Team Cosmos - Angry Accountant - A New Beginning.

[satacoy]

Hey Zac,

First, I'm tickled that people are still using the KE calculator.  It's quite possible that the units are wrong, I faintly remember there being some debate on the proper units back in the day.  I'll see if I can dig up the old Delphi Forum posts on it.  Eventually it seemed everyone agreed they were correct, and I believe that I got the math and units out of Machinery's Handbook, but it's always possible that it's wrong.

Secondly, it was great chatting at Motorama, but we've met before, back in the day.  I distinctly remember taking this picture:



Pete - Team Cosmos

[zacodonnell]

After re-reading my post (that I made well after I should have gone to bed) I realize my phrasing was bad. The math on the calculator works fine, it's just the label on the screen that I think is wrong. The KE calculation seems to be ok too.

You're right, we did meet way back then after Solaris beat up on my bot Scurrie. Such a long time ago now.

-Zac

[satacoy]

My phrasing was bad as well, I realize you're only talking about the unit label I'm using.  And my memory isn't that good, I remember talking to you in '07, but I don't remember fighting Scurry.

I couldn't find the old Delphi thread on the calculator.  I'm not sure if it was in the SubLight forum, the Battlebots forum, the RFL forum, etc.  I remember Eric Scott being pissy about the calculator, but then he was pissy about most things. :-)  I did get a kick while searching the forums on seeing old names and topics pop up.

Once I'm back in Boulder I'll dig out the handbook and see if I can understand why I used that label.  I bet you're right about it being off, I just want to look at the source one more time to see if I had a good reason.  I think I wrote that original calculator in like a day, didn't know javascript or the math behind KE, but just ran with it and it seemed to work.  The original version would only work on IE, if I remember correctly.

Pete - Team Cosmos

[satacoy]

I found some time to crack open the Machinery's Handbook to see if I can make sense of the units.  According to the handbook, there are three types of Moment of Inertia calculations typically used in engineering:  Moment of inertia of plane area, Polar moments of inertia of plane areas, and polar moments of inertia of masses.  I followed the equations for that third kind, which are specified to be used in equations involving rotational motion.

For this type of calculation, the units are described as thus:  "If units are in the foot-pound-second system, the units are ft-lbs-sec^2".  That does differ than the label that I give it on screen of "fp/s^2".  I abbreviated this "ft lb/sec^2" on the original version.  According to the above quote, this would properly be labeled as "ft-lb-sec^2", or something similar.  This is equivalent to slug-ft^2.

But, that doesn't agree with your findings of a timeless unit.  The other two types of MOI appear to have units of Inches cubed.

So, I'm not sure what the right answer is.  I'll update the page to reflect ft-lb-sec^2, since that matches more closely my source material.

Pete - Team Cosmos

[zacodonnell]

Thanks for digging in Pete. It is a useful tool regardless, and I've been using it for benchmarking robots for years. In fact, that and the online metals weight calculator (which also only worked in IE) were the only two bookmarks I had in IE for a long time. Now that I've got real CAD and you have updated this I can ignore my IE entirely

-Zac

[satacoy]

I feel good knowing that I've eliminated one small reason to keep IE around!  :-)

Pete - Team Cosmos

[iidrushii]

Mr. Pete. It was a pleasure going up against Angry Accountant with Odium this past AVC. One of the things that really surprised me was just how hard that bot was to damage. I may have to look into an aluminum unibody design myself.

Just one question if you don't mind. Going back a few pages, it looked like you said the weight of the chassis w/o wheel guards or top cover was a little over 3oz. Is this still the case in your current iteration?

[satacoy]

Hey David (I think I have the name right),

I would have to rely on that older post.  I haven't changed anything significant on Angry since this last build, and 3oz for the main frame sounds about right.  She may not hit super hard, but she has yet to break after 3 or 4 competitions.

It's a real challenge to get an all aluminum frame, dead shafts, and indirect drive on all motors into one pound.  When I started on this build, I intentionally went all aluminum just for the challenge.  I think you could make a similarly resilient bot more easily using a mixture of materials.  If I had to do it all again, I'm not sure I'd bite off the same challenge.  It was a lot of work and anguish.

Pete - Team Cosmos

[iidrushii]

A lot of work and anguish you say? Sounds like something I'd do

Thanks Pete