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This has been in the planning stage for over 6 months but finally work has begun!  To complement my Custom MFC build using an Arduino, this rig will be a dual purpose drag racing truck and daycab hauler.  It's going to be built for scale realism rather than speed - it'll have 3S 550 power through a reduction gearbox to give a very low top speed (around the same top speed as 1st gear from a Tamiya transmission) as it will only get use on small club layouts.

So - what's the deal?

Well - it's going to be a bit of a "wait and see" on this one because there's a lot of custom stuff to work out.  But in brief:

In daycab hauler trim, it's a plain old 10-wheeler with a 5th wheel.  In drag truck trim, the centre axle will be lifted up into the chassis using straps and I'll be using TLT wheels and cut tyres as drag slicks on the rear axle.  Front wheels will remain unchanged.  To hide the middle axle and to make it look more drag-racey, I'll build an aero cowl to clip over the entire back end and probably a front spoiler to clip onto the bumper.

So there's quite a lot of custom work to do here.  On top of that I also need to mount my reduction gearbox and 550 motor, somehow.

Here's a teaser shot to keep you going - this will probably be a long, long project as I'll be working on it alongside the Arduino MFC.  Actually the main reason I built the rig is so I have somewhere to put all the electrics while I'm working on the code :o 


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Didn't get a lot of workshop time this weekend but I managed to snag a couple of hours during baby naptime to make some drag slicks.  OK, they're not perfect, but they should look good once decorated with some Hoosier stencils and buried under some aero bodywork.

Anyway, these drag slicks started life as TLT-1 tyres.  For some reason I've got an abundance of TLT wheels and tyres, so I didn't mind ruining a couple, especially as I don't actually have a TLT-1.  Actually this particular pair came to me on something else - I forget what, exactly, possibly a half-finished sand rail buggy or a TB-02 chassis that was modified as an RWD Schlesser Buggy replica - and half the chevrons had already been painstakingly removed by the previous owner.  That meant I only had 20 chevrons to clip off with side cutters or slice off with a hobby knife, both fraught with their own risks and both ending up in injuries of their own design.  Well, it's not a proper afternoon in the workshop if you don't nearly slice the top of your finger off.

Having chopping the bulk of the rubber off, I needed to smooth off the tyre surface.  My original plan had been to put the tyre on a spare axle shaft and put it in the electric drill, but the chuck was too big to fit in the TLT wheels.  I tried the Dremel, thinking it wouldn't have enough torque - it turns out it has plenty of torque, it just doesn't have a low enough RPM. Even on its slowest speed the tyre bulged enough to come off the rim.

So there was nothing for it - I had to climb up into the RC storage area to rescue my WR-02 from lamenting in its box and stick it in the bench vice such that one wheel was grounded against the workbench and the other was therefore free to spin at twice its normal speed.  Tyres mounted on sacrificial rims, handset electrical-taped into full throttle position, 40 grit sandpaper at the ready...


Not a bad result for an hour's work:



Unfortunately I had a bit of cleaning to do afterwards...


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Attached the tyres to the rig at lunch to see how they look.



I was a bit worried by how close to the chassis the tyres are.  They don't rub, but visually they look a bit odd.  However, by happy accident, the inner bead didn't seat properly in the wheel rim and the result was more inner clearance and a fatter looking bulge on the outer wall.  Result.  I'll trim off the outer rim and seat the tyre against the inner portion of the inner rim - there's enough meat on the wheel and a bit of glue will secure it in place nicely.




I started looking at fabricating a mount for my 550 motor / gearbox combo but had to get back to work.  It was starting to look like being a lot of effort for ultimately a fragile solution - I can't machine metal or print 3D parts so it would have to be something I can cut up out of delrin or bend out of sheet metal and nothing was really looking like it would be strong enough.  By another happy accident, this afternoon a mate offered me a Lesu reduction gearbox already mounted to a Tamiya 35T motor and complete with the mount to attach it to the chassis, so now all of Feb's leisure budget is blown besides some spare cash to pay for a hotel at the next lorry meet, but I should be able to get the transmission mounted and running by the end of the week :)

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I had a bit more time in the workshop last night, so I decided to cut the inner rim off a new pair of TLT wheels and get them fitted properly.

No WR-02 this time - cutting rims needs a slower approach.  I used my CC01 Hopup rig, which has also had a lot of use as a test rig for the Arduino MFU recently.



Here's some side-by-side comparison shots of the tyre profile on the narrowed and stock wheels.  Stock wheel is on the left, narrowed wheel on the right.





