The Jaguar XJR-12 Group C I wanted in '91

[Pylon80]

@GToddC5 this is the first Group C chassis that I see with a MSC installed. Thank you for sharing!

 

[GToddC5]

@Pylon80 My first as well, I am very happy it came with it, so now I know the proper way to install when I build my vintage XJR-12 

[Pylon80]

I took the Jaguar out to a parking lot I don't normally go to. I wanted to see how well it would handle poor surfaces with cracks, pebbles and dust, after the subject was discussed here on TC:

I am sure there are some worse spots than this in the world, but this is really the limit of where I normally go, preferring the nice and smooth tennis or basketball courts I have close to my house. Well, the car really handles the roughness very well, thanks to the soft springs I installed at the front (50509). The rear could be softer but it didn't really bother me. What did bother me, but cannot be seen on the pictures, was the ridiculous amount of black dust that was everywhere. There is even a section where I would simply loose control of the car altogether because the dust was so bad. Then the entire chassis ended up covered in brown/black dust. So I decided I would do a full rebuild!

The Group C chassis is by far the simplest and easiest one I own to strip and rebuild so that should be quick and fun... except for the habit I have of changing everything. So I figured I would improve all the small and less small issues I have observed so far. I really hope to be able to enter the first round of Tamiya Club Endurance Racing by Post  I hope lots of other members participate in this 30min race as well.

Servo and Servo Saver

While the basic Hitec 322hd works perfectly in terms of centering, speed and torque, irritatingly it uses a 24 spline drive that forces me to use a Kimbrough servo horn/saver. I spent too much time shortening, re-drilling and painting that ugly servo saver from red to black and I was never really happy with it as the black paint eventually starting chipping. What I really wanted was a Tamiya HT servo saver with an aluminum blue cap. I also have a Hitec D485HW that was in one of my TT-02's. I will build a bonkers TT-02 for Postal Racing next month (@Andreas W it's on mate! ) with a nice coreless servo and so the 485 is now available to the Group C. The 485 has the 25t spline drive, it's very accurate and I absolutely love it. You really can't beat that for 20$... It still has plastic gears but as I wrote already, if I ever hit something with the Jaguar shell, that 20$ servo will be the least of my worries!

The HT servo saver set has these horns for F1 that nobody ever uses and turned out to be the exact length that I needed:

Left to right are: the 25t futaba servo saver base, the normal long horn, the F1 short horn that I will be using and the Kimbrough modified/painted servo saver of doom that is going in the bin very soon. And on top the aluminum cap which actually makes a difference in how the servo saver performs but I will digress on that some other time. For today, it's blue and looks awesome.

As you can see the short F1 and the modified Kimbrough part have exactly the same dimensions. The one caveat for me to use the F1 horn is that it is as you would expect drilled to <2mm for the traditional F1 ball studs to screw in, but I am using the easier to source standard 3mm screws and ball nuts. So I had to redrill it and the edge distance is very marginal. That is doable in a drill press with sharp bits but I would not have been successful with a pin vise. So marginal edge distance, yes, but again if I crash and break that horn it will be the least of my worries; I also have a huge stash of these from other HT servo saver sets.

There was a snafu with the wide Hitec screw that didn't fit the aluminum cap. This screw is a self tapper as that servo is using (carbon reinforced) plastic gears. As such it is sort of proprietary and I didn't want to rethread the final drive gear. So I rectified the screw head, using a drill and a belt sander. The drill and belt are working against each other so to speak which provides a better finish:

The result fits the aluminum cap perfectly. Sometimes I enjoy this sort of tinkering more than the rest of the build.

And here is what it looks like, exactly the looks i was hoping for initially:

The remaining tasks for the rebuild are as follows:

- protecting the battery compartment from chaffing

- attempting to implement thumb nuts for battery changes (more snafus!)

