18-12-2008 11:32

sdcantrell56

Re: pic: 1503's Off-Season Project

Very Very nice work! Time for some questions. How heavy is the entire thing without electronics and with electronics? Are those the banebots wheels? If so how are they holding up and how is traction? Does this drivetrain have the ability to climb ramps and if not would it be easy to modify it? How are the chains tensioned?

Overall I love this design and it looks very similar to many of mine. Good job guys!

18-12-2008 11:44

M. Mellott

Re: pic: 1503's Off-Season Project

Love the double banebot wheels--we had a similar idea.

Nice looking transmissions as well--are those 4-speed?

Could you give us some performance numbers for those of us who cannot access YouTube from our non-home computers?

Nice clean look! A great layout example for other teams with the new control system.

18-12-2008 12:04

Sagar Vyas

Re: pic: 1503's Off-Season Project

Pretty impressive perfomance, seen it over the weekend...

Clean design as usual. Looks like the team is doing great.

18-12-2008 12:24

=Martin=Taylor=

Re: pic: 1503's Off-Season Project

30 Shore A wheels!

And to think we had too much traction with 70-75 Shore wheels, and they wore through .5" of rubber over the season

It does look very cool though. The apparent lack of tensioners is especially clever

What are you planning to use those extra drive sprockets fore? Drive-train powered mechanism?

18-12-2008 15:08

Macdaddy549

Re: pic: 1503's Off-Season Project

All I can say is WOW. Great job!!

18-12-2008 15:17

Aren_Hill

Re: pic: 1503's Off-Season Project

Does that thing have a 4 speed? And i love the layout you have no idea, very slick and very compact

18-12-2008 15:45

NickE

Re: pic: 1503's Off-Season Project

I'm lovin the green and red wiring.

That is a very impressive drivetrain. Nice work!

18-12-2008 16:06

RyanCahoon

Re: pic: 1503's Off-Season Project

A couple of questions of my own:

Since you're running traction on all 6 (12) wheels, how much have you dropped the center wheels?

I've heard some reports of the banebots wheels blowing out, have you done any durability testing on them yet (getting pushed sideways and such)?

--Ryan

18-12-2008 16:23

GarrettF2395

Re: pic: 1503's Off-Season Project

I agree, the layout is amazing!
The mix of 80/20 and custom frame is really well done too.
I wonder how well the wheels hold up while making a sharp turn though...

18-12-2008 16:42

Jonathan Norris

Re: pic: 1503's Off-Season Project

That's hot Pat... You deserve another cookie for this.

Interesting that you used 80/20 and #35 chain, looks like a 4 speed shifter. Good work again by Spartronics, see you guys at GTR.

18-12-2008 18:35

AdamHeard

Re: pic: 1503's Off-Season Project

What's the weight on that?

How easily can wheels be swapped out? These wheels were field tested by a lot of combat robots at robogames, and they found them to wear down quite fast (and that was on steel).

and purely out of curiosity, is the electrical board garolite?

At Robogames the wheels themselves proved to be rather durable, the tread layer is just a lot thinner than they appear and since they are a very soft rubber, wear down rather fast.

18-12-2008 21:37

Pat Fairbank

Re: pic: 1503's Off-Season Project

Thanks, everyone, for the comments.

We never measured it without electronics; with them, it's sitting at about 60 lbs (sans compressor). Of course, there are 26 steel gears in there, most of which we'd weight-relieve for a competition robot.

Yes, they're the 30 Shore A Banebots wheels. We're really happy with the traction, and may switch to a harder grade if they wear down too easily. We're prepared to switch the wheels out fairly often since they're $5.25 each and a couple of minutes on the CNC takes care of the mounting holes.

It should be able to climb most ramps just fine. If not, we'll just mess around with ground clearance (currently 0.75") and wheel spacing.

As with our 2008 robot, the wheel spacing is such that the chains are an integer number of links. I've always been wary of over-tensioning chain, and would rather avoid the friction and added complexity of tensioning systems. If the chains stretch and become too loose, we'll just replace them.

