Again another Marui project : Super Wheelie and Big Bear!

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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

Dadio wrote: Thu Jun 22, 2023 8:06 pm Makes you think all metal transmission for vintage cars being within reach , to my mind the gears are the biggest bottle neck to really driving it like its the 80's
Thinking the same - lot of ideas in :-)
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by Dadio »

Refreshing to see it driven hard :D , you see so many YouTube films of people really driving so slow and careful , just seems a shame to see such dynamic machines reduced to crawling about .
If a jobs not worth doing then its certainly not worth doing well.
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

I'm quite confident that if there is a weak point it is the diff, I needed to test it :-). So running hard is the way :-)
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

A bit of disappointment today after yesterday's success...

I took the Super Wheelie and mounted the SLM printed idle gear...
Image

Shaft hole is perfect, and the movement seems fine until I close the gearbox. When the gearbox is closed, the shaft is in the right position and it's too tight. I suspect the root diameter is too large of .1 or .2 mm.... It would be still in the specs of the printer, but too big for the use... It worked perfectly for the Big Bear this is not the case for the Super Wheelie, they were in the same print batch, and the conclusion is that the result might be unpredictable...

This need more work again :-)
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by Dadio »

I'd try swapping them to see if it's a difference in the gears or gearboxes first , there's a lot of possibilities , I found quite a spread of sizes with genuine yokomo 834b gears of different generations .
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

Dadio wrote: Fri Jun 23, 2023 7:21 pm I'd try swapping them to see if it's a difference in the gears or gearboxes first , there's a lot of possibilities , I found quite a spread of sizes with genuine yokomo 834b gears of different generations .
Well, I measured the gears and external diameter of the SLM printed gear is definitely larger and it gives an outside diameter of 19.4mm instead of 19.2 mm for the outside diameter reference as per a gear calculator. MJF PA12 gear was 19.2... This confirms the print predictability issue, as likely the inside diameter and tooth profile are offseted on this gear. And yes, it is still in the printing specification.

Spoiler : it's not the same situation on the Big Bear, where the gear drops in perfectly.

In fine more tests and prints are required, but i'm not sure what I can do to mitigate this : If i apply an offset to give more space to the gear, the profile of the tooth wont be the same, and if it prints more accureatly it would be wrong as well...
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by Dadio »

Tolerance problems suck , I'd guess that if you had a complete set of steel gears then you could accept printing them at a -% of full scale and they would still be strong enough , I've played with scaling gears to get them to be the same size as the original, as I mentioned with the Yokomo 834b they are meant to be 0.8 mod but they measure smaller than a gear generated in Fusion with the same tooth count so I scaled them down fractionally , it's not so demonic to good mesh as you may imagine , I think the issue with the 834b gears was probably from contraction when cooling after injection molding, but they ran against metal pinion gears that will have been correctly machined to spec without issue .
If a jobs not worth doing then its certainly not worth doing well.
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

Well, I'm still puzzled as the Big Bear idle gear which is 9T-25T mod 0.8 is right while the 9T-22T mod 0.8 is too big while printed at the same time in the same printer: not sure how to scale to get it right...
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by Dadio »

Do they list their printing tolerances for printing ?
If a jobs not worth doing then its certainly not worth doing well.
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

Dadio wrote: Sat Jun 24, 2023 6:58 am Do they list their printing tolerances for printing ?
yes, and it's in the printing tolerances, as mentionned previously...

EDIT : I initiated discussion with the provider to recheck this point. Tolerance is announced as +/- 0.3mm or within 0.4%. And 0.2mm on 19.2 makes it for about 1% so more than 0.4%. The or is the question. I'm getting confirmation with the support and I'm likely to file a quality complaint based on the result.
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

The printing specifications are the following for SLM
Image

I had quick discussion with the support and it was dissapointing... The support guy just killed the principle of the rapid prototyping using 3D printing in one single statement.
Image
The way the tolerances are stated "±0.3mm OR within 0.4%" makes this clearly not suitable for gears.

I'll check with other providers for SLM...
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

That being said, i'm tempted to order a few to see what is the deviation and assess how I could design a part which fits the requirements with a higher percentage of chances...
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by Dadio »

I guess if you were printing mod 1 gears you could easily allow for the tolerance but with mod 0.8 it's harder .
If a jobs not worth doing then its certainly not worth doing well.
A problem shared is a problem halved but an advantage shared is no advantage at all.

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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by silvertriple »

Yes, but there is absolutely no room to make this in mod 1 in this gearbox... I had a quick look at cnc and cost would be crazy high... I need to think more...
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Re: Again another Marui project : Super Wheelie and Big Bear!

Post by Dadio »

silvertriple wrote: Sat Jun 24, 2023 8:15 pm Yes, but there is absolutely no room to make this in mod 1 in this gearbox... I had a quick look at cnc and cost would be crazy high... I need to think more...
The honest way forward may be to publish or sell the file and let people decide for themselves how to proceed .
If a jobs not worth doing then its certainly not worth doing well.
A problem shared is a problem halved but an advantage shared is no advantage at all.

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