Hirobo 44Bs and Zerda :-)

[silvertriple 4084]

I was a bit sick yesterday evenning, and did nothing...
This morning before my day of work, I thought about some parts I should have somewhere in the box with all Hirobo parts, as I ordered those specifically for this (And I almost forgot about it): Kyosho Optima differential innards...

Both teeth numbers and mod are the same. Which means it is the same cone. A quick check showed the diff body needs some adaptation : there is not enough room at the back of each big bevel gear to insert a shim washer to avoid the pin to grind in the diff body, but beside this it would work perfectly with an original diff... I decided to create additional version of the diff bodies (MXL and GT2) suitable for optima innards and including a ball bearing sleeve for 5x8x2.5 bearings.

Then I did a quick definition of the shafts this version of the diff would require...

A print followed to do some testing...

It works perfectly. I'll have to find a way to do few shafts (have what is required to equip 4 diffs this way in terms of bevel gears).

After this I had a bit of work for the presentation side... I made some specific parts targeted for FDM printing, and I wanted those to be visible in my main presentation of the part set... And I believe I need to make the way to print them easy to understand. I printed them in a certain way, and I'm sure it works as I run my Hilux with those parts...

The current state of my parts preparation is now the following.

 I still need to work out version of rear hubs and knuckles adapted to modern axis with double bearings instead of the big bearing. I still have to identify the proper parts for this, I have some options, but I would prefer to keep the original width than to have a larger width because of the axis...

[silvertriple 4084]

I'm off from the work for the day, so it's time to work on the wheels shaft...
Thanks to threesheds user on rc10talk, I identified a long time ago HBX wheel shafts could be a solution for this. They are easy to source (widely available), they are cheap, and they are shorter than many other solution I could look at. So this is my pick.

I have one set at home, I modeled it in order to figure out the adaptations required... Here installed in the fron knuckle. I designed an adaptor, which will both allow to fix the bigger bearing and center the smaller one.

As mentioned by threeesheds on rc10talk in his Zerda thread, only some filing is required to make this work with an original part...

The adaptor itsefl looks like this. I decided to go for countersunk screws which will allow to run with hex. The idea is to adapt rims in order to limit the 3mm adapatateur impact to the minimum vs the car original design...

And it works for the rear too

Looking at it, I have more and more envy to make a Zerda from nowhere from this project...
I therefore have to deal with the metal parts which are not necessarily easy to find nowadays, and I refuse myself to use the few already bended parts I have remaining from the Zerda I got initially...

I'm not too far from being able to launch the order for final validation printed parts. I just need a few additional checks before that, and this project might enter in sleep state for some time from now...

[silvertriple 4084]

Modified the adaptor design in order to have something more reliable, with no contact between the bearings. I replace the smaller bearing by another one with a flange (105-2Z)...

This is much better now... I'll also update the knucles and rear hub carrier by introducing a small chamfer...

[yogi-bear 2468]

I haven't followed this thread in a while, you have come a long way!

For the metal gears etc, is it worth trying to find other brands that are similar and modifying to suit?

[silvertriple 4084]

9 hours ago, yogi-bear said:

I haven't followed this thread in a while, you have come a long way!

For the metal gears etc, is it worth trying to find other brands that are similar and modifying to suit?

Well, in everything I do I try to find a good balance between authenticity and cost. In the case of those Hirobo, the few parts required for the transmission are :

- small pulleys (originally MXL, but GT2 could be a good fit with printed diff and big pulley) : those are easily available so there would be no modifications

- differential internals : I had consideration for printing them in metal (cost without taxes and shipment : about 30€ per diff), but it's more expensive than adapting Kyosho bevel gears as a set of Kyosho internal gears is going to cost about half of printed parts for one diff

- out diff drives : there is two things to take into account are the bore needs to correspond to the diff shafts and the wheel axis input format that needs to be the same. Finding suitable element may not be easy for some cars, but here it should be piece of cake, due to the way the shaft is driving the part.

- wheel axis : one key difficulty. Those cars design was based on a single bearing. Therefore they are short. Nowadays, most designs are relying on a double bearing in the hub. That constraints the design if you want to get back to the original width and behavior of the car

- dog bones : it's mainly an issue of length, and generally, they are easy to source...

