you really need quadrature? Wouldn't a tachometer solution be good enough? I do not now what the under side of the coaxial pulley looks like but, could you put some reflective tape strips on it and use a optical reflective sensor? We used a magnet solution last year and will use optical this year.

It was (MOE cheer right after the video cut out ) If you were referring to the pulsating of the sound I think that was because most of the noise was coming from the bevel gears and their location was changing relative to the mic, but I will look into it. Do you grease yours? We also have not played with tension of the rotation motor belt, we will look into that next meeting (we did notice it affected the speed of rotation between modules) We will definitely be keeping an eye on the amps and have Jags on every motor to monitor that, The RoboRIO should also make that easy when it arrives. We will hopefully get driving by Monday. Our programmers already have a basic crab drive program and are working on fancier moves now. I think we would love to have some swerve on swerve driving! You and your team have already been a great help this summer, I will ask the drive team about this at the next meeting and get back to you.

As for the encoders we debated this, but we haven't had very reliable results from magnetic sensors in the past, and there is not much room to mount an optical sensor under the pulley. We also had all the encoders we plan to use in stock so we just went with them.