- installing longer front body posts (kit ones are just 1mm or so too short)

- balancing the rear pod as the car ends up drivable but certainly tweaked if you don't do it

- installing a 40mm HV fan as the Formula Tuned gets too hot for my liking

- rebuilding the diff which has suffered from the heavy black dust of the last run

Stay (formula) tuned

[Andreas W]

Nice to see the Jag out in the sun. I think a leafblower is the solution. I have not got one myself yet, but it's on the list. For now I am sweeping the surface. That's OK for normal Postal Racing size,  but when we now scale up it's a lot more work. I tried the Carten on Våler for the last time yesterday. There must have been traffic on the road since last time. My patch is a little clean Island on a road otherwise littered with small gravels and some larger stones. I thought the surface was good,  but it's astonishing how many new small stones you discover when you start running such a low car. 

 

Of course looking forward to another TT-02 build.

[Pylon80]

Today I finished the installation of the D485 servo.

I think every single step I took had to be undone and a different solution had to be found. In the end, I was able to make everything fit and provide the right amount of Ackerman; I now have the steering links reach the servo saver from the back side. It works, but with very little clearance to spare.

 

In the picture above the Ackerman was still excessive; I reduced it by removing and re-installing the servo a little bit more aft (for the 5th time today).

Also note that I used this opportunity to install blue M4 nuts at the front, ahhh... better!

I checked the angles and Ackerman effect in my trusty setup station:

A touring setup station is usable for pan cars but it is a bit tricky. I used the white 'bearings' that come in large quantity in a lot of Tamiya kits in order to attach the gauges. The trick is to always loosen and retighten the setup nut before measuring anything as ideally there should be a ball bearing enabling free movement of the gauges as the steering angle changes. Not ideal, but I just can't justify acquiring a Pan Car/F1 setup station just for that! Also if anyone is wondering how much the fixed, non adjustable and non dynamic camber is at the front, it's about 0.5deg 😉

The Ackerman 'effect' came back at 25deg inboard wheel / 18deg outboard wheel which seems like a good starting point for the Endurance racing that I intend to enter this month. I also set the toe to 0deg like on almost all my cars; again a good starting point.

Another 'cleanup' item I did was to shorten the giant servo wire; Hitec has a rich RC Airplane heritage and their servos tend to come with very long wires. These make no sense on a 1/10 car and so I shortened it to about 10cm:

The wire at the bottom is the portion I removed! That must be at least 250mm length out of the box. Now, my electronics still look like spaghetti but these days I feel like I want to press on with the driving and setup rather than invest another 5 hours stealthing every wire in black, at the perfect length etc. Also I now use the same ESC and Rx in every one of my cars (the ones using a brushed motor at least) and so it makes sense to keep certain wires longer. Plus the temporary aspect of the electronics installation makes the spaghetti looks more bearable. I can always promise myself that I will clean things up further this summer when it is too hot to run anything

 

Next up I will look at the battery compartment!

[skom25]

On 4/2/2024 at 10:22 PM, Pylon80 said:

hat did bother me, but cannot be seen on the pictures, was the ridiculous amount of black dust that was everywhere.

Same here. On my spots, everything looks nice and clean. When I ran car, it was totally dirty just after about 30 minutes.

Now, after each sessions, I have to clean it with brush and compressed air. Wheels and body are washed with water.

I believe it is somehow related to debris from cars.

[Pylon80]

Battery Installation

As I mentioned before, I could not get the round lipo battery that I wanted (Core RC) to my location and so I ended up trying my usual shorty lipo pack, the one I use in almost all my cars. Well, I am glad I did, because it happens to fit perfectly in the square portion of the battery compartment! Sometimes you get lucky and sometimes you don't. The only catch is that it is not possible to insert the battery when the "truss" parts are installed - A1 and A5, the ones I cut, sanded and polished  in a previous post. So I started getting into the routine of screwing and unscrewing these A1 and A5 every single time I would run the car. Normally they use 6 screws but the 2 outboard ones are really not necessary. One could argue that they stiffen the chassis in torsion, but I don't think that is significant and even if it were, here is certainly a chassis that would  benefit from being more flexible anyway.

