Stress testing a Rhino
 

So, our team did a stress test on the Rhino drivetrain last night:

Slow motion Youtube video of the drop.

We loaded it to the max weight of 120 lbs. and dropped it intentionally on a corner of the drivetrain. We elevated it approximately 9 inches off of the ground, which we believe is a reasonable test and could easily happen when traversing the defensive elements.

Overall, it performed well. There was no bending or damage of any kind. So far, we are happy with the performance.

Re: Stress testing a Rhino
 

Excellent work! Thanks for sharing.

I think the Rhino will receive additional stress tests as the Stronghold season progresses.

Re: Stress testing a Rhino
 

Awesome video!

Has anyone tried T-Boning the rhino chassis to see how it handles that defensive scenario?

Re: Stress testing a Rhino
 

Always good to test and plan for extremes! Something to keep in mind is that your robot can be a max of 120lbs but you have an additional 14lb battery and bumpers that can be up to 20lbs.

I agree with Mike I'd be very interested to see how the Rhino tracks hold up to sideways pushing under defense.

Re: Stress testing a Rhino
 

Total weight was actually about 130 lbs. We ran out of steel tubes after that... We were pleasantly surprised by how solid the rhinos were. (Surprised is a little strong, I generally trust AndyMark to make quality products, but it was still nice to see.)

For anyone wondering, they're tied together with 4 bars of 1010 80/20 extruded aluminum, which is heavier than the REV Extrusion recommended by AndyMark. We already had the 1010 in the shop, REV Extrusion was sold out, and we didn't mind a little extra weight to have fewer worries about how solid base of the chassis was.

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.)

Re: Stress testing a Rhino
 

Watched the video and one thought came into my head... what if it did damage it? Did you have a backup plan in mind? :)

Re: Stress testing a Rhino
 

Better to know now, before competition.

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

This is a good test. Thank you for providing this video. We did some tests akin to a Dukes of Hazard ramp jump, which was less quantifiable than this drop test. We also did a "run it into a wall" test which proved to be successful (no broken parts).

Sincerely,
Andy B.

Re: Stress testing a Rhino
 

Cool test. 9 inches of drop can be a pretty significant amount of impact. What was the surface it was dropped on? Carpet actually does help a bit with distributing the force over a longer time.

Count me in on the T-Bone question/interest. I think those of us interested in this is less about the frame getting bent, and more about the dynamics observed on carpet as well as possibly throwing a track when really high side loads are applied.

Re: Stress testing a Rhino
 

What speed?

Re: Stress testing a Rhino
 

Agreed. This is my primary concern.

If anyone has test video and would like to share, much appreciated!

-Mike

Re: Stress testing a Rhino
 

^ +3 for the T-Bone Test. :)

We will be doing that sometime next week (build suspended by mid-terms now) so if anyone gets results sooner, sharing them would be appreciated.

Re: Stress testing a Rhino
 

One of the reasons we haven't chosen the rhino chassis is because we were afraid of it being T-boned and the belts getting of it.

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

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

Re: Stress testing a Rhino
 

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?

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

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

Re: Stress testing a Rhino
 

Photoshop challenge. :cool:



March, or die!

Re: Stress testing a Rhino
 

here you go

Re: Stress testing a Rhino
 

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

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

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.

Re: Stress testing a Rhino
 

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!

Re: Stress testing a Rhino
 

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).

Re: Stress testing a Rhino
 

Actually what the drop down omins do is allow you to dynamically change your center of rotation on the fly over a large distance. When actuated it makes the pivot point of your robot be about the two traction wheels or section of tread that are still on the ground Instead of in between the wheel set or tank section was on the ground. You don't even have to power them to get this effect. This allows you to spin out of T-bones. They also make turning and aiming easier because there is less scrub making more precise, small movements easier.

Re: Stress testing a Rhino
 

Maybe slightly but not much worse. Its hard to tell without test how much the extra turning scrub will affect it. Evens solution may give you the best of both worlds though If you have the weight and the space.

Re: Stress testing a Rhino
 

This is really interesting to hear. How does AndyMark typically validate a product before it commits to selling it to teams?