Nikko 1977 18 wheeler rebuild and mod

[Nikko85]

Another week, another questionable Nikko purchase. This one was a Nikko 18 wheeler that I picked up for £15. I thought at the very worst it'll make a push along toy for the toddler. A few rattling pieces inside, so knew it was going to be a resto mod with new parts.

On the outside it looks great. Somewhat smaller than my road express but perhaps the same scale

The inside was less pretty. Some damage and a very complex gearbox which used the same motor to power the 5th wheel and drive. Lots of tiny, noisy gears.

I decided to remove all the old electronics and most of the gears.

I am left with a diff stuck to the two axle halves. I can't remove the wheels without damaging something so it is all one thing.

At the moment the axle can somewhat float around.

My plan is to 3D print something to lock the axle in place and then print a motor mount that allows a pinion to engage directly with the diff as a spur gear. It's a 50T 0.6M gear, so an 8T pinion should give me a gear ratio of 6.25. Now this is pretty high but the wheels are small and I'll be running on the flat. I plan to use a brushless motor running 4.8 volts so I shouldn't melt anything. Any thoughts on this? I might be able to find a step gear if needed but I am just trying to keep it simple. 

For the front I can drop in a servo and steer it using the rack it's got already.

5th wheel will be another micro servo in the gearbox. Those two are easy but not sure about the drive gear.

[Nikko85]

So this build took a little more effort than usual. The gearbox had to go, resulting in a home made gearbox, which really is just holding the axles the correct distance from the spur gear. In the end I counted 48 teeth on the spur gear, meaning I've got 1:6 gear ratio, not too bad considering the tiny wheels. It will be powered by a fast 370 motor, but running around half speed.

The main complication was the diff/axle/wheels unit is all one thing, I can't take the wheels off. So rather than push the axle through a hole in a gearbox I need to slide it through a slot.

In the end I developed this:

The axle slots into the back and then a small block with a semi circle cut out at one end plugs the slot and creates the hole for the 4mm axle to run. I found making the slot 4 mm and the hole 4.1mm allowed for the axle to run smoothly and feel looked in place.

The gearbox is screwed in with three screws which go from the bottom of the chassis straight into the three tabs, drilled to 2.5 mm. 

A first prototype is below, you can see the black screws holding down the plugs.

Quick plug in with a battery (4.8 volts) to the motor suggested it was smooth and quiet and quite powerful! I don't have mesh adjustment, but used the gearing calculator and some Pythagoras to get the distance spot on. I mig add a mm either way for fine tuning.

Getting the height right was tricky, if the wheels sit too low the spur gear touches the bottom of the chassis, too high and the rear of the truck squats too much, in the end a 0.5 mm shim between the gearbox and the floor of the chassis was perfect.

...which gives me a perfect right height. Now to finish the rear axle (non driven, but has lost the supports following the removal of the original gearbox so just rattles along), steering, 5th wheel and battery/wiring!

However the gearbox was always going to be the tricky thing to do (before buying I had no idea if it would be possible) so with this in place the rest is quite straight forward! 

 

 

[Nikko85]

Updates! Rear floating axle locked into place with a support bracket. To be honest the rear axle/wheels functionally do nothing, you just don't want them either pushed down to the point they lift the drive axle off the ground or conversely  floating above the ground so the wheels don't make contact. The means you realistically need some travel on the axle in the z axis. I printed out these guides for it to float in, it's got around 3 mm of travel either way so the wheels rest lightly on the ground. It means a small pebble under the rear axle can't lift one drive wheel off the ground by pushing up one side.

I do wonder if I could use a chain or rubber band to link both rear axles together to make a 4x6 vehicle. Probably overkill, this only drives on a living room floor!

Here is the updated gearbox - seems to work.

The 5th wheel was super simple; a micro servo with a metal link (an old hair clip) attached to the original lever of the 5th wheel did the job. I had to drill a very small hole to attach into the original lever, but it seems solid.

Steering servo was really simple, just the same mirco servo attached to the original steering rack.

ESC and gear stuck in, a 7.2 volt AA battery sits in the old battery tray. I had meant to use the original 4 x C batteries, but just could not solder anything onto the battery tabs!

