Mardave Cobra Sport

It happened!!

I found a used Cobra in great condition!

So I bought it!

OVERVIEW

A complete rolling chassis with a painted body (yellow w/red stripes; not my favourite colours but it will do) and clear decal’d rear wing and some lovely new-ish Schumacher tyres on the wheels. It comes with a few extra nice bits too. Some of the screws were replaced with hex hardware, which is nice (although a mix of head sizes) and it also has 3D printed steering servo stays, which is a big improvement I would have made myself. The original was all about the double sided tape on the servo! The number of times, when I was a kid, I had the servo fall off when running it in the rain was amusing!

I’m going to stick in some hardware I have knocking around at home for the meantime just to get it running and get the excitement flowing! I got it running on a spare Tamiya Torque Tuned Motor, and a Hobbywing 1060 as a power train; but I've had to source a new servo as the old Acoms I have knocking around won't fit in the Servo stays due to the cable exit being halfway up the body... in fact the 3D printed servo stays aren't quite right. The pre-drilled screw holes are slightly off alignment for an actual servo, so may need a re-drill when the new one arrives.

OLD SPARES

Handily I found a box of old spares from the 90's in the basement at my parents house. 

- A set of wheels and a bunch of very well used tyres.

- A bag full of original screws of various sizes.

- One of my original painted wings in red and a shell, in blue, with a broken nose (I’ll fix that up with some shoe glue and body tape).

- A completely clean original bodyshell and wing set! 

- A complete ball diff, idler gear, and lay shaft.

Those old tyres are all dried up scrap, but the wheels are all in pretty good nick so will grab some new tyres for those and build a range of pre fitted tyres to use on different surfaces. For now I’m just going to bash this down the gravel roads near my house and have some fun with some new LiPo batteries. Maybe I'll look for some vintage racing for it when I'm more comfortable setting it up and driving it fast!

RESTORATION

A few bits of the car are a a little tatty. Some of the fittings need a bit of tightening. I inspected the gearbox, and made sure that was all moving nicely and dirt free. I also replaced the idler gear with a new bearing mounted one from Mardave. At the moment the ball diff appears to work, if a bit stiff, but I have a spare from my original bits box and also got some new diff balls for a rebuild in the future. 

I think I’ll also need to re-oil or replace the shocks as they currently feel massively over damped, and I don’t want jumps breaking the suspension arms.

MODS?

I found at least one basic modification that I think might be worth doing to bring the performance up a tiny bit, but means modifying the original suspension arms, so might hold off.

This tip from The RC Racer “to make the car more planted and responsive in turning”: flip the dampers round to the front of the shock tower, and the upper arms to the back. (https://www.thercracer.com/2010/06/mardave-cobra-front-suspension-mod.html)

I understand the logic of it; putting the shock in the middle of the front arms to balance load into the shock closer to the a movement axis of the wheel, rather than the shock being activated more by energy on the back of the arm which would twist the arm under load.

WHAT'S NEW?

I’m trying to keep the buggy as original as possible but with modern electronics. I've put in a half decent brushed motor, the Holmes Hobbies Retro 15T and a new 20kg SRT DL3020 servo, which is inexpensive but seems pretty solid, if not too exciting, so far. 

After some deliberation I’ve also decided to replace the original shocks, as they have been set up with way too heavy an oil, the springs aren’t original, and the shafts aren’t quite as smooth as I’d like. New parts for a rebuild are super hard to come by, so I’ve gone with some relatively inexpensive Yeah Racing Big Bore Go shocks. So far pretty pleased with them with some CoreRC 400cst oil. Though I think I’ll swap the piston heads in the rear set with one of the other supplied ones with fewer holes to increase resistance slightly for jumps, as I’m getting a lot of slap on the rear on landing. But saying that, the car already feels way more planted and stuck to the floor with the more fluid damper movement though. Massive instant improvement to the drive.

MARDAVE SPARES

I've ordered some spares and other bits direct from Mardave, as they still carry a fair few of the most commonly required spares for this car!

