I don’t understand how the high strength shafts are support to work with motors or even wheels.
I say this because isn’t the hs shaft thicker then the older shafts
You’re not supposed to use the high strength shafts with motors. You can use them with the 4" wheels by pulling out the inserts and the new 2.75" wheels. You can also use high strength gears. Besides spacers and shaft collars, that’s about all you can use with the high strength shafts.
They’re not designed to work with motors. They were made for wheelbases, arms, or anywhere else where high strength applications are useful.
edit: edjubuh beat me to it
The HS shaft is meant to go from gears to wheels, or other high-strength applications. Such as gears to gears.
They really need to make couplers that fit high strength shafts because for me its the pinion gear that gets twisted not the arm gear.
What is the point of a high strength shaft then. The axle will just twist at the coupler.
Short answer: they arn’t supposed to work with motors, and you will probably need new wheels to work with them.
People have wondered this before:
How???
You’re twisting the 1/8" axles with a single VEX motor? Something is very wrong there.
VEX wouldn’t give you motors that can twist the shafts they give you.
Maybe he means the middle pinion in a compound gearing setup. That axle could easily twist.
Considered that, but this thread is about directly connected motors to axles.
That (compound gearing) is a valid case that could benefit from the high-strength axle, but compound gearing can (and should) be avoided in most all cases in VEX. I suppose you could broach out the metal pinions, but then I’d be worried about the strength of the gear itself.
in my own personal experiences ive never had a axle twist on me but other teams at my school they have axles twist on them all the time.
Axle twisting has more to do with build habits than the strength of the shaft itself. If you support your shafts well with bearings and don’t make it bear insane loads, it won’t twist.
Agreed. I’ve personally never had an axle twist (I had one bend to a point of almost snapping due to a horribly designed planetary gearshift but we won’t talk about that) but I have seen them twist. It is usually due to poor support of the axle in high stress applications such as the driven gear of an arm. Best solution is supporting the axle better, not taking the easy way out and using a bigger axle.
What is this “support”? You can make a shaft less likely to bend by supporting it at more points, since a shorter distance between applied loads reduces bending moment. This doesn’t work for twisting because a shaft’s torsional strength is independent of its length. Short of using a thicker shaft, there’s no way of supporting it that will allow it to carry a greater torque without failing.
If you try to put 120 inch-pounds of torque through a standard vex shaft it will twist. There’s no way around that. All you can do to avoid twisting shafts is reduce their torque load, either by distributing the torque over a greater number of shafts or by transferring the torque in some other way. An example of the latter is bolting the driven gear of an arm directly to the arm itself, which reduces the torque on the shaft to effectively zero.
This is true, but if a shaft is not well supported, friction may increase the torque that is being put through the shaft, and make it more likely for the shaft to twist.
Friction can only increase the torque through a shaft if the shaft is moving. If when you apply friction to your shaft the torque increase is sufficient to twist the shaft, then you were operating way outside of the shaft’s tolerance to start with. If your shaft twists with a bit of extra friction then it won’t last any time at all when the full torque of the motors is applied to it (i.e. when it is stalled).
Your design should allow for your shaft to be held stationary with the motors running at full power without causing the shaft to twist. In this scenario, friction is irrelevant because the torque through the shaft is limited by what the motors can provide and not the shaft’s output. If your shaft can’t be held stationary with the motors running at full power then your design isn’t practical for a Vex robot, for a couple of reasons:
- You want to be able to accelerate from rest at full (or close to full) power. If your shafts can’t handle this then you will have to accelerate and decelerate more slowly which will limit your ability to react to things.
- Sometimes Vex robots unexpectedly encounter something which causes a mechanism on the robot to stop abruptly while the motors are still running. If you twist a shaft every time this happens, then you don’t have a robot that can practically compete in a Vex competition.
I’m sure there are some engineering applications (turbines are probably one) where it’s reasonable to run a shaft off a motor that could easily destroy the shaft if it stalled. Vex isn’t one of them. In those applications slow acceleration and deceleration would have to be acceptable and torque load at any time would have to be very predictable. Those are two attributes that don’t apply to Vex.
So basically they can only be used in those sizes of wheels?