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Nice one JR, Yes I will also enjoy this build  

caprinut wrote:

For that ride I had to spend some time in the MP arrest, but that's another story..

That's a very intresting build...and looking forward to see the progress !

I tried removing the 10T, 0.8mod pinion from the 380 motors ...

Info on the web was very lacking, sources generally tended to be people asking how to do it, and responses being of the theoretical variety passed off as actual knowledge, reminding me of something I read about a scientist being asking how to give a pill to a cat - "Well, from an engineering standpoint, a cat is simply a tube..." and so on.

The "best" response was that you could lever it off, but you weren't going to be able to use the motor afterwards.

Most responses were of the the "use a gear puller" variety - which is total bunk as they rely on a pin pushing the end of the motor shaft - and the pinion end is solid.

No-one ever came back with a sucessful method.


The "best" response I think is probably still wrong - I tried it, just to gauge how firmly the pinion is pressed/bonded on ... I still don't know, but I found out the bit that holds the windings in place is not held on the shaft anything like as strongly

Having (probably) trashed a motor by massively increasing the end float, I didn't feel too bad about experimenting further on it.

Conclusions: 1 - if you lock the rotor with long screws through the mounting holes, you can accurately drill a hole in the centre of the pinion (with a centre drill), exposing the end of the shaft. I don't think you could make it big enough to get the pin of even the smallest off the shelf gear puller on there though, not without using an end mill at least.

2 - attempting to turn off the pinion a couple of 1/1000" at a time takes forever, but does work ... right up until the point it doesn't - that point being when it meets the slightest bit of resistance, when it turns out that bending the motor shaft takes a lot less energy than getting that resisting flake of brass off


It's not a (total) failure when you can learn something though - I think I can give a definitive answer to a couple of Tamiya 380 motor related questions:

Q: How do I take the brass 10T pinion off a Tamiya Grasshopper etc 380 motor to use it on a different motor?

A: You don't - you buy a different 10T, 0.8 mod pinion instead.


Q: How do I take the brass 10T pinion off a Tamiya Grasshopper etc 380 motor so I can put a different pinion on/ use the motor for something else?

A: You don't - you buy a different 380 motor, one without a pinion already pressed on.
     




nb - I wasn't prepared to trash any more motors, so followed the above & bought "bare" RE-380 motors instead.
 

Couldn't you cut the pinion between 2 teeth with a carbur disc on the dremel?

Third solution use a hammer. And if it is not enough, take a bigger hammer.

Me thinking right now : If you can't fix it with a hammer, it's an electrical problem...

Can you use a bit of heat on the pinion? its should expand and come off easier. 
 

First, the easy bit ... replacement 380 motors arrived:



Also tested the trident Xt-20 ESCs - they appear to be genuinely instant reverse I had them hooked up to "sweep" function on a servo tester & there's no evidence of any difference in delay going from one direction to the other, and no evidence of them being reduced power in one direction.

This is a good thing, as it means I can use them to drive the steering motors


I also expended some skull sweat on just what the steering motors would drive. First thought was a post, fixed at the bottom but free to rotate. This would have a large round hole through the side, which would have a fat pin fitted. That pin would have a threaded hole through the "side", through which a length of studding/allthread would rotate. The post would have slots on both sides to accomode some difference in angle between the two chassis.



This would involved a lot of milling that I can't do, so would end up being filed with inevitable poor fit and/or finish. I also don't think it's particularly elegant, and is quite "tall" (for want of a better word) with mismatched height of fixing at each end.

Plan B (for "better", I hope)  would instead involve an internally threaded tube with a rose joint on the end (for horizontal and limited vertical compliance), effectively making a pseudo- hydraulic ram. I'd hope to buy the tube rather than make it, and it would need to have some pressure/vacuum relief somewhere near the closed end. A rubber boot to hide/protect the thread is an option. Travel would be limited in the "inward" direction by the studding hitting the end of the tube/rosejoint fastener, and overextension would be prevented by having a 2nd "ram" operating in reverse on the other side. Length of both tube and studding would be critical for correct operation. I'm thinking M10 x

I can't see anything wrong with the plan ... but it did kind of pop into my head fully formed, which makes it a bit suspect

Thinking some more about this, the ram design is ok, but would be less work if the fixed end with the rosejoint was the threaded bit, and it was the body that was driven by the motor ... even less work if the body was a tube with a long nut in the end. Let's call that plan B2

I'm thinking that the motor end also need to be able to rotate as the ram gets shorter/longer & the angle changes. It wouldn't matter if the trailer was just trailing, but as it's powered there's a likelihood the whole arrangent will parrallelogram, and the trailer look like it's trying to overtake the forward car I'm not sure how much the angle changes and whether a UJ would be enough to cope with it - an how critical the geometry / UJ position would be.

Looking at the construction of the chassis, it's the bare minimum it needs to be to save weight, the sides are 1.6mm aluminium & the base and ends are flaxible plastic around the same thickness.

I'm now thinking that all the extra weight of two extra 540 motors, gearboxes, eSCs, rams, bracketry & fasteners is going to be a real problem ... and does it even need it? Could the two chassis simply be fixed together & the whole thing driven skid steer, with one ESC for both tracks on each side, and two vertical sticks on the TX? Does it even need to bend in the middle? A single trailer point type hitch allowing movement in all directions is more elegant than two links only allowing up/down movement, even if it is a little heavier & more work ... it also relies to the angle changing - and changing back - by which side is taking the longer/shorter route. I can see it also needing some sort of angle limiting, to stop the tracks running in to each other.

I think I need to do some experimenting ... but I'm still waiting on the spare gear frame & pinions.

I've also spotted that the arm for the snowplough will occupy the same space as the end of the right 380 motor

You maybe use 2 unibals axles and nearer from the center or only one in the middle. Avante type uniball. ?