I have fitted the carbon front and rear shock towers and a new chassis tray. The carbon towers also required a new Schumacher wing mount set. I also fitted the bearing mounted idler gear to help free up the transmission a little more too! I did want to get hold of the slipper clutch but it’s rarer than hens teeth. Thankfully Mardave sent me a handful of extra spur gears when they had some missing items from my order so I can burn through those when put in a more powerful motor.

Final Thoughts

This rebuild has brought me an immense amount of childhood joy. I love the way it drives with the new shocks, and the extra speed from the 15 turn Holmes Hobbies motor. The Mardave tyres are pretty rubbish on everything except mid length grass, but look great on the shelf; I’ll be using Schumachers for the majority of my driving!

Final Additional Parts List

- Holmes Hobbies 15 turn brushed motor

- Hobbywing 1060 brushed ESC

- SRT DL3020 servo

- Yeah Racing Big Bore Go dampers

   - Front 80mm and Rear 90mm

- Mardave Cobra EVO Carbon Shock towers front and rear

- Schumacher rear wing mounts

- Mardave Rear Red Dish Wheels

- Mardave Front White Dish Wheels

- Mardave 32DP Spur gears

- Mardave new Idler gear on bearings.

- Schumacher 16T 32dp pinion

- Core RC 4000mAh 30c/60c LiPo

Update!

Mardave had a slipper spur assembly in stock so I grabbed one set and also the smaller sized slipper gear to achieve some higher speeds on that fast motor. Early testing puts it pretty rapid! Really want to test it on something grippier than my paving stone drive.

There’s a couple of local clubs to me so hoping I can take it out on some astroturf or carpet soon!

Core RC 4000mAh LiPo Review

This Core RC LiPo is quite simply a great way to get a LiPo into an old Tamiya chassis, which has the classic rounded battery holder for the old NiCads and NiMh battery packs. This LiPo from Core RC exactly replicates the shape of those packs and fits great in both my M03 minis and TA03RS battery slots.

It’s got great energy density at 4000mAh, and a decent C rating of 30C constant and 60C peak, which should be plenty for your slightly retro stick pack cars.

It replaces a NiMh pack of a similar energy density, but which only has a C rating of 10C. So this new CoreRC LiPo is capable of delivering triple the power without any sweat, and peaks at 6x the power output of the old (but still quite modern) NiMh pack.

What does C rating mean?

C rating is a way of describing the potential power output of a battery. It allows you to work out if the current output of the battery from the batteries capacity rating. Put simply: 1C is the batteries capacity, so for example this CoreRC battery has a capacity of 4000mAh, which makes 1C of that battery 4 Amps. 10C would be 40 Amps. 30C is 120A and 60C is 240A.

As a point of contrast my Absima 4100mAh NiMh is rated at 10C so can deliver 41 Amps. That’s the only number on the battery so presumably it can go for short bursts higher but it’s still relatively limiting.

Now, I believe that high capacity NiMh packs are perfectly fine for cars that are running their stock 540 silver can brushed motors and offer a perfectly acceptable driving experience in that kind of car and any performance gain from a LiPo is fairly mild. However once you start getting into lower turn motors and brushless setups then LiPo’s are a must. The potential power draw from those systems exceeds what most NiMh batteries are capable of delivering. This can cause unstable running as the voltage drops and current ends up being insufficient.

I run this in my Tamiya TA03RS Porsche 911 GT1, which runs a Hobbywing 10BL120 ESC and 10.5T 3200kv motor. It goes way faster with the LiPo; to the point where I think I might need to gear it down to make the speed more sensible for my running space.

It also gets run in my vintage Mardave Cobra buggy, with a 15T motor and Hobbywing 1060 ESC. The car runs really nicely with the LiPo in there and gets a very respectable run time.

I’m also going to properly test it in my M03 Mini, which runs a Hobbywing 1060 ESC and a Tamiya Torque Tuned Motor and see if it gets a bit quicker… although more wheel spin in that car might make for very short lived tyres!

These batteries are in stock at lots of hobby shops and the main online retailers. I picked mine up from my most local one, which was a treat to go to after 20 years of being away from the hobby.

