Kit-bash Capra aka. the 'Super Chump' Dakar buggy

[JennyMo 3526]

I've had an idea... actually, it's more of an idea since today the aluminium sheet arrived so I could finally cut my front subframe and tie the two halves together, hence waiting until now to start this thread, as I have something other than a pile of random parts to show you...

And random they certainly are - this latest build being what a consider the epitome of 'kit-bashing' - in an effort to hopefully create something unique and fundamentally not seen before (if google can be trusted) - and as such, while I will endeavour to include a number of traditional scale elements to this build as usual, since the two primary donor vehicles are not what you'd consider 'scale' build material in the traditional sense - this is going to be more about building a basher style runner than a full-on shelf queen.

So what have we got?

 

photo. Axial Capra cage/body, skid plate and a solid [straight] axle at the rear...

 

As a bit of background, I already have a 4WD Capra which I built up from a bare cage cassis (very reasonably priced at $35 these days) and modified with much more narrow RC4WD Yota II axles and more modest diameter (115mm) tyres:

It is such a hoot to drive, and since fitting a 13T 5-slot motor recently has quite the turn of speed now too, while remaining smooth and controllable for trail style crawling... and it was that speed element which got me thinking - what If I put an even faster motor and more simple transmission into a Capra cage, just power the rear axle, and install a [wider track] independent front suspension to try and keep thing thing going in a straight line?

 

A tale of two halves...

The rear end was simple enough (as per the photo at the top of the page) - in this instance the 4WS Capra cage set (for info. it's $5 cheaper then the original version, and is basically the same other than the cage is slightly tapered upwards at the rear above the axle), plus an aluminium aftermarket skid-plate assembly together my own custom 4-link set-up using a series of shortish rods and ends, so that the axle was located just behind the shock tower brackets on the cage. The SCX10 width aluminium straight axle is supported on a pair of 80mm long Gmade RSD reservoir shocks, in this instance with some much softer aftermarket springs installed - so ultimately there is nothing really new under the sun here - these are all parts I've used before on other builds, and so was confident will be more than up to the job in this slightly higher performance iteration too.

The front end however did initially cause me some head-scratching - not least as I didn't want a huge disparity between the front and rear track widths (most 1/10 scale IFS buggies being significantly wider in track than a 1/10 scale crawler for example...) and in that regard an obvious independent front end to utilise might have been the Element Enduro IFS conversion kit... however, not only is that technically a 4WD set-up and correspondingly a $100 since it includes a front differential assembly I'd not be using, but since it has now been discontinued (for some reason?), it seemed my only option was to look at which buggies might offer a more affordable set of wishbones, uprights, steering knuckles, and most  fundamentally a separate shock tower/wishbone mounting assembly which I could ideally mount on a flat custom chassis plate...

After a bit of noodling around looking at parts and build instructions online, it transpired that actually the 'lowly' Tamiya DT-02 chassis (RWD) buggies appeared to offer exactly what I needed - fundamentally a solid plastic shock tower which locates both the wishbones and the shocks, with a flat bottom that included a series of mounting holes - result!

 

In addition, the main benefit in choosing Tamiya parts is their various plastic part trees tend to be very affordable, and in the case of the DT-02 and 03 models (being their entry-level racing buggy platforms), there are any number of upgrade/replacement parts available too - including Tamiya's own hop-up options such as adjustable turnbuckle links to replace the plastic upper wishbones, and also plenty of aftermarket aluminium versions of the various wishbones and uprights etc.

I finally settled on a combination of Jazrider aluminium DT-02/03 front lower wishbones and uprights (in anodised black to match the rear straight axle and suspension links), and Tamiya's own 'Hop-Up' kit of turnbuckle upper links (so you can adjust the camber) and steering rods, together with a pair of Hornet steering knuckles, which have cranked arms rather than straight, so would clear the narrow offset wheels I planned to use.

I apologise I didn't actually take any photos of this step of the build, but suffice to say it all went together easily and gave me a self contained IFS subframe which could be simply bolted to a flat chassis plate - which was the key to getting this whole caboodle together:

 

photo. cardboard template used to mock up the proposed wheelbase and mounting locations to the existing Capra skid-plate, and the front Tamiya IFS tower assembly.

 

Photo. front chassis/subframe cut from aluminium sheet - initially with a fine jigsaw blade before being hand finished with a bench grinder and files.

