[WIP] Tayga 6455B (aka KrAZ 255 2.0) off-road truck - Snowrunner series Ep.2

[keymaker]

Hi,

 

I usually do not create WIP topics for my MOCs, especially from the beginning of work on project. But I decided to give it a try in this case. I hope it will be fun and useful at the same time for me and at least some of you

I would like to continue the Snowrunner series I started with my Chevrolet CK1500. So the next project will be unnamed (yet) 6x6 off-road truck. As I am going to use 30mm rims, this truck will be quite similar to my first “official” MOC – KrAZ 255. The plan is to include all mandatory features I plan for vehicles in this series and to create truck, which will be an improvement in every aspect when compared to KrAZ 255.

 

The mandatory features for all vehicles in this series are:

•          RC drive and steering
•           All wheel drive
•           Suspension for all wheels
•           RC winch

I of course started already and did some work, so let’s move to designing and building section to have something to discuss.

 

As usual, I decided to start with the front axle, which is in my opinion the most complicated element of the MOC. As mentioned earlier, my plan is to improve basically every aspect of KrAZ’s elements and make truck, which at the end I won’t be ashamed to put next to my most advanced and successful MOC – UAZ 3151.

Start conditions for front axle comparing to KrAZ's axle are:

•           keeping 11 studs wide for standard 30mm rims
•           keeping using of live axle
•           improving ground clearance from 2 to 3 studs
•           improving pivot point for wheels
•           making the axle comparable with new tractor tires
•           make axle smaller, as compact as possible

As I spent some time and developed couple of versions of axles, I would like to share some short story behind designing process. All axles were built in real life and tested quite extensively.

 

Axle 0 – KrAZ 255

I still like this one, even if I know what problems are hidden there. Everyone can build this one, using free instruction on rebrickable for KrAZ mentioned earlier, or from yt video like this or this. Long story short, this is the starting point and reference level which I use to compare the final version of axle.

 

 

Axle 1 – Chevrolet CK1500

I designed this axle with plan to improve in my opinion the most important thing in off-roading – ground clearance. So I increased it from 2 studs to 3 studs which, I believe, is the maximum with those rims and tires. I also tried approach where there are no shock absorbers and the axle is suspended only on swing arms, which uses 2 studs rubber pieces. It was success and my Chevrolet is very capable off-roader, which you can check here, but at the same time I learnt what are pros and cons of such type of suspensions.

 

 

Axle 2

After dealing with ground clearance problem, I decided to address second issue – terrible pivot point which was located 3 studs from center of the rim. With such distant pivot point, wheel needs a lot of space to operate and steering is also inefficient. I was able to improve it drastically, switching from cardans to CV jonts, using a lot of half-studs technics and new mustang rims. As the result, I decreased distance of pivot point from 3 studs to only 1 stud from the center of the rim, which is also in my opinion the maximum, if you are considering making steering axle also a driven one. I even added ackerman geometry, but as I was told later, it was reverse ackerman geometry… So it couldn’t be the end of designing.

 

 

Axle 3

Here the first thing to address was reverse ackerman geometry. I fixed that quite easy by putting steering rack behind the axle and getting proper ackerman geometry. Next things I wanted to improve were reliability of steering rack and steering input angle, which was 90 degrees and it is caused by using CV joints. I almost did that, almost… I needed one tile of height to make this work, but all I got was half of stud. So this version of axle turns out to be a failure because 0.17 stud. But not a completely failure since I learnt that 180 degrees of input movement for steering is possible even when using CV jonts.

 

 

Axle 4

I believe this version had the biggest number of variations, changes, different concepts, but all in the range of the main construction. I will only describe the final form. As you may noticed, since the version of axle no. 1 I still didn’t back to the shock absorbers used in the KrAZ axle. There was the case in axle 4 also, but after many changes I decided, that I like shocks more than rubber pieces (because of couple of reasons). So the final version again is using shock absorbers. I also fixed the problem of one dimension mounting point visible in KrAZ axle. Now shock are connected to the axle in a way allowing them to move in two dimensions. So no more stresses for shocks. So what was the improvement regarding  the Axle 3? This one worked, and it worked beautifully.

 

 

Axle 5 "the final"

So why next version, if axle 4 works so great? Two reasons: I wanted to make it smaller, I believed I’m able to make it one stud shorter. And in this scale of building, one stud is a lot and compactness is the king. Second thing was steering input angle. I couldn’t forget the solution I learnt during working on failure axle 3, which allows increasing input range from 90 to full 180 degrees of movement. It is important because bigger range of movement – more precise steering and secondly, 180 degrees makes this version PF servo friendly. At the end, I was able to do that and this is the final version of front axle, were I thought over every single part in it trying to find the way something can work better, or to work the same but to look more “clean”.

