F150 6x6 Tow Truck

[Mad Ax 6705]

Here's a little idea I've had floating around for a couple of months, now.  6x6 scalers seem to be the big thing, but I've never really liked how long they are.  It seems they're more about looking impressive than actually getting around a course.  There's always a compromised between wheelbase and ride height, and ground clearance and centre-of-gravity.  To my mind, a 6x6 solves these problems by giving a marginally longer wheelbase, but having a third axle in the middle to compensate for the hang-up problem caused by a longer wheelbase.  Except nobody does that - everybody tags another axle on the back, makes a huge, cumbersome rig that still gets stuck when trying to go over a ridge.

I digress.  The original idea was to build a stubby truck using a short cab and some spare axles.  And that idea still stands - but this isn't it.  This became something different.

I found myself with two solid days in the workshop - plenty of time to get the scalers sorted after the Nationals, clear down the workbench and make a good start on something completely new.  It's been a while since my last scratch build, so I thought this would be a good project to get me back in the flow.

Here's what I started with.  Note the wheels and tyres are just for an idea here - I want a similar size (around 95 - 100mm diameter) and these were lying around to help me get an idea of size.  The body is a really old Blackfoot that I've had for years, attempted to use on a few projects, then abandoned.  I had previously tried to length it for a monster truck build, but I'll just use the cab for this project.

And now for the axles.  Front is a TLT, rear is 1:14 big rig.  The wheels I'll be using on the rear are RC4WD deep dish wagon wheels, which are almost wide enough to match the standard width fronts.  I'll probably have to narrow the front end slightly and maybe put some spacers in the back to get it just right, but that's a problem for another day.

Those old mud slingers won't fit on the RC4WD beads, so they're just pushed over for now, but they give an idea of how it should look.  A new set of RC4WD wagon wheels will go up front.

[Mad Ax 6705]

I went with the standard Tamiya crossmember to keep the rear installation simple, and used some alu L-section left over from a 1:14 trailer build.

A bit of spray paint down the hole helped me mark the right spot to drill

Standard Tamiya drop bracket installed

Then I turned my attention to the front, and started making a rough 4-link bracket for the TLT axle.

For appearance sake, I decided to add just a little bit more wheelbase than originally planned.

That took me up to close of play on Saturday, whereupon I cooked myself a pizza and watched a film.

[Mad Ax 6705]

Festivities resumed on Sunday with a lot of head-scratching over the rear suspension.  My original plan had been to put the axle in place with the Tamiya linkage, then gradually replace it with a proper 4-link.  But I couldn't really see a good way to do it that wasn't going to cost loads of space and give minimal articulation, unless I added loads of ride height between the axles and the chassis rails.  That didn't feel right, as I'm using small wheels, so in the end I opted to keep the leaf spring and walking beam arrangement.

One of the downsides of a walking beam on a high-torque crawler, is it tends to lift the middle axle when climbing.  (It's like the entire rear assembly does a mini-wheelie under the truck).  To counter this, I went with some Tamiya CVAs and put extra-stiff black springs on the front.  Articulation is already minimal with the Tamiya assembly, so I don't think I'm missing much.  There should be plenty of traction once the diffs are locked.

[Mad Ax 6705]

At some point I got fed up with the Mud Slingers falling off the RC4WD rims, so I tried some old Tamiya BFGs instead, but these weren't any better.  At least they're tough enough to hold the rig up, though.

While the chassis rails were out, I drilled another spot for the front right lower link so I could bolt up the axle, albeit with only the lower links installed.

I really love the stance in these photos.  The height is necessary to clear the transmission, and I think it'll look superb once I've got some slightly bigger tyres on.

[Mad Ax 6705]

Talking of transmission - I've got an Axial unit that I've had for years, I'm not sure it's ever been used in anything.  I made a plate to bolt it up front under the hood.

[Mad Ax 6705]

At this point I had to call it a day.  My wife had got back from her solo beach holiday and I had to go fetch my daughter from her sleepover, but at least I was pleased with my technical progress.