So I kept screwing and unscrewing parts for the past couple of months, but I got worried that at some point, dirt and grit would ingress into the threads and cause damage. So I formulated a Grand Plan to use fixed, permanently installed studs (20mm long grub screws) and fit tiny black serrated M3 nut from the top. It would look very stealth but it would still require using a 5.5mm box wrench every time I want to access the battery.

Having to use tools to install and remove the battery is not the end of the world really. After all, my F104 ver.II requires undoing 4 M3 screws to install and remove the battery and that does not bother me at all. But there is something that happens with serrated nuts whereby they spin the studs every time inside the tub. So I started thinking about using thumb nuts; blue ones obviously. These might look strange or they might look really cool, I am not sure yet; they do make installing the battery much more pleasant than using the screws and also somehow they do not turn the studs inside the tub. Also, having these studs guides the A1 and A5 parts so I don't have to search for the threads anymore when re-installing A1 and A5.

As usual there was a hitch... The thumbnuts did not fit and I had to grind them using my now tried and tested drill plus belt sander trick:

Using this technique I obtained a nice shiny 45deg chamfer and the nuts no longer interfere with A1.

I also installed some chassis protector and thin foam to prevent chaffing between the battery and the bathtub (invisible on the picture). The damage was already present after only a few hours of run time.

So here it is! Not sure if it looks nice or if I already got used to it, but I really like it.

And here is where the rebuild stands as of today:

 

Next up I think I might build a different shock and I will explain why

 

 

[Andreas W]

That's a clever solution for the battery mount. Now I'm looking forward to see how it does on the Endurance Postal Racing course doing what the 1:1 version is intended to do. 

[Pylon80]

One step forward, 2 step backward: Battery Installation

In my quest to get the Group C exactly as I want and then just run-maintain-repeat, I have changed my mind on a few things again.

I decided that I would not keep the giant blue thumb nuts and pondered how cool it would be if someone would make the same thing but a quarter of the size, since that particular application does not require any sort of torque at all. Hmm, a quarter of the size... That's about the size of these serrated M3 nuts that I have.

So I used long grubscrews and found that they grub screws once adjusted to the proper "depth" into the chassis no longer spin when I attach the serrated nuts; also the serrated nut have all the grip I need to turn them with my finger (no tool required) and the magic of the serrations being what it is, they seem to be gripping very well. It takes much more effort to unscrew that to screw, so to speak. I really like the looks better now - I only wish someone would make aluminum serrated nuts in M3 size and Tamiya blue aka sky blue aka light blue, but my research came up empty.

Yep, much nicer now.

One step forward, 2 step backward: Damper

So I made a great point about how I really wanted to use the RM-01 damper and it is really very well suited to the car; however I now want to try the Group C without any spring. My build is probably the lightest you could ever come up with... shorty lipo, plastic gear servo attached with double sided tape, all unexplainable parts omitted , all tabs and protrusions cut off etc. So I think the original F101/F102/Group C T-bar is plenty stiff all by itself. The stock spring included with the kit was also the softest I had ever seen.

Now since I like deep diving into everything, the spring, even a soft one does play an important role: it cancels out the play at each of the attachment points of the damper. This is why play normally does not really matter in a damper; the spring keeps everything loaded in compression. Now with my idea of running the damper without any spring the play was just excessive and the t-bar would wiggle up and down at least 1mm without any damping taking place.

So I took out my TRF "special damper", the one Tamiya released for the F103GT. It is as boring as it gets since 90% of the latest Group C builds are probably using it  but I want to be able to use standard tools and hardware which the 3mm piston rod enables me to do.

I initially tried 900 oil, then went back to 400 before even doing a test drive as it felt almost locked. I am using the 3 hole piston as well. Compared to that picture I have switched to using a short adjuster (50797) at the 'bottom', since I know these are the tightest fitting and lowest play adjuster made by Tamiya. I am also now using the black coated brass ball nuts, for the same reasons.