 

And when I was thinking, that I did everything I could, @Fluwoebshowed up with this topic and I couldn't resist myself to give this idea a try. It opened so many possibilities unavailable in such scale. Because if I can have double, independent input, then I can use differential, which cannot be located directly on axle without losing ground clearance. And if I can have differential, then I can have locking differential as well, so I had to try. Especially that differentials with locks aren’t common thing in models in such small scale and I love to have one since this feature is one of the main features for vehicles in Snowrunner.

I knew it will be a hard one, so I started slowly...

 

Axle 4 – double input

As axle 4 was big enough and the strongest one from all my versions I prepared, after a couple of tries, version of axle 4 which had all the features as original and double independent drive was done. I wasn't easy, but couple small things (like for example 1,5 stud deep hole instead of 1 stud deep in CV joints) made this constructions possible.

 

 

Axle 5 – double input - The Final version

It was inevitable, that as before, I will try to prepare double input version of axle 5. I spent couple of long evenings looking for optimal solutions and dealing with many problems which pop out like crazy, when you want to squeeze so many thing in such a tiny space. But at the end, I believe I delivered.

 

List of most important features of this axle (there is more, but if you were able to reach this place you have probably enough of reading :D):

•           3 studs of ground clearance
•           great pivot point, located just one stud from the center of the rim
•           180 degrees of input for steering, which makes it PF servo friendly
•           ackerman geometry included
•           independent drive for each wheel, which allows to use differential

I am sorry for such long post. I hope some of you will find it interesting. I'm going to think about next thing on my list, and it will be "power distributor" which is also present in KrAZ and since this truck is going to use such a complicated front axle, then it needs such module too. And I definitely need a break from working on axles :D

 

 

Edited August 15, 2022 by keymaker

[gyenesvi]

I like the design process so far, dealing with all the problems I typically also encounter with driven and steered live axles. Curious how this double drivetrain turns out, how you place the diff in the chassis. I guess it will be easier in a longer truck than in a small Jeep.

BTW, can you summarize what problems you found with suspensions using the rubber piece?

[GerritvdG]

Thanks for sharing, really interesting!

[keymaker]

@gyenesvi Double drivetrain sounds complicated and problematic (and it is) but I am up for a challenge. Especially that this is a mechanical challenge and not next "build accurate body" type of challenge. There is possibility, that all this complications will cripple off-road capabilities, but I'm going to do all I can to prevent this scenario (after all I can prepare two versions of the truck, one - complicated and full of unseen in this scale features and second one, much simpler - ready for heavy off-road trials). I did some thinking already about this "power distributor" and those are goals I would like to achieve:

• it should have two diferentials, each with locking mechanism (one for front axle and second one for both rear axles)
• both diffs should be connected each other (to benefit from both motors)
• it should fit two C+ L motors for drive (I forget to mention, that I will use C+ electronic in this MOC)
• outputs from one diff should be located in front, low, ideally in the center of the section and they must rotate in opposite directions
• outputs from second diff should be located at rear, low, ideally in the center of the section and they must rotate in opposite directions
• it should fit two C+ L motors for drive
• it should fit C+ L motor for steering with output located at the center of the section, high
• it shoud provide output for working steering wheel
• it should provide output for fake engine
• it should allow to somehow lock both differentials from the cabin
• it should be some kind of reduction from motors to diffs to decrease speed and increase torque
• it should be robust, stiff and be ready for adding to the stiff frame of the truck
• it should be as simple as possible to prevent losing power because of friction etc
• it should use new heavy duty CV joints (I forget about this conditions in axle description, but this is one of my idea for improving powertrain - get rid of cardans and old cv joints, only new heavy duty CV joints in powertrain)
• it should fit in space with dimensions: 15x11x5 studs (based on space availabe in KrAZ)

Wow...I did not realized that this list of "wishes" is soo long until I put them here... Heh ok, I will try to fulfill them all :D

 

I case of problems with rubber pieces I encountered when designing suspension for Chevrolet CK1500:

- they need to be connected to very stiff elements of the frame because they are quite stiff and they will bend the frame

- they are not very bouncy and not very responsive

- swing arms need limiters to keep them in the range of rubber pieces - and this is quite problematic because often such limiter doesn't use one stud resolution to be properly connected

- they tend to deform much faster than shocks

 

 

Edited August 16, 2022 by keymaker

[Mechbuilds]

Awesome! Gonna watch this thread for sure. 

[keymaker]

To take a break from mechanical aspects I played with those new rims and visual idea of brakes, which I very like in Mustang set and I also added in my Chevrolet MOC - photo. There I sacrificed one stud each side of axle to put them, so here it was not the option. But stil I would like to have some sort of brakes inside rims. It turned out, that space insade mustang rims allows for some creativity in such situations. All solutions were built in real life, no touching, no scrubing of any sort. What do you think?