Addlestone Model Centre is my local. It’s a small outlet run by a bunch of enthusiastic hobbyists. Their website doesn’t have everything they stock on it, but most of the main stuff is listed. 

https://addlestonemodels.co.uk/

Tamiya Porsche 911 GT1 ‘96 - TA03RS - Restoration for Running

When I saw this kit pop up on eBay, I couldn’t resist having it. The Porsche 911 GT1 ‘96 is one of my favourite race cars of all time and I also have a model of nearly this exact car in my childhood Scalextric collection.

On collection, the previous owner told me that he used to work for Porsche in some capacity, which makes sense as this car is in mostly German language packaging and listed as pre-assembled. From what I can tell this isn't something that was widely available off the shelf. Upon closer inspection of the car itself it was obvious it had been well used at a time, with a few minor cracks in the front of the shell and some scrapes to the chassis and body of the car, but really in good nick for something that had probably last seen the light 20+ years ago. 

Once I got it home I gave it a quick go straight out of the box, with a knackered old NiCad (before I’d started buying new batteries), and it worked fairly well on first test but definitely needed a bit of work. The stock pinion seemed pretty slow, but I think it was as much down to the battery. The original Acoms transmitter also didn’t power on as it was all corroded in the battery compartment so I used my own old mint Acoms Transmitter with the crystal swapped out.

I never really got on with the old mechanical speed controllers. They either never reached fully open, or they got stuck and you get a runaway car... so that needed replacing with a new ESC and the old Acoms radio gear could do with replacing too. The original transmitter was actually non-functional as old batteries had corroded the contacts in the battery compartment so I kept the crystals and binned the transmitter.

As always, the first thing to get upgraded was the bushings to bearings!

I don’t understand how or why bushings can be considered acceptable in any level of RC car in this day and age, especially given how cheap a set is. It’s just so obviously a business decision by Tamiya so they can sell you an upgrade straight away (so I obviously went with a third party manufacturer)… anyway tiny rant over…

Full teardown soon commenced and bearings added along with a bunch of Hop Up upgrades from eBay. I also greased the diffs and the transmission while I was in there.

We have two small unforeseen complications that come with this particular chassis kit (mostly because I'm a total noob to RC!). The first one is that the 911GT1 kit is a short wheelbase 237mm TA03RS, meaning the shell can't be transferred to any of the modern chassis’ because none of the new ones can be set up that short. Equally if you want to use the chassis with a different shell then it's nigh on impossible to find 237mm wheelbase touring bodies for anything other than astronomical prices... Secondly this is a discontinued chassis, so original hop-ups are quite hard to come by and often expensive, being sold by collectors. Occasionally bits pop up that are part of teardowns of non-functioning cars so come a bit cheaper. What's annoying is that there have been TA03RS reissues in the not too distant past. In 2022 there was a Porsche 911 GT1 Street that was released on TA03RS, but Tamiya seemingly didn't put out any additional spares or hop ups for it so there's still a wild second hand market and a handful of small companies making spares in China and Japan, which of course is slow and expensive to ship to the UK. Stabiliser bars are like hens teeth and generally mostly only attached to full builds. It's odd because they come as a set with other hardness bars, but those other bars appear to also have gone missing.

Anyway, over the course of a few months I managed to source alloy c-hubs, rear uprights, gearbox cover/motor heatsink, and front knuckle arms. I like to have metal parts for bearing to sit in if possible and the gearbox cover/motor heatsink felt necessary for larger pinions and the planned brushless motor upgrade! Who knows how effective it will be though as it’s basically just a metal plate attached to the motor mounting plate, so heat transfer via the screws is not exactly going to be the most efficient process.

Initially I found a used Hobbywing 10BL120 brushless sensored system with a 10.5T motor on eBay; presumably removed from some sort of racing buggy. The ESC needed new battery connectors, as it was wired with bullets for shorty Lipos, so I stuck a Deans T Plug on it to match my batteries. I’ve also popped in a new servo, which has drastically improved the steering response! The old Acoms AS12 just wasn't doing the body justice, so I went with an SRT CH6012 9KG 0.07s servo, which I'd highly recommend (see review post).

First test after the new electronics went in, with the biggest pinion you can fit in the chassis (25T), and it runs fast! Outrageously punchy. That upgrade to the steering servo has made a big difference too, and a lot of the slop in the old servo saver negated by upgrading it to the newer Hi-Torque one, and using the aluminium arm upgrade. I’ll also need to glue the tyres down as they nearly peeled off the wheels!

