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  #161  
Old 19-10-2011
Miggers Miggers is offline
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Hmm,a B4 spur,I'd go for about an 81-82t and a 22-23t pinion with a 27t stock.

Did you use standard B4 pads with it?

What dimensions are your PTFE slipper plates?

The lad can get his mitts on PTFE round bar and they have a lathe
where he works so I might just be on to get him to make me a pair.
Though knowing him,it'll be like trying to get blood out of a stone

Edit.
Just asked the lad about PTFE round bar,he says they threw it out a few
months ago because no one used the stuff anymore,groan!!!.
So that's that plan buggered,rats.

Mark.
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  #162  
Old 21-10-2011
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Here we go Adey.

Slipper plates: 30mm x M8 Penny/repair washers

Centres: M4 brass or steel nuts.

M4 nuts are 8.1mm across the points.

Run a 4mm drill bit through the M4 nuts.

Carefully open out the 30mm washers so that the M4 nut just fits in.
Use a good quality epoxy resin for the brass nuts or find someone who's
good with a MIG welder for the steel ones.

Finally,file a slot on the back of one nut to take the top shaft's drive pin.

There you go,slipper plates for your Cobra.

Mark
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  #163  
Old 22-10-2011
bazza373 bazza373 is offline
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Default cobra

Good reading in this thread chaps.

I have a std Cobra which I plan to dust off and bob my brushless stuff into.

Quick question about the diffs, whats the best solution to date? B3GB/mardave mod? Meteor diff halves on the Cobra diff gear? Ansmann diff built into cobra housing?

Any progress on stronger drivershafts? The mardave ones do look venerable!

Cheers
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  #164  
Old 22-10-2011
Miggers Miggers is offline
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I wondered about the Ansmann diff unit,but the only thing is that it's
bearings are 2mm smaller/1mm larger than the Cobra's on the I.D and O.D. and to fit
any other spurs than the stock 80t,you need modified B4 plates.

The Cobra'box isn't keen on brushless at all without some modifications or replacement by another make altogether.
It needs fully ballracing,the intermediate gear needs boring to take a steel or ally insert and shaft.
The diff halves need about 0.50mm skimming off their faces so that you can fit B3/B4 wear rings and both halves need boring out to take the B3/B4's
diff screw and end nut.

DerbyDan has a complete Losi XX'box fitted to his,Adey has a custom'box in his,others have fitted a B3/B4 guts into the Cobra's cases(though that's a lot of work apparently),others have fitted a complete B3/B4 'box onto the Cobra chassis.

I have Meteor diff halves on a Cobra diff gear in a fully ballraced Cobra'box but I'm only running a 27t brushed at the moment.
Adey says a B4 diff is easy to fit if you modify it as he mentions.

There are a few ways to get the thing to take big horsepower as you see.
The standard diff and intermediate gear won't stand it for long plus the
standard slipper is reputed to be a mare to get adjusted properly.
A quater turn of it's adjuster takes you from locked solid to free spinning
with not a lot in between,so either a homemade or a B4 slipper is needed
with a better slipper spring(a Losi is said to work well).

Hot Bodies D4 rear CVD shafts are said to fit straight on.

As you may have seen,mine runs on JC Racing RC10B series five spokes all round,with the rears
fitted to the Cobra rear axles.
Just run them through with a 4mm drill bit and fit an old nylon bearing behind the drive pin as a spacer.
The fronts are on B4 front axles turned down and shortened to fit into Meteor swivels.
Front bearings are RC10B series 3/16x3/8x1/8 to fit the front wheels.

Mark
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  #165  
Old 22-10-2011
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the best advice as regards to running a brushless system in a cobra is to retro fit another gearbox. Modifying the standard gearbox is ok but its not easy or cost effective. I have fitted a b3 gearbox, a b4 gearbox will fit and i am sure the ansmann could be made to fit also. Which ever gearbox you choose is at least easy to get bits for when required. I am trying tamiya front db01r driveshafts. While basic, they are strong. The best mod other than the gearbox is to move the steering belcranks to give better ackermann. I makes the car more predictable in the turn. Despite how basic they are, they can be made to go very well.
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  #166  
Old 22-10-2011
bazza373 bazza373 is offline
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Thanks for the advice Mark & Adey, I will look into it.
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  #167  
Old 22-10-2011
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post pics of your car.
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  #168  
Old 23-10-2011
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You can pick up all the parts(shafts,gears,casings,motor plate,etc)for the
Ansmann Macnum/Mad Rat 'box for £16.99 on E-Bay.

http://www.ebay.co.uk/itm/ANSMANN-MA...item483fd9e9da

http://www.ebay.co.uk/itm/ANSMANN-MA...item48412cbd6f

http://www.ebay.co.uk/itm/ANSMANN-MA...item5d2e30d518

That doesn't include bearings(15x10x4,2 off/10x5x4,4 off) though.
You'll also have to make up mountings to suit the Cobra chassis and
rear shock tower.

