Vex Shift Rod through 3/8 Hex Shaft?

[AdamHeard]

Originally Posted by KohKohPuffs

My applications for using a shifter rod in a 3/8" hex shaft is for a brake for an arm gearbox. I would prefer to use COTS parts for the sake of machining time and because I know through experience that those work perfectly well without failure (as much). My main concern is if there's a limit to what size hole you can make in a shaft for the shifting rod to go through. Of course, I'm not going to make a hole in a shaft and leave only 0.01" of wall thickness, but I'm wondering if there is a general rule to follow.

A dog gear doesn't make a great brake. It takes quite a bit of force to remove under torsional load compared to more traditional brakes.

[KohKohPuffs]

Originally Posted by AdamHeard

A dog gear doesn't make a great brake. It takes quite a bit of force to remove under torsional load compared to more traditional brakes.

The gearboxes I designed for 649's shooter arm this year had a brake component, which utilized an AM shifter block with the rod and a custom part which acted as the dog. It was basically a plate that shifts against a urethane brake pad. I didn't see the thing in action very much, but people tell me that it worked very well during the competitions and has never needed maintenance (not too sure about never failing).

I guess this would counter that a dog gear doesn't make a great brake. Compared to a traditional brake, not so sure. I don't really know what traditional brakes look like (... is it a bike brake?).

In general, hollowing out the center of an axle doesn't cause too many strength issues. IIRC 1/2" thunderhex is 92% as strong as standard 1/2" hex even with the hole through it.

Despite a horrific history final coming up tomorrow, I did some work today, and currently I'm expecting to make a 3/16" hole in the hex shaft for a custom shift rod with a diameter of 1/8". At some point I will run the shaft through Solidworks Simulation with these dimensions.

[R.C.]

Originally Posted by KohKohPuffs

Despite a horrific history final coming up tomorrow, I did some work today, and currently I'm expecting to make a 3/16" hole in the hex shaft for a custom shift rod with a diameter of 1/8". At some point I will run the shaft through Solidworks Simulation with these dimensions.

That is a lot of clearance for the shift rod. Why not make the hole bigger or the shift rod larger?

[AdamHeard]

Originally Posted by KohKohPuffs

The gearboxes I designed for 649's shooter arm this year had a brake component, which utilized an AM shifter block with the rod and a custom part which acted as the dog. It was basically a plate that shifts against a urethane brake pad. I didn't see the thing in action very much, but people tell me that it worked very well during the competitions and has never needed maintenance (not too sure about never failing).

I guess this would counter that a dog gear doesn't make a great brake. Compared to a traditional brake, not so sure. I don't really know what traditional brakes look like (... is it a bike brake?).



Despite a horrific history final coming up tomorrow, I did some work today, and currently I'm expecting to make a 3/16" hole in the hex shaft for a custom shift rod with a diameter of 1/8". At some point I will run the shaft through Solidworks Simulation with these dimensions.

What you described is a traditional brake. It relied on contact force and friction, not the interference of a dog in a mating part.

[roboruler]

If this is an off-season project/design you might have enough to try some other methods of braking such as a disc brake.

[KohKohPuffs]

Originally Posted by R.C.

That is a lot of clearance for the shift rod. Why not make the hole bigger or the shift rod larger?

If there's a lot of clearance, wouldn't you make the hole smaller?

Originally Posted by AdamHeard

What you described is a traditional brake. It relied on contact force and friction, not the interference of a dog in a mating part.

Oh... I guess that gearbox I made had a traditional brake after all. Silly me.

Originally Posted by roboruler

If this is an off-season project/design you might have enough to try some other methods of braking such as a disc brake.

I've seen a lot of disc brakes in Recycle Rush for the lift mechanism. However, for my intentions I'm not sure if I would be able to fit one in the gearbox I'm making, even if it is a custom-manufactured part. You are right though. Offseason is a great time to explore new concepts and designs: something I failed to do last offseason by designing WAY too many drive gearboxes and drivetrains.

[R.C.]

Originally Posted by KohKohPuffs

If there's a lot of clearance, wouldn't you make the hole smaller?

Sorry thats whats I get for responding on mobile. But yes hole smaller or shaft bigger. I would personally use a 3/16 shaft with a .201 or .196 clearance hole.