With the original kit dark gold wheels (which are the wrong colour for the car)

I have now swapped the Hobbywing system for something more controllable for this model. The SkyRC Toro TS50 combo with 17.5T motor. It seems a lot more sensible interms of speed, still with a fair bit of punch. It's not going for land speed records but it might make for some fun running at an Iconic Cup some time in the future.

Original Kit:
Tamiya TA03RS Porsche 911 GT1 (Pre-Assembled kit - import from Germany?)

Upgrades List: 
- Full bearing set Sealed
- Aluminium Rear Uprights (Tamiya)
- Aluminium Front C-Hubs (Tamiya)
- Aluminium Front Steering Knuckle Arms (Chinese repro)
- Aluminium bearing steering assembly (RC Dampers)
- Aluminium Motor cover/heatsink (Tamiya)
- 25T Pinion  (Tamiya)  (a range of other pinions from 20T for tuning)
- Stabilizer Set Medium (Tamiya)
- Carbon Shock Towers Front and Rear (RC Aidong)
- Carbon front foam bumper adapter (RC Aidong)
- Tamiya Foam bumper
- SkyRC Toro TS50 ESC
- SkyRC Toro 17.5T Motor
- CoreRC 4000mah LiPo battery
- SRT CH6012 Servo
- Tamiya Hi Torque Servo Saver w/ Aluminium arm
- Tetsujin Chrome Wheel Rims and Gold Daisy Inserts
- Tamiya Slick Racing Tyres

Finished Shots

What is a C Rating on RC Batteries?

After seeing some confusion on this topic on Facebook and other social media I thought I'd write this for anyone who wants to find it... No judgement at all if you don't know. When I first saw a C rating I had no idea what it meant either.

The C rating of a battery pack is the potential power delivery to the ESC, motor, radio and servo(s). It's not a straightforward number though. Two batteries with a 30C rating may not necessarily be equal. If they have different capacities then the actual power delivery could be quite different.

The maths is thankfully quite simple, but I'm going to start at the very most basic level just to make sure everyone is in the same starting point. Almost all batteries are measured in mAh, and the numbers are often in the 1000's but we can simplify the number. The m before the Ah is for milli which means "1000th of", in this case, an Amp hour* . So 4000mAh is actually just 4Ah. This in turn means the battery can supply 4 Amps for an hour. And that is what 1C means. 

1C is equal to the listed capacity of the battery in Amps So in our 4000mAh example we get 4 Amps.

10C is simply 10 times that. So in our 4000mAh battery we get 40 Amps

100C would be 400 Amps !

This is typically the range of the common batteries for RC cars, with 100C and up being really up at the top end of the scale racing grade LiPo batteries, and 10C being the lowly NiMh.

Here are a couple of typical examples:

This Absima 4200mAh NiMh battery is rated at 10C. Meaning that it can deliver 42 Amps to your motor. Some batteries offer two C ratings, one for constant and another for peak-burst output. This one may also go a little higher for short bursts of acceleration. Solid for your stock "silver can" motors, but may not quite push the most out of upgraded motors as they'll end up current starved.

This Core RC 4000mAh LiPo is rated for 30C / 60C which tells us that it can maintain 30C, but can do bursts of 60C for acceleration. 30C is 120A and 60C is 240A which is more than excess for a brushed motor setup and ESC and probably plenty for most mid powered brushless systems. This particular one is great for vintage 1/10 cars as it is exactly the same dimensions as the old NiCad's that used to come with Tamiya's and a number of other cars.

*Almost all Amps are measured in Amp Hours so to simplify things most manufacturers just write Amps

SRT CH6012 HV CL Servo Review for GT Style 1/10 Touring

I picked up this servo as an upgrade to go in my ancient Tamiya TA03 Porsche 911 GT1, which I’ve been renovating from box stock to something resembling race spec and a speedy street basher over the last couple of months. (See the actual build log for that one in another post!)

The original steering servo was an old Acoms AS-12, which was ok for it’s time, but a bit low on torque and a little sluggish. I “upgraded” to a servo that came with a GoolRC motor/ESC combo but that, while strong, was actually somehow slower and made it practically undriveable. 