 

I elected to cut the chassis from 2.5mm thick aluminium (rather than the more usual 2mm, which is much easier to work with and fold) - factoring in that since this vehicle was likely to be driven and higher speeds and potentially jumped from time to time, the relatively narrow portion of this chassis where the IFS tower mounts could do with being that much thicker - especially as it essentially doubles up as a skid plate too.

 

photo. initial bends made with a bending brake tool for precision - handy if you like to work with thin sheet metal.

 

I'd calculated as best I could the angles both the IFS tower would need to be mounted (to not only clear the Capra cage rails above, but also I noticed that the DT-03 buggies have their front suspension canted backwards presumably to increase the trail and improve stability), and also incorporated a front bash-plate section which would line up with the existing Capra cage/headlight panel above.

Taking my time to bend just enough to get the initial angles spot on, I found that I needed to trim just 3mm off the top of the bash-plate portion and it mated up a treat!

 

photo. this was the first and fortunately only chassis plate I had to cut to get this to go together! Ultimately once the front suspension tower camber angle was set, the bash-plate just had to be trimmed slightly to line up with the cage rail above.

 

photo. The DT-02/03 front suspension bolts directly to the narrow portion of the alloy chassis, and the steering servo mounts directly behind on a wider section which in turn bolts to the Capra skid-plate.

 

photo. bash-plate portion trimmed to fit - I might end up drilling a series of vent holes in the front, or maybe just fit a recovery hitch and/or some stickers!

 

photo. the final chassis bends - note that I did have to cut out two short sections of the plastic cage so that the shock towers fitted up under the hood - otherwise, it really appeared to be made for this IFS conversion!

 

photo. the complete front subframe-chassis, the rear portion is shaped to fit flush inside the aluminium skid-plate of the Capra body using the four screws which would normally mount the traditional Capra transmission, the result being the whole chassis is very rigid indeed.

 

Currently I have tapped the 2.5mm thick aluminium chassis with M3 threads to bolt the two portions together, however I feel that ultimately it will be stronger to bolt all the way though with a nut on each screw - once I've decided on the final transmission layout.

cont.

[JennyMo 3526]

cont.

I have to admit, I am rather pleased with how this all went together first time - using a cardboard template certainly helped to get the initial dimensions in the ball-park, but ultimately a bit of eyeballing and some good luck resulted in me only having to cut one chassis, and take my time filing, grinding and drilling to make sure everything lined up as I envisaged:

 

The result is a 290mm wheelbase, with the chassis canted slightly forward/nose-down - factoring you'd probably want it that way anyway for landing any jumps on the rear wheels.

Currently there is no motor or electronics installed just yet (which may level it out a little), and the neat thing about the Capra cage is that it includes a battery compartment below the windscreen under the hood which takes a shorty 2S Lipo - however, that is likely to bias the weight distribution slightly more forward of course, so it's going to take some tweaking to get the final stance settled I feel - perhaps using a combination of softer springs at the rear and/or stiffer ones on the front?

 

photo. front 75mm shocks, with aftermarket springs.

 

Rather fortunately I've been able to utilise a pair of Tamiya Frog rear shock bodies on the front, and these are actually the same diameter as the Gmade RSD shocks on the rear, which means I could purchase a set of alternative springs and mix-and match as required (for info. it's the RC4WD King Shock spring assortment for their 90mm shocks, which use a pair of 35mm long springs). I have to say, these shocks are super plush and really well damped - so much so that I will need to rebuild the rather springy Gmade shocks and use a thicker oil too I think to make them more evenly matched.

 

photo. with these buggy wheels, the track width is 205mm at the front (vs. 185mm at the rear) - although being rather top heavy compared to a traditional buggy I suspect this will actually pay dividends with regard to handling and stability. Plus the long-arm wishbones at least offer a decent amount of travel and ground clearance...

 

photo. the rear axle is a CNC billet aluminium aftermarket option based on the SCX10 II dimensions (I've used the same ones on the Ghetto Vanquish and have been impressed with the quality), and I've added some scale hex hardware to the diff cover, just because it looks kewl!

 

Now admittedly while these buggy wheels are not exactly 'scale', they are very nicely finished (again, these are Ebay aftermarket aluminium options for the DT-02/03), I do feel in this instance the buggy is likely to handle better on these than it might on taller and more narrow tyres...

