Mixing bushings and bearings?

[paradoxum]

Does anyone have any data on the stress points in the gearbox? For example, I was thinking, the spur gear for example is bottom heavy and usually not shimmed up much, whereas the top side is just the shaft and opposite the side taking the most stress from the bevel gear, right? So what about putting a bushing on the bottom, and a bearing on the top? 

 

And how about the other gears, bushings on side of bevel gear with the teeth, bearing on the other side? Maybe bearings both sides of the sector?

 

Has anyone mix/matched before like this, any data out there on whether there would be a benefit? I'd like to try it - I might - someday - even sit down one day and mix/match them in lots of different ways and then check for RPS with each setup and log everything - don't suppose anyone has done that before?

 

Edit: 

I found this on retroarms:

https://www.retroarms.com/news/the-difference-between-bushings-and-bearings

Quote

In some scenarios, there is possible combination of the bearings and bushings, for example using bearings on the motor gear and using the bushings on the piston and spur gears. It is only individual and these setups depends on every airsoft technicians, where they prefer different kind of solutions. There is of course the need to count with all forces on every bushings or bearings with wanted lifetime.

 

I think I am going to try:

Bevel - bushing on gear side, bearing other

Spur - as above

Sector - bushing on side that grabs piston, bearing opposite

Edited February 1, 2022 by paradoxum

[Asomodai]

Some manufacturers have indeed mixed and matched. I believe my SOC AR was mixed and matched from factory.

 

Also P90s tend to have a solid oval bushing and can use bearings for the other two gears. 

 

Sadly I have no science or knowledge as to why one is picked over the other for specific gears etc. 

Edited February 1, 2022 by Asomodai

[paradoxum]

2 minutes ago, Asomodai said:

Also P90s tend to have a solid oval bushing and can use bearings for the other two gears. 

 

Yeah I did that with my pulse rifle (thompson). Got steel oval bushings and bearings for the others. That was just to upgrade from the plastic ones it had though and I wasn't thinking about performance like now.

Edited February 1, 2022 by paradoxum

[Adolf Hamster]

It is a thing, personally i've generally stuck with matched ends (ie upper and lower side if you're looking during assembly).

 

Bushings on the sector make sense, as it takes the most direct load in terms of the spring and impact loadings and spins at the slowest speeds.

 

Likewise bearings on the bevel make sense in terms of it having the lowest loadings but highest speeds.

 

However for the most part i've not really been too fussed about bearings/bushings, but then i'm building my guns to a 1j limit so i'm not as concerned about the mechanical loading on the box.

[paradoxum]

I'm really just trying to min-max as much as possible, I could just go with either or and probably never notice a difference, but part of the fun is tweaking stuff and optimizing it as much as possible for me.

 

I'll go with bushings on bevel and sector like you say and bearings on spur I guess just to start with.

 

ZCI steel bushings and EZO bearings

Edited February 1, 2022 by paradoxum

[Iceni]

It's not worth overthink TBF. I tend to run bushings because they don't collapse.

If you are building for performance then we don't have the same demands as the USA market. Less motor loading, less gearbox stress.

It is more than possible with the UK 350fps limit to get 25rps with a 7.4v lipo and bushings.

13:1 gears, HT 16TPA motor, S/S 2 teeth on sector, M110 spring or there about. Radius the shells if needed, Grease well and treat it nice and it should run for a very long time without any issues. And it's about all you could ever want from a gun.

Where the wear points are on the sector bushing/bearing. I have no idea. It's not as simple a question as it seems. You have a force from the spur, A force from a spring been compressed, and it's rotating. The rotation causes some strange things when it comes to wear points, and I think a degree would probably be needed to work the answer out correctly. My guess would be the wear point is the top of the bearing due to the main load been from the spring - that force wanting to push to 3 o'clock but the precession in the rotation forcing that to be 90 degrees ahead of the applied force. The sector effectively climbs into the load. You then have a torque been applied both by the rotation, the offset spur force, and the offset mass. That torque is going to want to act at the 3  o clock position on the upper bearing and 9 on the lower... So as a rough guess 12 o'clock to 3 o'clock on the lower bearing, but more like 1 o'clock to 4 o'clock on the upper bearing. It's a crazy guess tho, I'd love for someone to do the proper maths on it.

