# Ri3D 'Snow Problem 2019

#42

#43

gotchya

#44

Cool design. It looks like a spring is below the top of the at the end of the climb .
Is this ok or does entire robot have to be above the top level? Technically, according to the rules, this robot is supported by the top of the HAB platform and its bumpers are above that level. Did I interpret that correctly? If so, then how far can a piece hang down below that? Can it hang down so it’s within a 1/16" of the bottom platform?

#45

@Hadi379 To address your edit - It’s possible the robot was contacting the front face during a climb, but this was definitely not the case during the vast majority of our testing.

#46

Only the bumpers need to be above the top level. The other stipulation is that the robot is only supported by the top surface of the Platform.

#47

According to the rules, yes. Only the bumpers need to be above that level of the HAB. As long as you are supported by only that level, then the climb should be OK.

Edit: Sniped by Ginger_Power

#48

That’s the only way to read the rules we saw. All that matters are that your bumpers are above the top face and that you are supported only by the top face. That is - yes, some piece of the robot could be just off the level 1 platform and still be a level 3 climb.

Edit: Two others answered before me in less than a minute, but at least we all agree!

#49

I’m not in agreement with the answer to Q50. They are conflating “supported by” with “in contact with”.
Those are completely two different things.
This robot in this video is not “supported by” the side of the HAB when in its final climb state.
Now, the caveat to that is you do not want to leave it up to the judges discretion as to whether they are “supported” by the side so all in all it is prudent to release those grippers so they are not in contact with the side.

If the game designers didn’t want your robot to be in contact with any HAB surface below the level you are trying to climb then they should have just said that.

Simple change to 5.3 makes this better…
“2. the ROBOT is only in contact with:”

#50

We have just released our Robot Walkthrough video! This is meant to give a quick overview/explanation of each subsystem in video form. More detailed information on the designs can be found in the link to the 2019 Robot CAD and also the Technical white paper, both of which were released earlier!

#51

If that becomes an issue, it wouldn’t be too hard to integrate the spring into the 1x1.
YMMV

#52

Whats the weight of your robot Snow problem.

#53

Approximately 110 lbs.

#54

We have a similar style climber and we’re struggling with how to calculate the amount of clamping force necessary to lift our robot. In the video, it said your “hug and tug” climbing mechanism achieved around 200lbs of clamping force. Was 200 lbs plenty or do you think having more would be better?

#55

Here is an example of the calculations we did to figure out what type of forces we needed. One thing to keep in mind is that these are for the static situation, with the robot moving, you want a safety factor, so the 230 lbs is a minimum number. One thing our design provides is that as we winch up the robot, the force of the lift increases the clamp force, similar to how a device such as this works.

#56

Thanks for the quick reply! Our hangup was not being able to find good info for the coefficient of static friction for the clamp on the HDPE. Earlier, you indicated that CoF was 1 with SBR rubber, but in the force balance equation, you used 0.3. Was this intentional or for factor of safety purposes?

#57

We had found some documentation during the build that suggested the CoF would be around 1, but when looking today I couldn’t find it. I used 0.3 as it is the number given on most HDPE data sheets, and should be a worst case number.

#58

You can find the coefficient of friction between the HDPE and rubber by slowly raising an HDPE ramp until a block/piece of rubber starts to slip. You can do some basic trig and find the coefficient of friction given the mass of the sample (make sure you take in account the size/location of COG of the sample if you want super accurate results, since moments are a thing…).

#59

http://www.aspbase.com/assets/files/testing/Coeffcient-Test-of-Static-Friction.pdf

Here is the source for coefficient of friction ~1 for dry rubber and HDPE. It’s possible there is a significant difference for the textured HDPE, but we assumed there wasn’t.