I was less pleased that I had some a bunch of new, expensive and in some cases rare parts to make something that, really, has no purpose.  With leaf springs and small tyres it's unlikely to be a capable crawler.  With a TLT axle it will have a terrible turning circle, which will ruin its performance on the courses.  I couldn't really justify the build to myself, other than that I was enjoying it, and wanted to see what I could do with the parts.  It felt like it was going to turn into another albatross that gets abandoned when it's 95% complete because I fall over on some silly final hurdle, or realise it isn't going to be any good without a lot of money thrown at it.  And money is part of the issue here - those RC4WD wheels will only take RC4WD tyres, and I'll need 6 of them.  That's £100 already, plus I need two new wagon wheels for the front.

Then a thought came to me, and for the genesis of this thought, we need to go way back, around 6-7 years, to when I started going to Iconic bashes at places like Snetterton and Broxtowe.  Because these were open, non-racing events, we relied on volunteer marshals on the track to rescue our cars if they got stuck.  Problem was, everybody either wanted to drive, pit, or chat.  Nobody really wanted to hang around on track pushing cars back onto the tarmac.  This meant a good deal of frustration for drivers on the rostrum (myself included) who would sometimes manage 2 or 3 corners before getting stuck again, having to walk all the way down the steps, onto the track, rescue the car, rescue a couple of others at the same time, walk back off the track, go back on to rescue another car, go back up the steps, start driving, manage another 3 corners and do the same thing all over again.

I figured what we needed was a tow truck that could be parked in the pits and come out to help.  It would need to have good traction, as it would have to cope with grass, and it would need a remotely operable crane on the back that could hook under a touring car body to pull it back on track.  Maybe even have some kind of movable front bumper / shovel to help push, if the crane couldn't get underneath.  For a really long time I planned to used my F150 Baja, which had been sort of modded into a scaler anyway, but soft rear springs and a saggy independently sprung tub would have made for a poor performer with a load on the back.  I've had a few other ideas (including adding a crane to the BOM that I recently built), but as I was driving back from my parents on Sunday evening with my daughter chattering away to herself in the back, I realised I had just made the perfect donor rig for this project.

The need for this sort of thing hasn't gone away with Iconic's move towards racing, because Tamiya Junkies have taken their place.  I've been to a few Junkies meets this year, and every one has had the same problem: if we're all on the rostrum driving, nobody is marshalling.  Admittedly it's harder to make something that can flip a 1:10 buggy over, but even having something that can help nudge a buggy off the track barrier without getting stuck is better than nothing.

• Wide wheels with narrow track made for an easily-manouverable truck when accuracy is key
• Stiff leaf-sprung rear won't sag under the weight of a touring car
• Dual rear axles give extra traction where all the towing weight goes
• Custom ladder chassis will be easy to drill and mount a crane assembly
• F150 cab has the perfect vintage tow truck look (although it should ideally be rebranded as an F350)

That cheered me up no-end, and completely renewed my enthusiasm for the project.

The other thing I was struggling with was the front axle.  I had planned to 4-link it, but the axle has already been smoothed by a previous owner, so it has no upper mounts.  I was going to make some, but there's a distinct lack of clearance between axle and chassis rail and I didn't want to have to cut too much out.  I then remembered I have some more TLT axles tucked away for a potential future project, and they have an aftermarket 4-link kit installed.  But then I had another idea: since I had already decided to stick with leaves in the back, why not put leaves up front too? 

In typically long-winded Mad Ax fashion, the rear axles came from a King Hauler kit, which is currently wearing a single rear axle from an unbuilt Scania R470 kit.  So I now have an R470 with no rear end.  So, it doesn't really matter if I steal the front leaves and hangers from that kit either (except that it's currently in a transit box right at the bottom of my NIB stack right at the back of my storage space, which is only 4 feet high and infested with giant spiders - I know this for a fact because I had to get it out on Sunday to fetch the splined hexes for the axles, and I could have got the springs and hangers out at the same time).

Another thunk occurred to me that the drive direction on the TLT is reversed to the big rig middle axle, so the TLT axle is actually in upside-down.  Hence, the 4-link kit would be useless anyway.  So that's it, then - decision made.

I have installed a TLT front axle on the front of a big rig before, on my 6x6 Grand Hauler tipper (yet another project that I really should crack on and finish).  I used the standard truck springs up front, which actually lifted the rig quite a bit - I had to use lift blocks between the axles and springs on the back, and I made a longer drop bracket for the lower links, but because the front end is basically all mine, I can install the spring hangers wherever I like and set the ride height how I want it.