I'm pleased with the results.  The tyre wall looks a lot more chunky, like a proper drag tyre, on the narrower rim, but surprisingly the curve of the rim isn't exacerbated at all, so it doesn't look too much like a motorcycle tyre.  I guess all the curve has been taken up in the shoulder.  I haven't glued the tyres yet (since I usually make a total mess of it) but they will need gluing before use, I struggled just to tighten up the wheel nuts!  With no inner rim on the wheel's back face there's nothing to stop the back of the tyre from dislocating, which it will probably do under load.  It sits just fine on the workbench though.

Here's how they look fitted:




I also made some progress on my Arduino code last night (follow-up post in that thread later - duty beckons) so I was able to centralise my Futaba steering servo and get it fitted.  The rig is taking shape.  Next truck meet is 23rd Feb and it would be great to have an unpainted but functional rig to demo, at least to get some live running on the Arduino MFU.

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This truck is Killer! 

now is it for the Drag Pulls? with the inclined trailer and weights?

i've been wondering what to build next after my Three Irons in the Fire are finished.

you helped me figure on the next build i had not given any thought to do.

I'll Thankyou but the bill fold won't:o

there was a fellow on OSE some time ago and had something similar, it was rough lookn' but his suspension  was unreal.

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At the moment I'm going for a quarter-mile tarmac drag race look.  There's not really a lot of inspiration pics out there since quarter miling isn't really a bit thing for a big rig.  There's lot of videos online of people drag racing their street legal haulers with regular trailers on the back but not much for solo rigs.  The best example is the Bandag Bullet, which has become more about burnouts and donuts than straight line racing.

That said, there is someone who goes to the Bristol meet who has an inclined trailer.  I'm pretty sure it has a mobile weight that rides forward during the run.  I'm not sure if it's fully functional - I'll ask him about it next time I see him.  There's no reason why I couldn't make up a 3rd set of aero bodywork that retains access to the fifth wheel and allows fitment of regular paddled TLT wheels for proper mud-sledding duties.

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you figure some Marine Offshore racing boats use diesels that some how Big Rigs would follow suit with X-over mechanical and tech to really launch these things.

i've seen similar videos of what you mentioned.

once one kit is finished i always either go off onto my slots or trains (the house always needs something done and doing so for a living) i'd rather build and work on my hobbies, it's actually more of a challenge. iam rather running out of room to display everything that i've done through out the years. but they're like my kids they are all just so different and want to build more (but no more kids).:lol:

i'll be following your endeavor here, this is quite fun.

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just found this for ya,

i've built four 1/24th Slot dragster cars, but this WHOA! now lets do this in 1:14 are you ready?


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@ACCEL I like that a lot!  Even for some basic detailing around the front end.

I considered a roof chop on my rig (and I'm still considering it) but I'm not sure if it would look odd when the truck is in road-hauler trim.

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OK - quick update, since it's been a while since I added any photos.

As I mentioned earlier (or elsewhere, I forget) I bought a cheap 550 motor attached to a planetary gearbox, but I don't have access to a milling machine and making a bracket out of plate metal or Delrin was likely to be awkward, ugly, flimsy and/or brittle.  Fortunately a friend got in touch to say he was selling a little-used Lesu reduction gearbox attached to a genuine Tamiya truck puller motor.  The chassis needed some drilling to fit it (actually I drilled it twice as I wasn't happy with the first location) but otherwise it went on without a hitch.  In the end I installed it so that the drive cup is in the exact same location as it would be on a Globe Liner.  For some reason this means I don't get full upward suspension articulation on the middle axle (seems to be the same problem on the Globe Liner) and if I try to achieve full articulation on the rear axle the propshaft pops out.  Never noticed that on the Globe before but then I only run on smooth surfaces.  It's noticeable on the Drag King because I'm currently running with no middle wheels and nothing to tie the middle axle up.

The complete solution will either be to fit a propshaft with a slider or to get rid of the middle axle (which I've long been thinking about anyway).  I'm not sure what changes I'd need to make to remove the middle axle.  I'd have to go through the instruction manual for a single rear axle rig and see what additional parts I'd need.

I also started fitting up the electrics.  I'm trying to cram a lot of stuff into a very small space (remind me again why I went with a day cab..?) and I'm struggling.

Here's where we're at so far:

ESC and receiver taped under the cab mounting plate


Plate mounted on chassis


Motor and transmission mounted up underneath


Wiring neatly hidden inside the chassis rails



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I figured a large underbonnet cavity would give me plenty of room to build a storage compartment for all the other misc electrics.  Ultimately there will be two Arduinos, a circuit board for the LED system, possibly a second circuit or proprietary amplifier for the sound system and a small speaker.  Oh, and a 3S lipo...