Other elements are shafts and sleeves, and it is always easy to adapt...

At the end, until now, I rarely found something fitting without any adaptation. And in a case like this project, I'd like the files to be usable to replace original components, with all what is around...

 

[silvertriple 4084]

GT2 pulleys have a different pitch than MXL pulleys... 2mm for GT2, 2.03mm for MXL.
While for the short pulley, this appear to be something we can neglect, this iis not the case on the long belt.

I made the diff in 42T in GT2,  like for MXL. The outside diameter in GT2 is a bit smaller than the MXL one. I had to draw the pitch line, measure each segment, and sum them to get the length.
This means identify the pulley diameters, offset them to identify the pitch path, and for the rollers, you have to do the opposite.

Measured length is 666.8, and taking into consideration the top roller is not in the lower position right now we should be able to go for 668 length, which means 334 tooth. MXL belt is 336 tooth.
I'll have to check this in real and reconfirm. The same should apply for the 44B-LWB chassis (the difference linked with he kickup is very small).

For the 44B-SWB chassis, the original belt is 280 MXL. We can target 278 Teeth for the GT2 belt (or 556 length)... Once again, I'll have to check this in real...

Today, I made some additional checks on the upper deck. I even printed one in PLA, to confirm the length (I still have a doubt because of the servo collision) : the whole car relies on the parts flexibility, and therefore, doubts will be there until I build a car with the parts...

[silvertriple 4084]

Assuming the principle we want to target the original geometry or be as close as possible of it, we have to rework the rims for this if using the HBX axis and the double bearing adaptor...

Here is the original rim with the orignal axis

I defined an hex specifically for this, and modified the rim accordingly... This way, there is actually no impact on the rack width...

For the 44B, the situation is slightly different : the rim center is not thick enough to do the same. I made an offset of the external faces in order to make room for the hex. The rim circle remain positioned where it was initially...

Last checks were done here and there. I may still have to modify the upper deck post and the shock tower once everything is going to be printed in order to make sure the servo is fitting there. The upper deck position is key, and since there is some flexibility involved, this is never easy to deal with... This will wait the order and delivery of the key printed parts...

I may still need to include elements to rigidify the main chassis part for printing and that is something that may push some discussion with the printing provider, I guess...

[silvertriple 4084]

Prints for the Zerda were ordered last week. I'm crossing fingers on the chassis which is the main part with deformation risks.

I'm currently thinking about finalsing this project. When the parts will arrive, I still have to find out a few elements to complete my build (beside ball bearings). The diff will rely on Kyosho diff internals as previously mentioned...

But this will require some custom shaft.

The plan is to use 5mm rods, to cut, drill and machine the flat area...
For this I thought about a small set of two parts which will allow to make sure everything is lined up properly...

Print is ongoing, rods should be there by wednesday... Let's see where it goes...

[silvertriple 4084]

Parts arrived today around 3pm. I had to wait until my work was over to start looking at the printed parts...

My main concern was the chassis. I was worried as there was clearly a risk of deformation. That being said, if I need to do something about it, I need to understand what deformation we are talking about...

It's here, so now, I know.

And de facto, there is some deformation. This being something I should worried or not is a key question... But before trying to respond here, let's look at the rest...

Yes, all plastic parts were 3D printed. I also printed 2 set of front hubs (one is for 44B, because I forgot to remove it from the order - I might have to key another order to build a 44B next  :-) ).

Now, trying to answer the key question :

First, only the chassis is having some deformation. It's not as bad as I thought initially. Belt cover as no deformation at all. Roll cage parts seem fine as well (MJF printed, I will do a black cage, after all, this is a kit). Another indication is that when I put the central part of the roll cage in the chassis, the chassis is getting back close to the expected shape, and it is not yet fixed together with screws... I would expect that once everything is in tension, it should be fine and more or less in shape...

Last question I will need to answer : should I keep the parts white or should I color them. And if I color them, should I color them red of something more unusual?

[silvertriple 4084]

Now that the printed parts are here, I had to complete the set of parts to be able to make this Zerda...