So - there we go!  Watch this space  

[87lc2 2050]

The stance on the truck looks great.  I agree about the majority of 6x6 vehicles on the market being too long.  I really like that you're going with leaf springs all around.  I've recently become a big fan of leaf springs and will be using them on more builds in the future.  Of course a 4-link setup is more capable, but considering I spend more time looking at my trucks that driving them that's fine with me.  

Looking forward to more progress on this, I think it will turn out great. 

[El Gecko 1195]

12 hours ago, Mad Ax said:

I figured what we needed was a tow truck that could be parked in the pits and come out to help.  It would need to have good traction, as it would have to cope with grass, and it would need a remotely operable crane on the back that could hook under a touring car body to pull it back on track.  Maybe even have some kind of movable front bumper / shovel to help push, if the crane couldn't get underneath.  For a really long time I planned to used my F150 Baja, which had been sort of modded into a scaler anyway, but soft rear springs and a saggy independently sprung tub would have made for a poor performer with a load on the back.  I've had a few other ideas (including adding a crane to the BOM that I recently built), but as I was driving back from my parents on Sunday evening with my daughter chattering away to herself in the back, I realised I had just made the perfect donor rig for this project.

The need for this sort of thing hasn't gone away with Iconic's move towards racing, because Tamiya Junkies have taken their place.  I've been to a few Junkies meets this year, and every one has had the same problem: if we're all on the rostrum driving, nobody is marshalling.  Admittedly it's harder to make something that can flip a 1:10 buggy over, but even having something that can help nudge a buggy off the track barrier without getting stuck is better than nothing.

After reading this I'm thinking... Every RC track should have a couple RC tow trucks or end loaders or something with an attachment that can easily flip a car over. Then just place a few of them in key areas so they can get to any part of the track quickly. They don't even have to look very good or scale as long as they do their jobs reliably!

Surely driving an RC marshalling rig from the rostrum would be more enjoyable to most people than running around the course bending over

[Mad Ax 6705]

16 hours ago, 87lc2 said:

I really like that you're going with leaf springs all around.  I've recently become a big fan of leaf springs and will be using them on more builds in the future.  Of course a 4-link setup is more capable, but considering I spend more time looking at my trucks that driving them that's fine with me.  

Yeah, I hadn't intended that, but I'm really happy that I made the decision.  (The downside is I'll need to replace the axles and springs that I took from the NIB Scania before I can built it, although I might do some upgrades on my MAN rig next year so maybe I'll have some spares left over for it).

I originally got this TLT axle along with its sibling to go under a leaf-sprung Clod-Bod scaler, I even still have a set of aftermarket leaves that I bought purely for that project.  But the world has moved on and TLT axles don't really work for a scaler build.

They are, however, perfect for a solid axle monster truck build, and I've also got a pair of TCS X-trail chassis rails (remember those?), so I think my next custom build after this 6x6 is done will be a solid axle monster on leaves.  I think I've even got some original TLT shocks which are mysteriously missing their springs and hangers which would make nice scale-looking dampers.  That's a project for another day.

So yeah, pretty excited to see how this all comes together, it would be nice if I can at least have the front axle mounted on Sunday.  That'll be my first job, probably after that the steering servo (chassis-mounted, no reason not to with leaf springs), then the transfer box and propshafts.  But we'll have to see, I'd like to get my hearse running ready for trick or treating on Sunday night, plus I need to give my drift car and big rigs a once-over ready for their first outing since the pandemic and the next double-header on my calendar  

[87lc2 2050]

Have never heard of TCS before, looked it up and definitley nice rails for a solid axle monster truck.  Can't wait to see what you do with that & the TLT axles.  I have been wanting to convert some of my smaller SCX10 monster trucks to leaf spring, but the current axles on the trucks wont work with leafs and I can't really find a suitable 'monster truck' looking axle that will (other than the RC4WD Blackwells of course, but they're crazy $$$ for a truck that will mostly just sit there).  

Anyway, back to the tow truck.  Glad it's leaf sprung and excited to see how this comes out.  

