paper: 2014 HOT Tech Notes

[Adam Freeman]

Originally Posted by MrRiedemanJACC

Adam, The step file looks great. Not so sure I'm glad I saw this, I won't be getting much sleep now!

It always amazes me how well designed your robots are and how you can push something right to the limit. The first thing I noticed is that you don't direct drive any of your wheels on the drivetrain. Is there a specific reason for that? Or do you just want to keep the weight of your Cims and gearbox centered?

Also, I am impressed with the 9 mm belts, seems like that is just too close to breaking, but I like that you were able to do that.

In the model it looks like you raised the outerwheels about 1/8"? Is that what you went with or did you need more and shaved the wheels a bit?

Thanks for posting this!

We've used this chassis setup for a couple of years now, so most of it just carries over from year to year. At the start we decided that it was easier to leave the gearboxes centered for packaging and CG purposes. At this point we are comfortable with the gearing and chain/belt routing that we've just left them there. It helps us get a jump start on the season knowing we can get a chassis design solidified quickly so we can move on to more game specific components of the robot.

We actually switched from the 9mm belts to 15mm belts after we broke a belt practicing before the season. We had quite a bit of practice time on that belt and only one side broke, so I would guess something might have happened to that belt when it was re-installed (we had just replaced wheels before it failed). We ended up using 15mm kevlar re-inforced belts to ensure that we didn't have any drivetrain issues. We had the space and weight, so better safe than sorry.

The only drivetrain issue we experienced this year was picking up some debris in the drive that flipped the belt over and shredded it.

We stayed with the 1/8 raise on the outside wheels. We didn't shave the wheels, but the turning performance did increase as the outside wheels wore down. We had some issues throughout the season with popping the main breaker, which I'm sure the turning scrub had quite a bit of influence.

Overall we weren't extremely happy with the chassis performance from an agility standpoint, getting out of t-bones, avoiding defense, etc. We will probably do a complete re-evaluation of the chassis size, shape, # of wheels for next year.

[Andrew Schreiber]

Originally Posted by Adam Freeman

We've used this chassis setup for a couple of years now, so most of it just carries over from year to year. At the start we decided that it was easier to leave the gearboxes centered for packaging and CG purposes. At this point we are comfortable with the gearing and chain/belt routing that we've just left them there. It helps us get a jump start on the season knowing we can get a chassis design solidified quickly so we can move on to more game specific components of the robot.

We actually switched from the 9mm belts to 15mm belts after we broke a belt practicing before the season. We had quite a bit of practice time on that belt and only one side broke, so I would guess something might have happened to that belt when it was re-installed (we had just replaced wheels before it failed). We ended up using 15mm kevlar re-inforced belts to ensure that we didn't have any drivetrain issues. We had the space and weight, so better safe than sorry.

The only drivetrain issue we experienced this year was picking up some debris in the drive that flipped the belt over and shredded it.

We stayed with the 1/8 raise on the outside wheels. We didn't shave the wheels, but the turning performance did increase as the outside wheels wore down. We had some issues throughout the season with popping the main breaker, which I'm sure the turning scrub had quite a bit of influence.

Overall we weren't extremely happy with the chassis performance from an agility standpoint, getting out of t-bones, avoiding defense, etc. We will probably do a complete re-evaluation of the chassis size, shape, # of wheels for next year.

Was this a VP belt that snapped? I ask because we ran belts on our intake this year and ended up having to replace every single VP belt at least once. We had one non VP belt from a different supplier (SDP-SI?) and it survived the entire season. Trying to see if our experience was unique or if others have seen that the VP belts have a shorter lifetime than those of other suppliers or if there was something different between the runs.

* And anyone who is worried, VP belts are probably fine for anyone who does a sane season. 125's was NOT sane.

[DampRobot]

Originally Posted by Andrew Schreiber

Was this a VP belt that snapped? I ask because we ran belts on our intake this year and ended up having to replace every single VP belt at least once. We had one non VP belt from a different supplier (SDP-SI?) and it survived the entire season. Trying to see if our experience was unique or if others have seen that the VP belts have a shorter lifetime than those of other suppliers or if there was something different between the runs.

* And anyone who is worried, VP belts are probably fine for anyone who does a sane season. 125's was NOT sane.