It's very very complicated in there. But bushings don't collapse.


 

Edited February 2, 2022 by Iceni

[Sewdhull]

I've always figured that the bevel gear gets bearings and the rest get bushings.

However I would have thought that good bearings could take the forces, I just don't know how good the bearing I have access to are.

[Lozart]

22 minutes ago, Tang_Killss said:

Adding a bushing on the bottom and a bearing on the top of a spur gear in a gearbox can potentially help distribute the load and reduce wear, especially if the top side is taking more stress from the bevel gear. However, the effectiveness of this modification would depend on the specific gearbox design and the type of stresses it experiences. It's essential to ensure that the components fit correctly and that the modification doesn't introduce any alignment issues or excessive friction. Additionally, lubrication and maintenance are crucial to prevent premature wear and ensure the gearbox's longevity. To find any parts, you can visit here: Bearing Designations And Dimensions Inquiry System

 

[Rogerborg]

9 hours ago, jannickz said:

Your idea of using a combination of bushings and bearings in your airsoft gearbox is interesting and has merit. While there isn't a wealth of publicly available data on stress points specifically, some information exists, and your proposed combination aligns with existing knowledge.

 

Are you a fairly well programmed AI? 🤔

 

TEST: in a world where crunchy peanut butter exists, what reasons are there to buy smooth?

[Sewdhull]

There's loads of those pointless summary posts.

[Rogerborg]

On 13/12/2023 at 13:01, Sewdhull said:

There's loads of those pointless summary posts.

 

Yup, that's all them has posted. They're either top notch AI, or very peculiar human.  Didn't even say hello. 😢

[Adolf Hamster]

6 minutes ago, Rogerborg said:

They're either top notch AI

 

if that's what top notch ai can bring to the table methinks humanity is safe for now......

[Sewdhull]

Well they hold up favourable against some of the human posts I see.

[Cannonfodder]

43 minutes ago, Sewdhull said:

Well they hold up favourable against some of the human posts I see.

Looking at reddit or quora before watching the matrix or terminator can really alter who's side you're on

[Rogerborg]

9 hours ago, Cannonfodder said:

Looking at reddit or quora before watching the matrix or terminator can really alter who's side you're on

 

Truly one of the posts ever made.

[Sewdhull]

Yes, one of the posts ever made.

 

At least we know you are human

Edited December 15, 2023 by Sewdhull

[Cannonfodder]

3 hours ago, Rogerborg said:

 

Truly one of the posts ever made.

One of 1096 apparently 

[Lozart]

29 minutes ago, Cannonfodder said:

One of 1096 apparently 

 

Obligatory meme response:

 

 

[Cannonfodder]

13 minutes ago, Lozart said:

Obligatory meme response:

 

Well it's 1098 now

[Lozart]

1 hour ago, Cannonfodder said:

Well it's 1098 now

 

Don't sell yourself short, it's 1,910!

[Pseudotectonic]

I don't see the point of mixing bushing and bearings because as per airsoft physics, the differences and variables affecting the three gears do not make them considerably different from one another in terms of the type of loading and the amount of force behind them

 

The different surface finish on the axles themselves with different gears already makes it impossible to work out the precise newtons applying on a bearing because if it is anything but perfect it is going to have a bit of wobble, and the brand of bearing alone (and the size, and the amount and type of grease, heck even the amount of dust exposed) will determine your shock load capacity of the bearing which is what ultimately makes using bearing worth while for the speed advantage

 

But since every particular setup is different, even the best bearings you can find will have a risk of exploding, again because of airsoft physics and tolerances

 

If you have to be mathematical, the bevel gear spins the most, followed by spur and sector gear, so the bevel gear will benefit the most from the less resistance from a bearing, in theory, but if you are willing to take the risk of exploding bearings there is no reason to not use it on all three gears