[MadInventor 3753]

You're not the only one to build a 6wd albatross:

This is sat around doing nothing. The free floating walking beams at the back I think would get around the problem you talked about the middle axle lifting. The beams also give a bit of a portal lift. I planned to run it with an open rear diff as the diff can't slip unless both the rear wheels slip on one side. However, the downside is that the walking beams holding the gears it makes the whole axle assembly wider than a normal high lift axle, which I think is going to make the turning circle worse....

When you talked about your model not having a good turning circle with the TLT axle, is that because you intend to run it with a locked diff, or is that just down to poor steering angle ?

Enjoying what you're doing so far

[Mad Ax 6705]

I've spent a good part of today messing around with my TL01 hearse, but managed to find a couple of hours to get the front axle on the tow rig.

First thing was mounting the big rig leaves on the TLT axle.  I've done this before on a 6x6 tipper truck, and it wasn't an easy job then.  The leaves need to have 3mm holes drilled about 12.5mm apart, but sprung steel is difficult to drill.  Even getting the centre punch to mark it in the right place was a pain.  One side came out OK, the other went a bit off and needed some filing to get right.

Anyway, with that done, the axle looked like this:

Then I put the chassis rails on some tyres to level them off so I could work out where to hang the front axle leaves.

I realised my chassis rails were actually slightly too short to mount the axle where I'd intended - I hadn't originally planned to use leaf springs, and although I'd deliberately left a lot of overhang on the front of the chassis to allow for plan changes, I was about 5mm short for putting the front axle in the original spot.  But that's OK, because I'd moved the rear axles back about 20mm from where I'd originally planned to put them, so there was enough room to pull everything back a little bit.  I haven't made any body mounts yet, so nothing needs to change.

TLT axles with leaves are a tiny bit wider than a big rig front axle with leaves, so the stock big rig hangers need spacing out.  3mm either side was about right, and that was great because I had some 3mm ally sheet to cut some spacers from.

I still need to cut some spacers to mount the rear hangers, so they're literally just hanging for now

A bit of a rough throw-together, as most bits aren't bolted on, but this is how I finished up today.  Despite having an extra hour on the day (clocks fall back here today), I had to come to eat an early dinner (a rare treat, my wife cooked today!) and get ready for the neighbourhood kids to come trick or treating.

[Nikko85 2405]

I am really enjoying this design. I agree about the axle that the back, this looks much more neat.

I think a little lifting plough at the front would be great, and a crane at the back. 

A few spare 1/10 touring car tires as accessories on the back would complete the look.

[OldSchoolRC1 673]

Excellent thread as always good sir!

Ever consider some dualies out back? Should look perfect with the wider front axle, no? I mounted up some Proline Carbines on my 6x6 last year and they are pretty nice. Not to mention traction with 10 crawler tires and locked diffs is astounding. Should easily be able to shove buggies back on the track. 

[Mad Ax 6705]

2 minutes ago, OldSchoolRC1 said:

Ever consider some dualies out back?

I thought about dualies, but I've already got these wide RC4WD wheels to use.  I don't have any other plans for them, and they're an expensive wheel to sit gathering dust and getting chipped in the wheels box.  Traction should be pretty good with 6 soft RC4WD tyres on them, plus I'll get a bit more ground clearance with the bigger tyres.

I need to measure up the clearance between the wheels later to work out exactly what tyres I'll need.

I do have a 6x6 Grand Hauler-based tipper rig under construction, which has dualies, and will eventually wear some proper crawler tyres so it doesn't get stuck on the dirt at the club layout.  Although I might mix and match the rears with road and off-road tyres, I've seen that done on some big rigs that spend part of their time in the dirt and part on the tarmac.

[Mad Ax 6705]

The first weekend in November was spent at the Bournemouth RC Trucks and Construction meet, my first big rig outing since the pandemic started, so it's been two weeks since I had a chance to look at this truck.  I got up bright and early on Sunday morning and cleared off the workbench (it tends to get used as a dumping ground during the week) so I could start with a nice clear work area.

Then I cut the spacers I needed for the front spring hangers, and got them bolted up.  I went for a "full assembly" of the chassis to make sure everything was fitting nicely so I could measure up the transfer box location.

