Hirobo 44Bs and Zerda :)

[silvertriple]

My 44B-LWB chassis plate was 1mm to short... 336 instead of 337. I noticed that when making supports for my 44Bs. The radio box was therefore having a mm issue somewhere...
The fact is : most of my parts relied on that single chassis plate. Move the rear of the chassis plate and all goes with it: dependancies are a nightmare in that case in (con)fusion360.
Reworking the radiobox required a review of the rear gearbox side (which I know at 100% sure to be right in initial design). I decided to break the link with the original design of the chassis plate to remove the dependancy to make it easier to work out the radio box. if not, I have to redo the gearbox sides, with all risks of making it incorrect.
After a morning debugging, my radio box should be good now. I'll print one in PLA to check it is fine.
Next is the radio box lid...

[silvertriple]

Finally my radio box is good. I printed one in PLA for testing. The lid is currently printing. Next will be one picture with mix printed radiobox and lids...

Even the supported side don't look too bad, this should be quite easy to post process for a nice finish...


I assembled the parts further...


There is a few parts I can't validate right now : many of the Zerda parts are too long for this. Worst case scenario, I will have to get a Zerda printed for the cause (which means I need to find a way for the transmission, as I have no diff for one additional car in the plan).

[silvertriple]

The lid was printed. It goes nicely on both radio box (the original one and the printed one, just like the original one). That being said, I made an additional test, this time on the 44B City. This is the only car where the roll bar is fixed at the rear of the radiobox; other bodyshell relies on the rear body mounts. It was good that I made this test, as I could notice that the lid was difficult to put in place. I modified the design accordingly, and it will now be fine...

For the Zerda, the main belt cover is possibe to print on my X1C. I decided to print it, and to print the chassis splitted : I will use the belt cover to attach the two half parts to check the dimensions properly, after having check the belt cover is having right dimensions...


I also modified the pulley belt cover to give a bit more space around the 55T pulley. This will go for a test print as well over the week-end...

Speaking about pulleys, long time ago, I thought one element that could be consider to make those cars more suitable to nowadays way of running a car would be to convert the pulley to Powergrip GT2 standard. This would allow to run with more torque, and likely less belt skip. This is not really an issue on the 44B, as the chassis is rigid enough on those, but on the Zerda, this is slightly different : if you want to avoid belt skip, you need to get the belt tight, and that means loosing autonomy, and the chassis flex, which is an advantage in some conditions. A powergrip GT2 train would definitely make the things better. That being said, a GT2 belt is thicker than the MXL belt. The kickup of the Zerda might be an issue for this as the belt sides are not running parallel. But apparently, this would work.

I believe I have already the 55T pulley and the diff body somewhere in GT2, because that's the way I initially model them for the Bearcat SS. I will check this, and if not I'll redo them.

[silvertriple]

Looking back in a massive project like this is sometimes hard... Specially when you have lot of dependancies...
The Belt cover for the Zerda is printed. It will require a review to reinforce it : it broke on the front area when removing the supports.
Now, while the center are is good, the front area needs to be reviewed as well: there is an issue in the are where it joins the front gearboxes... Probably linked to the fact that some projections are lost due to some manipulations in one of the files it depends on, and even though I have a valid projection after relinking it, I can't find a way to get the line matching what it should : this screams redo the front part. (I love when a plan comes together )

[silvertriple]

Few test prints done...


The chassis splitted is printed as well


I did some checks and it looks good.


I had not much doubts on the holes positions, as they were already corresponding to the belt cover...


Each hole allow to see the screw head under it...

The profile and size are also good (the front cut on the side is not exact, but I do not see this as critical)


While the print was ongoing, I revised the belt cover file to introduce reinforcement (there was more work due to the fact some projections were lost). I'll do the same on the 44B front belt cover.

[silvertriple]

Reviewed belt cover is printed (the non reinforced part broke at the front, which means I had to reprint it anyway).
I mounted one of the PETG printed gearbox walls, and fixed the two parts of the chassis together with the belt cover...


The rear profile matches with the rear original gearbox (not really a surprise, as my printed gearbox is matching the profile of the original radio boxe)... There is less and less doubts about the chassis and belt cover... I will still do one profile print aiming to check the position of the key screws at the front (I have no doubts at the rear anymore).

The printer is working currently : I'm printing a diff case to recheck it before doing a GT2 version...

[silvertriple]

I printed the diff case, the pulley, and the pulley cover.


Everything is good (I think I already checked the diff case, but I can't see evidence in my recorded pictures).
The next step is to work out a GT2 pulleys... The profile is a bit more complex, but it allows much bigger area of contact between the pulley and the timing belt, allowing for more torque and higher speed than MXL. And both timing pulley and timing belt are widely available (any 3D printer use generally GT2 belts).

[silvertriple]

I made a pulley and a diff case suitable for GT2 standard. I will have to evaluate the belt length required for the Zerda/44B LWB and the 44BHilux.



On this image, there is both GT2 and MXL pulley. Powergrip GT2 allows more contact between the pulley and the belt, which means less wear, more torque, more speed, and less skips for the same tension...


I also printed some bevel gears to put in the diff to check them...


The fact is that I would miss some diffs internals if I want a printed Zerda, as well as diff cups, dog bones and axles... What if I get those printed in Metal?




At least, they are fine as printed parts are working properly in the diff body...

I have a lot of things done and ready.


I thought also about the axles. I could use other axles, and rework the knucles and the rear hubs to work with them and avoid the big bearing or the adapter to use double smaller bearings I made for the original parts... That is going to be one of my next activity.

[silvertriple]

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]

I'm off from the work for the day, so it's time to work on the wheels shaft...
Thanks to @threesheds , 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 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]

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...

[Mango]

A game developer should pickup your files and make a racing game with it, that would be fun!

[silvertriple]

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]

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]

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...