Kyosho Scorpion 4x4 build project
 

As the title suggests this is a build project of a Kyosho Scorpion conversion to 4 wheel drive .
Aims
1 period possible with 1980's tech/parts
2 to keep it looking like a Scorpion cosmetically
3 to be functional ,not a shelf Queen
The plan is to use chain drive from the rear to the front , Optima front steering hubs and a front diff .
I've started by making a replacement for the front steering hub king pin , as standard the king pin passes through the steering hub but if fitting a driven hub I had to think of an alternative system . My solution is to have a king pin under the hub that passes through twin flanged bearings fitted it the pin that passes through the front suspension arm .
The first issue I've come across is that with a wheel fitted to test it's increased the front track to make the front wheel 10mm wider both sides than the back so I'm going to have to find ways to bring it in again , I think I can move each wheel 6mm inward so I've got another 4mm to go .
Here's pictures of the king pin arrangement and Optima steering hub installed .
http://i1042.photobucket.com/albums/...pshhcv2nvk.jpg
this is a comparison of the stock steering hub and king pin next to the Optima hub and king pin .
http://i1042.photobucket.com/albums/...pse50an7ac.jpg
hub installed
http://i1042.photobucket.com/albums/...psmf5usqtp.jpg
and view from front showing increased track .
http://i1042.photobucket.com/albums/...pscjm2tmrb.jpg
there's surprisingly little slop ,at least comparable if not better than the stock king pin setup , hopefully the tiny flanged bearings don't wear out too quickly.

Just made the new adjustable front suspension hanger , at the moment the servo saver fouls on the joining sleeve but that's kind of a mute point as it won't be there when I'm done as the front gearbox will be there ,I also modified the king pins to bring them in a bit ,overall it's about 5 or 6 mm narrower ,I've ordered some Optima front axles as well as they were recommended on another forum to help reduce the width . Sorry about the photo quality ,kids are on the PC so I can't use the digital camera and download decent pictures ,these were done from my tablet but you get the idea.
http://i1042.photobucket.com/albums/...psiww22qs5.jpg
http://i1042.photobucket.com/albums/...pskxatxv3s.jpg

Nice project dude....looking forward to more info etc :thumbsup:

I found time to modify the Optima front axles that arrived so they can take a standard 12mm hex ,fitted them and now the front track is 2 or 3 mm narrower than the rear YAY !
http://i1042.photobucket.com/albums/...pslrslbn7i.jpg
http://i1042.photobucket.com/albums/...pspltkgraa.jpg

http://i1042.photobucket.com/albums/...psaa43qujw.jpg

Next instalment.
i got the chance to make another attempt at the extended rear lay shaft and this time it all went smoothly yay !
The shaft is over long right now but can be shortened to the correct length when i decide where the chain will run . The extended end for the sprocket has to be 4mm as that's the internal size of the bearing in the gearbox , the internal diameter of the sprocket is 6mm so I had to make a sleeve to fit between , the shaft may have to extend further than i'd like from the gearbox and if that's the way I go then I'll make up a support with a bearing in that can be secured to the side of the gearbox with either the diff cover plate screws or the motor support screws , again i might find a way to have it flush with the side of the gearbox ,in witch case i can shorted the shaft and sleeve .
You might notice if you have a keen eye that there's no groove to fit the circlip that retains the shaft on the motor side of the gearbox , this function will be performed by the sleeve that goes between the shaft and sprocket , the sleeve is extended to butt up against the bearing in the gearbox , i did this because in was worried that a 4mm shaft extended that far might bend and having a groove cut into it would further reduce the diameter , the sleeve also helps to support the shaft and prevent it flexing .
http://i1042.photobucket.com/albums/...pslx88arxn.jpg
http://i1042.photobucket.com/albums/...psfw40ljrm.jpg
http://i1042.photobucket.com/albums/...psg2z8nv4m.jpg
http://i1042.photobucket.com/albums/...ps2srijafw.jpg
http://i1042.photobucket.com/albums/...ps7ezdswwq.jpg
http://i1042.photobucket.com/albums/...psut5pg7fz.jpg

And the front Lay Shaft made up , again its over long and can be shortened later.
http://i1042.photobucket.com/albums/...ps3eha2phh.jpg
http://i1042.photobucket.com/albums/...psif782dqs.jpg
http://i1042.photobucket.com/albums/...psntjcnnnh.jpg