Yeah, they're 4-speed transmissions, inspired largely by AndyMark but entirely custom (with a shifting mechanism that addresses several maintenance-related issues we had with our Gen 2's last year as well as making the parts much easier to machine with our shop). From a drive strategy perspective, I wanted a 3-speed, but decided that the best way to accomplish it would be to design a 4-speed and just not use one of the speeds. The (calculated) speeds are 5, 9, 11 and 19 fps, with the 9 fps speed being ignored.

We mostly picked those wheels for now because they match our team colours. The sprockets are there for now so that the front and back wheels are interchangeable.

The center wheels are dropped 5/32", same as our 2008 robot. Given the flat nature of the wheel tread as compared to the roughtop we used last year, though, I'm thinking we could probably get away with less.

We haven't done any extensive field testing yet. We cut some wheels apart and were happy with their composition and with the way the treads are bonded to the wheel, but breakage from a side load is still a potential issue. Our attachment point to the wheels is fairly far from the axis, though, so I'm not overly concerned.

Geez, all this talk of cookies, and yet nobody ever follows through...
The extrusion is actually Bosch; we were lucky to obtain it for free. As for the chain, I know that by the numbers, #25 is perfectly acceptable for drivetrains, but it's less forgiving of slight misalignments and stretches more readily. I'd rather waste the weight on #35 chain and be secure in the knowledge that we're never going to have issues with it in the heat of competition.

It's just a matter of sliding the axle out. We'll have an extra set of wheel assemblies ready and a bunch more pre-machined wheels for swapping with those on the inactive set.

Not positive, but I think so. It was a piece of some sort of fibrous composite that was kicking around our back room. On a competition robot, though, I'm leaning towards using carbon fibre.

18-12-2008 21:57

s_forbes

Re: pic: 1503's Off-Season Project

Very cool chassis design! The four speed transmissions look really neat, what kind of shifting mechanism are you guys using? I wasn't aware of any issues with the AM dog shifting design, but I'd like to see what you came up with.

The chain tensioning (rather, the lack of it) is cool, too. How often did you have to change out chains on your 08 robot, and how loose did they get before you changed them? It seems like a great set up if they don't loosen up too incredibly fast. Also, are those custom one piece sprockets on the wheels?

19-12-2008 08:03

JesseK

Re: pic: 1503's Off-Season Project

I like how organized everything is, even on a congested electronics board.

I also like how the 80/20 'standoffs' are tapped for bolts for easy attachment of the outer side rails. Even better is that these 80/20 pieces could easily serve as chain tensioner mounts for a light-weight chain tensioner, should the design not have an auto-tension system.

Only criticism (and it's small!): I don't think it has enough ground clearance to traverse an elevated field component, nor is this particular design versatile enough to easily change a component to allow it to.

Great work!

19-12-2008 11:33

Aren_Hill

Re: pic: 1503's Off-Season Project

depending on the type of field element, I believe this design would do just fine with ramps and the like. Ground clearance isn't quite the defining factor as the frame will almost always be sitting on one of the 12 wheels present. Also depending on how they accomplished the lead in and trail exposure of the wheel this could climb very well

19-12-2008 12:18

Pat Fairbank

Re: pic: 1503's Off-Season Project

I'll preface this post by stating that I don't mean any criticism at all to AndyMark shifters; we've used them unmodified in a few of our robots with great success. Most of the "improvements" we've made are because of stuff we want to do which most teams don't (such as shift at 60 psi and shift two transmissions with one cylinder), or just to make manufacturing easier for our student shop, since, with the exception of the 12 and 40 tooth gears, this design requires gear and shaft sizes that AndyMark doesn't offer.

That being said, here's a list of the issues we encountered and the solutions we came up with. Here's an Inventor screenshot of the shifting interface.

