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/