The SRT CH6012 has certainly solved those problems. This is a very fast steering servo. It's fast and quick to react but also somehow smooth in it's response. Compared to my other fast servo, an AGFRC A81, it's maybe very slightly slower, but defenitely smoother and possibly a little more linear in feel. The SRT also works great on standard 6V power, with a little bump in performance if your ESC can go up to 7.2V. I also got rid of the old Tamiya servo saver and replaced it with the hi-torque version, which instantly improved a lot of the play in the steering system.

Here are the tech specs:

Torque @ 6V: 9KG
Torque @ 7.4V: 12KG

Speed @ 6V: 0.07Sec
Speed @ 7.4V: 0.06Sec

Operating frequency 330Hz

Metal gears: Copper and Aluminium 

I also tried this servo in my Tamiya M03 Mini Cooper, and that was a great fit for that car. Brilliant direct control of the steering, and plenty strong enough for the smaller scale M-Chassis model. I think this might become a really solid go-to servo for racing M-Chassis stuff and other models that sort of size and weight.

The servo feels really well made, with the external plastics feeling really solid, with the whole unit feeling really solid all round.

If you’re looking for a reasonably priced reasonably high performance servo, this gets a strong recommend from me. 

Here’s a completely non-sponsored retail link for the store I bought mine from in the UK:

https://www.modelsport.co.uk/product/srt-ch6012-hv-cl-servo-90kg-007-sec-at-6v-semi-m-case-433882

I believe they’re being carried by quite a few shops. I also saw them on the MB Models website when I was browsing for pricing and stock levels.

Tamiya M03 Rover Mini Cooper Racing

My first project that brought me back to the hobby is to completely renovate my old RC car that has been sitting broken in its box for 20+ years.

What happened to it 20 years ago you ask?

Well, basically I built it stock around my early teens with plastic bushings and at some point in the first test run (I hadn’t even painted the shell), one of the bushings fused to a shaft in the gearbox and melted part of the gearbox casing (which is also the chassis). The holes where the shafts sit had melted and actually moved around while they were still hot. What I believe to have happened was that I didn’t grease anything when I built it and that caused the heat to build up. 

Anyway fast forward 20 or so years and the M03 is no longer in production and chassis replacement parts are hard to come by. eBay turned up  several complete chassis though and a couple of overpriced limited edition parts so I ordered a few bits.

First to arrive was this lovely blue plated plastic chassis. This was expensive and shipped from Australia... It looked awesome and on initial inspection seemed to be in great condition. So I started the rebuild in this chassis armed with a reprinted manual, as my original copy had gone missing. 

What a satisfying process the rebuild was. The M03 is a super easy kit to build “and a great starting point for someone starting in the hobby” (is what I would say if it was still 1997). The main hop up I stuck in there was a set of bearings to replace all those terrible plastic bushings. Pretty much everything else is stock, except for some lovely blue aluminium C hubs. Even the original motor was still working fine and I even made use of the old Acoms servo (which is a bit slow but will do for now). The main replacements from the original parts came in the electronics. I got a new receiver for a modern 2.4GHz controller and a Hobbywing 1060 ESC to get reliable motor control. 

Anything else broken?

The body mount posts were bent at funny angles from years of sitting upside down in a box under a load of other boxes… making it very hard to get the body fitted straight to the chassis. I tried a few things out to straighten them out with little success, but then remembered something from my A-Level Design and Technology… that most plastics like these are mouldable with heat and could even return to an original shape with just the heat. So I boiled the kettle, popped the plastic parts into a pan (so they could lie flat) full of boiling water and like some sort of witchcraft they began to straighten out. Couple more runs with the boiling water and we got to 99% straight which was enough to find the body holes without too much faffing about.

First rebuild looked great. First drive... not so much! I clipped a slightly raised curb on the edge of my drive and the entire suspension assembly on the front right snapped completely off at the chassis. Turns out vintage plastics can go brittle quite quickly… not only that but the shock tower part of the chassis had also cracked through. So I went about gluing it together with ABS plastic cement, which melts the two sides of plastic to together to form a bond "99% good as the he original moulding". Upon even closer inspection there were cracks all over the chassis shell. At that point I decided to finish patching it all up with the plastic cement, and setting it aside for a shelf only blue build. Thankfully more chassis parts had just arrived.