Issue #1: The split pins connecting the dog and shifter block to the shifter shaft (the small shaft that slides inside the output shaft) are hard to add/remove during maintenance, and tend to shear when shifting at 60 psi.
Solution: Our shifting shaft has a #8-32 thread on one end which screws directly into the dog (and is prevented from unscrewing by thread-locking compound), and a #10-32 thread on the other end which goes through the 3/16" bearing which is held on with a nut. This has the added benefit of being much easier to machine, since you don't have to drill perpendicular holes in a tiny shaft.

Issue #2: The AndyMark dog gear is difficult to machine, as are the surfaces on the gears with which it mates.
Solution: Replace the dog gear with a piece of 1/4" steel square bar, 1" long, with a hole in the middle tapped to #8-32. Since all our gears come with hubs that we have to machine off, leave 1/8" of the hub and cut a cross into it slightly wider than 1/4".

Issue #3: We need longer equivalents to the AndyMark output shaft, which is difficult to machine (for our students who do the work on manual lathes, anyway) since a hex shaft needs to be parallel-turned to round along most of its length and then have a keyway milled into it.
Solution: Use pre-keyed 1/2" hex shaft, and just mill a slot into it where the shifting dog needs to go. To space our driven gears apart like the hex in the original shifter does, we instead have a ring-shaped spacer that fits around what's left of the hub of the smaller gear, and rubs against the larger gear (right now it's aluminium, but the plan is to make it out of bronze later).

Issue #4: The tiny screws that hold the shifter block on to the 3/16" bearing are very difficult to access on the robot when the transmission needs to be disassembled for maintenance. Also, the 1/4"-28 thread tends to strip from the non-axial forces when we shift both transmissions with one cylinder.
Solution: Replace the aluminium shifter block with a custom steel one (not pictured). The screws that hold the 3/16" bearing in now come in from the top, and it's their shank that holds the bearing in instead of the head.

I don't remember exactly, but it was something like once or twice over three competitions. They weren't anywhere near loose enough to come off the sprockets, but enough to be occasionally contacting the ground.

19-12-2008 12:39

Brandon Holley

Re: pic: 1503's Off-Season Project

Pat,
This looks great! Kudos on a successful pre-season project that will pay dividends come the build season.

Just a quick question about the banebots wheels, because we were very strongly considering using them (we ordered several in different durometers, etc.)... Did you do any kind of testing with them? Such as, seeing if the hex within the polypropylene hub would strip out? Or if the urethane shears off when being pushed sideways?

We were in the process of designing tests to determine if these wheels would be able to handle the rigors of FIRST season.

Thanks alot,
Brando

19-12-2008 13:24

s_forbes

Re: pic: 1503's Off-Season Project

Thanks for the great details about the gearbox, it's a very clever design. The simplicity of the engagement mechanism seems like such an obvious design now, it's strange that this is the first one like it I've seen.

19-12-2008 13:27

computerboi1503

Re: pic: 1503's Off-Season Project

We've really only driven it around the hallway a few times, just to see if everything fits and works as planned. There is still no shifting hardware, but everything else is there.

On the middle wheels, we are noticing some notable peeling on the rubber itself, only from maybe 15 minutes of usage, on a smooth concrete-like surface. Also, these wheels like to pickup everything and anything on the concrete that we run it on. We have yet to do any heavy testing such as being pushed sideways or anything. We also have yet to run it on carpeted surfaces.

At any rate, we shall see what these wheels stand up to. I personally love the fact that we have finally built a robot that actually rolls smoothly

Also, the centers of the wheels are machined so the holes are enlarged, and we simply have spacers and bearings riding on an axle on the corners, and a hub for the centres driving the other four wheels. Thus, we are not concerned of stripping the drive configurations that the wheels are shipped with because we dont directly apply power to the center of the wheels.