We had frequent 9mm belt snaps in our drivetrain, and heard similar things from other CA teams.

[Adam Freeman]

Originally Posted by Andrew Schreiber

Was this a VP belt that snapped?

Yes, it was a VP belt.

We ran at least 6 other 9mm VP belts/robot that survived an entire season (2 on intake, and 4 on outer drive wheels).

I'm pretty confident that something else happened to the one belt that snapped. We had just replaced the wheels that afternoon. Right after that, they called me and said the belt broke. I think they tried to roll the belt on to the pulley and cut it, instead of assembling it correctly with the belt on the pulley.

[JohnFogarty]

I've been analysing a lot of drive train design this summer and I've been meaning to ask since watching this year's Einstein matches. Where It seemed your drive had the worst time in escaping t-bone pins. Do you think there is a simple method to improving an 8WD to escape t-bone pins so that the power and robustness of the drive can be maintained.

The drop-down wheels that have begun popping up on various team's drives offers an interesting solution, but I'd just like to hear what you think.

[waialua359]

Originally Posted by JohnFogarty

Do you think there is a simple method to improving an 8WD to escape t-bone pins so that the power and robustness of the drive can be maintained.

The drop-down wheels that have begun popping up on various team's drives offers an interesting solution, but I'd just like to hear what you think.

We had an 8WD setup as well and T-bone pins were a problem at times. Besides the drop-down wheels solution, others employed the "hexagon" shaped frame perimeter. We plan to look at the drop down wheels as our 1st option for next season, if necessary.

[Adam Freeman]

Originally Posted by JohnFogarty

I've been analysing a lot of drive train design this summer and I've been meaning to ask since watching this year's Einstein matches. Where It seemed your drive had the worst time in escaping t-bone pins. Do you think there is a simple method to improving an 8WD to escape t-bone pins so that the power and robustness of the drive can be maintained.

The drop-down wheels that have begun popping up on various team's drives offers an interesting solution, but I'd just like to hear what you think.

I agree with your assesment... I think we were extremely bad at getting out of t-bone pins.

I'm not sure there is a simple solution to the problem. I don't think the issue was only b/c of the 8WD drivetrain setup. I think that the combination of the 8WD, long chassis, rectangular chassis shape, and driver ability all resulted in us getting stuck in a lot of t-bones.

Drop down omnis are becoming more and more common. We entertained adding breifly them during the season (after MSC), but never really pursued it to far. It would have require quite a bit of designing and changes that would have only resulted in marginal gains at Champs.

We actually started running different combination of omni wheels in the offseason that helped a little bit, but we still had issues with pins.

As Glen mentioned, we will probably evaluate different chassis shapes to help lower the chances of a full on side pin. I think it will be a point of focus for our chassis design next season.

I don't think we are ready to add in drop down wheels to our drive system. Teams like 469 and 254 did pretty well without them on a standard 6/8WD setup. I'd like to see more of a square chassis setup next year and some better driving to avoid defense. We haven't entertained switching to 6WD much in the past couple years, but it might be something to look into next year.

[AdamHeard]

Originally Posted by Adam Freeman

I agree with your assesment... I think we were extremely bad at getting out of t-bone pins.

I'm not sure there is a simple solution to the problem. I don't think the issue was only b/c of the 8WD drivetrain setup. I think that the combination of the 8WD, long chassis, rectangular chassis shape, and driver ability all resulted in us getting stuck in a lot of t-bones.

Drop down omnis are becoming more and more common. We entertained adding breifly them during the season (after MSC), but never really pursued it to far. It would have require quite a bit of designing and changes that would have only resulted in marginal gains at Champs.

We actually started running different combination of omni wheels in the offseason that helped a little bit, but we still had issues with pins.

As Glen mentioned, we will probably evaluate different chassis shapes to help lower the chances of a full on side pin. I think it will be a point of focus for our chassis design next season.

I don't think we are ready to add in drop down wheels to our drive system. Teams like 469 and 254 did pretty well without them on a standard 6/8WD setup. I'd like to see more of a square chassis setup next year and some better driving to avoid defense. We haven't entertained switching to 6WD much in the past couple years, but it might be something to look into next year.

This is all conjecture, but it looks like your chassis might have the ability to twist some vertically.

I've had a running theory for a while that a chassis such as that gets shoved into the carpet a bit odd under high defensive forces, contributing to the "locking up" affect.