BTW,Macnum g/box parts are the same as the 'Rat,but a £1 cheaper.
Search Mad Rat and you'll see what I mean.
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  #169  
Old 23-10-2011
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Nothing to see with the car at the moment, just whipped the shock towers off for a friend who should be able to knock some up for me in carbon.

Thanks for the links, weighting up weather to go for the RAT set up of buy a B3 and use the GB, steering & links.

My Cobra, I think, is the basic one. Yellow chassis & plastic turnbuckles, for all your non-adjusting needs!! Not sure if the TQ kit came with actual hinge pins? Mine has what can only described as 'pointed wire' joining hubs to wishbones etc. Perhaps rob a B3 of them too?
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  #170  
Old 23-10-2011
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I'm pretty tempted to stick a madrat gearbox on mine. My cobra has never really got on with the 13t brushless I have in it. It seems to slip, but it isnt the slipper clutch.
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  #171  
Old 23-10-2011
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Quote:
Originally Posted by qatmix View Post
I'm pretty tempted to stick a madrat gearbox on mine. My cobra has never really got on with the 13t brushless I have in it. It seems to slip, but it isnt the slipper clutch.
It'll be the crappy Mardave diff.

Pretty tempted to go the Macnum/Mad Rat route myself.
The Cobra box has about as much strength as a chocolate teapot
with anything more than a 27t stock in it and even then it's iffy.

Then again,for £60,I'm tempted to buy the 'Rat and ditch the Cobra full stop.
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  #172  
Old 23-10-2011
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Just wondering guys,weren't mardave working on an uprated diff at one time for the cobra,did it ever get released??
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  #173  
Old 23-10-2011
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yes they were. Chris wikinson promised to give me one but it never materialised. It was essentially standard diff halves modified to take b4 plates and thrust bearing. I made my own this way and it was fine. My car was the one on the mardave site and everybody was asking if i was developing a new cobra.
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  #174  
Old 23-10-2011
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Quote:
Originally Posted by karlmark1 View Post
Just wondering guys,weren't mardave working on an uprated diff at one time for the cobra,did it ever get released??
They were and it didn't.

There isn't any mention of the Cobra on Mardave's swanky new website
either.
No exploded diagram,no spares list or prices,nothing on the uprated
modernised Cobra they were touting a few years ago,absolutely zilch,zip,nada.
I think they've quietly given up on the thing and dropped it completely.

Chris(the Mardave owner),just isn't interested in it at all,he only wants
to race and sell those piddly V12 1/12th circuit racers.
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  #175  
Old 23-10-2011
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miggers: the cobra is a pain to make reliable with the standard gearbox and its up to you weither you ditch it or not. I would be happy to send you my diff halves modified to accept b4 parts which is what mardave were trying to develop if you choose to carry on with it. Personally i would chose a cobra over a madrat as they are retro, different and go very well on track when sorted. but i would say that !.
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  #176  
Old 23-10-2011
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yeh, thats right. My car was on the old mardave site. Chris wilkinson isnt interested in the cobra, which is a shame in my view. Up to people like us too keep them alive. Lol
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  #177  
Old 23-10-2011
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right i have just bought a cobra as i used to race one as a kid,i want to stick a brushless in it but im running it as a laugh but reading this has got me confused. in lamuns turms what have u got to do with the diff to make it reliable or what do u have to do to get a b4 diff to fit?
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  #178  
Old 23-10-2011
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you can either drill out the standard diff halves and add a step to the face of the diff halve to enable the use of the b4 diff plates and thrust bearing or remove 0.5mm off the inner diameter of the standard diff bearings to enable the use of rc10 diff halves.
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  #179  
Old 23-10-2011
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Quote:
Originally Posted by adey View Post
miggers: the cobra is a pain to make reliable with the standard gearbox and its up to you weither you ditch it or not. I would be happy to send you my diff halves modified to accept b4 parts which is what mardave were trying to develop if you choose to carry on with it. Personally i would chose a cobra over a madrat as they are retro, different and go very well on track when sorted. but i would say that !.
I can send you a complete Cobra diff in exchange if you like(I have two).

I'd love to get it so that it can run reliably with big brushed horsepower.

Probably still buy a 'Rat too for serious brushless power though.
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  #180  
Old 24-10-2011
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pm sent miggers
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