Indeed, I did initially purchase a set of 1.9 size 100mm diameter BFGoodrich tyres, together with some of my favourite Method Roost alloy wheels which utilise the SLW hubs (you can get a 2WD freewheel version via Locked-Up RC, which I used on the SRB Cage Racer for example), so that is an option in future perhaps - although it does increase the track-width at the front by about 15mm unfortunately, hence these positive offset buggy wheels and lower profile tyres being fitted in their place for the time being.

 

photo. DT-02 shock tower fits perfectly in the gap created by removing two short portions of the lower cage braces - note also how neatly the steering servo sits under the batter compartment in the Capra cage!

 

Power!

I've currently fitted a shorty servo as a placeholder, since I'm not sure how much room I'm going to have in the centre of the cabin to mount the motor and associated electrics - particularly as I'd like to try and incorporate some sort of dropped/scale interior too, albeit a simple one to reflect the primary 'runner' nature of this build.

My plan is to use a 12T 3-slot 550 motor (which is pretty much the fastest for the budget I'm prepared to invest so far in this folly), paired with a 3:1 planetary gearbox, which then directly drives the prop-shaft to the rear axle (which of course has it's own further reduction ratio). I haven't even begun to try and work out the final gear ratio and potential top speed, it's going to be very much suck-it-and-see I suspect - although it ought to be appreciably faster than the set-up in my current Capra... as long as it does donuts and jumps on demand I'll be happy!

Mounting the motor and transmission longitudinally down the centre of the chassis ought to leave some room either side for an interior of sorts, and I already have a pair of bucket race seats which will suit the style of this build perfectly...

 

photo. playing around with some old Capra body panels in my collection... these custom carbon [covered] hood and roof panels would work well on this style of vehicle I feel?

But equally, I think these aluminium 'Hooli' hood and side panels are probably the direction I'll go in - not least as it adds to the high [bare] metal content in this build already?

 

 

 

So I'm now just waiting for the motor and gearbox to arrive in the [Christmas] post, and then should have a runner...

More soon!

Jenny x

[Badcrumble 4204]

Ooooh, that looks fun 

[OldSchoolRC1 983]

Very cool, I love "spare parts" builds. That IFS tucks right in there - nice work! 

[Nikko85 3454]

Once again a brilliant build. Are you going to widen the rear to match the front?

 

[RustyHunter 42]

Really impressive how the aluminum chassis came out! Looks like it should be a lot of fun to run. Out of curiosity, is the rear axle locked or unlocked?

[JennyMo 3526]

On 12/22/2022 at 3:19 PM, Nikko85 said:

Once again a brilliant build. Are you going to widen the rear to match the front?

 

Hi Nikko - probably, although the disparity isn't all that bad, and the wider front track ought to keep it tracking in a straight line for the comparatively short wheelbase and higher centre of gravity...

As I mentioned above, I also have set of alternative wheels with 100mm diameter BF Goodrich MT style tread for a more scale appearance, and have ordered some SLW hubs from Locked-UP RC so I can mount them to the 2WD stub axles and hexes on the rear - in that regard, I've chosen the version of the rear hubs which are approximately 9mm wider that the fronts on either side, so that essentially the track width with then the same front and rear - although visually perhaps overly wide at the back? - I'll post some photos once those parts arrive.

Jx

[JennyMo 3526]

4 hours ago, RustyHunter said:

Really impressive how the aluminum chassis came out! Looks like it should be a lot of fun to run. Out of curiosity, is the rear axle locked or unlocked?

Hi Rusty - currently the rear axle has a solid (locked) spool gear (as per a crawler style iteration)  which should make for some authentic 'SRB' style sideways action!

I'm not sure if there is an open diff option for these SCX10 II style axle housings, but if so that might well be a consideration eventually... in other news, I managed to snaffle a pukka Tamiya ball-diff on Ebay recently for my dormant SRB 'Mega-Bug' Scorcher project, so we might see that dusted off shortly too!

Jx

[kontemax 1725]

Capra is Italian language and means goat.

Max

[JennyMo 3526]

6 hours ago, kontemax said:

Capra is Italian language and means goat.

