With the new high powered motors and all, the shafts bed…ALOT. Vex should come it with stronger shafts next year. The shafts still have. To be compatible with low and high powered motors though so maybe just a stronger metal?
I can barely understand your post, but I have had no problems with shaft strength that are somehow caused by new motors.
Well designed mechanisms/well supported shafts never bend, so go rebuild.
k.gen04 is right. We have never twisted or bent a shaft mechanically. (We bend our shafts when we pound the axles in :D) Even with the new stronger motors, they haven’t caused anything drastic to it.
Bearings help. So does minimal space between the axle’s one point and the next. When using spacers, I prefer the black spacers over the white ones as for they have a smaller hole size, preventing flexing.
If you would like, maybe give some specifications to what you are doing that bends the axle?
I have broken a Vex axle by twisting it, but it was with 2 3 wire motors on a 25-1 gear ratio. But this was not being used in a good way, so im not complaining about it.
We have twisted plenty of shafts. All with the same robot. Last year we learned that we were putting way too much stress on them, and with both our 15:1 and our 5:1 gear ratio that we later changed it to we had twisting problems. Most of the time they would twist until they broke, and we couldn’t see the twisting until that did happen the first time.
Moral of the story: If you’re twisting or bending shafts, don’t ask VEX to give you stronger ones. Instead redesign your implementation, look at it closely, discover why the shaft was twisting or bending, then fix the problem with a redesign.
When we use shafts with two high powered motors on them, we often have problems with them twisting and bending. one way to avoid this is to screw two high strength gears together, this helps, but does not completely eliminate the problem. Vex does need to improve shaft quality and strength.
The problem really has nothing to do with high strength motors and everything to do with putting a few hundred inch pounds of torque on a 1/8" axle. Of course it’s going to fail that way.
You can’t just make axles “stronger”. You can switch the metal alloy for something with better properties, but usually that’s prohibitively expensive. You could step up to a thicker shaft, but that requires a redesign of more or less Vex’s entire product line.
Well i definately understand everyones point, and that the distance between the shaft and the object will definately make a change, and i will fix that. But they should come out with new ones with a stronger metal because some times not all engineering is in the mechanics, it may be the material in some circumstances
I agree with your assessment; however, I think it is much more practical to perhaps to make some modifications to your robot than for the VEX kit to be redesigned or the dramatically increase the cost of axles for a marginal performance increase.
On the subject of averting bent axles, we have had this problem as well. What you might consider is transferring power directly through the gears rather than through the axle. To do this you can “bolt” gears together using standoffs. I Think a good example of this can be seen on 254A’s '09 robot, Rambo.
the axle is running across the width of the robot and they transfer the power through the standoffs and metal rather than through the axles.
Best of luck!
This is exactly what we did with our Clean Sweep robot after having problems with shafts twisting. This completely fixed the problem, however as we were not using clutches caused the motors to burn out a lot… :o We were definitely straining the motors too much with that robot. But hey, we were using steel, and expected our robots to preform the same as people’s who used all aluminum, like we do this year.
We’ve never tested the torquing strength of the driveshafts as far as twisting them but I can attest to the fact they’ll hold upto about 400lbs before breaking, in a typical 4 wheel configuration
I’m not sure what you are trying to convey.
“400 Lbs” describes a linear force (and a pretty big one at that).
I wouldn’t expect to find a (static) 400 Lb force exerted/created in a typical 4 wheel configuration.
Do you have a picture you can use to illustrate what you mean?
It wasnt exactly a typical design, but it was a carrier for our competition robot, that we built to be extremely solid but light 12x12x5 inch wheeled platform, (He’s a hefty robot at up to 30lbs depending on which ones of his modules we have on) and after we finished someone decided to stand on it and it held up just fine, so out of curiosity we towed Billy as we called the carrier to the weight room and stacked weights on him until he bent. The drive-shafts bent at about 400lbs. Not something most people are going to have to worry about in competition but interesting to know none-the-less. He had about $500 in metal on him though so he was disassembled but I’ll try to find a picture.
After an initial glance at this robot, a number of intriguing things keep bringing me back to it. I hope you don’t mind if I have a few questions.
On your intake device, why do you have chain zig-zagging back and forth – is it to balance the speeds on both sides? I’m assuming that you have intake rollers on alternate axles (the ones connected to the 4 gears & sprockets) that move cubes down the line.
I’m seeing a motor in the back left corner, which I’m assuming is driving a 12-tooth gear that moves up the racks. Where/how is that motor anchored? What are the chains connected to that axle driving?
Re: the gear-standoff assembly at the top – where is it being driven from? Is it being used to lift the intake structure?