To my surprise, the length came out right at 57mm, and after unscrewing the adjuster one full turn, I am smack bang on my target of 57.5mm  No need for internal shimming and I can adjust the pod droop as much as I want now by using my usual home made shock pliers - without even removing the damper from the car! Note that the instructions call for one o-ring on the outside to prevent puncturing the bladder if you bottom out the shock; that will not happen in my case so I omitted the outside o-ring.

Once installed onto the car, the 'bottom' is nice and tight but the 'head' still has tons of play. I will experiment with an o-ring slipped on the ball nut (low hope on that) and if that does not cure it I will do something I had wanted to try for a long time, which is to install a tiny grub screw inside the shock 'head' in order to dial-in the play. At least I am having fun!

Rear Pod

No pictures but I have rebuilt the diff (well, polished the plates, clean everything and re-grease).

I have also started working on balancing the pod. As I have mentioned the original pod is symmetrical and with the weight of the diff and the motor on the right side it is very heavily unbalanced. This is a very old design and it shows! I think it will take a lot of dead weight to balance it out but I have a solution I am working on. I will just say that cutting and filing 2mm brass stock is a lot harder than cutting styrene!

Endurance Racing?

We are 1/3rd through the month and I am still tinkering on the Group C. I have a RWD/Front Wheel Brakes Porsche 911 RSR that is pretty much ready to enter Endurance Racing by Post in the GT3 class. I might simply enter the Porsche for this month.

[ThunderDragonCy]

@Pylon80 Loving this thread. For lack of slop in the top mount, 54871 is your boy. Hard to find now weirdly, but i just bagged a set from PJ. 

[TurnipJF]

17 hours ago, Pylon80 said:

I decided that I would not keep the giant blue thumb nuts and pondered how cool it would be if someone would make the same thing but a quarter of the size, since that particular application does not require any sort of torque at all. Hmm, a quarter of the size... That's about the size of these serrated M3 nuts that I have.

I think thumb nuts are a great solution for this particular application. I use them on my F104V2 Pro battery hold down. Although I get it that yours look a bit, um, large. Exotec make more compact examples specifically for battery hold downs that might suit your tastes better, being about the same diameter and height as an M4 wheel nut - a great match for the flanged nuts up front. Here they are on my F1:

Mine are black as the car is a Black Special edition, but you can get them in Tamiya blue too under part number #EXO1191MBL.

https://rcracecontrol.store/en-gb/products/exotek-m3-twist-nut-medium-blue

[Pylon80]

@ThunderDragonCy thank you for the tip, actually I will grab a set for my touring car. Last night I tried the o-ring slipped on the ball nut trick. I had tried it years ago and it is not a usable solution on a touring car because it considerable slows down the rotation of the ball in the shock. On a pitch damper however it works extremely well since there is negligible rotation anyway. In fact, it worked so well that I decided to give another try to the RM-01 damper. I will do the ultimate back to back test drive with the TRF damper and with the RM-01 damper, in both instance with no spring at all.

@TurnipJF Exotek make superior products for F1. I have my eyes on these thumb nuts for my F104 ver.II actually (same as your). I am not sure they would fit on the Group C as the front part of A1 is very steep - at least 45deg - which would require grinding the thumb nuts. I really like the serrated nuts now. I can spin them with my fingers, they grab just right on the plastic and they are not in the way visually. Now, if only someone made blue ones it would look fantastic!

I had more thoughts last night about the pod. With the Formula Tuned motor I have the room to move the motor to the left by at least 2mm, both in terms of shaft length and pod clearance. I will probably make a 2mm shim to slip between the motor and the mount. Also the 40mm fan arrived and even at 6V it's moving a lot of air! I can even crank the BEC to 7.4V now that I have a high voltage servo; I just need to swap the Rx with the HV one in my M-05. I will offset the fan to the left, blowing over the comm and one of the slots in the bell. I am also preparing pieces of brass to attach to the left side of the pod. Everything will help balance it out!

[Pylon80]

I had to dig the thread from the second page of The Builds! One thing I particularly enjoy about TC is how active the builds' section is. So much amazing work is very humbling for me.