Onto rebuild number two then! This was the same silver style chassis that I’d had on my original. I inspected it closely and, with my new knowledge of what to look for, found nothing wrong with it. The plastic felt a little more supple with a little bit more give to it than the blue plated one.

This build also went great and the test run also went well. I might fill and seal the diff at some point to make it a bit more grippy as it's quite loose with just the grease inside it. Generally pleased with how it turned out though, and super pleased to have my old RC car working again. Even the old 90's standard 540 motor runs great! 

Original Model
- Tamiya M03 Rover Mini Cooper Racing

Retained Parts
- Acoms AS12 Servo
- Tamiya 540 Silver Can motor

Current Upgrade List
- Full Sealed Bearings

- Aluminium Front and Rear Hubs (Jazrider/RCJaz)

- Hobbywing Quickrun 1060 ESC

- Tamiya Torque Tuned Motor

- SRT Servo

- JK RC Oil Filled Shocks

- Absima Radio Rx/Tx kit

- Absima 4000mAh NiMH

Final Form

One thing I’ve skipped over is that in my desperation for new chassis parts I’d also done some late night bidding on a couple of complete rolling chassis with wheels and motors. So now I have three complete M03 chassis… I’ll talk about them in another post!

Welcome to Revive RC!

Hi, welcome to the blog!

I'm a dude approaching 40 getting back into my childhood RC hobby. I'll be fixing up old cars, maybe building some new ones and possibly even doing a bit of racing, and trying to get some of my mates into it too.

My main aim is to have fun while I fiddle with old RC cars and see how well I can get them running. Hopefully some of what I do and document as I'm doing them can be helpful to you or someone else too!

Here's a little about my history of RC cars and the toys that preceded them.

As a child of the late 80's and through the 90's I had a number of RC toys from the likes of Tomy, Nikko, Tyco and so on. It was a golden era for cheap exciting toys you could bash around the house or in the garden. Stuff like the Tomy Char-G, Tyco Triple Wheel, Tyco Rebound and a great Nikko speedboat among quite a few other bits and bobs. We had some other cars too, there was a small tracked car, and I think a Tyco buggy of some kind, along with some Lego Technics motorized cars.

After the toys my dad got a Mardave Cobra for us to build together. I think was an attempt to get us off the video games quite so much, and he was also desperate for us to get into building stuff with him, but we never really liked Meccano he tried us on before.

The Cobra was a lot of fun. We bashed that car around our garden all the time. The real flaw was that the old 90’s NiCad battery packs were pretty low capacity and lacked the punch of even NiMH packs. Much later I did buy a couple of decent NiMH packs for the Cobra, but by that stage the Cobra was already in a bad way reliability wise. 

Eventually it broke and it was deemed beyond repair so it was binned(!) between a couple of house moves. An action I now regret, as now I want to get a new buggy!

Around the same time my brother wanted a car too, so he got a Mardave Mini. That was a fast car! But it wasn’t as fun bashing around the paved bit of our garden or the dirt paths near our house. We didn’t really understand that it was a racing car designed for use on a properly prepared surface, like carpet. That car also got smashed to bits and was eventually thrown out too. Which is a shame too, but that was also heavily damaged. 

Sometime around 1999/2000 I picked up a Tamiya Mini kit on the M03 platform. I wanted a new Mini, but with a bit more in the way of suspension for bombing around our uneven paved drive and the unmade dirt road down the side of our house. Unfortunately in running it for the first time, as an excitable teenager, something seized in the gearbox for some reason. I put it down to the lack of lubrication in the plastic bushings, but it could have been any number of things even down to just bad luck and bad driving. When that bushing seized it caused the axle to heat to such a level that it melted the part of the chassis that it sits in and all of the gears ended up way off axis meaning the gears didn’t mesh so it stopped. I hadn’t even painted the shell…

There ended my engagement with RC cars, until 2023, when I decided to get the Tamiya mini out of my parents basement and get it running, which is where we begin with my next article.