Totem Pole and the Sundance kid

[John Clarke]

I'm actually along way from completing this truly wonderful monster of a model, even just to get it moving will take me well through the warranty period. So I've come to the conclusion I might as well upgrade the drive system and put my own mark on my build.

Just like the original tank, my model will evolve and will be upgraded with different options. Yes, it will mean a few mods. I've completed a few already, decorative and automotive. Now is the time to give some thought to the drive system even before it actually gets fitted, it'll be so much easier to work on being an open shell.

Funnily enough I'm going to call the motive upgrades X Y & Z, not historically correct but there are three stages. so why not.

The options packs provide the model with some sophisticated electronic equipment and some very powerful motive power, It has to be to push the brute about. The added rubber pads on dry hard surfaces will have far more traction than the slippery alloy track of the big cats.

Torque is the Friend and the Enemy, harness it and it is your Friend. Let it loose and it will knock your teeth out.

I do have limited tooling, but I do know if I can keep the tolerances to the minimum, it's possible it will reduce torque stress and with a couple or three simple mods I think I can get maximum torque to the sprockets were it needs to be.

So, plan X, I'll be adding support to the very heavy motor and gearboxes and lock them down This will reduce any twisting motion on the three M5 mounting bolts when the drive takes up and during direction changes.

Plan Y,Gearbox, Set end float to the bare minimum, there are very few components in the gearbox. To get a good low ratio output (High torque) the component teeth will be very small, to prevent our friend torque trying to push the teeth apart, a tiny end float will to be setup and maintained.
I'll have fun with this. Too little end float and the gears will wear out or break up, too much end float and the teeth will skip over each other with the cold rasping noise to freeze the heart.

Plan Z, To improve output shaft stability, I've worked out a way to add an extra bearing fitted inside the motor gearbox mount spacer. It will mean splitting the output shaft extension pinion and adding a machined support sleeve, but carefully setup, it should improve alignment and take away some of the stress from the inner original shaft support bush.

I cannot advise others to do as I am doing, sadly access the the machining requirements will also be restricting, though all the parts are there.

It's a bit like the old Morecambe & Wise piano sketch note parts "all the right parts are there". Classic

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From the outside this looks like a similar type motor and gearbox we use. Yippy Ki yay

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[Adrian Harris]

Interesting to see you are also doing this, there are a couple of us who have decided to improve the shimming in these gearboxes.

I've started on the gearboxes for the Toasty Tiger, as they were dismantled anyway. It's amazing what a small shift in the alignment can do to the smoothness and quietness of their operation.

Will be interesting to see what you do with the Chieftain. I don't have machining facilities but tuning the shimming seems to remove most of the backlash, so I'm hoping the bushing supplied will provide the support.

Adrian

[Phil Woollard]

So what was the verdict on the gearboxes that have already failed? I've not seen anything. It sure would be interesting to know exactly what has been failing and why!

[John Clarke]

Hi Adrian, I would have liked to have added a bearing to the inner model gearbox housing, but the pinon gear is to big to facilitate that.
I had also contemplated changing the shaft aligning brass/ bronze bush with a superfine bearing too. But poo poo'd the idea with the thought it could fall apart and destroy the final drive gear.
The brass/bronze bush is the most simple type of bearing, sturdy and long lasting and if lubricated correctly should last the model out, adding the beefy 6204 2RS to the shaft line should extend that time line
My old 1/5 scale Chieftain ran almost entirely on bushes (200kg)

Phil, What failures?

[Richard Goodwin]

Its interesting that several people are considering re-shimming the new Armortek flange mounted gearbox. This would suggest that they are not optimally shimmed in the first instance!

Bearing in mind I'm about to start a long test run, I'd be interested to hear what Armortek have to say about this preferably before i start it?

Over to you Armortek.............

[John Clarke]

Y and why not
Operation time, I'm going to open up the patients, examine, measure, make a change if I feel I need to.
First, I wondered how much the gear teeth actual mesh together. Using allen keys, I'll released the rear cover until the gears fail to mesh and measure.
Wow 0.5mm.
Exciting.

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[John Clarke]

With the dissection complete, I see a simple amazingly small gearbox with some very nice components.

I do see a couple of strange occurrences though.

First, on my gearboxes I seem to have a lot of end float. Through a process of elimination with various shims I found by removing the original 0.1mm shim washer and replaced with a 1.0mm shim washer, I now have the teeth meshing at around 1.5mm with a float of around 0.2mm.

Second, on my gearboxes I found that the large 0.3mm thick spring washer was set behind the output shaft bearing. This means the whole bearing has to float in it's housing to work properly, it could jam. I'll upgrade this part with a smaller spring washer same thickness in front of the bearing. This way the main bearing can be secured in the bearing housing with the full support of the cover plate and the smaller spring washer will spin freely with the output shaft and still do it's job.

Here's a simple rudimentary basic picture including my proposed changes, although both gear boxes share the same components they are not identical.

