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Old 18-03-2018
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Default Doggy Bag YZ-834b Runner Build

This might read a little strange at first as I've done a big copy and paste from another forum I'm on and this is half a dozen posts wrapped together .

I have ended up with a few left over parts for the venerable Dogfighter YZ-834b , some parts i made , some CNC parts that I've swapped out for genuine and a few that came as a bundle so i have surplus , I was tempted to sell a few bits but looking at the pile it sort of started to look like enough to get started another car from , then a few more bits popped up on eBay and that sealed the deal .

I'm not looking at a perfect car here , more of a runner , I'm starting to get a bit protective of my already complete (ish) Dogfighter . I'm planning on bringing it on a bit , wider , longer ,belt drive , slipper and hopefully a front diff if possible , 4 shocks etc and probably a Brushless system .
All the new parts will go onto my existing car and the older stuff to the runner .
Never thought I'd have a shelf queen ! its kind of never been a thing for me but my existing car may end up retiring ! :shock:
Right progress so far .
1 Transferred the new gearbox and genuine lower front suspension arms to my original car .
2 Made a hybrid ball diff from a genuine diff gear and balls and Team C diff out drives and thrust bearing , this means that any wear will be to modern replaceable out drives and modern shafts .
3 Fitted scorpion Re Re stub axles and bearings to the rear suspension arms as well as the 12mm hex conversion parts , these give almost another 20mm to the width and allows modern wheels to be used .

So far I've only sourced the diff gear and the second gear with shaft for the rear chain sprocket , however the idler gear between these gears is a plain 20 tooth gear so this will be replaced with a pair of pinion gears to make up the width needed . The spur gear or first gear is more tricky as its a reduction gear with both 46 and 21 teeth , however I'm planning on attempting to make a slipper clutch made with a 21 tooth pinion and a spur gear , probably a modern 48dp gear of a very similar diameter to the original , again this will mean any probable damage or wear will be to a modern easily sourced part .
I've now got a nice sheet of 3mm GRP to make an extended chassis , the old doggy is about 30mm short by modern standards , i don't want to go that far as its going to look obvious but i think 15-20mm could be done by moving the gearbox and trailing arms further back without too much visual impact .
Anyway a few pictures of what i have so far.



The rear diff was a lot easier than I thought it would be , I have an old Team C TR02V2 that I was using as a spares car so I nicked the diff out of it , the center of the Yokomo diff gear has a 9 mm hole and the support bearing on the team C diff was 8 mm so I made a 0.5 mm thick sleeve on the lath (outer 9mm inner 8mm) out of plastic , I used the Yokomo ball's and then just assembled it. Next was the gearbox bearing on the diff ,it's a 12 mm inner 24 mm outer , the out drives on the Team C diff are 10mm so again I made up a pair of aluminium sleeves that I secured to the out drives with green locktight , the only slight difference is that the original Yokomo diff has a spacer to off set the gear to one side of the gearbox inline with the other gears but the modified diff sits centrally , this is not a huge issue as the idler gear ( small 20 tooth gear ) that it is driven by is the full width of the gearbox .
I'll post up some pictures later .
The slipper is still in my head but will hopefully be a combination of a repurposed diff gear as a spur gear , a 21 tooth pinion gear and a set of turned down Team C slipper plates and pads on a custom made shaft that will exit the gearbox through a hole drilled through the gearbox inside one of the bearing supports , hopefully it will have an adjustment nut and spring next to the motor to the rear on the gearbox side , the trick will be to make it all thin enough to fit inside the gearbox .
A little more progress , last night i made up a new roll bar , that was a little frustrating as i had two bars of aluminium the same measurement and one was a hard alloy and the other soft but i forgot to label them so i obviously chose the wrong one and it snapped on ... you guessed it the last bend :evil: anyway i made another with the right bar and it came out better than the one i made for my first dogfighter so i swapped them over .
This afternoon i cut the chassis plate adding 5mm at the front and 10mm at the rear to extend the wheelbase by 15mm overall , i had fun attaching the vacuum cleaner to the jigsaw , i had to do it because i had a mask on and the dust was covering the cut lines , it was a bit clumsy but not too bad , overall im quite pleased with the chassis , still needs a little more cleaning up but not too bad for a first attempt .
I've also added a few pictures of the hybrid diff .




complete diff with sleeved out drive .

not a great picture but you can just make out the black sleeve around the bearing.

