Weighing the Robot
 

Last year we were a little bit more than 30 lbs overweight :yikes:. The guys at the weighing station said that in all their years they have never seen anyone so horribly overweight :ahh:. Needless to say, we spent the next day and a half tearing everything we possibly could off of our robot.

In an effort to thwart the repetition of past events, we would like to find a way to weigh our robot as we go along. I was personally looking into buying a scale meant for people in wheel chairs, but then i found out they run between $450-2,000. There has got to be a cheaper way to weigh the robot without dishing out so much money. Just to clarify, I am looking to weigh the robot as a whole, not one part at a time. Any methods or general ideas are welcome!

Thank you,

Evan Shegoski

Re: Weighing the Robot
 

drive your robot into publix and put it on the scale! lol

Re: Weighing the Robot
 

Last year we were able to find someone who owned some car scales (the kind where there's 4 seperate parts, 1 for each wheel). I assume they were very expensive, but if you know anyone who is a mechanic or works with cars, see if you could use their scales.

Re: Weighing the Robot
 

For starters, weight one part at a time and add them up. For sub-assemblies, try a fish scale. Get one that can take a lot of weight. For the full robot, use a bathroom scale with something on top to hold the robot (if you can).

Re: Weighing the Robot
 

Our rookie season we didnt concern ourselves about weight until the last day or so. We knew a person that had a scale used for weighing larger shipments, so we borrowed it. We found out we were about 40 lbs overweight! That night we had three people just going at it with hole saws getting rid of weight. Our robot was almost completely clear that year and the holes were straight, so it really didnt look to bad. We later named it the "Holey Roller". We got to the competition and found that we were JUST over. We took a sawzall to the back of it, which we now call the shotgun hole, or the battle wound. We got it under, but if we would have kept track of weight, we could have avoided all that. Ou next year we did, and were about 20 lbs under. Weight does matter, and sorry taking out white space in the code does not really work.
Joey

Re: Weighing the Robot
 

Start out the season by learning how to calculate the weight of parts, such as aluminum and steel and plastics and whatnot.

Aluminum weighs 0.10 pound per cubic inch.

Steel weighs 0.28 pounds per cubic inch.

Plastics mostly weigh about 0.05 pounds per cubic inch.

Weight the other parts like motors and transmissions and chains and stuff on a small scale...are there any in your science rooms? or the mail room?

Make a weight budget, starting with the chassis and electronics and pneumatics, the stuff that HAS to be on the robot. Then figure out how much weight you have left over for the rest of it, and if your design weighs too much, then you need to change your design before you start building it!

Re: Weighing the Robot
 

When you CAD, set all of your material properties :rolleyes:

Re: Weighing the Robot
 

I have, and solidworks refuses to tell me the mass of multiple parts in an assembly at once. :confused:

And I don't put the bolts in my assemblies.

Re: Weighing the Robot
 

If you are at a school you most likely have a doctor's scale in a nurses office or in the phys. ed. dept. for wrestling, etc...you can actually weigh the front of your robot (with wheels resting on boards or stock metal laid across the base plate you stand on) while the rear wheels rest on a stack of stock/ boards on the floor and level with the front rests...record the weight minus the boards/stock that was on the scale's base plate and then turn the bot around carefully and weigh as you first did (minus the support stock/boards weight of course)...just add the two weights up and you are set! We have always been within a half pound of the expensive scale used at the competitions...this is of course a way to tell total weight but it is better to weigh and record components before you assemble and again a typical scale will get you decent weight information...

Re: Weighing the Robot
 

We usually set two 2x4s across a medical scale, set it to zero, then set the robot on, and it reads pretty much exactly what the scales at regionals do.

Re: Weighing the Robot
 

Two years ago (Aim high) we were forty pounds overweight three days before ship date, we litteraly took a sawsall and cut two feet of our robot, as well as taking out every other bolt. remember to account for all your nuts, bolts and washers as well!

Re: Weighing the Robot
 

We bought a wrestling scale. Then we put two Aluminum 2x4 box extrusion bars across it, and zeroed it. Once that's done, you're left with a nice little platform to put the robot on.

Re: Weighing the Robot
 

in years past, we borrowed the scale from the wrestling team, put a couple 2x4s across it (for the weels to be on), zeroed the scale and then put the robot on. This year, we invested in a scale our own so we won't need to borrow one anymore.

Re: Weighing the Robot
 

675 calculates (egads)

we also use a bathroom scale to verify. Works well for us. Last year, before ship, we were just under our max height, just under our max dimensions, just under max weight. It owned.

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I forgot to mention how my team weighs stuff :P

We have a combination bed lift/scale that we have had on permanent loan from our high school's nursing classroom for the past few years. It works quite nicely via slinging the robot in rope or some such.

