I’m curious where everyone is in their robot weight this year. I’m seeing a lot of similar designs so I’m curious where things are landing in the weight department. These choices below are for just the robot (no battery or bumpers). Since we are just a few weeks away from play, where do you think you will land? If you want to also add how much your bumpers are on their own in a comment below that would also interest me. Thanks!
Robot weight at your first event
- < 80lbs
- 81 - 90lbs
- 91 - 100lbs
- 101 - 110lbs
- 111 - 120lbs
- 120+ we will need to drill a few holes
- Get the hacksaw…
Love the “Get the hacksaw…” choice.
Bumpers should weigh in at about 12lbs, since we have a front bumper gap and use poplar lumber, small steel mounting brackets and dacron sailcloth along with the (hollow) pool noodles.
For us onshape says the robot weighs ~120lb with battery and bumpers, however it does not include wire weight and overestimated the weight of 3dp
you know the robots can be 125lbs?
Regardless of actual weight a safety factor of a couple pounds would probably be a good idea due to scale preciseness.
TBH, I’ve been trying to convince our coach to buy 125lbs of calibrations weights. Both so we can check our own scales, and also so we could bring them to events to detect poorly calibrated event scales for exactly this reason.
What kind of weights are you considering getting? Are they actually calibrated? If they are not actually calibrated, one can take it to a calibrated scale, say at a UPS Store, and write the actual weight on it.
I recently purchased a large postal scale with a remote display capable of going up to 150 lb. To check it out, I put a bunch of barbells on it. I found up to 5% mismatch between barbells that were supposed to be the same nominal weight. The barbells I used ranged from 5 lb. nominal up to 25 lb. nominal. The mismatch was repeatable and consistent.
Event scales come with a set of calibration weights. If you’re not sure the scale is calibrated, ask the LRI to recheck the calibration while you watch.
Now, whether the event floor affects the weight… that’s another story from the FRC Middle Ages.
Are those weights calibrated to some standard? I have used them when setting up the Inspection Station but didn’t pay much attention to them. I will try remember to see how different the two weights are at the events I volunteer at this year.
I don’t know for sure–never seen a cal sticker or certificate for 'em. But, per process, they’re the weights for the event…
I would probably not expect the LRI to admit a team’s calibrated weights as evidence the scale was wrong, TBH. There’s a whole slew of reasons why, mostly dealing with “chain of custody” and “how do we know you didn’t fudge these”. I could be wrong on that, and if there was no evidence the weights were tampered with since their last calibration then I’d expect the LRI would at least reference them against the official weights.
The other item I noted is that in the past, where people stood could affect the scale readings. e.g., if you calibrate the scale with the inspector at the table, and the floor is a hair soft (read: basketball court hardwood, suspended, see also: gym floor), when you get half a team crowded around to see if their robot makes weight or not, it reads slightly off (lighter, usually, I think? could be heavier). Since the calibration started that helps a bit.
Calibrated weights side note: It MAY be in FIRST’s interest to have an annual calibration for their weights. Send 'em all to a cal lab, cal lab marks 'em, certifies 'em, returns 'em, and FIRST loads them with their certs back into the cases. LRIs then need to use the marked/certified weight. But that’s a big job to set up the first time, and another big job annually.
I can only speak for NEFIRST events, but our field kits come with calibration weights.
Yes. Understood. I don’t know what the weights used as calibration weights are originally meant for. If they are meant to be used as calibrated weights for use in a lab (like larger versions of what we had in our high school chemistry and physics labs) they should be good enough. If they are like my barbells, there is no real expectation of accuracy. Perhaps the weights used at weightlifting competitions are calibrated.
Oh no! After such a long break my brain defaulted to the old weight limit. Haha whoops
From McMaster (for example): Legal-for-Trade Grip-Handle Test Weights with Calibration Certificate
The Calibration Certificate is definitely key, otherwise you’re just some random person bringing in some random weights, and as @EricH says, you could just be fudging the numbers and I would expect an LRI to reject it. I would expect a reasonable LRI to accept a calibration weight with a certificate however. The downside of getting weights with calibration certificates, of course, is that they’re prohibitively expensive.
My understanding is that all FRC scales are all supposed to come with a set of like 2x 20lb/25lb calibration weights, but the advantage to having exactly 125lbs of weights is that if the scale is wrong, you can put the weights on the scale, check the weight, then put the robot on the scale, and as long as they’re the same weight (regardless of the actual value on scale’s read-out) you’re good. This could be especially important in a case where it’s not actually possible to properly calibrate a scale (if for example the scale is broken, or it’s being used on particular types of flooring).
I recall the weights we pulled out of the shipping crates looked like the ones from McMaster you linked. If they are those weights, the ±0.002 lb tolerance for a 20 lb weight (±0.01%) should be more than good enough for FRC applications. I didn’t notice any certificates in the crate but then we weren’t looking for them either. The cost of these weights and the scales they are used with are probably invisible to those who complain about the cost of running events.
We finally got around to attempting to weigh the robot today…best guess with our hokey use of the bathroom scale is still 81-90 lbs. A lightweight. I guess if we had more students, we could have built more stuff? All it can do is pick up off the floor, score low hub, and climb the second rung.
Revision. I voted “111-120” but we are struggling to keep it under 125. Did some swiss-cheesing and some more effective ways to cut ounces. Still need to do more (we’re at 123.5 but (a) need to add a few things and (b) want a 1/2 lb (at least) cushion.
We estimated from CAD but having a lighter drive train the past few years got us out of practice, we haven’t really had to think about weight much since 2017. Mecanum (and now with omni wheels for tracking) is seriously heavy.
The calibration weights used in the PNW district are Class F - 20 kg (Grip-Handle) I do not believe that ours are certified as there are no unique markings on the ones we have.
Note the scale is accurate to +/- .1lbs and reads in .1 lb increments, so the certificate and its added expense is not needed.
Ours got inspected yesterday and weighed in at a solid 79.1 lbs. We did make some small changes to it afterwards which may have added 1-2 lbs but still, its a featherweight.
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