Max

Indeed - although this particular one is going to be more of a sprinter than a climber I feel ;o)

Jx

[JennyMo 3526]

OK then! A quick update to this thread since some more parts have arrived in the post...

photo. what can be make with this little lot then?

 

As mentioned previously, I've taken a punt on what is essentially an in-line transmission (which can then be mounted down the centre of the cabin) - using a Homes Hobbies 12T 550 motor (basically the fastest non-brushless option they offer), together with a short (approximately 1" long) 3:1 planetary gearbox, and rather fortunately already had this rudimentary motor mount kicking around in my used-spares stash...

What has turned out to be most fortuitous is that the length of the motor shaft while being a touch too long to fit inside the planetary gearbox without trimming down, is actually the perfect length if I were to sandwich the mounting bracket between them - which in turn helps to balance out the weight of the two which would otherwise be very heavy towards the unsupported (front) end!

I also purchased a 3mm to 5mm shaft coupling - which turned out to be both much longer and chunkier than I expected - still, it might work well as a flywheel and/or to minimise any transmission vibrationed perhaps, in what will be a directly mounted prop-shaft to the rear axle:

 

photo. note the gearbox output shaft will of course be trimmed a little shorter than shown here...

Ultimately I might well just cut a short spacer from a length of 3mm I/D and 5mm O/D tube, much as I did before with the  which features a similar transmission (using a short prop shaft between the 3mm planetary gearbox output and traditional 4x4 transfer case), and mount the prop directly to the gearbox shaft, if only to save a little space - but equally this coupling might well prove the most satisfactory solution to convert the 3mm output shaft to a 5mm stub axle for the prop to attach.

 

Wheelie good!

The other thing currently under consideration is the adoption of the larger diameter wheel/tyre combo after all - not least as they add a heap of scale detail (particularly with the hex wheel-stud hardware), and while the track width is now 225mm at the front (and 220mm at the rear with the offset SLW hubs), I feel that the overall stance while certainly 'aggressive', is not too far from what it might be for a 1:1 long-arm desert racing buggy that you might find ripping around Johnson Valley etc. - although in that regard perhaps I should have chosen a heavily braced F9 style axle instead?

 

photo. my favourite [Method Roost] 1:1 style wheels, and with some pretty scale BFGoodrich MT style soft and skinny tyres fitted too.

 

photo. 725 width SLW hubs to help* compensate for the disparity in front and rear track width in using an SCX10 II width solid axle together with the long-arm independent front end from a Tamiya DT-02 buggy.

 

*Note that I purposely chose to retain a slightly more narrow rear track width (although it's hard to spot once all four wheels are fitted), factoring I can always widen the rear wheels a little further with some Vanquish XD hub covers I also have in my stash - which actually sandwich between the wheel and the SLW hubs, adding a few more mm width on each side.

 

So I trust that with the new wheel and tyre combo in place, you'll agree that the buggy is looking a lot more Capra-esque now? - and at the same time from a practical point of view ought to be usefully more stable with the slightly wider footprint... I guess it's time to rig up the electronics and find out!

 

 

 

 

More soon!

[JennyMo 3526]

Well, I finally got a chance to hook up some electronics this afternoon, and you know what? - it works!

 

photo. initial motor/gearbox location - ultimately I had to move the assembly rearwards 10mm as the battery ended up resting on the edge of the motor once the [hard case] 2S Lipo was installed...

 

However, while dynamically I'm pleased with the overall pose and stance, and handling on those plush shocks - there are a couple of issues which I've only begun to resolve...

The good news is that despite taking a stab in the dark, the combination of the 550 12T 3-slot motor and 3:1 planetary gearbox (together with a further reduction in the rear axle pinyon and ring of course) means the speed and acceleration is similar to my SRB based Cage Racer for example, and similarly with a locked rear diff means donuts galore - result!

The bad news however is that I feel the motor is struggling to spool up initially, drawing more amps? than ideal, and the result after about 5-10 minutes running with a basic 1040 ESC meant both the motor and ESC got really hot - too hot to touch comfortably for more than a few seconds...

 

So I swapped out that [un-programmable] ESC for a Hobbywing 1080 which allowed me to disengage the drag-brake element completely and run it freewheel/overrun mode too, so offering throttle characteristics more akin to a traditional RC buggy than a crawler, and the ESC seems to be handling the current draw much better than before - although the motor, and now the gearbox too I realise is still getting very hot after a few minutes high-speed running.

photo. revised set-up: motor/gearbox moved backwards on the chassis plate, and a 1080 ESC installed to handle the current draw of the fruity motor.

