Hirobo Bearcat SS - Let's start something else...

[silvertriple]

Would the revised gearbox halves still mate up with the original ?

Well : revised version halves are going together... It won't work with the original halves. I took the principle you would print both halves if you have to do it: I'll mention this on the page when I upload the files...

Other note : on a French forum someone highlighted it would be great to replace the single bearing on the rear hub carriers by two to get a better axle guide... I'll look into this as well, although this might turn to be a complex task, taking into consideration the axle may be the real limiter there as too short for two bearings...

[GoMachV]

I’m sure you have seen this but if not…
I really like the way he went about this. With a pair of 6x10x2.5mm wide bearings you might have a chance

[Dadio]

I’m sure you have seen this but if not…
I really like the way he went about this. With a pair of 6x10x2.5mm wide bearings you might have a chance

I can't take credit for the idea , I think even back in the day it was a custom part you could buy . Might be harder for the Zerda than the Coyote as the Coyote had a pair of bronze thrust washers spacing the wheel away from the bearing retainer screws and the space of those thrust washers being removed added just enough room for the double bearing , on the Zerda the drive is transmitted to the wheel by a friction disk and the friction disk is a taper fit on the axle , this negates the need for the thrust washers so there is probably not enough space unless you change the axles , changing the axles could mean you could use modern hex drive hubs so no bad thing in the end but it adds to the cost and complexity .

[GoMachV]

Ahh good call. I couldn’t remember if there was a shim or washer, basically that would be the thickness you could have for a separator.

[Dadio]

[silvertriple]

@GoMachV and @Dadio , thanks for the idea...

But in the present case, and I did not check the Zerda which is not yet in parts, here is the problem data :


The axle have 5mm for the bearing, and then comes the hub (conic pressure driven). Extend to anything more than 5mm of bearing would require:
- either axixs change
- either find a bearing that goes around the cup and get the carrier done to fit it (cup external diameter is 9, maybe possible, but I'm not sure there would be enough clearance left around for having a solid carrier...

It appears the most reasonable approach is to change the axle for something longer. I'll have to check what is in the Tomahawk kit box for the axles...

[GoMachV]

I’m picturing 6x10x2.5 flanged bearings (MF106-ZZ) which would be 2.5mm and the flange is spec’d at .6mm wide and 11.2mm in diameter. That leaves some meat to fit the 5mm wide 13mm diameter hole pretty easily.

[silvertriple]

I’m picturing 6x10x2.5 flanged bearings (MF106-ZZ) which would be 2.5mm and the flange is spec’d at .6mm wide and 11.2mm in diameter. That leaves some meat to fit the 5mm wide 13mm diameter hole pretty easily.

That's a way, but i'm actually questionning the interest for the axle guidance : that would not change anything compared to a bearing of the original size (I finally found some)... And looking at it, the carrier may have more play impacting the guidance than the axle in the ball bearing itself... Not sure it is worth the effort, except to reduce the cost of the assembly (which could be interesting, that being said, considering four 5x13x5 ball bearings are about 22 € without the shipment - and I have some MF106-ZZ sitting somewhere)

[GoMachV]

The two rows of smaller bearings vs the one row of larger ones imo would be worth the time and effort. Instead of the axle support only in the middle, it would have support both on the inside and outside of the axles bearing surface

The bearing size I saw in the manual was 6x15 (696ZZ), is it actually 5x13?

[silvertriple]

The two rows of smaller bearings vs the one row of larger ones imo would be worth the time and effort. Instead of the axle support only in the middle, it would have support both on the inside and outside of the axles bearing surface

The bearing size I saw in the manual was 6x15 (696ZZ), is it actually 5x13?

The manual you displayed here is likely the Zerda one... That being said, it's right, I typed it wrong (maybe I'm bit more tired than what I thought :-/ )... it's 6x15x5.. Damn! Luckily I did not ordered any bearings yet!
I did not thought about the what you mention, and effectively, it would make sense. Only need to find the proper bearings...

[silvertriple]

and to remove all possible confusion :
- ball bearings for the shaft in the gearbox 4x13x5
- ball bearings for the rear wheel axle : 6x15x5
- ball bearings for the diff : 9x17x5

[silvertriple]

for the wheel axis, using the proposed method and flanged bearings en 6x10x2.5,





That will do it, and i'm likely to have just the bearing needed for this in one of my boxes

Need to check if I need to adapt something for the shaft 4x13x5 bearings or not... (EDIT : no - easily available and there is one bearing on each side of the shaft, so not worth the effort)

And obviously this should work with the Zerda as well...

[GoMachV]

Clearly hirobo didn’t think about bearing sizes when they designed these things Cant we all just 5x8 and 5x11?

[silvertriple]

Clearly hirobo didn’t think about bearing sizes when they designed these things Cant we all just 5x8 and 5x11?

Let's remeber they were the first to deliver a car full ball raced. They might had an approach slightly empiric, based on availability and costs (same as Akira Kogawa when considering ladder chain vs timing belts : the choice was likely cost and availability conscious, based on the period)...

[silvertriple]

Within the last straight line for the Hirobo Bearcat SS push to Thingiverse...

It's currently about finetuning and test print...

I started by trying printing a topdeck section to check my chassis measurements. The print failed multiple times, and therefore I stopped trying and just checked the dimension from the elements which were on the bed at the last fail.

Good news is that it is corresponding... I worked then on the printer to get the bed cleaned and to level it again to get prints working again. I still have an issue in a specific area of the bed that I can't explain, and it doesn't allow me to print the top deck as it hits that area...

I then printed the left part of the gearbox (not the modified one but the original one)

The target here was to check the correspondance with the original right side of the gearbox : it matches and the inside dims are right as well. With the left side, I was also able to check the fitting of the motor plate (perfect), and the fitting on the chassis (perfect again).

I launched a print of the bonnet as I do want to see how it looks in real and how far it is from the original one...

During the prints I did work a bit on the differential : I wanted to check it is right, and rechecked dimensions. I won't print it now, but the diff should work. I'm planning to do a full Powergrip GT2 version of the gearset as well (should be printable even for the small pulleys in MJF PA12 glass filled).

Then I decided to focus on the front knuckles. The axle is inserted while hot with pressure. It works ok, but once you get a nut locked on it or too tightly torqued, it goes with the wheel once you are trying to unscrew it. I have a brand new set of knuckles but I want to provide a solution for those who are not able to find new knuckles...

Basically, using a M4 bolt, we should be able to replace the axle easily. I reviewed the plastic part of the knucle to work with a bolt inserted in it...


Once this was done, I just reinforced by extending the diameter around the axle.


I may still do additionnal mods to include M3 holes instead of M2 for the pivot balls... But at least I made some progress today...