Stress testing a Rhino

[Daniel_LaFleur]

Originally Posted by AngryCalculator

Our team has ordered the treads, and I've been a little worried about just the four crossmembers. Although it looked fine in the video, I think a bellypan and/or diagonals would really help.

I'm not convinced a belly pan would help. In fact, it may hurt.
Look at the 11 second mark, that frame looks to flex, which may help in keeping the frame from being damaged.

[philso]

Originally Posted by Daniel_LaFleur

I'm not convinced a belly pan would help. In fact, it may hurt.
Look at the 11 second mark, that frame looks to flex, which may help in keeping the frame from being damaged.

This is the thinking behind the energy absorbing structures in modern cars that allow them to protect occupants better than older cars with "a massive frame" where the forces from the impact are transmitted through the frame to the passenger compartment.

[Racer26]

I can't speak to the Rhino units in particular, but the belts on them look awfully similar to some belts made by Brecoflex that my old team used for several years. They were expensive (read: $150+/belt) and had a tendency to break under heavy side-loading. With all the up and down shock loading of the drivetrain in 2016 traversing DEFENSES, I would be extremely skeptical of any belted drives.

[Malm]

Thank you all for the information!

I am now also very interested in the T-bone test, hopefully we can do it soon if nobody else is able to post results earlier.

Regarding the belts breaking - I am also very concerned about that. We have 2 spares (from our practice chassis), hopefully that will get us through our first regional if they start breaking.

[Andy A.]

Reminds me of one of the coolest pair of videos on youtube (to me, anyways)

Dropping a F-18 Hornet at maximum landing weight from 20 feet up.


In slow moation


Bonus of the F-35C undergoing the same sort of test

[Malm]

Originally Posted by sportzkrazzy

I think Mike is searching for its ability to spin off of a robot playing defense on it not the structural integrity. If a track drive is hit close to its center of rotation it may have issues spinning off a robot playing defense on it creating a death spin type scenario where you cannot drive forwards or backwards out of the Tbone. This results in both robots making circles locking your robot up instead of enabling it to score. A lot of wheeled Tank style robots have had this issue as well. One way to mitigate this is to use low coefficient of friction bumper materials. This decreases the amount of friction between the two surfaces that your robot is trying to slide off of. You could also think of a way to change your center of rotation by dropping an omni wheel. Remember its not a pin unless your robot is up against a field surface so in theory they could do it the whole match.

Quick question to the group:

The middle of the 3 wheels contacting the ground on the Rhino has an 0.15" dropped center. We were planning on keeping our center of gravity roughly over this axle, so when accelerating forward it should drive on the portion of the tread between the the back two wheels and when accelerating backwards it should drive on the tread between the front two wheels, shifting the center of rotation by about 9". Obviously we still need to do the actual T-bone test, but does anyone think that this shift in center of rotation would be significant enough to solve the problem of being permanently locked to another robot?

[Breakaway3937]

Originally Posted by Malm

Thank you all for the information!

I am now also very interested in the T-bone test, hopefully we can do it soon if nobody else is able to post results earlier.

Regarding the belts breaking - I am also very concerned about that. We have 2 spares (from our practice chassis), hopefully that will get us through our first regional if they start breaking.

One of the things you have to remember is how you support the track that is on the ground or the will be impacted during play. If you have a wheel over the backing of every bit of track that touches the ground, the belt has very little room for traverse movement or elongation. Especially since the Rhino Tread has a v groove backing. However, as you remove idler pulleys or wheels from that area, you belt has a lot of room for extension past its length. It can only handle 600 pounds of force, as I have read on the AndyMark website, so the more it extends or deforms, the more force that builds on the tread. Just make sure that if you are using the tread, you make great considerations for hitting the defenses wide open with a 140 pound robot on a section of tread that is not supported. This is probably the number way to break these treads in this years game.

[Bob Steele]

I saw the title of this thread and was expecting something different
I was wondering where you would get a big enough tread mill.....

[Richard Wallace]

Originally Posted by Bob Steele

I saw the title of this thread and was expecting something different
I was wondering where you would get a big enough tread mill.....

Photoshop challenge.



March, or die!

[Bob Steele]

here you go

[Bob Steele]

I guess this would work....zoos actually use these to exercise elephants... Rhino=Elephant?

[sportzkrazzy]

Originally Posted by Malm

Quick question to the group:

The middle of the 3 wheels contacting the ground on the Rhino has an 0.15" dropped center. We were planning on keeping our center of gravity roughly over this axle, so when accelerating forward it should drive on the portion of the tread between the the back two wheels and when accelerating backwards it should drive on the tread between the front two wheels, shifting the center of rotation by about 9". Obviously we still need to do the actual T-bone test, but does anyone think that this shift in center of rotation would be significant enough to solve the problem of being permanently locked to another robot?

Think about it like this. If a robot Can hit both centers of rotation with the span of its front bumpers will you be able to spin off of it? How hard will it be for a defensive driver to line up on you? You can still experience these issues with a drop center wheeled drive as well. Just some food for thought.

[evanperryg]

Originally Posted by Malm

The sides of the Rhinos are 3/16" aluminum plate with supports every few inches and are incredibly solid, so we are not too worried about T-boning. (That said, we are planning on having full length bumpers and external frame rails to help protect them as well.)

Will the huge amount of grip make T-bones harder to get out of? Plenty of teams have relied on lateral slipping to get out of T-bones in the past (find 118's 2013 reveal video, there's a little clip of drop-down omnis) and the insane traction from the Rhinos may have the exact opposite effect. I'm also curious if a hard lateral impact will shove the tracks off the pulleys temporarily. Unfortunately, we can't test these things in-house, but I really would like to see more of the Rhino Drive so we can get a feel of how they will perform in competition. From what I've seen so far, they are really good with the B/D defenses, but it still begs the question- why aren't tank treads popular, except for games with terrain? If they came with repercussions as significant as their benefits, I could see why they aren't very common. Yet, so far, the Rhino drive has shown pretty much no significant disadvantage versus a traditional tank drive.

[Malm]

Originally Posted by sportzkrazzy

Think about it like this. If a robot Can hit both centers of rotation with the span of its front bumpers will you be able to spin off of it? How hard will it be for a defensive driver to line up on you? You can still experience these issues with a drop center wheeled drive as well. Just some food for thought.

That makes sense. In this case, do we expect the tank treads to perform any worse than drop-center wheels with the same spacing?

Edit: Didn't see evanperryg's response, that answers my question

Thank you all!

[sdcantrell56]

Originally Posted by evanperryg

Will the huge amount of grip make T-bones harder to get out of? Plenty of teams have relied on lateral slipping to get out of T-bones in the past (find 118's 2013 reveal video, there's a little clip of drop-down omnis) and the insane traction from the Rhinos may have the exact opposite effect. I'm also curious if a hard lateral impact will shove the tracks off the pulleys temporarily. Unfortunately, we can't test these things in-house, but I really would like to see more of the Rhino Drive so we can get a feel of how they will perform in competition. From what I've seen so far, they are really good with the B/D defenses, but it still begs the question- why aren't tank treads popular, except for games with terrain? If they came with repercussions as significant as their benefits, I could see why they aren't very common. Yet, so far, the Rhino drive has shown pretty much no significant disadvantage versus a traditional tank drive.

I think the reason we don't see more tank tread drivetrains is the lack of performance advantage compared to well-designed conventional wheeled drivetrains, while at the same time introducing substantial disadvantages (cost, unreliability, even reduced performance).