 

If anyone with more electronic and gearing knowledge can chip in with some suggestions I'd appreciate it, although I fear the issue is primarily that I'm trying to run what is essentially a crawler motor and gearbox combo at much higher [rotational] speeds than they were really designed to do?

As such, it's possible I'm going to have reconsider my live-axle rear end on this build, and perhaps use a more traditional 2WD buggy set-up - either from Tamiya [again] or even a 2WD Traxxas Slash or similar?

 

photo. so far it's been great fun testing it wizzing up and down the road - although it's on the dirt I think this RWD buggy is going to really shine...

 

So I'm going to look at some alternative transmission options now - and as I mentioned above, would also welcome any advice/suggestions with regard to the current set-up and how I might reduce the heat and improve things there...

More soon!

[ThunderDragonCy 7881]

@JennyMo Generally, high motor temps and current draw mean its over geared. Can you try fitting a smaller pinion? That should let the motor spool up easier and ultimately might lead to higher speeds because the motor can get on top of the gear and spin faster. 

[JennyMo 3526]

12 hours ago, ThunderDragonCy said:

@JennyMo Generally, high motor temps and current draw mean its over geared. Can you try fitting a smaller pinion? That should let the motor spool up easier and ultimately might lead to higher speeds because the motor can get on top of the gear and spin faster. 

 

[JennyMo 3526]

Hi Thunder' - yes, that is my current (aha, see what I did there?) conclusion...

The issue is I'm using a planetary gearbox with a 3:1 reduction, so there is no way to change that initial reduction ratio in the same way as you might with a pinyon and spur gear... and that while there is an initial reduction of 3:1, the prop-shaft then directly drives the rear axle with a further reduction of around 3.2:1 (since those Axial axles tend to have an 8 tooth pinion and 24-30T ring gear), which is pretty reasonable for this style of vehicle?

However, this means that while the overall wheel speed would appear to be similar to something like an SRB for example, it appears that potentially the motor (and ESC) is working harder to get the transmission to turn - ie. it requires more torque, resulting in more heat being generated - than it might otherwise? - certainly initially, and that the motor and initial reduction of 3:1 from the planetary gearbox is having to spin up the prop-shaft before it gets to the second/final reduction gears in the rear axle.

for info. the reason I went with this 550 12T motor is because it does appear to offer a lot of power and spins/accelerates very fast once the vehicle is rolling, so no issue there - however, it's possible that the relatively few turns (as I understood it, traditionally with 3-slot motors, more turns = more torque, but at the expense of overall speed) means it does struggle to get it moving initially, which as you suggest is could potentially be compensated for with a change in gearing... it's just I'm not sure where to begin if I'm to retain that planetary gearbox as the primary reduction?

I shall continue my experiments!

[ThunderDragonCy 7881]

40 minutes ago, JennyMo said:

Hi Thunder' - yes, that is my current (aha, see what I did there?) conclusion...

The issue is I'm using a planetary gearbox with a 3:1 reduction, so there is no way to change that initial reduction ratio in the same way as you might with a pinyon and spur gear... and that while there is an initial reduction of 3:1, the prop-shaft then directly drives the rear axle with a further reduction of around 3.2:1 (since those Axial axles tend to have an 8 tooth pinyon and 24-30T ring gear), which is pretty reasonable for this style of vehicle?

However, this means that while the overall wheel speed would appear to be similar to something like an SRB for example, it appears that potentially the motor (and ESC) is working harder to get the transmission to turn - ie. it requires more torque, resulting in more heat being generated - than it might otherwise? - certainly initially, and that the motor and initial reduction of 3:1 from the planetary gearbox is having to spin up the prop-shaft before it gets to the second/final reduction gears in the rear axle.

for info. the reason I went with this 550 12T motor is because it does appear to offer a lot of power and spins/accelerates very fast once the vehicle is rolling, so no issue there - however, it's possible that the relatively few turns (as I understood it, traditionally with 3-slot motors, more turns = more torque, but at the expense of overall speed) means it does struggle to get it moving initially, which as you suggest is could potentially be compensated for with a change in gearing... it's just I'm not sure where to begin if I'm to retain that planetary gearbox as the primary reduction?

