Fixing gearbox assembly inconsistancies

[Monochron]

We recently got some Toughbox Nanos from AndyMark and noticed that after we switched the output shafts that some of them could no longer be turned by hand when a CIM was installed. I tweaked the tightness of some of the CIM mounting screws and occasionally saw this problem disappear. On one I loosened the center bearing retainer screws (seen below) so that they no longer contacted the bearing, and I was able to spin the shaft by hand again.



It is a weird intermittent problem, but the difference in gearbox operation has me worried about how consistent our drivetrain will be. Intermittent problems like this have cause huge headaches for us in the past and we would love to find a reliable way to fix this. I'm hoping that this is a type of problem that experienced teams know how to work around, or know the cause of.

Can anyone offer ideas, suggestions, or even guesses as to what we can try to fix this? Thanks in advance.

[BrendanB]

Have you guys talked to AndyMark yet? They would be the best people to advise you and they are very quick to respond.

[gpetilli]

The two middle gears have a hub spacer on one side and not on the other. Make sure the two flat sides are against each other and the two spacer sides are pushing on the inner races of the bearings.

Other than that, there should not be an issue with the retaining screws being a bit loose.

We had problems last year with a student who held the box in a vice while she worked on it and introduced a bow that caused the CIM motor not to mesh well when its screws were tightened. We wound up shimming the motor to reduce the gear engagement.

[oison75]

In the past, we've also had some issues with aluminum vs. steel gears. Aluminum gears tend to warp under pressure and get jammed, while steel gears don't. (Keep in mind this was with a 3-CIM Andy Mark gearbox and not the toughbox nano).

[Cory]

Originally Posted by oison75

In the past, we've also had some issues with aluminum vs. steel gears. Aluminum gears tend to warp under pressure and get jammed, while steel gears don't. (Keep in mind this was with a 3-CIM Andy Mark gearbox and not the toughbox nano).

What aluminum gears? VEXPro?

We've used aluminum gears extensively from VEXPro and ones we custom made...never seen one "warp under pressure and get jammed".

It is highly likely you had another issue that was independent of the gear. For sure more information is needed before making a blanket statement that aluminum gears are worse than steel.

[gpetilli]

Originally Posted by gpetilli

The two middle gears have a hub spacer on one side and not on the other. Make sure the two flat sides are against each other and the two spacer sides are pushing on the inner races of the bearings.

Other than that, there should not be an issue with the retaining screws being a bit loose.

We had problems last year with a student who held the box in a vice while she worked on it and introduced a bow that caused the CIM motor not to mesh well when its screws were tightened. We wound up shimming the motor to reduce the gear engagement.

Since the topic of aluminum gears came up, we used VEXpro gears last year in what was a punishing game. We had no issues. That said, the VEXpro gears have the above mentioned spacers on BOTH sides of their gears and are therefore wider than the AM gears. We machined off one of the spacers and again we oriented the gears flat side to flat side.

[Monochron]

Originally Posted by gpetilli

The two middle gears have a hub spacer on one side and not on the other. Make sure the two flat sides are against each other and the two spacer sides are pushing on the inner races of the bearings.

Other than that, there should not be an issue with the retaining screws being a bit loose.

Yeah, I doubled checked that the middle gears were oriented this way, no problems there. As far as I could tell only one gearbox reacted differently to loose or tight retaining screws, the rest just won't spin by hand regardless of screw tightness.

Dissembly and reassembly would often allow me to turn one by hand, but I haven't found a method that works every time.

[Jrizo]

Check to make sure your CIM mounting screws are not to long. That can cause The tuff box nano to not want to turn. Also check to make sure that the bearings did not get reversed.

[StealthMentor]

We sent two back this year one for a gear that the bore was broached crooked, and the other was not the right width causing a lot of slop. The ones we got as replacement where fine but the included kit to mount the gear to the CIM with the two washers below the gear (as per instructions) the washers actually hit the next gear and make it so it wont turn. The washers are too big in diameter. We removed one washer and it now works fine. Andymark needs to step up their quality control!!

[Monochron]

Originally Posted by StealthMentor

The ones we got as replacement where fine but the included kit to mount the gear to the CIM with the two washers below the gear (as per instructions) the washers actually hit the next gear and make it so it wont turn. The washers are too big in diameter. We removed one washer and it now works fine. Andymark needs to step up their quality control!!

I was wondering about that second washer, it makes it so that the CIM pinion gear doesn't mesh centered on the next gear. I was hesitant to remove a washer because the kit came with two . . . but if that could be causing my problem it would be an easy fix.

[Shu]

Originally Posted by StealthMentor

The ones we got as replacement where fine but the included kit to mount the gear to the CIM with the two washers below the gear (as per instructions) the washers actually hit the next gear and make it so it wont turn. The washers are too big in diameter. We removed one washer and it now works fine. Andymark needs to step up their quality control!!

That was the exact same problem we had with 4 Toughbox Nanos we got for a summer project. We fixed them the same way.

[Zyrano]

We had the same problem with the these gearboxes last year, you just need to play with the spacing of the gears relative to each shaft. We were able to use some hardware store nylon spacers to make everything work. if you look closely, you'll see that some of the gears are able to interfere with each other when you push the slop one way or the other. It was somewhat fustrating as my students had to assemble and disassemble multiple times before finding the problem.

[Monochron]

Originally Posted by StealthMentor

The ones we got as replacement where fine but the included kit to mount the gear to the CIM with the two washers below the gear (as per instructions) the washers actually hit the next gear and make it so it wont turn. The washers are too big in diameter. We removed one washer and it now works fine.

I removed a washer from each gearbox and the problem disappeared. I really have no idea why there are two there, unless one is intended to be a spare? When I called AndyMark asking about this the rep just said to run the gearbox for a while which would, I presume, just grind away at that gear/washer. Glad I didn't do that.

Originally Posted by Zyrano

you just need to play with the spacing of the gears relative to each shaft. We were able to use some hardware store nylon spacers to make everything work. if you look closely, you'll see that some of the gears are able to interfere with each other when you push the slop one way or the other.

Yeah the middle gear cluster has at least 1/8" of slop to it. I'm not familiar with gearbox design, but I wouldn't think that is optimal, why not send another spacer in the kit? Either way they are working now for testing. We might consider adding some spacers that are on order, but it means removing and disassembling the gearbox.

[oison75]

Originally Posted by Cory

What aluminum gears? VEXPro?

We've used aluminum gears extensively from VEXPro and ones we custom made...never seen one "warp under pressure and get jammed".

It is highly likely you had another issue that was independent of the gear. For sure more information is needed before making a blanket statement that aluminum gears are worse than steel.

These were the aluminum gears that come with the Andy Mark gearbox. When it was all assembled, we tried manually spinning the shaft (with the CIM attached), and it kept jamming (meaning we couldn't turn it). We disassembled the gearbox and took a closer look at the gears: they were physically warped. Even laying them on a flat surface you could literally see gaps between certain areas of the gear and table. My guess is they were poorly manufactured. However, the steel gears were not warped, and did not jam.