pic: 4242 Preliminary CAD 1

[K-Dawg157]

Originally Posted by faust1706

Have you done a stress analysis of this yet? I don't know the material used, but looking at the design, the thought that when you try to lift a stack of totes, your elevator at the top might begin to bend depending on a few factors. I'm a programmer, though. Take this with a grain of salt.

You have a valid point, programmer.

It would all depend on the material being used, and the orientation it was being used in. Also, how high the support from the back is up the side rails would be important.

I did some calculations with an engineer, and we figured it out that the maximum load the robot (assuming 6 tote or 5 tote bucket and noodle capabilities) would be holding, cantilevered at 6' in the air, would be ~400 foot pounds...

Make sure your material is all good and the supports will hold it and you should be set.

[eddie12390]

Originally Posted by K-Dawg157

I did some calculations with an engineer, and we figured it out that the maximum load the robot (assuming 6 tote or 5 tote bucket and noodle capabilities) would be holding, cantilevered at 6' in the air, would be ~400 foot pounds...

Given the configuration of this robot, what does the CoG look like at that point? It seems like you'd have to have a fairly hefty counterbalance to keep it from faceplanting.

[faust1706]

That was really my only fear for robots this year as far as damage; could they handle the torque of picking up a stack of n totes + the bin and not get deformed over the course of the season?

Side note: I think demos of robots this year will actually be pretty cool if they can either lift a lot of weight, or stack autonomously, or both.

There is also the concern of center of gravity, as eddie12390 has pointed out. I haven't been around frc long enough to see robots fall over because of game piece weight, if it has even ever happened.

[Christopher149]

Originally Posted by faust1706

There is also the concern of center of gravity, as eddie12390 has pointed out. I haven't been around frc long enough to see robots fall over because of game piece weight, if it has even ever happened.

My freshman year (2008), at least one robot fell over at the Wisconsin Regional (and IIRC, almost tried to fall out of the field). This was a combination of height and trackball weight.

[asid61]

Originally Posted by K-Dawg157

You have a valid point, programmer.

It would all depend on the material being used, and the orientation it was being used in. Also, how high the support from the back is up the side rails would be important.

I did some calculations with an engineer, and we figured it out that the maximum load the robot (assuming 6 tote or 5 tote bucket and noodle capabilities) would be holding, cantilevered at 6' in the air, would be ~400 foot pounds...

Make sure your material is all good and the supports will hold it and you should be set.

400ft lbs?
For totes cantalievered like 14" out from the front of the robot, I only get arounf 70ft-lbs for a 60lb load. I though you were only supposed to consider the X-distance, not the Y height for torque caused by gravity.
Could you please share your calculations?

[apm4242]

I really like the ramp idea. How much have you prototyped that/ how well does it work?

Thanks. To answer your question - not at all. It's on the to-do list. We have some .25" clear acrylic laying around and will try this soon. We may have to put a single driven wheel at the bottom corner of the ramp to prevent totes from leaning against us rather than sliding off at the end. The downside of the ramp idea is that if we're feeding totes to the field, we're not stacking...

Other stability questions

The plan is to put hefty weights in the back. Probably around 25lbs, maybe more depending on testing. The material is aluminum t-slot. It should be fine but we'll probably move the support a bit higher. Either way, we don't plan to lift more than 3 totes or 2 totes/1 bin if hooked from the long edge OR 2 totes or 1 tote/1 bin if hooked from the short edge.

Thanks for all the replies!

[Orion.DeYoe]

Originally Posted by K-Dawg157

You have a valid point, programmer.

It would all depend on the material being used, and the orientation it was being used in. Also, how high the support from the back is up the side rails would be important.

I did some calculations with an engineer, and we figured it out that the maximum load the robot (assuming 6 tote or 5 tote bucket and noodle capabilities) would be holding, cantilevered at 6' in the air, would be ~400 foot pounds...

Make sure your material is all good and the supports will hold it and you should be set.

Um... You need to check those numbers...
The load is not cantilevered the height of the elevator. The number you should be using for your moment arm is the horizontal distance from the center of the carriage to the COG of the load (something like 12-16 inches). Multiply that distance by the weight of the load (60 lbs we'll say) and you get something like 720 - 960 in*lbs (60 - 80 ft*lbs).
It appears everything is made from 1x1 8020 extrusion. It's pretty beefy stuff and the elevator appears well-supported. I wouldn't anticipate anything horrible happening to it.
I probably would make the carriage taller though (as someone else mentioned).

[K-Dawg157]

Originally Posted by K-Dawg157

You have a valid point, programmer.

It would all depend on the material being used, and the orientation it was being used in. Also, how high the support from the back is up the side rails would be important.

I did some calculations with an engineer, and we figured it out that the maximum load the robot (assuming 6 tote or 5 tote, bucket and noodle capabilities) would be holding, cantilevered at 6' in the air, would be ~400 foot pounds...

Make sure your material is all good and the supports will hold it and you should be set.

EDIT:::

I have realized my mistake... I was assuming the wire would be pulling from the back of the robot, and the bottom tote would be at the top of the "pillars". I was calculating the wrong Moment of Inertia and wrong placement... I'll redo that.

Sorry for the confusion.