Using the stock holes in the chassis rail, I mounted some threaded rod to make some storage shelves.  Aluminium tube from B&Q to space the shelves.



Shelf made out of 2mm plasticard.



LiPo neatly fits between the seat mounts.  Might need some modifications to the interior but this seemed the best way to install the battery.



View through the grille showing where the battery sits



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As you can see - the battery takes up most of the space and leaves nothing over.  This is a bit of a bummer, TBH, and I think I'm going to struggle with these batteries.  I should have seen sense and bought smaller packs to start with but I was drawn in by the large capacity and the hope of running my other cars on the same packs.  I don't regret buying these packs - they'll get some use - but I'll have to wait until next month to buy some smaller packs for the rig.

Anyway, I went ahead and cut another shelf to sit on top of the battery, for now.  As and when I get a smaller battery I can drop this shelf a little to make space above it for the LED board.





Here's the LED board.  Transistors take the low-current logic voltage from the Arduino pins to switch the higher voltage from the BEC.  The resistors under the red (positive) wires protect the Arduino pins from over-current through the transistor base, and resistors after the transistor emitters protect the LEDs from over-current.  Annoyingly this is just a few mm too tall to fit here and clear the hood.  I will need to source some laydown (90 degree) connectors to reduce the clearance, and/or drop the shelf once a smaller battery arrives.

Ultimately this board will be taped to the underside of the hood, as it will have a single multi-plug to connect it to the rest of the truck, making it easy to plug on and off.  The LED strings will each have their own plug but mostly they are mounted onto the body anyway so won't need to be plugged and unplugged when removing the body.  I'll probably install a multiplug at the back of the cab for tail light duties and (eventually) IR-LED trailer lights.



Clearance view under the hood (without LED board installed):


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So, what next?

I keep asking myself the same thing.  I mentioned elsewhere that I'm having some bad glitching on the steering servo with the Turnigy 9X radio.  I've tried different channels and different servos but it's always the same.  I haven't tried another receiver since my other Turnigy receivers don't seem to bind, I guess they have a different (FlySky) protocol.  The 9X is quite an old model now.  I did a lot of searching online, some people say it's a Turnigy issue and not to use the 9X at all, some people say it could be a whole host of different problems with Tx or Rx, some people say to throw out the Turnigy module and fit a FrSky or other module.  However one source said it could be an interference problem caused by the servo leads picking up nearby frequencies.

Well - it happens when I have just the Tx, Rx, ESC and servo connected (with no Arduino or other boards) but it's definitely worse with the Arduino hooked up with long jumper leads.  So it could be interference.  It's also worth noting that I only ever get time to work on the truck when my daughter is sleeping and there's a baby video monitor switched on nearby, which are notorious for interfering with **** near everything (my WiFi drops out all the time when the monitor is on).  So when I install the electrics for the final time I'll custom-make the leads as short as I can get away with (it'll be like a wire tuck on a stanced car!), hide them behind the chassis rails for best shielding, and maybe add some other shielding to them.

Also - although this is more relevant for the Arduino thread - I'll add a 'smoothing' module to the code that will ignore any big spikes in the channels.  The only sudden spike that will be allowed will be a return to deadzone (otherwise I might have a stuck throttle on the layout!)

Another job I need to do is get hold of the Arduino that I'll be installing.  I've been testing with an Elegoo Mega2560 but it's quite big.  I might be able to use it in the final project if I can fit it on the shelf where the battery currently sits, but I'll probably need that space for an amplifier board.  I can't install a less powerful Arduino as I need a lot of PWM outputs for the LEDs and servos some additional interrupts for the PPM input.  However, hunting around on eBay I found some very tiny Mega2560 boards that seem to be full-featured but with a very small footprint, and they're only £6.99 each.  A couple of those would probably fit underneath the battery shelf, just along from where the ESC and Rx are, leaving space for the amplifier on the battery shelf.

I've measured up for a smaller battery from HobbyKing and I'll have to do away with the stock seat mounts.  I'll create a shelf for the seats to go on with the battery sliding in underneath.  I'd like there to be foot space for a driver figure and at the moment it looks like it'll fit.

Other jobs on the list:

  • Remove the stock rear bumper and fabricate a new tail piece with surface mount LED lights
  • Fabricate the rear aero cowl from Plasticard
  • Find a suitable way to tie up the middle axle or modify the suspension to remove it completely
  • Fabricate the front aero cowl
  • Fit all the LEDs and route the wires
  • Test and replace some transistors on the LED board that don't seem to be working
  • Buy / fabricate a cab rear door and make it openable so I can change the battery
  • Probably lots more that I've forgotten right now, bearing in mind I haven't even mentioned the "paint and decals" stage yet...
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