Screw joints vs high strength shafts

With all of the two bars this year would a screw joint be able to handle the weight or do you need a high strength shaft

Well a shaft is a shaft and a screw is a screw, they serve different purposes, usually if the joint isn’t powered the screw, should be able to support it’s weight.

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The screw is being powered it would be the pivot point of the 2 bar

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Usually use screws. They are stronger and cause less friction because they are round. With a screw you can still power the joint by attaching a gear/sprocket using the other holes they have.

If you need to send power though the joint, which doesn’t come up too often then use an axle. They however have higher friction due to being round. Also the high strength shaft doesn’t have much of an advantage over a normal shaft if the two sides of the joint are close together (which they usually are in a joint).

When doing a screw joint use two nuts (nylocks preferably). One to screw the screw directly to one of the sides of the joint so that it cannot rotate. Then the seconds side of the joint and a nut, but not as tight.

(Edited)

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The screw itself would not be powered (ideally), it would be fixed to the tower, and the arm would rotate around it. You should definitely use a screw joint, because they have less friction and slop than shaft joints, and the 2 bars this year aren’t carrying enough weight to cause problems.

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Even with the weight of rollers lifting the arm to score and descorre cubes from towers? This particular use I’m talking about is that the screws would be run through a c- channel that is a part of the 2 bar and then through the gear that is being powered and then it goes through one c-channel that is the support for that side

However if the joint is for a 2 bar, it’s better to use a single axle for the entire system, to allow for consistancy between the two sides.

If you’re referring to the driven gear when you say powered, then we’re talking about the same thing. A screw can’t be powered by a motor. The type of screw joint to which I was referring is called a single bearing screw joint and is usually the best joint to use for vex.


The only weight on the 2 bar comes from the intake and sometimes 1 cube. This isn’t very much weight. The only time when loads were heavy enough to cause damage to bearings on screw joints was starstruck, but even then the joints could last for a while before they needed to be replaced.
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if yall ever do decide upon a screw joint, definetely use bearing blocks with screws. I had no bearing blocks on my dr4b, it would constantly skip gears and shake. now with bearing blocks it is just as good as shafts, much less mass and easier maintinence.

You should use bearings with every type of joint, ideally only one for a single bearing screw joint (hence the name) unless you were to create an extension off the other side of the gear to increase stability in which case you’d use two.

It should be a lot better than a dr4b with shaft joints, not just as good.

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well it depends. bearing blocks are thicc. many people just use screws alone because it is good enough and they don’t want to take up too much space. You might as well do 2 bearing blocks, you only solve 1/2 of the problem with 1 bearing. You also still need 2 because the one without a bearing will still get the metal cut into over enough use.

I would venture to say this is false in most cases.

The precondition of a single bearing screw joint is that the screw is locked to a structure (in this case the tower) with a keps nut and the rotating arm is the only thing that actually moves. In this case, you only need one bearing, as putting bearings on the tower is useless since the screw is fixed to it. You would only use the 2nd bearing if you wanted to make an extension from the rotating arm to increase stability by giving it a 2nd point of contact around the screw, but a gear can accomplish the same thing if it attached to a gear.

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just checked up on how you use the keps nut to lock it onto a structure. this is definetely an insteresting concept but if at any time the keps nut loosens, the mechanism is worthless. maintinence would be difficult, and you would have to tighten the nyloc perfectly so that you keep the keps on. this is too unreliable a method for me.

Wait, for the two bar, isn’t there no place to use a screw joint? Assuming a 1:7 (7:1?) torque ratio, the 12t would have to have an axel because it’s being actuated and the 72t need an axel through it because it’s powering the other side of the lift, right?

still possible to use it.

it actually wouldn’t be too bad of an idea, if you use 1 motor for the arm, you could use a high strength shafts or even normal shafts, to power the 12 tooth. then if you use 84 tooth gear with screw joint, you don’t need a shaft to connect it, meaning you can have your arm parralel to the tray, making it more effictent.

Let me introduce you to the concept of overtightening. On a serious note however, this has never happened for my team, and I’ve never seen other teams experience this problem. If you are truly worried about it, you could use threadlocker. The screw is fixed to the other side of the tower with a keps nut or nylock, so even if the keps nut does come loose, the only problem you should have is friction, but you can always retighten the keps nut if you need. Single bearing screw joints are by far the best vex joint and are used by many teams, so I would encourage you to put your prejudices aside and at least try using them before you conclude that they do not work.

Any joint that isn’t directly in a motor can (and usually should) be a screw joint. You could easily make the rotating arms on both sides screw joints because they minimize slop and them brace the two arms together.

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The only downsides the screw joints are

  1. not being able to be fed directly into the motor.
  2. the screws can only be max 2 inches long, so any longer and you would need axles
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If you’re driving the lift directly with a screw joint, how would you track it’s position?

Currently I’m using a potentiometer on my shaft joint for my lift, but I do notice slop, and friction.
What’s the best solution for this with screw joints?

we’re not driving it with a lift. our team uses a 100rpm with a high strength gear, and a really short shafts so we have everthing else on a screw joint. then we track it using gyros, one on the left side and one on the right side, to check if it is tilting or not. based on the angle we can use an equation to track the height. you cant drive anything with a screw lol