Re: Weighing the Robot
 

Ah, sorry, I use Inventor. Our mentor claims Solidworks can do that, but I've never used it, sorry...

For physical measurements, we use a bathroom scale and a force plate that's part of our mentor(physics teacher)'s classroom materials.

Re: Weighing the Robot
 

I don't know if it does work, but I saw my host father that hug the doggy and scale and just minus his weight..

If it is not that heavy maybe you can try this too. My team did it but I don't remember how they did it.. I will learn it for you tomorrow..

Re: Weighing the Robot
 

If medical or athletic scales are not available, there is one simple method that we have used in the past. Take your robot down to the nearest parcel shipping store (FedEx, MailBoxes Etc., UPS Store, and others). Tell them what you are doing, and ask if they will weigh your robot on their shipping scales. It is so different from what they usually are asked to do, that most of them are more than glad to help.

-dave




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Re: Weighing the Robot
 

I might just convince my team to do this for the hell of it. Not to mention the publicity.

Re: Weighing the Robot
 

Team 228 has two scales for weighing robots/parts, a 150-lb scale and a 400-lb scale. Here's a link to the 400-lb scale (which is the one we primarily use) that we have, which Staples sells for $150.

http://www.staples.com/webapp/wcs/st...plesZipCodeAdd


Like the previous posters, we just add on two cross members of aluminum and re-zero the scale, then weigh the robot.

Re: Weighing the Robot
 

We do a combination of ideas already mentioned. We keep track of individual weights right from the start as we check the kit of parts. The wrestlers have an awesome digital scale that they let us use.

Last year our robot weighed 119.6 pounds when we loaded it into the crate. And it weighed 119.8 pounds when it was checked at competition.

Moral of the story..... leave room for error.

Cheap Scales
 

Hi Guys,

Need an inexpensive scale? Try this for $49:
http://www.northerntool.com/webapp/w...7409_200307409

It only goes to 110lbs, but that should probably be a good goal anyway ...

They have scales that do more weight - search on "Hanging Scales"

Re: Weighing the Robot
 

We just use a bathroom scale and tip the robot up on one edge, balancing it with one finger, While this is admittedly kind of dicey, it is accurate enough so that we have a good idea whether we are legal or not. When we have gone to a scrimmage or regionals for an official weigh in, we generally aren't to far off the mark, and we haven't had to shell out $$$ for a pricey scale, or drive to a different location to get an estimate of weight. Quick and cost effective.:)

Re: Weighing the Robot
 

I have a theory for weight management for the robot. In the shop the robot usually weighs in OK, the problem is when we unpack it is mysteriously over weight! I think the robot does some eating while at drayage or on its FedEx trip. Influenced by our heavy pizza eating during build the robot makes poor dietary choices causing it to gain unwanted weight. This year i will weigh the robot on the scale in the trainer's office. I think the robot will get jealous of the featherweight wrestlers and will suck it in as to not be over weight. To aid in the shipping process I plan on hanging a poster of the new food pyramid and hope for the best!

Best of luck everybody and think thin!

-Jordan

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scales in the school cafeteria

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Last year we were 0.8 pounds under the maximum weight. We calculated just by parts.. We took alot of weight off just to be safe.

Re: Weighing the Robot
 

Wrestling Scales and Shipping Scales here at the university.

Re: Weighing the Robot
 

We use two identical bathroom scales, putting one under each end of the robot. Add the two readings and we have the weight of the robot. It's not perfectly accurate, but usually close enough for us.

Re: Weighing the Robot
 

In 2006 we used four old bathroom scales (one in each corner) and we were off by about 20lbs (thought we were ~5lbs under, and really were 15lbs over). Last year, we used a large scale a parent had, stuck a sheet of plywood on it, zeroed it, and then placed our robot on it. We thought we were tenish under and really were five under. I think part of the issue in 2006 was that we used freshmen to zero our scales (I'm not kidding, we had freshmen who new their current weights very accurately [from sports] and used them to zero our scales), and since the human body fluctuates so much (as any wrestler can tell you), our zeros were all kind of iffy.

Re: Weighing the Robot
 

Yes, Team 766 puts a board on a scale, zeros and loads on the robot. Also, if you weld the robot, remember the extra metal. We were able to gain space and lose quite a bit of weight just by angle grinding down our aluminum welds.

Re: Weighing the Robot
 

I have found that you can hide the parts that you don't want to mass, and then unclick the check box that includes hidden parts in the mass. Not exactly the cleanest way to do it, but it gets the job done. Select the entire assembly (That should show up as one item in the mass list if you are doing this correctly) when you do this.

My preferred method is to just mass each part one by one, and then add the masses up in your head. I am just too lazy to hide the other parts.