I saw in another 834b build thread on here what was thought to be a front ball diff but it was decided to keep the build stock and the diff was NIB and no very clear pictures through the bag so I got no clear idea of the design of it .
I have ideas but I'm stuck on how to make it strong enough while passing through a 5mm inside die bearing , I'm really tempted to drill out the front bulkhead to 12mm so I can fit 6mm inside die bearings then I'm sure I can make it work , it's just a bit non reversible .....with a very rare part .......
I had a first attempt at a shock tower for twin shock's up front , its freehand and not quite symmetrical but i can sort that on the second one , not sure weather to stick with GRP or use CF instead (i have both) for the second one , it does work well even if its slightly pissed .
I also made up an idler gear for the gearbox , its a 1/8th scale 32dp with a 5mm bore so perfect for the 5mm shaft the bearings take , its actually the second pinion that i ordered , the first was exactly the same on paper but it was a machined gear and looked a bit harsh to use on stock plastic gears , this one is a Traxxas (pause to spit) one and looks like it was forged or stamped but either way the gear teeth are far smoother more polished and should be less abrasive to the plastic gears , its not quite as wide as I'd like , there's about 1mm on each adjacent gear that's not meshed so i also have some plastic gears coming that are half the width but i should be able to link two together to get the full width so , well i don't know witch way to go yet but this gear will work for now.
Oh the rear shocks are only temporarily mounted in the picture and will not be that way eventually .





the other diff gear arrived today and i had a little time so i got started on the slipper , the diff gear is going to become the spur gear , at first i planned to use a Team C slipper modified to fit , i try'd this using some thin rubber for slipper pads but i just could not make it thin enough , so plan B I've used the slipper from a Re Re Scorpion and this should fit nicely , in order to lock the pads to the diff/spur gear ive punched out holes in the pads where there is a raised ring for the ball's in the ball diff , i have a 21 tooth 32 dp gear with a 5 mm bore that I'm going to cut the boss off and weld to the slipper shaft , looks like this so far .
first picture has the Team C parts to the left .

this one of the modified pads and the slipper plates from the Scorpion

Made a start on the slipper shafts , one is attached to the 21 tooth gear and has a keyed central shaft for the slipper plates and then passes on out through the side of the gearbox next to the motor , the other will be a sleeve that passes on the spring pressure to the plates , I've made the first more complicated one , I was going to weld the steel 21 tooth gear onto the shaft but i was worried that the shaft would warp when welded so I've made it an interference fit onto the 5 mm section of shaft shaft and a wider section that goes into the hollow side of the gear , its also secured with green lock tight , the lock tight alone might well have been enough but there's no harm in doing both .After the section with the slipper plates the shaft drops from 5 mm to 4 mm , the sleeve shaft will be 4 mm internal and 5 mm external and fit over the 4 mm section of the main shaft.
The shaft must exit the gearbox so a hole was drilled inline with the bearing to a slightly larger than 5 mm size of the inner bearing .
Tomorrow all i need to make is the sleeve shaft and i can put it together , i won't know how well or badly it works for a while though as the rest of the car is far from ready .




Finished the last part of the slipper ,i now have a complete transmission YAY !
Here's a few pictures to show how it works , I'm quite pleased with it but I still don't know how it will work under load , the adjuster nut is in an awkward spot when the gearbox is fitted in the car but i can reach i with a spanner .



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Old 4 Weeks Ago
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Few more bits done , made a new front drive spindle and out drives to fit the Kyosho sprocket and chain that I'm using , I was going to make up a diff but i thought i could use thrust washers and ball's from a thrust bearing i already had but it was to big to fit ,I've ordered another smaller thrust bearing so it is still in plan to make a front diff just on hold . Also made a start on the battery tray , its not finished but so far it has cable tie points for full size and shorty packs , a shorty pack can be held either in the middle , to the left or right if i want to help balance it , there will be a couple of large holes cut through it and probably be made narrower between the cable tie points , I plan also on mounting roller guides under it to prevent the chain hitting the underside .
To the rear I've added two ball link tie rods between the rear guard and the roll bar , I shamelessly stole the idea from Bloodclod's belt drive 834b build thread . Up on the roll bar I've bade two shock mounts for the upright twin shocks .