This transfer box came from @MadInventor and is very well made.  I need to get some pinions for it, so at the moment the shafts are loose.  Really I just needed to line up the propshafts.

The propshaft angles looked like they were going to be rather steep, so to get the best possible angle I measured the midpoint between the to axles.

[Mad Ax 6705]

I used the propshafts off my CFX-W for this.  I managed to snap one on the second gate of the first course the CFX-W had ever seen, so I know they're not the best in the world, but they did come with a lot of spare centre sections and they should be stronger over a shorter length.  Besides, this rig isn't going to see near-vertical climbs and crazy articulation angles, it's mostly going to drive around on flat grass.  If the driveshafts fail in use I'll have to get something more serious for it.

[Mad Ax 6705]

Then it was time to look at the transmission-to-transfer-case shaft.  It's here that I realise an error in my choice of transmission.

I'd grabbed it out of the Drawer of Scale And Mechanical Parts, thinking it was a spare Axial transmission that I'd got from somewhere, but when I came to unscrew the dogbone drives from the output shaft I realised they weren't actually bolted on, they were part of the diff.  So this isn't an Axial at all, and that should have been fairly obvious, if I was paying attention.  I think it came from an Ansmann Mad Monkey that I briefly raced, then boxed away when the diff exploded, then stripped for parts a few years ago.  So this transmission has been lying around waiting for me to make something for ages.

Potentially, not something scale-oriented, though...  The dogbone-type drive isn't ideal due to the angle, the gear ratio might be wrong (although I can leverage the clever design of the transfer box for a bit more reduction if I need to) and, perhaps most critically, it has a ball diff, which will be hard to permanently lock.  So possibly in the long term, I need to be thinking about a different transmission up front.

For now though I figured it was worth forging ahead with the build, at least for a proof of concept.  That meant making a dogbone.  I have done this before, it's not easy without a lathe but I at least decided to mock something up, even if it wasn't perfect.

So - this post is titled How to make a dogbone without a lathe or milling machine

You will need

• some 6mm brass rod
• some Tamiya drive pins (the type that go into the back of 12mm wheel hexes)
• a really, really good 2mm drill big (and ideally some 1mm and 1.5mm bits to get started)
• a drill vice
• a drill press / bench drill / pillar drill
• a cordless electric drill
• a bench grinder, or lots and lots of patience
• various grades of abrasive paper

1: Cut your brass rod to approximately the right length.  By approximately, I mean slightly too long.  There's no point in cutting it slightly too short and then trying to add some length later, brass doesn't really work like that.

2: Clamp your rod horizontally (and I mean perfectly horizontally) in the drill vice

3: Beginning with the 1mm bit, drill a hole in the exact middle of the rod.  This is the hardest part because the bit will want to wander off the edge if you haven't got it lined up right.  Trying to do this will a hand-held drill is likely to end in loss of temper.  Move up to the 1.5mm bit, then the 2mm.

You should end up with something like this:

Slip the rod into a cordless drill chuck, set it to high speed, spin up your bench grinder and then just sort of put the spinning metal against the spinning stone until you sort of end up with a sort of dogbone endy shape.  If you get it right you'll have a nice dogbone endy shape.  If you get it wrong you'll have this:

Still, this is only supposed to be a prototype, we'll worry about doing a proper one later, possibly involving someone who has an actual lathe and isn't a complete muppet.

4: Push a drive pin into your dogbone hole and line it up in the drive cup.  Check your angles.  If you don't have enough range of movement, go back to the grinder and punish the metal until it fits properly.

6: Check the length of your dogbone.  Now is the time to shorten it if you made it too long, or add more brass if you made it too short (if you work out how to do this, let me know)

7: Repeat steps 2-4 on the other end

8; Assemble your transmission and step back to admire your handiwork

[MadInventor 3753]

Glad to see the transfer case is going to get used.

These help a lot with preventing wandering when drilling holes. They're centre drills for lathes but you can use them in a normal drill. great for getting holes started, and they're only a few quid each for the small ones.

Let me know if want any help with the drive shaft, I will help if I can.  Maybe use a UJ at the transfer case, and half an old dogbone at the other, with a lathe made adapter in the middle.