I’m assuming the large gear (w/potentiometer) tilts the intake structure for scooping cubes from the floor and tilts up to deliver on the back end. Correct?
Hope you don’t mind the “duh” questions.
This was 254A’s first design for Elevation, second robot ever, and only robot without a loss, so there are some aspects of it we’re proud of and others which make me wonder what we were thinking…but to answer your questions:
The zig-zag is only there to ensure the chain didn’t skip or rub - the only functional axles are the two at each end (with the intake rollers). Both ends pull in at the same time, and they run off one motor. You can see that on the right intake roller nearest the camera, the 24T sprocket is there to route the inside chain run around the left intake roller chain, while the 40T sprocket routes the outside run around the inside run. There are no intake rollers on the inside; we scored with the intake pointed at a steep angle and let gravity push them to the bottom (lots of sanding metal on the inside…).
We didn’t have rack brackets then, so we made our own. The motor side of the “bracket” looks much like the visible side, with two pivot gussets and a 2x2x4 steel angle. The motor drives two 15T sprockets chained to two 24T sprockets (redundancy, we didn’t and still don’t trust normal chain), and that’s the axle with the 12T gear on it. The only reason we geared down was because the sliders wouldn’t stay put with just a 12T gear on them, and we weren’t code-sophisticated enough back then to apply up-current based on the arm’s position.
As Drew mentioned earlier, all the standoffs were there to ensure that NOTHING bent along the top of the robot (happy to say we succeeded there). The 84T gears can be thought of as the shoulder joint on a normal robot - the unnecessary redundancy is a remnant of our 08 monstrosity philosophy that you might remember from the NorCal Quad Quandary competition. The shoulder joint was one of the tightest spaces on the robot; you can see one of the two shoulder motors peeking out from under the 8" rail and behind the left slider. From there, the motor was geared 60:12 upward (obscured by our logos), then 84:12 upward again to form a dog-slow ratio of 35:1.
Correct! We’d bought a potentiometer a few weeks before this, had no clue how to program it, and had no clue it had a range of 250 degrees. We spun the intake round and round and wrecked that thing so badly by the end of that competition…
Probably the best way to explain all this and more is with video of the robot in action. It performed like a very, very slow version of [eventual 09 World Champion] Team 44, autoloading up once in autonomous and spending the rest of the match scoring.
In an attempt to get this thread back on topic, we originally didn’t attach the driven 84T gears to the sliders, opting instead to separate them with a drive rail. We pointed the arm 90 degrees upward, let it go, and watched in horror as the arm silently swung back to the position shown above, wrecking two pristine 12" shafts.
We spent the next week finding a way to attach the arm to the driven joint, and every 254A robot since then has had bolted shoulder joints (or any other high-torque joint for that matter).
Thanks for your detailed explanation and videos – they give me a much better picture of what’s happening. And you’ve given me some ideas on challenges to move the team to the “next step”, like monitoring for position and applying up-current (we’ve toyed with elastics with variable results).
We seem to be continually running into “geometry” problems that derail our progress – trying to fit drive motors into places that don’t collide with other parts of the robot or force the design to extend outside the 18" cube. Our students often see videos on the forum that they try to copy without a good understanding how they work, with rather dreadful results, so I’m always looking for designs that are just a step ahead of where they are but within their range of understanding.
P.S. Sorry to get off topic, everyone.
the square shafts definitely need to be looked over because almost everyone in our club has bent them and twisted them. the older ones we have dont have this problem as frequently and can last alot longer, but the shiny new ones seem to bend alot. we torqued a few with our hands and a wrench. I much rather have to pay a bit more for a higher quality part and VEX should be concerned about the youth and not making more money by skimping on materials
Now that i look through this i really dont think vex should make new shafts. If vex is like a school program they want you to learn. Learn how to not bemd them. I think just making stronger ones is a cheap way out. Theres a way not to bend them we jsut have to figure it out
I don’t think there is any material difference in the new vs old shafts. Our roboteers can bend both the same way. Engineering on what you are trying with (or to) the shaft is important. This is the thing that separates VEX from other competitions. You need to work within the physical limitations of the parts. It’s not hard, it just takes some thinking. Brute force is never an option. You are seeing the aftermath of the brute force issue with the new high strength motor “burn out / overheat problems”. In all the examples I’ve seen the fix has been better engineering of the robot.
Way out of line at this point. The engineering staff and the management team has customer satisfaction and the kids as #1. Making pennies on a shaft isn’t their game plan.
If you really think you are being “shafted” I suggest calling McMaster, buy some 1/4" keyway and test them out. (They bend just as fast)