New shimming technique?

[laurence]

Quite clever i thought, might give it a try http://www.youtube.com/watch?v=1F0zpkmNux4

[Icebass]

Re: New shimming technique?

A friend told me about this a few weeks ago so i tried it in my m4 (shoots at about 39rps). The motor is running a lot cooler. I'll be shimming like this from now on instead of going from the spur gear.

[Caveira]

Re: New shimming technique?

Quite a few techs on here have been using this technique for a while now, but seeing the video does make it more obvious why.

[North West Outpost]

Re: New shimming technique?

Suggested this a while ago, not many were particularly interested in fact several were still saying they were going to continue with the spur gear first.

Really so long as you check the pinion/ bevel relationship as any decent tech would irrespective of method you will be fine.

[laurence]

Re: New shimming technique?

I guess it would be a little more tedious this way, but hey, it will same you some time i bet in replacing a pinion.

[BioSniper]

Re: New shimming technique?

Saw this some time ago when Midas first suggested it I think.
My main concern would be, what would drilling a hole in the bottom of the gearbox do to the strength of it? I would guess not much because its barely a stressed point, but it's still something I worry about.

[Bachelarius]

Re: New shimming technique?

How do people do this on V2s though? I mean, the hole is all well and good... But the grip covers it up anyway, does it not?

Again, lovely technique, would very happily use it, and do use everything bar the hole drilling.

It's just on a V2 it is such a pig to apply, half the time I end up having to change the motor height afterwards anyway! And then what was the point of setting it in the first place?

[Caveira]

Re: New shimming technique?

half the time I end up having to change the motor height afterwards anyway! And then what was the point of setting it in the first place?

I might be wrong, but working from a locked-in motor (by screwing the pistol grip into place while shimming) should remove the need to adjust the height as far as I can work out.

Drilling the whole wise, it's way away from any stress points so I can't see any issues there, though someone more techy might be able to correct me on that.

[Bachelarius]

Re: New shimming technique?

should, yes, but a grip screwed into a v2 with only 1 half attached wobbles all over the place. Not by much, but enough to throw it off. Trying to shim the gears with only half a gearbox on is next to useless anyway, as the bevel just rests on the pinion and goes off at an angle, so as soon as you screw i back together, it's too tight on the motor. So if you cannot see where the motor is through the hole and can't shim the gears correctly with half a gearbox on... What do you do? Go back to listening to it's noises?

[Caveira]

Re: New shimming technique?

should, yes, but a grip screwed into a v2 with only 1 half attached wobbles all over the place. Not by much, but enough to throw it off. Trying to shim the gears with only half a gearbox on is next to useless anyway, as the bevel just rests on the pinion and goes off at an angle, so as soon as you screw i back together, it's too tight on the motor. So if you cannot see where the motor is through the hole and can't shim the gears correctly with half a gearbox on... What do you do? Go back to listening to it's noises?

Mmmm, good point.

I was working on the theory that you'd set the bevel gear first using the hole, taking it apart as many times as needed, then pop the grip off and do the rest as usual

[Bachelarius]

Re: New shimming technique?

To me, I thought the idea was to maximise the amount of surface area in contact between the bevel and pinion, maximize the distance from the end of the pinion and the bevel gear's shaft, thus maximizing the available torque, all the time making sure that you reduce any angular force on the bevel by not over-forcing the pinion into the bevel.

In essence there is one and only one sweet spot for the pinion and bevel to sit in, so the edges of both form a perfect right angle, i.e. if you are looking directly down the gearbox, with the motor running perpendicular to you, the bit where the pinion teeth end and the pinion shaft begins is touching and forming a right angle with the outer diameter of the bevel. The bevel MUST be perfectly upright and meshed with the pinion. But the magnets in the motor do not allow you to make sure this is the case by rotating the pinion and checking all positions of the gear/pinion mesh.