19-12-2008 14:13

Pat Fairbank

Re: pic: 1503's Off-Season Project

Now that you mention it, I remember some issues with the Banebots wheels that I should share. We ordered some keyed and hexed wheels to test with, and weren't very happy with the quality of the wheel manufacturing. Some of the hexes were visibly off-centre, and produced as much as 1/8" of runout when mounted on hex shaft. We also found that some of the molded surfaces weren't always perpendicular or flat. So we gave up on the idea of being able to drive the wheels directly by hex or keyway, and instead made a fixture consisting of a 3-7/8" circle milled into a block of aluminium. We clamped each wheel into the fixture and ran a CNC program to mill out the wheel centres to 7/8" and drill a bolt hole circle matching the sprockets, using the OD to locate. So, our centre wheels are driven by the shaft via the keyed hub they are bolted to, and our front and back wheels are driven by the sprockets they are bolted to (and are mounted on dead axles).

As far as the tread material goes, I'm not concerned about it shearing off. We cut a wheel in half, and the outside of the molded plastic wheel has a section in the middle which sticks up into the tread (i.e. the tread/wheel interface is not flat). The adhesive also seems to be ridiculously strong.

30-12-2008 02:50

sanddrag

Re: pic: 1503's Off-Season Project

Any more updates on how the Banebots wheels are holding out? How's the handling and wear?

30-12-2008 12:20

Boommaster713

Re: pic: 1503's Off-Season Project

after a close look at how your electronics are laid out I have a few questions

1. On the cRIO I noticed that the first and last boxes (cant remember the name) are connected in series, I am wondering what purpose that has?

2. Have you noticed a performance issue with how your robot is so off balance, and would a sliding battery cause any additional problems with robot control?

30-12-2008 15:13

computerboi1503

Re: pic: 1503's Off-Season Project

We have not been in the shop, due to the Christmas Break, since teh 19th, and even then there were very few hours on the robot. We have noticed a little peeling on the center wheels though, but no loss of traction as of yet. We still at this point have no real tests, (such as being pushed sideways, or any carpet testing,) as of yet.

1. The modules that are connected in series is just to route power to both on one spot on the PDB.

2. The end with the battery is ALWAYS on the ground, and we have had next to no use on the front wheels, so its almost like driving a four wheel drive base rather than six. I am sure that when we get into serious testing we will balance this out with some weights, as we would like it to weigh 120 pounds during our testing.

Go ahead and fire more questions if you have any!

Nick

31-12-2008 02:01

Tanwad11

Re: pic: 1503's Off-Season Project

Very nice and clean set up of your electronics.

Are most teams planning on adding lexan covering to their systems this year? Don't know if it'll be as much of a priority because of the better protected Jags.

31-12-2008 11:29

computerboi1503

Re: pic: 1503's Off-Season Project

I personally would want protection of some from of the analog and solenoid breakouts, wether it be the cRIO mounted sideways in the bot and covered with lexan or put in a lexan box... either way, those guys are a great target for another 'bot to come along and slice it in two. Every year our robot's electronics have been completely covered in lexan/polycarbonate with no overheating issues of any kind. I really reccomend that many teams do this, as I saw countless robots being disabled for a match after having their electronics penetrated by another robot, usually with fatal results.

Thanks for the great comments guys! Look out for us in FLR, GTR and the Championships!

Nick

31-12-2008 11:37

-e-

Re: pic: 1503's Off-Season Project

yeah but don't forget to allow air to flow through or you will over heat your board and once ya do that you are finished...

oh and labeling wires is a huge help!

31-12-2008 11:48

Racer26

Re: pic: 1503's Off-Season Project

Lexan armor is great if you can afford the weight. Historically 1075 hasn't built a bot that had room in the weight budget for it... we've only had 1 major mishap where a radio connector got ripped off the RC in 2007, and a couple minor ones where a pwm got pulled in 5 seasons of on-and-off season events.

31-12-2008 14:27

computerboi1503

Re: pic: 1503's Off-Season Project

Lexan armour is fantastic, and I can attest to that.

During Ra Cha Ruckus on '07, I operated the arm on our robot, for anyone who is familiar with our Rack n Roll robot. Anyways, we forgot to put one of the lexan shields on that covers our main power breaker.... and I managed to drive the claw straight into it, shutting our robot off for the match... but our PDB was dead at the start, so we had virtually no base control during the match, so I guess there was not much of a change in results.