Bormac's Nichimo Midships 443 WDS - An unexpected project

[silvertriple]

After the short but effective Samurai break, let's get back on the Nichimo...

First, I was highlighted that there is some differences between the Midships to chassis and Exceed top chassis. Analysis of the instruction manuals shows they use a different MSC. My car is a indeed a Midships chassis with an Exceed roll cage. I therefore contacted an owner with multiple instances of Exceed to get some measurements and further detail pictures...

Few minutes later on that was sorted out, and I have now as well an Exceed top chassis.


I also worked out the shock towers (Spirit/Vantage minus one bent), and the battery retainers (inverted from the FF cars).


(and if you are asking yourself, this is actually a picture of each chassis in its current state)...

Then had a look at my front gearbox to note down some key information, that will be of use later on.

(I could spend hours looking at those views)...

This morning, I started by putting some additional elements on the front train....


And as I'd like to be able to complete the front gearbox, I need to get into the details of the center differential
Spur gear is 54T, Module .8. Once this is clear, that was quite quick to get the part into Fusion360...


Next is the two pressure rings - very easy to deal with as well...


Had a look into the bevel gears, and they are in module 1. Smalls are 10T while bigs are 14T... This is my next activity, basically

[silvertriple]

My wife was managing a go live in her company this morning, and she is having her desk in our room when she is working home. The result is that I woke up quite unusually early this morning. And it seems that my neurons are melting right now...

I did progress this afternoon, but sometimes it was more difficult than usually...

First, I did check the data for the bevel gears on the same calculator I used when I did the bevel gears for the Spirit.


Once you know the cone information, it is easy to derive the data from there. First you use a plugin to create spur gears in the proper module and move them as per their definition rings.


Next you pivot them on their contact point as per the angle defined by the cone (check the calculator for this). And you Loft the profile of the tooth on the cone...

And you repeat this for the next bevel gear


Then a mirror for each bevel gears, and you get your diff bevel gears....


Next was the rest slipper rings and spring rings...

(I may need to do the full transmission like this. On the box art there is just this representation (with different colors), and I find it would make sense to have the same with the front and rear diffs as well )

I've put the diff in the gearbox, and I'm not too happy with it.


I do have to model a few elements which would add into the gearbox : flanged ball bearing and setting system. and there is one of the axis missing. once this will be done, i'll have 5 part to add to get the full transmission done... It definitely goes faster than what I expected...

[XLR8]

Extraordinary work as always sir.

That center diff is interesting. The small bevel pinion gear appears to have a square section projecting from the back that interfaces with a 90 degree notch cut in both inner rings.
I'm probably missing something here but doesn't the notch prevent the pinions from rotating when the diff is fully assembled, installed in the diff housing and the wave springs are applying a load to each ring? If so, then why have friction discs?
Sorry for the questions, mechanical things fascinate me; I always want to understand how they work.

Anyway, thanks for making such detailed posts.

[GoMachV]

The 10th post on this topic has a link to my YouTube video showing the center diff in action. It’s an odd duck for sure

[silvertriple]

Extraordinary work as always sir.

That center diff is interesting. The small bevel pinion gear appears to have a square section projecting from the back that interfaces with a 90 degree notch cut in both inner rings.
I'm probably missing something here but doesn't the notch prevent the pinions from rotating when the diff is fully assembled, installed in the diff housing and the wave springs are applying a load to each ring? If so, then why have friction discs?
Sorry for the questions, mechanical things fascinate me; I always want to understand how they work.

Anyway, thanks for making such detailed posts.

First, Doug, thanks, and second, please don't worry to ask questions: first it helps me also to understand or formulate things in a better way (that's the way I work), second, when meeting students, I'm used to say there is no stupid question, but eventually stupid answers.

As @GoMachV showed in his video (revert back on the first page of this thread), this is exactly working like this. The parts are plastic (except the small bevel gear), and I suppose the friction discs, which are actually cloth more than anything else are there to reduce the wear of the plastic parts on which they sit.

The internals of those Nichimos were somehow quite innovative (and known for that) and still fascinating today. The Spirit and the Exceed Pegasus looked like ugly Hotshot copycats, but the reality is slightly different : they were much more inventive than the Hotshot actually. The ugly ducky look did not help for sure, neither the newspaper reviews pointing complexity, low ground clearance (about a centimeter), and other elements...

Any case, after my last post, I was supposed to stop the Fusion 360 work... But I'm in vacation currently, it was raining outside, and I have this front gearbox bugging me...
Review all the parts and positions one by one, identified a few mistakes (i'm no perfect), and corrected everything, and completed with the additional missing parts, washer and spacers. Only things missing are now the motor and its pinion...


At this stage, some of the parts of the differential don't have the minimum thickness to be printed anyway... I'll try to do something, but when you have .5mm of material and no room to increase this there is no other option than to reinvent the differential. I may eventually do that at some point (I've been contacted by a Nichimo owner asking for a solution to be able to use an Exceed without the slipping differential issue), but for the time being, I'll finish the CAD model, and I'll try to understand how this things work in reality (I suspect I'll have to work without printed gears this time but that may be for later...)...