 

So it comes down to whether your setup is so marginal that your motor and battery cannot handle the negligible amount of extra resistance from bushings that you have to sneak in one or two or three bearings to lower the resistance, and choosing how many bearings to use is just a matter of risk management, because more bearings = more points of failure

 

In my opinion, bushings work fine, they are more reliable, the speed difference is not worth the risks of failing bearings because they fail catastrophically in almost all cases

 

If you want to put in bearings, I would start with putting on the bevel gear first, then spur, then sector gear, but in reality it does not matter because again, airsoft physics and tolerances is a pure chaotic mess therefore there is no theorycrafting possible, in reality it might even come down to the finishes of your particular gearbox and whether your shimming is making one of the gears rubbing on any one of the bearings, for example, so again, no theorycrafting is possible, because it is ultimately up to you and two million other variables

[Sewdhull]

Yea, when you start min maxing it's clear you are in small gains territory.

 

Unless you can find quality bearings you are just guessing. Bushings are easy to make consistently and wear rather than fail, as are happy with loads that aren't rotational ( read side to side). Bearings, whilst efficient, have issues with loads that aren't rotational and are complicated to make. Air soft gears also tend to have variable shaft diameters which batters the bearings as the shafts wobble about.

Decent cages are essential to keep the balls in place.

Stainless bushings are essentially metal on metal, impregnated bushings like phosphor bronze self lube to a degree. Lubricating bushings is largely a waste of time unless you regularly relube them.

 

Bearings are very quiet and efficient ( if you lube them correctly), shielded bearings will come lubed and you shouldn't have to touch them again. Open bearings require at least the same  attention that bushings do, but they wear slowly and at low loads often don't need any lube ( lube for airsoft)

 

Gearboxes are very quiet with bearings and it does make it noticeable when they wear, and they will keep the gears in place better than bushings as they wear.

 

If you can fit 3mm deep bearings you are raising the load ability quite a bit and if you actually service your gun regularly you can keep the bearings in good condition.

 

For airsoft in the UK, with our low powers and soft springs a bearing should be fine... but as Psuedo says with all the variables bushings are more reliable. If you build your gun well, use decent parts with decent tolerances, service it, which might only be some correct lube in the bearings and can detect wear before the bearing cages give way you can use bearings... I do.

But I also build with bearings in the fast bits and bushings for the sector gear. If you just shoot your gun, bushings only is probably better in that case.

 

The one thing I would say is that bearing failure is rare, they wear for sure, but failure requires the cages to collapse, which requires either a lot of wear to allow the balls to move, or uncharacteristic loads on the bearing. But quality, installation, servicing etc etc ...

 

 

[Leo Greer]

In my experience with V2 gearboxes, spur gear bearings are the most likely to fail by far. Over here in America we use stronger springs, so keep that in mind, but typically if you don’t use J-caged bearings they’ll inevitably fail above about an M110 or equivalent spring.

 

This is a general guideline and not a rule—as other have pointed out, the individual variables are endless—I have builds running 30+ RPS and 1.5J that still use the bearings that came with the gearbox shell (Lonex). However, I’ve also failed more than one spur gear bearing at similar power.

 

Currently, my general wisdom is that I’ll put 3mm J-caged bearings wherever I can fit them, and if not use either FLT 2.5mm bushings or RA 2mm if I need lower profile. This seems to yield a slightly quieter box than bushings alone. Of course, this is extremely variable, depending on your shimming skill, etc, etc, but I’ve been able to achieve near noiselessness on a few builds.

 

Nothing wrong with a little gear noise, but the satisfaction of firing and hearing nothing but the piston hit the cylinder head is wonderful.

 

 

[Pseudotectonic]

In terms of mixing, it appears that ALL the manufactures (at least on Evike) would agree on bearings on bevel and bushing on spur and sector

 

Not sure if this means anything

 

https://www.evike.com/index.php?cPath=28_24_68_518

[Sewdhull]

I wonder if bearing and bushing placement exists because that's what people say it should be like and that's what the customer then expects, or perhaps because you can do a crap job with bushings and the gun will be ok.