Any thoughts?

[Andrew Schreiber]

Originally Posted by AdamHeard

This is all conjecture, but it looks like your chassis might have the ability to twist some vertically.

I've had a running theory for a while that a chassis such as that gets shoved into the carpet a bit odd under high defensive forces, contributing to the "locking up" affect.

Any thoughts?

Could be a similar effect from what 33 noticed in 08 with the impact chassis rigidity had on their ability to turn (http://www.chiefdelphi.com/forums/sh...ad.php?t=68307) ?

[AdamHeard]

Originally Posted by Andrew Schreiber

Could be a similar effect from what 33 noticed in 08 with the impact chassis rigidity had on their ability to turn (http://www.chiefdelphi.com/forums/sh...ad.php?t=68307) ?

Exactly, 100%.

My thoughts are it allows wheels that shouldn't be touching to be forced to touch, causing a wheelbase longer than you're supposed to be on. Combined with the already huge lateral forces from the defender, you're STUCK!

If only a bunch of teams would be willing to mount gopros to the underside of their robots for a few events...

It's interesting how the drivetrain arms race has evolved.

[Andrew Schreiber]

Originally Posted by AdamHeard

Exactly, 100%.

My thoughts are it allows wheels that shouldn't be touching to be forced to touch, causing a wheelbase longer than you're supposed to be on. Combined with the already huge lateral forces from the defender, you're STUCK!

It certainly makes sense that it'd be possible. Got a rigid chassis and a "noodle" chassis handy? Seems a pretty quick test to see if it's easier to tbone a noodle chassis.


I'd also be curious to see how it deals with omni directional drivetrains (mecanums or 33/78 style omnis). Guess I should get drawing FBDs.

Originally Posted by AdamHeard

This is all conjecture, but it looks like your chassis might have the ability to twist some vertically.

I've had a running theory for a while that a chassis such as that gets shoved into the carpet a bit odd under high defensive forces, contributing to the "locking up" affect.

Any thoughts?

If I may request clarification - when you say "twist some vertically", do you mean the chassis bows upwards down the center parallel with the drive wheels due to lack of frame stiffness, and through this bowing all wheel sets are in contact with the ground?

[AdamHeard]

Originally Posted by Andrew Lawrence

If I may request clarification - when you say "twist some vertically", do you mean the chassis bows upwards down the center parallel with the drive wheels due to lack of frame stiffness, and through this bowing all wheel sets are in contact with the ground?

Corners (with respect to the other corners) move up or down as the frame twist.

As for Andrew's request, we only have rigid frames

[MrRiedemanJACC]

We have a flexible chassis from this year, for Andrew's testing! But we used mechanums and therefore we weren't as concerned with frame stiffness. I don't know for sure that is was a good idea though. I think the hard part was that the loading would change on each wheel therefore changing how it drove. We would keep contact with all 4 wheels though. Also in our third event we changed from mechanum to traction and kop wheels (4wd) to try to play more defense for other newer teams. Worked well, but not sure I'd do 4wd drive again. Too much power with 8 motors in the drivetrain and we tripped the main breaker in our last two matches.

It is interesting in the drivetrain wars, how much it has changed the forces the robots receive. There is much more involved than picking motors and gear ratios, the frame is definitely part of it and maybe the Bees were onto something with the Omni wheels. Maybe the frame doesn't need to be as stiff and that weight can be used elsewhere with the omni directional drivetrains. Or you have to go in the other direction of stiffness. It's always a tradeoff.

[Adam Freeman]

Originally Posted by AdamHeard

This is all conjecture, but it looks like your chassis might have the ability to twist some vertically.

I've had a running theory for a while that a chassis such as that gets shoved into the carpet a bit odd under high defensive forces, contributing to the "locking up" affect.

Any thoughts?

Never thought about it that way. I would guess no, since the entire upper structure tubing was mounted through the chassis so I doubt there was much flex in the drivetrain. We had an issue during the build season where the claw was misaligned to the frame....it was almost impossible to flex the frame and upper structure to straighten it. We had to seperate components to get any movement.

But, anything is possible we've never looked at a corner to corner stiffness in the vertical direction.

My honest opinion is that we put ourselves in bad positions during the match which lead to a lot of easy t-bones for the defense.