Schumacher CAT XLS build

[groomi]

Excellent. Looking forward to seeing that finished.

[groomi]

And here's a pic of mine that you were referring to - using my racing colours of yellow (with silver/white/black) used to recreate iconic racing car liveries.

At the back a 2wd CAT XL with Penguin reproduction of the Frewer Dog for Cat shell, livery inspired by Gold Leaf Lotus 49 and 72.

At the front a 'standard' CAT XLS with livery inspired by the 'Hippie' Porsche 917LH.

5th and 9th in their respective A-Finals at this years Iconic RC Revival.

Edited by groomi on Saturday 19th September 16:11

[dino_jr]

Thinking of getting a Cat too... I used to get thrashed by the rich kids in the 90s by these, so nostalgia has kicked in

I don't understand brushless motors: Schumacher website say 17.5T motor is the limit on the stock transmission, but a few forums have gambled on faster stuff.

I ask mainly as a 13.5T motor can be had for £30 ish.

https://hobbyking.com/en_us/turnigy-trackstar-13-5...

Whereas a 17.5T is way more money ???

[groomi]

dino_jr said:

Thinking of getting a Cat too... I used to get thrashed by the rich kids in the 90s by these, so nostalgia has kicked in

I don't understand brushless motors: Schumacher website say 17.5T motor is the limit on the stock transmission, but a few forums have gambled on faster stuff.

I ask mainly as a 13.5T motor can be had for £30 ish.

https://hobbyking.com/en_us/turnigy-trackstar-13-5...

Whereas a 17.5T is way more money ???

17.5T is a safe limit. Some people have successfully raced with the stock transmission with as low as a 7.5T brushless system, but ofcourse the manufacturers have no idea how much abuse the owners will put their buggy's through. I would say if you go below 17.5T you need to check the integrator, front diff and layshaft diff tightness after every run, along with the long belt tension. If anything is slipping when driving then you need to stop immediately and sort it as diffs will overheat and melt if they slip with that sort of power.

The 'problem' (depending on how you look at it) is the CAT is totally faithful to the original, so the transmission is not designed for the torque of modern brushless systems and the design of the car is not friendly for quick strip-downs and rebuilds. You really don't want to be taking out and rebuilding a diff trackside for example.

So the Pro Transmission upgrade or the Muzzoom version (disclaimer - I run Muzzoom Models) increase the capabilities of the transmission so you can reliably run more power - to a point.

TBH I would always recommend a cursory check on those items after every run anyway on these cars, as the consequences of a failure will ruin your day at the track.

Edited by groomi on Thursday 24th September 13:47

[lufbramatt]

Interesting stuff about brushless. Been looking at them recently as my lad wants his tamiya racing fighter to go faster and the stock esc can handle sensored brushless motors.

I’m running a 11x2 brushed motor in the cat, not sure how that compares to a brushless, but it’s what I used to run my touring cars years ago. I had a couple of decent 27x1 motors too but can’t find them (along with a nice high torque servo that would have been ideal to use).

Been doing some more of the bodyshell this morning and noticed the crash back o rings have all perished, not sure if they have reacted to something? Ordered 20 spares for £4 from eBay though so not a big deal.

Edited by lufbramatt on Thursday 24th September 11:51

[groomi]

An 11 double will be a great motor for a CAT. Broadly speaking it's probably comparable to a 10.5 brushless. The brushed might have a touch more top end, but the brushless will have a lot more torque.

While we're talking motors and transmissions, it's probably worth noting that today's tracks have a lot of jumps, whereas tracks from back in the day had few if any and certainly not as big. Now the CAT is never going to jump particularly well compared to a modern car anyway, so you won't be landing from 6ft in the air with it, but landing even small jumps puts more strain on the transmission and ofcourse the upgraded transmission options both include a slipper clutch, which makes it more durable.

The increased jumps and also the increased torque from brushless systems also makes the front belt tension more of a problem than it was back in the day. A nosedive landing (the natural stance for a CAT) tends to shift the front transmission backwards which slackens the belt a little, which then makes the belt slip under braking - amplified by the stronger brakes of a brushless motor.

There are a few things you can do to counteract this issue, but the easiest way is to fit the U7293 alloy front transmission housing -although purists will note it's more like a Procat in design than an XLS.

[dino_jr]

OK noted, so a 13.5T would be a gamble, and so keep an eye on the transmission tension if I got one. The car would be for caning around the garden with my nephews Tamiya's, I don't plan to go racing or jumping 6ft
I have a Tamiya Neo fighter currently with a Tamiya ESC and "Torque Tuned" motor, I may just try those bits first to see what speeds I get.

Is a 13.5T comparable to the Torque tuned brushed Tamiya motor or Lufbramatts 11t motor, rpm / torque wise? I want to keep the stock trans setup and its integrator etc. The trans upgrade loses that feature that's unique to this car.