I shall continue my experiments!

3 x 3.2 =9.6 FDR so that's in the game for a big wheeled buggy. Coincidentally it's not far off my dt03 truck. That planetary will create a lot of drag and therefore motor heat though. Reading around it on here a bit 550s are very amp hungry. Do you have a 540 you can try to compare? Even a silvercan would give you some frame of reference. 

[JennyMo 3526]

1 hour ago, ThunderDragonCy said:

3 x 3.2 =9.6 FDR so that's in the game for a big wheeled buggy. Coincidentally it's not far off my dt03 truck. That planetary will create a lot of drag and therefore motor heat though. Reading around it on here a bit 550s are very amp hungry. Do you have a 540 you can try to compare? Even a silvercan would give you some frame of reference. 

Yes, I wonder if that planetary gearbox is the main issue - as you say, drag from the gears, primarily designed for either crawling or the 1:14 scale trucks really...

I can certainly experiment with a different motor - my current go-to is actually the 13T 540 5-slot 'CrawlMaster Sport' motor from Homes Hobbies - I've slowly been replacing all the old 45T and 55T 3-slot RC4WD motors in my crawlers with those, and you do get a useful increase in wheel speed, plus some very nice slow-speed control... Unfortunately I don't appear to have any traditional silver-can style Tamiya motors lying spare around these days (and as I recall very few of my models sitting on the shelf have them either) to compare, but I'll see if I can rob something perhaps...

Thanks for the suggestion!

[OldSchoolRC1 983]

Looking awesome! Love the motor mount/trans mount idea, ingenious! 

I would agree the planetary is dragging down the motor, the gear ratio itself is fine. I have a few of those units...maybe open it up and clean out any heavy grease and re-lube with something light? I use red and tacky in mine and while it's smooth, it does add drag. 

Watch that output bearing on the GRU, it tends to walk out since there is nothing holding it in (as I just found out this weekend). I used a few Tamiya washers behind the pinion to hold it in place. 

[SlideWRX 785]

From what I could see online of what looks like the same planetary, They had no internal lubrication in there and no bearings/bushings for the planetary gears.  It looks like some lubrication is definitely in order!  If you tear it down, please post pics of what it looks like inside.

[JennyMo 3526]

A quick update to this thread...

Having finally got the chance to reconsider my transmission set-up in this build recently, I stripped out the 3:1 planetary gearbox which I felt might have been causing the issue - and sure enough, it would appear that something inside was dragging (not really being designed to spin at such high rpms perhaps, or equally just because it's a cheap Chinese ebay gearbox with dubious machining tolerances perhaps?), so elected to replace it with a more conventional 3-gear style transmission - all be it a 'high speed' version in this instance.

photo. looks like something was definitely rubbing/wearing inside here, generating all that heat and creating drag...

 

photo. My solution - for now at least - is this low profile 'high speed' transmission, although it does mean that the motor is now off-set to the centre line of the chassis...

 

It is interesting that while this new transmission (essentially designed to replace the standard SCX10 II style 3-gear transmission with the same mounting-bolt pattern) doesn't have a large spur gear/slipper and pinion in the same way - the fact it uses a tiny 8T pinion gear as standard means that the actual top speed is still not especially high - think the top gear of a 2-speed crawler gearbox* rather than an actual racing buggy.

*which of course it was designed to replace in a typical trail-runner installation.

 

photo. the very small pinion gear supplied means overall top speed (especially through an solid axle with a further reduction or around 3.5:1) is not much more than a brisk trail runner...

 

Fortunately there appears to be plenty of room to fit an appreciably larger pinion on the motor output - and indeed with this motor fitted, the 8T pinion was only just meshing with the gears - and I soon swapped it for a 14T version I had in my spares - instantly increasing the speed by around significant amount, although still not really anything like as fast as I'd wish it to be... 

 

photo. revised gearbox installation on my custom chassis plate - the motor is now offset to the right, and the corresponding output to the axle further to the left - rather than the in-line installation I had before... still, that ought to give a little more room for a dropped interior and solo seat driver figure - Beavis will find a home again!