[XLR8]

The 10th post on this topic has a link to my YouTube video showing the center diff in action. It’s an odd duck for sure

Oh yeah, thanks for that.
I guess it's meant to provide resistance (limited slip?) but it appears the amount of resistance would vary as the pinion rotates and spreads the plates. Sorta like a detent.
Apparently, there's a lot about center diffs that I don't understand.

[silvertriple]

Oh yeah, thanks for that.
I guess it's meant to provide resistance (limited slip?) but it appears the amount of resistance would vary as the pinion rotates and spreads the plates. Sorta like a detent.
Apparently, there's a lot about center diffs that I don't understand.

Yeah, even with the video, there is things that are unclear to me.
- how the big bevel gears are surviving to the treatment
- taking the assumption the diff is going to inflate by defaut, i'm not sure how the power is reaching the front and rear dif...

There was a few washers added between the front diff and the motor plate, I guess the springs are not as strong as they were initially and I'm not sure how this thing will really work. That being said, central diff is often unclear for me, and even worse when there is settings: it adds complexity and parameters to manage... And in the case of this Nichimo, that is even worse as it is simply not reachable easily (the number of screws to remove to access this thing is huge (even more on the Midships than on the Exceed/Pegasus)

[silvertriple]

Added knuckles assemblies within the rear gearbox


Once that was done, I went to the chassis to add the propeller shaft. I had a doubt on the full chassis dimensions but I think i'm not in bad shape


Transmission is now complete... (I'll have to work out an exploded full transmission). I still have to add motor, pinion and radiator material (2 parts), and this will be done in the chassis file, as I need both front gearbox and chassis for the dimensions...

While at it, I also added the servo savers.


Shocks are the same as the spirit, and steering tie rods as well, at the exception of the input rods (and there is 2 of them); sway bars are the same as the front Spirit one.

In short, still missing (not in CAD yet - taking into consideration what I have from the Spirit):
- radiator (2 parts)
- input steering rods
- servo horn
- Midships : body shell, wing, roll cage (10 parts), resistors support, tire, wheel hub
- Exceed : body shell, wing, roll cage and roof (8 parts) resistor support (wheels, hubs are the same as the Spirit)

[XLR8]

Oh yeah, thanks for that.
I guess it's meant to provide resistance (limited slip?) but it appears the amount of resistance would vary as the pinion rotates and spreads the plates. Sorta like a detent.
Apparently, there's a lot about center diffs that I don't understand.

Yeah, even with the video, there is things that are unclear to me.
- how the big bevel gears are surviving to the treatment
- taking the assumption the diff is going to inflate by defaut, i'm not sure how the power is reaching the front and rear dif...

There was a few washers added between the front diff and the motor plate, I guess the springs are not as strong as they were initially and I'm not sure how this thing will really work. That being said, central diff is often unclear for me, and even worse when there is settings: it adds complexity and parameters to manage... And in the case of this Nichimo, that is even worse as it is simply not reachable easily (the number of screws to remove to access this thing is huge (even more on the Midships than on the Exceed/Pegasus)

Sorry for beating a dead horse but I can't seem to stop thinking about this so I have a crazy theory to toss out there. The car's center diff with spring detent is meant to aid front wheel traction:

1) Traction control can be achieved through non-linear application of torque to the drive wheel. The momentary lose of torque permits a slipping wheel to re-gain traction.

2) Having a center diff is desirable while cornering because the front and rear wheels travel a slightly different arc so the speeds at the front and rear diffs are slightly different. The center diff accommodates this speed differential.

3) As the car accelerates out of a turn and down a long straight for instance, weight Is transferred to the rear wheels creating an imbalance in available traction front-rear and with an open diff (no resistance), the front wheels begin to slip. The resulting front wheel slip equates to a loss in forward drive. However, with an intermittently locking (or resistance) center diff, torque to the front wheels becomes non-linear which allows the system to function like traction control.

How crazy is that?

[silvertriple]

Oh yeah, thanks for that.
I guess it's meant to provide resistance (limited slip?) but it appears the amount of resistance would vary as the pinion rotates and spreads the plates. Sorta like a detent.
Apparently, there's a lot about center diffs that I don't understand.

Yeah, even with the video, there is things that are unclear to me.
- how the big bevel gears are surviving to the treatment
- taking the assumption the diff is going to inflate by defaut, i'm not sure how the power is reaching the front and rear dif...

There was a few washers added between the front diff and the motor plate, I guess the springs are not as strong as they were initially and I'm not sure how this thing will really work. That being said, central diff is often unclear for me, and even worse when there is settings: it adds complexity and parameters to manage... And in the case of this Nichimo, that is even worse as it is simply not reachable easily (the number of screws to remove to access this thing is huge (even more on the Midships than on the Exceed/Pegasus)

Sorry for beating a dead horse but I can't seem to stop thinking about this so I have a crazy theory to toss out there. The car's center diff with spring detent is meant to aid front wheel traction:

1) Traction control can be achieved through non-linear application of torque to the drive wheel. The momentary lose of torque permits a slipping wheel to re-gain traction.