It looks nice from out side and also it makes wheel hubs more thick, they look more heavy duty in my opinion. But of course, no impact on ground clearance.

I also wanted to mention, that because of lego parts tolerance and the place, where shocks are connected to the axle, there were a small negatve caster effect visible when suspension was suppresed - and I didn't want that. I fixed that by moving connection point for upper swing arms half a stud back. That way not only problem was gone, but also a new feature (used in real cars) - positive caster was added.

Edited August 19, 2022 by keymaker

[keymaker]

After a couple of tries I came up with setting I believe will work. Based on list of goals:

• it should have two diferentials, each with locking mechanism (one for front axle and second one for both rear axles)
• both diffs should be connected each other (to benefit from both motors)
• it should fit two C+ L motors for drive (I forget to mention, that I will use C+ electronic in this MOC)
• outputs from one diff should be located in front, low, ideally in the center of the section and they must rotate in opposite directions
• outputs from second diff should be located at rear, low, ideally in the center of the section and they must rotate in opposite directions
• it should fit two C+ L motors for drive
• it should fit C+ L motor for steering with output located at the center of the section, high
• it shoud provide output for working steering wheel
• it should provide output for fake engine
• it should allow to somehow lock both differentials from the cabin
• it should be some kind of reduction from motors to diffs to decrease speed and increase torque
• it should be robust, stiff and be ready for adding to the stiff frame of the truck
• it should be as simple as possible to prevent losing power because of friction etc
• it should use new heavy duty CV joints (I forget about this conditions in axle description, but this is one of my idea for improving powertrain - get rid of cardans and old cv joints, only new heavy duty CV joints in powertrain)
• it should fit in space with dimensions: 15x11x5 studs (based on space availabe in KrAZ)

 

Outputs are moved two steps from the center, but it ist the best solution I was able to prepare to maintain other features. I also did some frames to keep everything in place, but it is rather pointless to think about exact frame when there is no rear axles and the main frame of the MOC. The most important thing are gears, diffs, locks and motor placement and those parts will most probably stay where they are. I color coded outputs, so:

• red is drive
• green are outputs for front axle
• black is diff locking mechanism for front axle
• yellow are outputs for rear axles
• blue is diff locking mechanism for rear axles
• brown is output for steering
• gray is output for steering wheel
• white is output for engine

Edited August 20, 2022 by keymaker

[AutoBacon]

Loving the design story! I've been experimenting with driven & steered axles at this scale for a little while. The main issue for me was avoiding wheel flex, especially with a heavier model, the small deflection causes the wheels to walk off the short cv joint axles. I was just wondering how your final design copes in that situation, as it appears quite flexible given the steering pivot arm is only half a stud thick and hinges on a frictionless pin.

[Jundis]

For this scale, it is really impressive you included all the functionalities... I wonder how stable the front axle is when in action the axle joint is only held in the upper section?

[keymaker]

21 hours ago, AutoBacon said:

Loving the design story! I've been experimenting with driven & steered axles at this scale for a little while. The main issue for me was avoiding wheel flex, especially with a heavier model, the small deflection causes the wheels to walk off the short cv joint axles. I was just wondering how your final design copes in that situation, as it appears quite flexible given the steering pivot arm is only half a stud thick and hinges on a frictionless pin.

Thank you. I did what I could to prevent bending of the axle and possibility for wheels to fall off. As you can also see on renders steering pivot arm will be connected via newly introduced red pins with friction. Those will give the axle more stability and limit bending (and they shouldn't be a problem for L motor connected to the steering rack). I'm optimistic regarding this solution, but more off-road tests are needed.

@Jundis front axle bends a little, but this cannot be avoided when there is nothing below the axle to hold it steady. But the model will be light and bending is small, so I accept that.

I case of progress. Rear axles are ready. They, like the front axle, also have 3 studs of ground clearance, they are powered by two seperate driveshafts (one for two left wheels and one for two right wheels). Construction may look frigiale, but 11 studs flip flop lift arms are well secured from both sides and three 9 studs links do the job when it comes to preventing bending or unwanted movement. There are also rubber pieces used to add some level of suspension when wheels are dealing with obstacles.

I put all elements together to check if they fit. And they do. Now frame looks like total mess, but it is temporary. I'm currently working on new frame - light, stiff and elegant - to be able to have main part of the MOC ready.

Edited August 24, 2022 by keymaker

[gyenesvi]

That's a pretty interesting setup for the rear axles! Do I understand vorrectly that the 11L liftarms on the sides are pivoting around the central gear, and the center of the assembly where the CV joints join in are stationary? I like how the wheels on the same side are coupled by gears, they don't really need separate speeds and one diff for the four rear wheels is enough.

The frame is also looking okay so far in terms of dimensions!