 

Factoring that the 550 motor has plenty of grunt to spin a larger pinion gear still, I've ordered a set of Mod 0.8/32P pinions (the same pitch as this gearbox, and the RC4WD pinion I'd subsequently fitted) for a Traxxas Slash, and will now have the choice of 17T through 21T to experiment further. One thing is for sure, if it will pull the 21T then this thing ought to be pretty **** rapid at last!

More soon, once more parts arrive!

Jx

[pastimesteve 49]

Great build Jenny. What about the High Ratio Wraith transmission by SSD?

[Nikko85 3454]

love the simplicity of this build, really cool to see.

[JennyMo 3526]

16 hours ago, pastimesteve said:

Great build Jenny. What about the High Ratio Wraith transmission by SSD?

Yes, I did look at/consider a number of options at first - and went with this particular one mainly because it was only $28 on ebay (and made of metal) - and I'd say the internal layout is actually pretty similar to the stock transmission you get in the Axial Capra - ie. it is not as low geared since the Capra uses portal axles (with a further 2:1 reduction as I recall)...

Ultimately this is all a bit of an experiment for me (since I'm terrible at working out gear ratios, albeit pretty good at guessing and getting myself in the ballpark perhaps), and fortunately it would appear that this particular gearbox actually offers plenty of scope for fitting a much larger pinion gear if I desire - so once I get the 21T (vis the current 14T I have fitted) I'm going to try that first, and as long as the motor still has enough grunt to spin the wheels off the line (which I suspect will be the case), then I reckon I should have a pretty rapid buggy after all...

Fingers crossed!

Jx

[JennyMo 3526]

3 hours ago, Nikko85 said:

love the simplicity of this build, really cool to see.

Hee hee - wait until you see who's going to be driving - animated Beavis (from the original Capra Cornholio) will return!

Jx

[JennyMo 3526]

A quick update to this thread, now my [larger] motor pinion gear set has arrived...

I'm delighted to say that the 20T* gear has solved all the previous issues with regard to wheel-speed and/or the motor over-heating with the previous gearbox arrangement!

*I thought I'd try the second to largest size in the set first (the largest being 21T, or approx 5% faster still) - not least as there was limited room inside the gearbox for such a large diameter motor pinion. 

This is thing is FAST! - I mean proper fast now, while the 550 motor also has plenty of grunt to spin the wheels off the line as desired, do donuts at will, and all manner of other silly things - helped in no small part I'm sure by what are pretty modest width rear tyres, and a locked rear diff.

In fact I go as far to say as it's almost too fast for the current tyre set-up and wheelbase dimensions - requiring judicious use of the throttle if you're to avoid spinning the car either on acceleration or on the overrun (I've reduced the drake brake to zero on the ESC, but an aggressive throttle off can still cause the rear end to slightly brake traction)... Fortunately it remains just this side of drivable - and indeed provides more of a challenge that simply full-throttle squirting everywhere - it really is a fun little buggy to drive now! HUGE fun!

for info. there was only one issue with my revised pinion set-up which caused me some consternation initially - in that once I'd screwed everything back together, for some reason the motor would not turn, and got very hot, very quickly?!

Thinking I might have meshed the gears too tightly, I stripped everything down again, only to find that the chunky pinion gear (and 3.2-5mm adaptor sleeve required to mount it directly to this particular motor shaft) was ever so slightly rubbing on the inside of the gear case, once it was screwed together - so all I needed to do was drill a 6mm hole in the cover (see photo below) so that it could spin freely - and boy can it now spin freely!

photo. hole drilled in casing so that the end of the motor-shaft/pinion adaptor is free to spin - note I also bought a dedicated UJ prop-shaft for this transmission, in an effort to have something pretty bullet-proof for high speed running.

 

So that is the initial development phase completed now, and the proof of concept, erm, proofed... and while it would probably have been far easier to just buy either a 2WD Traxxas Slash or even a cheaper Tamiya DT-02/3 chassis based RWD buggy, there is something about assembling a custom vehicle from a seemingly random and disparate collection of parts, especially when it turns out to be rather good as a whole after all!

The next phase is to fabricate some sort of interior and fit (re-fit?) a driver or sorts... the Hooli logos (along with my "I need TP" licence plates currently on the Capra Cornholio) would suggest that Beavis will once again find a home behind the wheel - not least as this really is a Hooligan vehicle now!

However, I've also had another mash-up idea seeing that this is such a 'fast car' now, which I might further experiment with first... stay tuned!

Jenny x