Need a 3.5 length axle. Should I cut or make a 3 length work?

[Carefree_Dude]

In a project i'm working on, I have a gear connected to a motor; between the gear and motor i need a brick and 2 small bushings. Ideally, to have an axle fully into the motor, I would need a 3.5 length axle. Sadly these do not exist; So, which is better: 

-Use a 3 length and only have the axle half entered into the motor

-Physically cut an axel or two (maybe a 7 length in half?) in order to get the length i need.

I'm fairly against modifying parts, but I fear only having half a stud worth of axel in the motor may damage something, especially since it is an XL motor. 

If cutting an axel is the best use here, what is the best way to cut one?

For those interested, this right here is my use case. 

 

 

[bonox]

do what ever makes you feel happy. I personally cut axles using a pair of side cutters - if you rotate the axle a few times and do light 'cuts' before snipping through the whole thing you can generally get very neat edges.

 

If you're purist, find another way

[allanp]

Well, the axle only goes half a stud into the weaker bevel gear so that will still be the weak point even if you are only half a stud into the motor. Try it first to see if the axle wanders.

[Didumos69]

Working with a 2 or 4 stud space is 'odd' anyway, I would say. Extend the distance between the motors by one stud, also between the shocks, use 4L axles and full 20t gears, which sit more solidly too.

Edited November 13, 2019 by Didumos69

[Saberwing40k]

Honestly, this approach would probably end up with something breaking no matter what, given that you have XL motors and thin 20z bevel gears. It would be far better to extend the space between the motors and use full 20z gears. What is this going to be used for? I feel like you are going to break a lot of gears if this is some kind of drivetrain for a vehicle.

[allanp]

Those are valid points. The little bevel gears and the CV joint aren't great for handling the torque of one XL motor let alone two. Those motors have too much internal gearing.

[Erik Leppen]

11 hours ago, Carefree_Dude said:

I'm fairly against modifying parts

Doesn't this answer your own question?

I have my doubts about the setup anyway. The dark-gray CV part is also supported only by a half-stud. So I would expect some gear slipping here.

Try it out, and see where the weakspot is by engaging the motors while holding the output axle. My expectation is that it's not the half-inserted axles.

Also, I'm slightly worried about the combo of XL motors and (single) bevel gears. Is there room to move the motors to the left (to the left of the gray 2x6 plate) and use three 24t straight gears instead?

[Carefree_Dude]

This is for a train I'm building. I may be able to move the motors slightly in order to use the full thickness gears, but I'm very limited for space overall. The CV joint is necessary to make the suspension work. 

Preliminary test haven't shown any issues, but I've only been able to run a partially built train with no cars.  

[howitzer]

What do you need the dual motors for? I'd imagine a train would move rather easily even with one motor, and the axles and gears aren't designed to handle much more torque than an XL motor can deliver anyway.

[Carefree_Dude]

8 minutes ago, howitzer said:

What do you need the dual motors for? I'd imagine a train would move rather easily even with one motor, and the axles and gears aren't designed to handle much more torque than an XL motor can deliver anyway.

This setup is for a Union Pacific Big Boy; the largest steam engine. The real life train can exceed 80 mph, and There is actually 4 XL motors total, with a second dual motor setup that will drive a second set of wheels. For now I'm using two lithium battery boxes, but will eventually replace with a non lego power solution. I want to be able to pull 50+ train cars with this thing; I know it can be done. The gearing I chose here is to try and have a faster train without losing too much torque. I also want it to be able to go up inclines. I see the concerns about using the smaller gears and how they may break. 

I had done a previous Big Boy setup that used only two XL motors, one for each set of drive wheels, and it didn't go terribly fast due to the gearing, and its load was limited. Also it had issues with uneven track where only one set of wheels would be on the track, cutting its overall power in half. I have added suspension into this new model to help fix this issue.