pic: 1503's Off-Season Project

[Aren_Hill]

Originally Posted by JesseK

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.

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

[Pat Fairbank]

Originally Posted by s_forbes

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.

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.

Originally Posted by s_forbes

How often did you have to change out chains on your 08 robot, and how loose did they get before you changed them?

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.

[Brandon Holley]

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

[s_forbes]

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.

[computerboi1503]

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.

[Pat Fairbank]

Originally Posted by Brandon Holley

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?

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.

[sanddrag]

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

[Boommaster713]

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?

[computerboi1503]

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

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.

Boommaster713
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?

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

[Tanwad11]

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.

[computerboi1503]

Tanwad11
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.

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

[-e-]

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!

[Racer26]

Originally Posted by computerboi1503

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

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.

[computerboi1503]

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.