Weight Advice


#1

My robot is currently 21.2 pounds and is obviously making our 4 motor high speed drive die. I was wondering if anyone has any weight saving tips so we can shed a few. Please keep serious and don’t comment about the horrible wiring or boxes in background(I’m moving). Pictures are attached. Robot is all aluminum except for screws, nuts, and shafts.
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#2

I’m not sure how that is 21.2 pounds, it looks like it should be much lighter. However, I believe that you may be able to remove a few things. On your base, there are a lot of standoffs holding the c-channels together, but removing a few would help save weight and not effect the stability of your chassis (2 on each side is a good amount). And, while it may not appear to be, chain can get quite heavy. While it is necessary on your chain bar, using it on your base may not be as important as you think. I have seen many bots without powered front wheels which can easily get over the 10 point bar. Finally, that high-strength shaft should be removed as it probably weighs a good 1 or 2 pounds on its own.


#3

I would agree…there’s no way that’s 21 pounds of weight. I would just say use 1-1 drive and get rid of chain and excess gears from that. The reduction of friction from this might fix the issue. We had similar problems to that earlier.


#4

If you’re using any steel, replace it with aluminum.


#5

How is that 21 pounds…

Anyways, I’d probably use half cuts for some parts of the lift.


#6

@RoboTurtleLord @pkrish @Dromeda , I just weighed it 6 times, 3x on two different scales and every time got 21 pounds! Thanks for the suggestions and I will def take out some standoffs and the high strength shaft, the only other ideas I had were to change some of the lift bars(the non-direct powered) ones to 1 by L. Also I am going to make the base direct drive (1 motor per wheel). Then if that doesn’t work I am going to take 2 motors off of the dr4-6b and put them on the drive (I unplugged 2 and it worked fine) PLEASE LET ME KNOW ANY MORE SUGGESTIONS… sucks when you can stack 16 on auto loader super fast but then just can’t drive for more than 30 seconds…


#7

@Joshua_84927A all aluminum


#8

My robot looks bulkier than yours and weighs less than 19. Check your scale, and check your drive is friction-less.


#9

@Dokkaebi, I swear the scale isn’t lying and the drive is frictionless except for the inherent friction in the gears and chain.


#10

Aight


#11

Yea, other than just removing what ever isnt essential, the only other thing to do would be to use 1xL’s.
Also, have you looked into aluminum and nylon screws/nuts? They helped us reduce our bot to around 14-15 lbs.


#12

@RoboTurtleLord, The aluminum screws and nuts might be a good investment, I will have to look through our budget


#13

I could definitely believe 21 lbs. I’m not totally sure what all the c channels are doing on your drive, so I can’t just tell you to take them off, but I can tell you that there should never be more than 6 or 7 non-moving c channels on a drive, unless your robot is extremely heavy, or you can’t brace in the normal way due to space constraints.
Oh, and one note: I can imagine a situation in which high strength axles would be the right decision, but every time i have used them on one of my robots, it has turned out to be a mistake.
Edit: I just noticed that you use 8 screws, 2 locking bars, and 4 1 inch standoffs to attach 2 rubber bands to the mobile goal. Unless I’m missing something, you could just ziptie those directly to the mobile goal.


#14

I think if you drive each motor of the base on its own wheel then it would distribute the force which should help. It would also take out the metal 12 tooth gears. Also, I calculated its BMI and it was 45 which is insanely obese. HAHA


#15

Friction is your number one enemy in Vex, and even small amounts of it will make things burn out much faster than they should.

I would highly suggest gearing each wheel with its own motor (but do keep the chain, it helps a lot with center of rotation when programming) instead of gearing them with pinions, which are metal and cause a ton of friction when out together. But if you must keep the gearing in the back, don’t fear with pinions. Because the coefficient of friction (if you know physics) between steel and steel is a lot higher than that of plastic and plastic, I would highly suggest gearing your drive with low-strength 36 tooth gears, instead. My robot is around 17.5 lbs and easily runs a 6 motor turbo drive just because the gearing is as frictionless as possible (front wheels are direct, back wheels are geared with 2 low strength 36 tooth gears).


#16

Torque instead of speed, especially with weight. this allows for the motors to function a little better than high speed and reduce your chance of dying motors.


#17

@Aeden_6007 first off, mad respect your robots are insane. Second thank you so much for the c-channel thing, I actually just added a full c and you made me realize that I could take off the back c-channel without any significant difference. I am definitely going to take off the rubber band things lol, those are from when we were an only mogo bot. I am also going to switch to direct drive so that we loose all the friction in the gears and it spreads the load better. Would you agree with @Mystellianne to keep the chain for center of rotation, or take it off to loose friction and a bit more weight?


#18

If you’re not very invested in programming skills, scrap the chain and just do direct. You can get away with that in autonomous since it’s only 15 seconds.

If you’re invested in a consistent high programming skills, chain is almost completely necessary. I’m not saying you can’t do it without chain (my robot doesn’t have chain and I’ve gotten 84, but only after extensive — we’re talking like 24+ hours of total work), but it will be a massive pain to figure out how the absence of chain affects your center of rotation. When you pick up a mobile gosl, not having chain makes your center shift super far forward, and you need to figure out how that will affect our positioning after each turn. I will also say that if you’re rotating 180 degrees with a mobile goal, not having chained wheels will actually offset you in the x dimension, so you’re not even on the same line you were before. This made things excruciatingly difficult to determine, and left me wishing I had chained my drive just for this occasion.

Our sister team can run a 6 motor turbo drive with their drive chained (although they run hi speed in case they run into defense bots that they need to out-torque). Knowing that a 6 motor turbo drive has almost the same stall torque as a 4 motor hi speed drive, I’m sure you can get away with keeping the chain. Just work on making everything else as light as can be.


#19

Thank you! :slight_smile: I personally dislike chain on drives in vex due to friction. I would definitely not keep it if the only reason is for your turning center. The only reason I would use chain would be to ensure that the front or back motors are not over-strained due to weight distribution. However, this would only really be worth it if your weight distribution was really terrible (which it doesn’t seem to be), or if you had 6+ motors on your drive (which you don’t). Even if you do need something like chain, I would use gears, because they are a insane amount lower friction (like 1/10 by my estimate).

Tl;DR Don’t use chain, but if you really want to, just use gears instead.

I really haven’t had that many issues with this, but I can see why you might. Out of curiosity, do you use an encoder wheel?


#20

@Mystellianne @Aeden_6007, I think I am going to do direct drive. Mainly for the friction and also because I focus more on competition than skills. Thank you so much for your help! Lemme know if you have any other ideas.