Looking good , things are happening

😊

/iso

yesterday I made up the centre part of the gear housing and flowed the edges , still needs more work but I'm pleased with it.
http://i1042.photobucket.com/albums/...psfyv5nzy9.jpg
http://i1042.photobucket.com/albums/...ps1yuq08l0.jpg
http://i1042.photobucket.com/albums/...psugdi1ckm.jpg

Today i made up the mounting plate for the front gearbox , this replaces the original chassis plate that would support the servo saver and the cross bar that goes between chassis rails , it all fits in pretty well , i'll have to chop some of the front of the plastic tub to give clearance for the gearbox and for the chain but it should be possible to leave the battery compartment untouched .
http://i1042.photobucket.com/albums/...psvug66bqb.jpg
http://i1042.photobucket.com/albums/...psxr4tfi1d.jpg
http://i1042.photobucket.com/albums/...pscyknrwit.jpg

I love this stuff!

Nothing like some properly executed, innovative engineering to sooth the soul. I dream of having the tools and knowledge to turn something old school back in to a competitive beast again.

Thanks , i very much doubt it will be competitive in a modern race , I'd settle for a successful conversion and fun to drive.

Great stuff. Will be following!

Agree the old vintage stuff will never compete with the modern racers. I would love to see a race series for vintage prototypes just to showcase everyone's engineering developments. I reckon it could be awesome fun....

That sounds like a lot of fun but i think the qualifying rules might be complicated .

Did a bit more cutting of the tub , its still a little rough round the edges but i think i have the clearance i need for the chain , i also cut the front under-plate so the gearbox fits into it and lowers the gearbox the 3 mm i needed , i might just get away without making new shock towers as there looks like enough clearance for the drive shafts , I'm going to have to extend the shafts about 10 mm but that's easy enough . One other thing on the list is to make up some guide pulleys and a tensioner .

http://i1042.photobucket.com/albums/...pshlsvjoqu.jpg
http://i1042.photobucket.com/albums/...psnaqhvuyu.jpg
http://i1042.photobucket.com/albums/...psqf9vtur0.jpg

Front gearbox mounting milled out , just off the mill so its not all prettyfied yet.
http://i1042.photobucket.com/albums/...psb3gmfmdq.jpg
http://i1042.photobucket.com/albums/...psodkrrlwl.jpg
http://i1042.photobucket.com/albums/...ps44gwx9w2.jpg
http://i1042.photobucket.com/albums/...psrxbxpbmz.jpg

Rc porn, stunning

Thanks , ive got to sort out the steering next .......should be interesting .

After experimenting with the drive shaft length I've redesigned the king pins to have an offset moving the wheel back 3mm , this gives the correct end float with the driveshaft .The new kingpin is at the top of the first picture.
http://i1042.photobucket.com/albums/...pscxpbcz6i.jpg
http://i1042.photobucket.com/albums/...pscjbox9xe.jpg

Pictures of the finalised transmission ,drive shafts extended , chain guide pulleys fitted and chain length shortened, there's a second guide pulley up front but its kind of hidden , you can see the screw that it runs on in the side of the tub in the second picture also a scratch in the tub i'll have to clean up before painting:(.
http://i1042.photobucket.com/albums/...ps5a8ykmyt.jpg
http://i1042.photobucket.com/albums/...psd3hdjkaf.jpg
http://i1042.photobucket.com/albums/...ps87vjkgbc.jpg

I got started on the steering system , there are a few areas that need attention as yet , i have a slight binding issue on the track rod ends with suspension compressed but i have a couple of ideas to overcome it , clearance is tight as the links go under the diff out drive cups and there's only 3mm so they are just over 2.5mm thick , bump steer is acceptable and probably less than stock , its not clear in the pictures I'm afraid , the top part of the top crank for the linkage is over size at the moment as i was not sure of the relative alignment of the top and bottom arms as its not 90 degrees so i thought I'd fit it and then mark the position for cutting later .
the really good news is that it all fits under the body.
http://i1042.photobucket.com/albums/...psafckfdyn.jpg
http://i1042.photobucket.com/albums/...psubvjkqm4.jpg
http://i1042.photobucket.com/albums/...ps5zolvsf8.jpg
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http://i1042.photobucket.com/albums/...ps76zurgru.jpg
http://i1042.photobucket.com/albums/...pszj9pqw5e.jpg

