Weighing the Robot

[fhsteam613]

Last year we were a little bit more than 30 lbs overweight . The guys at the weighing station said that in all their years they have never seen anyone so horribly overweight . 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

[Cooley744]

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

[gurellia53]

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.

[EricH]

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).

[Laaba 80]

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

[MrForbes]

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!

[rachal]

When you CAD, set all of your material properties

[Gertlex]

Originally Posted by rachal

When you CAD, set all of your material properties

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

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

[rachal]

Originally Posted by Gertlex

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

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

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.

[AustinSchuh]

Originally Posted by Gertlex

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

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.

[JB987]

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...

[MrForbes]

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.

[MasterMkanik]

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!

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.

[Otaku]

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.