2) Having a center diff is desirable while cornering because the front and rear wheels travel a slightly different arc so the speeds at the front and rear diffs are slightly different. The center diff accommodates this speed differential.

3) As the car accelerates out of a turn and down a long straight for instance, weight Is transferred to the rear wheels creating an imbalance in available traction front-rear and with an open diff (no resistance), the front wheels begin to slip. The resulting front wheel slip equates to a loss in forward drive. However, with an intermittently locking (or resistance) center diff, torque to the front wheels becomes non-linear which allows the system to function like traction control.

How crazy is that?

I like your explanation, and cI can relate with some elements in the real life with my experience with cars with ESP and front drive and the way it reacts in roundabout with the feet hard on the gaz (don't try this on the road)...

So far on r/c, I do not really have experimented cars with central differential. The Samurai is my first. The center diff have a setting, but in the case of the Samurai, it is more a linear one. At least it's easier to understand the more you tighten it, the more it is close to a simple gear which transmits the power on both rear and front the same way...

In the case of this diff, I still have some doubts on how the conditions the pressure rings are opening... I will need to do some tries in practice at some point...

And yes, it bugs me as well

[silvertriple]

Progressing small step by small steps...

Had to add the motor on the gearbox to build the cooler component... It's presently with a 15T pinion (there is 2 other positions for 12T and 18T pinions - I'll talk about it later ).


While at it, I checked the pinion was lining up with the spur gear of the differential.


Once this was done, my first action was to check the chassis... and I had to rework the motor cut slightly.
After having done the modification, I also check with the extreme position (18T) to see if it worked


Next I designed the motor cooler. 3 parts : one on each side of the motor, and another that close the chassis. The right part is also going under the chassis and participate as a reinforcing it...



On the bottom view, it gave me an occasion to check the position of the chassis fixation holes. and they were wrong of a 1/4 of millimeter. That was quite quick to correct


I had also a small issue on the top chassis, and that was corrected as well...

Yesterday evenning, I added the shocks to the common file


And this morning added all the rods and rear sway bar. The front one need to be added on the respective files as there is some specific part that also serves as support for the roll cage...


Front sway bar aside, all the mechanical elements are now done.

[Dadio]

Clearly a rushed and shoddy job , just look at the track control rod ends out of alignment
Seriously good work and quick too !

[silvertriple]

Clearly a rushed and shoddy job , just look at the track control rod ends out of alignment
Seriously good work and quick too !

I already spot rear input rod ends issue : the rear one is actually colliding with the top chassis at the rear end. Another mistake somewhere. I believe the servo savers are ok, so that means that either I did not used the right pivot balls (very much possible), one measure of my top chassis is wrong, or the servo is not properly positioned (too high, which means either the servo mount is different while I believed it to be common to the spirit or the mounting holes) or the servo horn is too thick... I will work out the Midships body shell first and will check later (I've got a todo list with some elements to correct on my notes - there is less and less of them to tackle - I prefer to do it later as the bodyshell may give some additional issues).

[silvertriple]

After my last post, I did tackle some Lexan (virtual one, even though I have a bodyshell to cut for one of the car I need to finish)...

First, I focus on the Ari scoop, which is common to both Midhsips and Exceed if my understanding is correct... I used the same principle as with the top chassis : multiple bodies and cut applied distinctively to bodies before combining them and apply the shell...


Then I had one other complex part to deal with: the body shell. Compared to it, the wing will be very easy.
First started to create a sketch to describe the top view (the picture doesn't have everything, as I added other thins later on.


Once that was done, I defined y different bodies. The platform, the center part, and other additions, and again applied features to each of the bodies distinctively before combining and apply the shell...


Once the shell was applied, I just had to finalise and work on the sides...


And I did not resist to apply some paint to it


(The summary is quite short compared to what it was really... )

[silvertriple]

Still in vacation, so I took benefit to move forward on that beast...

First, I wanted to complete the wheels. The hub is different from the Spirit hub, so I had to model it. At some point, i noticed something : what I was thinking to be a chamfer with wear is actually something else. I had to remove my glass and look closer to discover nuts ... It's useless, but since I know it is there, and the fact it is super easy to do, I did it


After that, I had to take care of the tire. I'm still thinking about TPU for printing tire, and I saw some videos with some rubber resin printed tires, and the result seems very good... I keep that in mind for later, but in the meantime, applied a profile, a revolve...


Then two sketch , 4 revolve and 2 circular patterns after, I got a tire...


This tire was later reviewed as the profil was too flat...

I also inverted the steering rod ends, so it looks proper now...


This morning, I started the roll cage, and I'm likely to post about it at some point tomorrow, as there is still one part to tackle... I did not finished today, as I got multiple interruptions within my day for lot of various reasons.