As I trudge through a difficult month with little RC time, I am happy that I was able to do the following in April so far:

- Get a crack at the Postal Racing with my M-05 (and I wish I could take a bit of time to update the thread...), it's fast and I think I could really put it on the podium if I could just get a few hours in, to learn the rhythm of this month's track and nail a perfect 5min run.

- I put together a GT3 racer for the new Endurance Racing by Post but it's just not handling the way I want and I need a couple of hours to tune it.

- I realized that the Group C could really enter Endurance by Post if I just installed a fan! It's not perfect but it's already handling quite good with the only manageable flaw of requiring pod balancing, and I am almost there thanks to one of those Eureka moments I had one morning as I awoke!

- This weekend one of my work mate and I are actually headed to an indoor off-road track! We plan on inflicting a maximum of damage to his 4x4 Slash as well as a rental (!) Slash for me, that I can apparently drive for 15$. I am excited about this change of RC scenery!

But today I will just show how I mounted the fan. I truly don't see how I could make a simpler and lighter installation. It's a tiny piece of black styrene, attached to the wing mount with double sided tape as suggested by @TurnipJF. There is only 1 screw. And I tapped threads directly into the styrene so there is no nut either!

The fan is helping a tiny bit with the pod balance and it is blowing over the comm/brushes as well as one opening in the can:

I am quite looking forward to seeing how effective that big fan is, especially since the temperature in Arizona are now well above 30deg C. Normally now is a "brushless-motor-only" time of the year for me. We will have to see how it goes. And I always have a 21.5t motor and ESC available if I really need - that one will run stone cold, especially on a pan car, and even in the heat of summer.

Next up will be the "Eureka" pod balancing system  But I can now drive the car anytime the stars align. If the motor isn't too hot after 5min, I will just give a try to the 30min Endurance race. There are 10 days left!

[Andreas W]

Well done and best if luck testing it. Hope the fan is effektive enough to make it through the full 30 min. It's probably worse for the driver in 30C temps . 

[Pylon80]

I had to search for my thread in Google to dig it up from the depths... It's been a while.

So here's a mini update for today 🙂

I have been entering the Endurance Racing by Post and now that I got more comfortable driving the Group C I'm trying to extract more performance out of it. I don't have much time for proper before/after testing of various setup changes sadly, but I found that it was still riding a little high, about 7mm. A quick check with @TurnipJF and I found that he had his properly set to around 5mm. I believe on high grip surfaces lower it's always better but I am not entirely convinced that this is always the case on low grip surfaces. At least my rally car proved this point wonderfully last year by being surprisingly fast. I don't know if the same will hold true for a pan car but it won't hurt trying, so next ERBP round I'll try 6mm, then the week after 5mm and hopefully I can get some Lapmonitor data to look at 😎

I have already showed how I made a series of shims for the front. Now I simply made 1mm shims for the rear. The car has one of the stock 3mm shims plus 1mm of custom shim.

2D printing 🤭:

Stock 3mm on the left next to the 1mm ones:

And installed ready for this coming weekend:

[Andreas W]

All the best for the testing,  my friend. Hope that Jag flies. 

 

PS: Somewhere lower down you have an XV-02 thread, which I am curious to read some more in. You inspired me to pull the trigger when one turned up in the classifieds and that is the next one up on the bench here. 

[Pylon80]

13 hours ago, Andreas W said:

All the best for the testing,  my friend. Hope that Jag flies. 

 

PS: Somewhere lower down you have an XV-02 thread, which I am curious to read some more in. You inspired me to pull the trigger when one turned up in the classifieds and that is the next one up on the bench here. 

The XV-02 is not forgotten 🙂 but I wanted to prioritize my son's TT-02 rally which is now usable and mostly complete. So the work on the Yaris body for the XV-02 will resume promptly with the goal of spraying before the spring heat is on again (it's already 27degC right now in the afternoon 😅). Then, finally I will get to the chassis which is going to be quality time for sure.

It's funny you mentioned the inspiration because you really make me want an XV-01 as of late! 🤣