Edited by dino_jr on Thursday 24th September 14:13

[lufbramatt]

I think the tamiya torque tuned motor is a 25*1 wind, slightly faster than a normal can motor which are 27 turn. so should be fine in the cat but I’d describe them as “nippy” rather than fast.

[groomi]

lufbramatt said:

I think the tamiya torque tuned motor is a 25*1 wind, slightly faster than a normal can motor which are 27 turn. so should be fine in the cat but I’d describe them as “nippy” rather than fast.

Yep, agree with that.

A 13.5 brushless would be plenty fast enough for garden bashing. I'd say it would be safe to go with as you're not doing any silly jumps and if you do detect anything slipping you can stop straight away rather than being tempted to finish a race.

[pete]

I'll second the point about the long belt slackening off. I had to tighten mine after every run at the recent Revival, not helped by the re-re using long pozidrive screws with heads made of chocolate to hold the front diff in place. I've replaced the kit screws with hex heads now, originality be damned, and the Procat-style front diff housing is next on the list of upgrades.

Here's my XLS in the background showing the "nose down" landing Groomi was talking about

[lufbramatt]

Job done. Finally.

[dino_jr]

Wow that colour scheme is fantastic, no way I'd try anything that clever.

FYI I received my kit on Tuesday



1st dumb question: Step 4 / the undertray... Does it really attach via the screws for the rear gearbox? So I have to torque the screws against soft lexan... Surely the Gearbox will rattle loose and/or the screws will punch through the undertray after a while?

In the pic you can see I got the screws4rc set too. It is not yet obvious which screws replace which from the kit, many are VERY similar lengths. I hope I don't use the wrong screws early in the build then find I need them later on

[lufbramatt]

Thanks much appreciated, have to say, modern masking materials make life so much easier than the crap cream coloured masking tape we had in the past- also helps when you've got more than pocket money to spend, so a buying a tenners worth of Tamiya tape isn't as big a deal!

re. undertray- Yes, doesn't appear to be too much of an issue though. I left mine off until it was time to tension the long drive belt. Gets in the way a bit if you do it first. The screws are self tappers into plastic so you don't have to go mad torqueing them down.

I used the kit screws without issue. Might replace the long front gearbox screws with something a bit stronger based on the above posts. Struggling to find countersunk high tensile machine screws that are long enough though.

Edited by lufbramatt on Friday 9th October 10:11

[dino_jr]

None of the screws4rc items are self tappers, all are metric screws. So a bit of violence is required to get them going into plastic

My brother just text me by coincidence, he has white and gold rattle cans, so I'll work out a colour scheme with those. Not the most obvious colour combination but I'll think of something... I think some 80s F1 cars cars were white/gold, I'll do some googling.

Are there window masks in the box? Haven't spied any yet.

[lufbramatt]

Yes mine had pre-cut vinyl window masks in the kit. Don't leave them on too long though as otherwise they leave residue on the plastic. Ask me how I know...

If you get hold of a tin of red you could do a Lotus 49 inspired scheme

[groomi]

Love the colour scheme lufbramatt, and that wing sticker has got to be worth a couple of tenths a lap!

Regarding the screws, they don't work loose underneath, unlike a lot of modern cars with alloy chassis pans. Maybe it's the squeezing of the lexan which keeps them in place?

If you're putting machine screw threads into plastic, then the serious way to do it is to tap all the threads, but nobody has time for that so just use a small drop of silicon oil on the threads and go steady.

[lufbramatt]

Haha cheers Groomi, was kind of going for something like this:



It’s a great idea to adapt classic race liveries though, can see me doing another one at some point. Maybe a purple/yellow/white silk cut jaguar scheme would work well.

If I was to take this racing locally (I’m in north Kent) are there any good value brushless motors and esc combos you would recommend that comply with vintage class rules?

[dino_jr]

groomi said:

If you're putting machine screw threads into plastic, then the serious way to do it is to tap all the threads, but nobody has time for that so just use a small drop of silicon oil on the threads and go steady.

Yep I'm not sure the screws4rc set was worth it... The hex heads are handy, but the eccentrics screw to the metal gearbox side plate with kit self tappers. No way am I threading the side plate for the hex screws, so already I'm not bothering with them.

I have cut the body / belt cover / undertray reasonably well. rear wing was a guess though, no cut lines?

Are these pulley fences directional? They look symmetrical but one side has 3 dots... Should the dotted side face toward or away from the pulley teeth?

[dhutch]

Seems daft the caphead screw set are not the correct type of thread?

[lufbramatt]

The dots on the fences are just ejector pin marks from the injection moulding process, don’t think they mean anything. I sanded the faces flat to make sure there were no protrusions that could catch the belt.