Actual chieftan gearbox2.jpg (91.09 KiB) Viewed 8470 times

[John Clarke]

While I wait for part's, I'll continue with my other do-able gearbox upgrade. Remember all this will void any warranties, so if your a Roy Rogers fan read on.
Onto plan Z upgrade, Tricky one this, If you don't have access to a lathe then this one could be a no show. It may be possible to get a local engineering company to do the job, machining and make up the sleeves for you. I've done this in the past when I wanted some key ways cut on another model.
Simply put, I'm going to add another bearing to add a bit more support and help alignment to Motor gearbox output shaft using the motor gearbox spacer. Parts required, Two modified Gearbox spacers,Two 6204 2RS bearings and two machined sleeves.
First, Machine the gearbox spacers to accept the 6204 2RS bearings, they should be slightly recessed ensure a good fit when it all goes back together.
The sleeves, the new bearing itself needs extra support as the bearing inner race spans two different sized shafts, 15mm gearbox output shaft and the pinion extension shaft 20 mm.
Once put together I had some concern over fitting the motor gearbox assembly, the spacer is physically fixed to the pinon extension shaft and cannot be removed without stripping down. But I can always release the inner "model" gearbox housing for wiggle room.
The new assembly all lines up and runs nice,
Unfortunately I won't get round to the X plan for a few of months.
But it's always nice t have a plan.(says the evil penguin)

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Beefy

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[Richard Goodwin]

Looks a nice job Roy

[David Battson]

Hi John,
Great work on investigating the inner workings of the spiradrive gearbox. Have your efforts made any improvement to the feel and noise of the gears in operation ? My gearboxes are quite noisy with a lot of resonance on overrun.
The input pinion either screws it’s self into the crown wheel or pushes away from it depending on direction of rotation. The gear supplier also makes their own gearboxes which use thrust bearings on the input shaft. As part of ‘Y’ upgrade have you looked at end float on the input pinion shaft, I suspect it’s should be minimal ? I can’t find end float values in the supplier info, but they quote an overall backlash value for their gearboxes of 0.1 degrees arc which, if my maths is correct, is not much !!
Interested to find out how you get on.
David

[John Clarke]

Hi David
These are my gearboxes, there are many like them, but these gearboxes are mine.

Definitely mine now.

The shaft end float appears to stop when spring washer is fully compressed behind the bearing. (This is as long as the bearing moves freely in it's housing/cover plate) if the beginning of the end float travel starts too early (ie the tooth mesh is 0.5 mm like mine were) then the end float appears to travel along way.
With the new shim I fitted, I think the end float on my gearboxes is now set to an optimum 0.2 mm ish because the gear teeth are already 1.5 mm in mesh before the end floats starts. When the new smaller spring washer Is fitted (on order) the end float will not have to rely on the bearing having to move. Well that's the plan.
I'll need to fit the new smaller spring washers when they turn up first before completely buttoning up the gearboxes.(15 mm dia spring washers are hard to find).
This type of gearbox can generate some noise in reverse, spiral gears do, think car differential, some what noisier in reverse. Forward should be reasonably quiet.
With the extra weight on Chieftains drive train, I think it will be essential for me get it spot on. It will be some time before my gearboxes are fitted and running, but they do now have tiny rotational backlash on the gearboxes you describe at the end of your post.

[John Clarke]

This last entry for a while hopefully shows the how the opposite gearbox differs from the gearbox already described and the changes on the motor gearbox output shaft lengths after re-shimming.
From what I've seen, and again we're depending on the build, the average depth of the pinon output shaft into the bush is around 3mm.
(The bush total depth being 5mm). giving a clearance depth of 2mm to the blind end.
If the re-shimming is around 1mm in each motor gearbox, there'll be +1mm added on to one shaft into the bush giving a 1mm clearance at the blind end, which is ok in my book. But -1mm taken from the other motor gearbox shaft depth, not ok, only 2mm depth into the bush. (3mm clearance to the blind end).
So I'm going to probably have to machine 2mm off one of gearbox spacer width to even up the pinion shaft depth into the bush on both sides.

Before all this happens, I'm going to have to prove depth of the pinion shaft into the bush. Using the old Bluetack blob trick.
Put a small blob of blue tack into bush recess on the blind end, offered shaft up in position and squeeze, remove the shaft and measure the thickness of the Bluetack blob, and proceed from there.

I must add, I'll be mounting the motor and gearboxes in the tank first, offering up the outboard gearbox to the motor gearbox pinon shaft. This way I won't have to worry about getting the alignment right with the heavy motor and pinon gear impeding the fit.

If all has gone to plan when the mods complete, the squeezed blob should measure 1mm approx, giving plenty of end shaft end clearance.

The more pinon shaft in the bush, the more pinon tooth area on the out board final drive gear.

I think I may have made it sound all a bit complicated, it's not for everyone, but step by step, it's straight forward stuff.

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Correct Chieftan Z.jpg (91 KiB) Viewed 7778 times

Happy trails cow poke's

[Jerry Carducci]

In your research and work with these units did you also consider which lubricants provide the best performance for the
spiral bevel gears used? Those gears actually require a lubricant that enhances the sliding action of the gear faces.
You undoubtedly have seen lubricants aimed at hypoid or offset axis spiral bevel gears used in most conventional
automotive differentials.

Jerry

[John Clarke]

Great question Jerry, I would have preferred to use wet oil lubricants, but as there's no oil seals in the gearbox assemblies oil levels would be uncontrollable, Even semi wet grease would leak eventually. The bearings are sealed for life so no problem there.
So I'll have to make do with some sort of sticky grease.
If you believe the hype and put enough in, I hope this will do the job.

[Gerhard Michel]

Btw just a question: may anyone please tell me the nominal current consumption of the latest Spiradrive motors (nameplate)? Are there different Spiradrive motors (means electrical data, like power consumption) in use between heavy and light Armortek models or only different transmissions?