I ordered this morning a few parts
- GT2 pulley 18T bore 5, GT2 pulleys 14T, 16T, 17T, 18T in bore 3.125 (I could not find any 15T, so it will have to wait)
- rods in 5mm to make the transmission shafts
- rods in 2.3mm to make the suspension shafts
- rit dye orange apricot to make a distinct non white color for my parts

Belts are already there, as well as HBX wheels shafts, 56mm dog bones (I have the reference somewhere), ball bearings, pivot balls, 3mm rod and associated rod ends (the same as the one I already used for the 44B Hilux with FDM printed parts), optima re-release differential innards...

Regarding the way to deal with the rods cutting and modifications, the plan is to rely on my dremel, a vice, a dremel drill press and printed parts to make the cuts, holes, flat areas and groove at the right place... Maybe I'm too optimistic, but it should work :-)

Last elements are going to be last few parts I will need to get printed, and there is a reason why they are not printed yet: the intension is to make those at some point, conjointly with the upper deck which needs some further thinking as it is what should rigidify my Zerda... 
And another element I need to plan for : out diff drives. I have 4 original Hirobo parts sitting in my parts bin, but I'm not willing to use those. I'd like to find a proper solution so I can say my Zerda have not a single original Hirobo part... I know that an easy way would be to use some Optima original parts for this, but the idea is really to use a part widely available in nowadays range...

[silvertriple 4084]

It is time to figure out something...

Can my plan work?

let's try out if this work with very rudimentary tools.

First the cut, with a manual saw. 

Execution 8/10. It's not perfect but it doesn't impact the functionality. Good enough.

Second, I drilled the pin hole. The Dremel is fixed to the drill press, but unfortunately, I do not have the proper chuck on the dremel. I will need to use the other drill machine. Execution 5/10. It should work. I'll do better on the next ones, once the proper chuck is arrived.

Then the idea is to grind the flat area. I'm quite sure I do not have the right tool for this...

Results
First the part was difficult to detach from the plastic as the plastic melted (not much an issue, that being said). This way to do the hole should work, but let's be clear, it's one jig, on part.

Second is the the flat area. It sucks. I was not able to make it properly with the tools I have : the bit is not the good one, and the drill press is also having some play and that means there is no way to make it proper with this tooling. Execution 1/10.

Need to print more jigs and find a better solution (having no clue about the speed to use with the tools for metal surely doesn't help)... I'm not a mecanician. Mecanician would surely, certainly, do much much better than me...

Anycase, I'm currently contemplating the idea to buy a mini drill with a proper drill press in aluminium from Arrowmax which is likely to have less play than this cheap Dremel workstation... I'm still not sure it would do the job for this specific topic...

[silvertriple 4084]

I decided to use a file, and it worked better...

I will proceed with this approach to do a few more parts, and this will be good to go :-)

[silvertriple 4084]

With a simple file, it works better...

And sicne this is working, it is time to elaborate a solution for the pulley shaft.
First step is cut and file...

Then the idea is to using a saw to do the groove for the e-clip. I had an idea for this (bearing and saw not present on the picture).

A few print later...

And it's time to experiment the solutions I thought about. The groove could be a little bit more deep, but now it his in, make it deeper should be easy...

Need to cut tensionner shafts, and to as well cut the pins and fnd a solution for the suspension shafts... But al of those should be easier than what is done already...

[silvertriple 4084]

I got the groove deeper just by applying more pressure to the saw for longer time with the same setup. It works :-)

[silvertriple 4084]

I still need to cross drill the differential shafts... The printed plastic hole doesn't work good enough for the centering of the cross drilling. I discuss with my friend Dadio, and he suggested to use a piece of rod drilled in the center section to guide the drill bit (super easy to do with a lathe, but I do not have one). 

But first I needed a more precise drill press... I ordered an Arrowmax mini drill during the black friday, and it arrived promptly... But I must say that I'm a bit disappointed by the platform : the drilling bit is not centered in the hole of the platform (seems like amateurish work - this version has a piece to allow orientation at angle, and I suppose the offset linked to that part was never taken into account - I would have expected something more toroughly thought)...

Once you know it, at the end it is just question of measuring to do the proper centering... Then I built over the idea and decided to use ball bearings...

Now, I just have to find a better drill bit. The one I use currently is already dead, but at least it allowed me to confirm the centering is working as expected. I'll get proper drilling bits in 2mm and I'll expect this to be a long drilling exercise due to the limited rotation speed...