Fantastic!! :thumbsup:

She went for a brief test run this evening , there are two little issues .
1 it has the turning circle of an ocean liner .
2 There is a little clearance issue with the chain .
I was kind of expecting the poor turning circle and have a cure , I'm going to drill and tap the steering hubs so i can fit the ball studs for the track rods closer in ,this will increase the turning angle ,probably increase it too much but i can reduce it by end point adjustment.
The chain clearance will be easy ,either adjustment or removing a little material .
This sounds bad but this is the kind of stuff you have to expect in a project like this , I'm actually pretty chuffed that it worked as well as it did first time out .

After adjusting the steering linkages i got a chance for a road test this evening , on the road it's a little low on straight line stability but i think that's largley down to tyre choice , there's no understeer anymore , in the short grass of my front garden it was really transformed , tracked nice and straight and turned nicely .
The only thing that surprised me was that it still pops wheelies even with the extra weight on the front axle .
I still have to make a chain tensioner as there's a little slack that makes it a little noisy but other than and a little finishing off of some parts and some paint then she's finished .

The cvd shafts arrived today and they fit the steering hub well but are slightly too long and the pin in the dog bone end is too wide , i have a set of Scorpion dog bones coming so it's a simple matter of cutting and joining the two shafts at the right length .
After that then all that's left is a chain tensioner and paint yay !
Oops i missed an update on this forum , I've been having issues with the front dog bones popping out so i decided to use cvd shafts instead , i know they are out of period for this build but they have they have virtually no visual impact and they solve a problem that was a curse on all 4x4 cars of the 1980s , my Hot Shot was forever dropping front shafts and I'd have given a pretty penny for cvd shafts back then .

The scorpion dog bones arrived today and I found a little time to make sleeves and cut and silver solder the two parts together but by the time I was finished it was 10.15pm , where does the time go ! So it's road test in the morning yay !!!

Well the test drive went perfectly , it even withstood a cartwheeling crash ! I'm not even sure i need a chain tensioner yet ,probably will as the chain stretches but not yet .
only downer is with Photobucket being too glitchy to work right now so i still can't give any photo updates , i'll try later , i'll see if i can persuade someone to help video it in action as well .

photo update showing cvd shafts and wheels , im more happy with the silver soldering on the shafts and i made the sleeves slimmer as well so they look neater at least to me .
http://i1042.photobucket.com/albums/...psynpnuwin.jpg
http://i1042.photobucket.com/albums/...psiti2cwrs.jpg
http://i1042.photobucket.com/albums/...psovorrwmb.jpg
http://i1042.photobucket.com/albums/...psouhx6gpq.jpg

Painting went well and I've given the chassis and wheels a scrub , I'm just waiting on a new set of decals and I'll get some finishing photo's before she gets all grubby and scratched up , after the photo session it's gloves off and a video of her getting some proper rough and dirty driving .

Looks nice, just wondering if the drive shafts won't start chattering when you steer the wheels, because these are already at an angle with the wheels neutral.

I've try'd to keep the end points limited to keep within the limits of the cvj's but to be honest it's not too much of a problem as there's more usable articulation than the dog bones before they fell out , the shafts are swept forward from diff to wheel at full suspension extension and swept back slightly at full compression , this gave me all sorts of problems with the dog bones and trying to get end float and no binding , I really didn't want to use cvj's as they are too modern but they have solved the problem .

A few finished pictures , video soon.
http://i1042.photobucket.com/albums/...ps4pdvyhef.jpg
http://i1042.photobucket.com/albums/...psg4exspiq.jpg
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http://i1042.photobucket.com/albums/...psmsinobqg.jpg

Well i made a short video with the help of a friend but its not great quality , its a stills digi camera taking video , i have now got trouble with the chain tension so i need to make a tensioner , i guess as the chain has run in and stretched a little . Anyway it was no surprise and i always expected to need a tensioner
https://youtu.be/8Zch4oMkta4

New ESC fitted and tested and running well , it's just a hobby king 120amp x car ESC but it's all I need .
I also cut a little more out of the tub where the chain was touching so I then finally got to re test it and it's all working well yay !