Just had another thought, I might be able to make something to attach the ball diff gear to an output shaft with a flat on, so that you can use a UJ at both ends. Throw away the pressure plates and balls, and make something that bolts to the diff gear through the ball holes, that is then fixed onto the output shaft with a grub screw or loctite. I've made similar things before in 3 or 4 transmissions. I'll see if I can find a Mad Monkey manual on the internet and have a look at how the gearbox goes together.

[MadInventor 3753]

So I found the manual for the transmission, and making something to lock the drive gear to a 5mm shaft is going to be tricky. I hadn't appreciated how narrow the inside of the gearbox is. The best thing I can suggest for locking the diff would be to remove the balls from the main diff gear, and the thrust bearing that goes over the 3mm centre screw, and clamp the whole lot up tight.

[Mad Ax 6705]

Thanks for the info / advice / offer @MadInventor, I'll definitely give you a shout if I need a shaft making.  I'll probably make a new brass shaft just to prove the concept (mine is slightly too long and binds a bit) but I might also put the Ansmann transmission back in the parts bin and see if I have something else that will work, the Mad Monkey gearbox would be a great donor for a RWD buggy project or something along those lines.

[Nikko85 2405]

A good punch is great for starting a hole cleanly, however you did a great job without.

In terms of adding length, one thing you could do is buy some tubing with same inner diameter as your dogbone's outer diameter (6 mm ID and 1mm or 2 mm wall thickness)

Cut your dog bone in half. Place into the larger tube and measure up. Cut your larger tube the the right size (you don't have to be exact).

Place each end of your dogbone in the larger tube and work out where they need to go, telescoping in and out to fit. Some Loctite red will stop it moving, or if the outer wall is thick enough you could tap grub screws into the outer shaft.

It also means you could buy a standard dogbone (are they 4 mm?) and then some tubing of 6 OD x 4 ID mm and make your own custom length dogbones that way.

 

[Mad Ax 6705]

6 hours ago, Nikko85 said:

A good punch is great for starting a hole cleanly, however you did a great job without.

I use a punch on flat surfaces but on a tiny bit of rod, it just wants to slip off the side.  I suppose with sufficient vicing and clampery it might work, but I was surprised how cleanly the 1mm bit went in.  I just held it in position and lifted the drill bed until the bit was tickling the workpiece, that gave it a nice little hole.  Good quality drill bits have completely changed my world.

[Mad Ax 6705]

Anyway...  Having got the transmission at least sort of mocked-up, I turned my attention to the steering (and promptly got so involved in drilling that I forgot to take any photos.

One thing I did remember to photo was the stainless threaded rod that I tried to bend by hand in the bench vice.  It snapped, which bruised my finger and caused an awful lot of cursing.

Anyway, never mind that, I found another piece of threaded rod and bent that instead.  I also found an Axial bottom link that was almost the right size to make a drag link.  It needs widening slightly, there's a bit too much toe in at the mo.

I think this servo might be the broken one that came out of the BOM, but it works as a placeholder and can probably be repaired if I open it up.

[Mad Ax 6705]

I then chanced to go a-clambering upon the storage floor in my workshop, and whilst hunting around within a box of old tyres I did come across a set of RC4WD Rock Stomper X/Ts, which turned out to be the absolute maximum diameter I can fit on the rears without extending the lower links or making a new drop bracket.  About 101mm.  And being RC4WD tyres, they fit on the deep rims (albeit with some persuasion).  These donuts are absolutely ancient - they came to me attached to a very well-used CC01, in fact my first ever CC01, well over a decade ago.  They're very hard (almost as hard as the Tamiya BFGs that were on the truck before) but they haven't split or cracked at all, so they're probably still pretty good on mud.  It's a shame I don't have another pair, as I could save myself some money on refitting this rig with 6 new tyres.  Sadly they're long out of production, so I might have to hunt around with wanted ads to see if anyone has an old pair going spare.

I wanted to get a feel for the clearance with the biggest possible tyre so I can gauge the body height, so I put two of them on the rear (they balloon out nicely over the wide rims and look pretty cool) and one on the front.

Then I cut a piece of 2mm FR4 sheet where the cab will go, to act as a cab locator and to give somewhere for the electricals to go.

I had to lift the cab and slide it back a bit to clear those big tyres, but I think it looks alright.