I know that this is mechanically the optimum position for the gears. But the only way to get there is by having the case closed to prevent the bevel from tilting and being forced to the side. As soon as this is done, there is no way to see the interaction. You can also not 'feel' the lateral force that the pinion is exerting on the bevel.

Sorry for the really anal analysis, but the positioning and not forming that L-shape as well as the lateral forces on the 2 gears are the primary reasons for any sort of motor faliure, from broken pinions to high battery usage. It's kind of a big deal and I really don't like the fact that it is an uknown...

[Bachelarius]

Re: New shimming technique?

Fantastic news, solution found! I am quoting TommyGunn from Arnies on this one:

People seem to have a problem sorting the Bevel to Pinion gear mesh e.g. the bevel wobbling, pinion height etc. While I was recently servicing my M4 I was also trying to figure out how to achieve a perfect mesh and I considered using a scrap gearbox half, with windows drilled into it, to allow inspection of the mesh. However, I came up with a much better and more precise method.

Here's my step by step methodology:

1) Take your two empty gearbox shells and place in your pinion gear and screw the two halves together.

2) Using a Vernier Caliper, measure the distance from the outer (centre) edge of the pinion gear to the outer flat of the gearbox , i.e. the surface the pistol grip mates to.

3) Keeping this measurement in mind, and with the motor mounted in the pistol grip, adjust the motor height so that the distance from the back edge of the pinion teeth to the mating surface of the pistol grip is equal to the previous measurement.

4) Take the gearbox apart and through a process of trial and error add shims to the bevel gear side of the Bevel gear (the big side/right side).

5) With a number of shims added, no shims required on the other side yet, screw the gearbox back together, take the motor out of the grip, attach pistol grip to gearbox and re-install the motor.

6) Take a small screwdriver, or similar, and insert it through the cylinder cavity window and test for movement, back and forth, of the bevel gear. What you are trying to achieve, with this initial shim job, is zero (or near zero, the slightest of slight ticks forwards and backwards) movement between the bevel and pinion.
You will need to have a shim or two too few on the bevel, as a starting point, and work up (trial & error) rather than having the bevel tight against the pinion. Reason being, is that if it is tight you obviously can't tell the precise error in the mesh.

This method obviously requires several builds and strips to get to the point where you have the correct amount of shims on the large/right hand face of the bevel gear. However, once done you will have a perfect mesh without the usual problem of the bevel gear wobbling all over the place and inducing error into the system.


For the rest of the geartrain my philosophy is to have maximum contact between the Sector gear and the piston tooth rack. The problem with this, and I'm refering to my CA gearboxes so can't comment on other manufacturers, is that due to slack tolerances there is a slight trade-off between max Sector/Piston contact and contact between the rest of the gears i.e. those points that involve the Spur gear.
Personally, I prefer to have max, or as near max, contact between the Sector and piston, max contact (smallest shim) between the Spur & Sector and then the largest disparity between the Pinion and Spur. It's all a matter of give and take and of course will all depend on the tolerances of your own gearboxes and gears.
Also, add the smallest of shims possible, e.g. between the Spur and Sector, so that they have maximum tooth contact but so that their side faces do not scuff. This also applies to gears and the gearbox wall.

Final thought would be to add shims to the other side of the gears , make sure your bearings are properly seated and that they do not rotate in the gearbox shells and always check for side to side movement of the gears by pressing, from the outside, on the gear axles with a screwdriver or whatever.


One trick to solve bearings that are rotating in your gearbox shells is to carefully place the gearbox and bearing on a large dowel of wood (small broomhandle etc), inside face down, and with a 1.5-2mm nail punch carefully tap with a hammer to bruise the gearbox metal around the bearing at the 12,3,6 and 9 o'clock positions. A small indentation is all that is required and this will lock your bearings tight.

Tom.

[Crude Skinny B]

Re: New shimming technique?

similar to this?
http://ftp.airsofttutorials.com/cent..._Shimming.html