 

A V2 or V3 gearbox has very similar gear alignment, it could be identical... I haven't checked. 

 

TLDR;

 

Radial force is a force at 90 degrees to the gear shaft, an axial force is in line with the gear shaft. The radial force on the bevel of the Bevel gear ( proportional to the tangential Force turning the gears) is a made up 1N of force to provide some illustration of the relative forces in an 18:1 gearbox, this is not torque nor what the forces actually are.

 

Only the bevel end of the Bevel gear bearings experience axial force, the bearings at the bevel end get an upwards radial force (1N) the other end a downwards radial force (3N). The axial force would be 2N on the bevel end.

 

The Middle gear has its radial forces all at one end of the gear shaft resulting in only about 25% of the force going into the bearings furthest from the gears and the force pushing up and back into the bearings at about 9.3N a the gear end and 3.1N at the other.

 

The Sector gear has the radial forces applied in the middle of the gear and tending to push forward into the bearing and down. It experiences the highest forces, but these are shared evenly between the 2 bearings, with about 11N each.

 

If you are worried bearings wont cut it, bush the Sector and the Middle bearing near the gears. If you aren't, then bearings everywhere. 

 

I've looked up the Newton ratings for some airsoft springs, an M120 spring was 80Newtons and someone else did some calculations for spur gears, it looks like 100N of tangential force causes 36N of radial force for those gear teeth on the web page. Looking up bearing specs it seems even the static load at 140N, rising to 460N dynamic will be fine for an 80N spring producing 28N of radial load spread between 2 bearings gives 14N for each bearing, 10% of static load and 3% of dynamic load.

 

Lubrication and shimming matter too, you need small <6mm shims for bearings otherwise you shim to the outer race, bypassing the spinny bit. No need to lube shims with bearings, nor gear shafts, just the bearing, regularly.

 

Anyway, thats probably enough of that.

 

 

 

 

 

Taking the Bevel gear, forces are created by the meshing of the pinion and bevel and leads to an axial force away from the pinion through the bevel onto the bearing or bushing via the shims and a radial force onto the bearing or bushing via the gear shaft again away from the pinion, the gear turns by the tangential force. This gear sees the lowest forces, axial force excepted.

The Bevel gear shaft then turns the middle gear, from its sector gear section creating no axial force, a radial force and a tangential force acting on the Middle gear. 

 

-The Bevel gear experiences radial forces in almost opposite directions at opposite ends of the gear, up at the bevel end and down at the sector end, and an axial force towards the bevel end of the gear.

 

The Middle gear has a radial force opposite to that on the spur gear part of the Bevel gear, the tangential force from the Bevel gear turning the Middle gear which creates a radial force from its interaction with the Sector gear spur and a tangential force which turns the Sector gear.

 

-The Middle gear experiences radial forces at about 90degrees to one another, almost at the same place on the gear shaft, up from the Bevel gear spur and back from the Sector gear spur. There are no axial forces.

 

The Sector gear has an opposite radial force from the Middle gear spur and a radial force from the interaction of the outer spur and the gear rack of the cylinder.

 

-The Sector gear experiences radial forces forwards and down, close to the centre of the Sector gear.

 

-The cylinder rack experiences a rearward and upwards force from the Sector gear.

 

 

 

 

 

https://khkgears.net/new/gear_knowledge/gear_technical_reference/gear_forces.html#:~:text=In the meshing of a,force acting on driven gear.

 

https://www.smbbearings.com/firebrick/ckeditor/plugins/upload/Uploads/Documents/bearingpdfs/SF693-stainless-steel-flanged-miniature-bearing-3x8x3mm.pdf

 

http://airsofttech.dk/Guides.cshtml?Page=SpringRating

Edited December 27, 2023 by Sewdhull
added artwork