The original had a clear plastic piece on top of the cab. On the press of a button this would spin between forward, backwards and 5th wheel functions. You would then let go when in the right position and use the action button to action the desired function. Very cool for the day, but I wanted to make mine look a little better. I 3D printed a round circle to fit exactly in the space. Originally I was going to paint this, or use vinyl to colour match, but I couldn't get the right orange tone, so I went with black with a "1" to match the livery.

So how does it drive? With full open diff on every wheel and a short wheelbase with good steering lock turning circle is tiny (50 cm or so) and the handling quite direct. The gearbox is quiet enough on around 40% power at 7.2 volts and fast enough for the scale, at 50% power it's a little crazy, so much so I don't want to try 100% power. The 5th wheel works perfectly too, so I'd say a big success! 

To completely finish I want to add a small 1/25 scale Edgarmon to drive it, and I want to give the lights some fresh stickers, as the chrome head lights are a little boring, and I think white or yellow would look better.

All in all super happy with this one, I took a punt not even sure I could get it working (having seen zero videos / pictures of the inside) so I'm glad I gave it a shot. More than happy to share STLs.

 

[Nikko85]

Well I just picked up another for £15. My toddler loves trucks so this will make a nice push along toy or I can do the same again.

This one has an orange trailer too.

 

[Krustybus]

This is really cool, what a nice little project. Surprised there hasn't been more comments to be honest!

[Grumpy pants]

Admiral rejuvenation of these little gems.

Really enjoyable seeing your progress and the ingenuity you use to make them more useable and fun 🎉

[Nikko85]

2 hours ago, Krustybus said:

This is really cool, what a nice little project. Surprised there hasn't been more comments to be honest!

Many thanks, to be fair this is Tamiya forum - and whilst the builds allow anything, I'm not super surprised when something that isn't Tamiya doesn't get as much traction!

1 hour ago, Grumpy pants said:

Admiral rejuvenation of these little gems.

Really enjoyable seeing your progress and the ingenuity you use to make them more useable and fun 🎉

Thanks - I only started making cars and any modelling at the start of lockdown. Whilst I've not really developed painting skills or certain tricks - I've certainly come a long way in 3D printing and fixing!

So, the new truck is distinctly dirtier. Given how much I enjoyed the last one, I'm very slightly tempted to make a smaller DAKAR truck using a 1/18 platform and merging the cab and trailer, but I think I'll leave as is. It may well just go to my toddler as is to start with - and then add a motor later. My current on is way over powered (I only run at 60%) , so I'll see what less aggressive motors I have. 

 

[Re-Bugged]

The second one should be breeze now bud 👍🏻

Excellent stuff. 

[JimBear]

Yep, adding to the choir ... I really like your builds, @Nikko85.

The Dakar idea sounds tempting ...

[Nikko85]

So truck number two turned up.

It is filthy, but seems intact. I really like the dirt, so although I will clean up I may  look into weathering and ways to age it a little.

Tires are all present and round. These are close to 50 years old, so that's awesome!

Chrome is starting to go from the exhaust stacks but otherwise pretty good.

Some sticker lift, but otherwise ok

All in all very cool. I like the orange trailer. I may clean and give to toddler, or I might get it back up and running with new everything like before. I think it depends what my spares pile is looking like!

Edit: Toddler spotted it on our bedroom wardrobe (usually he doesn't go into our room but the doors were open for the heat) so now he has taken it, and it lives with "his" monster truck, short course truck and GT1, all also "borrowed" by him.

Fair play to him, he lines them up on the sofa and has fake races, and gets more fun out of them then I do! Can't wait till he's old enough to drive them around...at the moment they join the robot vacuum cleaner and hoover as objects of terror whilst turned on.

This is quite a good scale match to the heavy dump, so as that has a working tipper I am looking forward to doing some roleplay in the garden with him! 

[JimBear]

12 hours ago, Nikko85 said:

Toddler spotted it on our bedroom wardrobe (usually he doesn't go into our room but the doors were open for the heat) so now he has taken it, and it lives with "his" monster truck, short course truck and GT1, all also "borrowed" by him.

Although our Junior is a bit older, I sure can relate! If I want to try to keep something, I have to bury it among other stuff or relocate it. And even that doesn't work ... "Dad, those rear tyres you have ..."