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Old 4 Weeks Ago
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The new thrust bearing arrived so I've made a start on the front diff . So the parts I've made are
1 The drive pulley , made from Acetal , I shadow cut it as a copy of a hardened steel gear with a dremel tool then drilled it for the balls .
2 The left diff outdrive , its not finished , it still needs the slots cut out for the drive pin on the drive shaft .
The balls in the thrust bearing were 1.5 mm , too narrow for the diff pulley so I just used the thrust washers , these are the grooved type so they will help align the left outdrive , i used 2.3 mm balls in the pulley . The little thrust bearing is 2.5 mm inner and 6 mm outer .
Tomorrow I'll finish it off and maybe it will even work .

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Old 4 Weeks Ago
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Back to the lath this afternoon and made the two other parts for the diff . The counter thrust bearing (the little one) is no going to be in the outdrive as there just was not space , instead its inside the right side of the diff inside a collar , the collar is then inserted into a sleeve on the spindle that takes drive to the right hand wheel , the spindle has a hole all the way through and this is where a hex key is inserted to adjust the diff , the two right hand parts will be green locktighted together , theres a large surface area for it to work on , if it does not hold then I'll add three grub screws as there's enough meet for a threaded hole but my guess is that the locktight will work , in order to service the diff counter thrust bearing it will mean heating it to melt the locktight but the sprocket can be removed before heating as its the only plastic part .
Anyway pictures , still not finished but you'll get the idea.
First next to a genuine but worn original drive , its actually 0.15 mm shorter from outdrive to bearing than the original.


Adjustment method.

The guts.

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Old 3 Weeks Ago
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Well its finished and it fits with no clearance issues or binding of shafts , i went for three grub screws to attach the spindle to the right hand side of the diff and it seems very secure , its all hardened and ready to go , even feels very smooth !

There may be a few folk who don't know how tiny this is so ....


I'd put up a photo of it in the car but you just don't see much .
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Old 3 Weeks Ago
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Only if it works ! The whole transmission is so experimental , I've kind of broken my own rule of doing one mod then testing untill you work the kinks out before doing another , I guess the proper way to go will be to remove the diff and test the slipper untill I've trouble shot that then refit the diff and start testing again , otherwise I might not be able to really tell what's going on , oh that's not forgetting having to set up the rear hybrid diff ..... So much can go wrong !
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Old 1 Week Ago
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I now have steering , its a modified BSD servo saver and a fibre glass wrack , actually works very well once i got a few clearance issues sorted , I've also started the top deck , no tensioner pulleys yet but it will have a spring tensioning system on the top length of chain and a single pulley on the bottom length to just give a little clearance to the battery tray , the bottom length of chain will only be redirected by about 2 mm so it wont induce too much drag hopefully .


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Old 1 Week Ago
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A nice sheet of 3 mm kydex arrived today to make a front bumper , never try'd forming kydex before but it was a nice simple shape so to cut then 135C in the oven for two minutes and roll it round a jam jar till it cools and job done .

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Lots of chores done so i found a little time to make the bell crank for the chain tensioner , so its install and testing time I'm actually expecting some failures in testing for the transmission , its got a newly designed slipper that i hope works , the hybrid Yokomo/Team C diff i have high hopes for but may need a bit of adjusting and the front diff has the highest possibility of failure of all and will also need setting up right if it works .......



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Old 1 Week Ago
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It's alive ! , finally got the steering set up this afternoon while watching the F1 GP , it was only a very short test drive as it's raining pretty hard outside but it all seemed to work , no idea about how well it handles or accelerates etc as wet tarmac has so little trip but it seems lively compared to my other doggy , the old one runs a 17.5t motor and this one a 10.5t , it does need more brakes so that's one adjustment I can make .



wish i was better at tidy installs
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Old 1 Hour Ago
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I got a little Video clip made , just after I'd cartwheeled it spectacularly :shock: :roll: its got a ticking noise on cornering in the Video due to a bent dogbone at the rear .... easily fixed.
https://youtu.be/H4aZ7CIzEGg
As you can see she's plenty quick enough
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