[keymaker]

2 hours ago, gyenesvi said:

That's a pretty interesting setup for the rear axles! Do I understand vorrectly that the 11L liftarms on the sides are pivoting around the central gear, and the center of the assembly where the CV joints join in are stationary? I like how the wheels on the same side are coupled by gears, they don't really need separate speeds and one diff for the four rear wheels is enough.

The frame is also looking okay so far in terms of dimensions!

Yes, you are right in case of rear axles. And yes, the frame has proper dimensions, scale of the MOC will be 1:23. But in case of construction, right now frame is a mess, it is a barely a proof of concept. I'm working on new one, which will handle all crucial elements in the proper way.

[Mechbuilds]

Wow this is interesting. Love how you manage to fit so much function inside a microscopic space scalewise. 

[keymaker]

Some upgrades.

Frame. Frame is done in 95%, only some minor adjustments needed when the body will be ready. Frame is stiffer than in original Kraz, also all visible blue pins are removed. I wish to keep two seats cabin, so mandatory feature - winch - is located and hidden behind rear bumper. I also added some small features and - as it should be capable off-road truck - I added proper shielding of underbelly of KrAZ, so no pointy rocks, sticking out branches can prevent this MOC from keep moving (similar to my Armored Trophy Truck). Some photos below (steering axle is disconnected deliberately at this moment).

Next step was the engine. In original Kraz V8 engine has 4.5 studs (plus 1 stud for camshaft). It is way to much and it brings problems with adapting such module into rather small MOC. I prepared new version of it, which needs only 3 studs (plus 0.5 stud for camshaft). Now I believe it is great engine to be used even in very flat small scale models. Such low height gave me a lot of freedom in mounting it into the frame and allowed me to even add some nonplaned features related to the engine.

When engine was ready and mounted I could focus on interior and trying squeezing there all features I initially planned when preparing central power distribution module. Transfering movement from module to the engine was quite easy (it required lego rubber band). Then levers for locking and unlocking diff mechanisms. I put switches on top of power distribution module, so I was able to quite easy locate levers to steer them at the central of the cabin, between seats (red and blue liftarms). The most difficult thing, due to very tight space, was introducing working steering wheel. After couple of failed ideas I came up with working solution which you can see on photos. I was also able to add some rather not available in KrAZas details like air condition or openable glove box with 3 cubic studs of usable space :D Colour of the interior probably will change later, depends on final colour choice of the whole MOC.

Now there is the hardest part for me (and unfortunately the most important thing based on which many people will judge this MOC) - preparing the body. I will definitely ask for your opinions and advices with this, as I did with my UAZ 3151 :)

Edited September 15, 2022 by keymaker

[Nazgarot]

This is impressive! I like how it is coming along, and I'm very excited to see your choices for bodywork.

Could you make a demo video to show how the dual drive system works offroad? The gear train seems a bit weak to me, but might be ok if the model is light enough... 

_ED_

[Jayden]

I love this so far.

 

Edited September 15, 2022 by Jayden

[keymaker]

21 minutes ago, Nazgarot said:

This is impressive! I like how it is coming along, and I'm very excited to see your choices for bodywork.

Could you make a demo video to show how the dual drive system works offroad? The gear train seems a bit weak to me, but might be ok if the model is light enough... 

_ED_

Thank you! I haven't tested it yet, I need to do so and make some video from tests. In case of drive train -  it was one of the goals to improve, simplify and making drive train more reliable when comparing to my original model of KrAZ. Due to introduction of differentials and lock mechanisms it is hard to call this version simpler :D BUT I still think this version is stronger and more reliable, mostly because of removing from drive train weak cardans and old CV joints (the only exception are CV joints located just next to front wheels). Also amount and types of gears in drive train is different plus there are two L motors instead of one. So double the power. My original KrAZ is available for free so you can check what solutions were used there.

[Jundis]

Looks really great, so much function in such a tiny space!

[keymaker]

On 9/15/2022 at 11:13 PM, Nazgarot said:

Could you make a demo video to show how the dual drive system works offroad? The gear train seems a bit weak to me, but might be ok if the model is light enough... 

As requested, I made some tests and it works pretty well considering design choices and complication of drive train.

I also made some progress with body work. All your comments are welcome, what is ok, what is not ok and why, what I can add/change etc.

Some comments about design choices:

- color of the body - I know it is not a blast, but due to used parts and their color availability I am quite limited in this matter

- lights are rather simple, but they are ready for LEGO LEDs

- roof is ready for some additional lights or roof rack, I will see what can be added

- still I am not sure If there should be additional step on the side behind fenders or not (original truck doesn't have them)

- I think that system pieces used on sides of the hood can be located one plate lover

- cable management is still not done

Considering the scale, I think that shape of the body looks quite similar to the original, I put blueprint at the end.

More photos you can find here

Edited October 11, 2022 by keymaker

[piterx]

this is awesome dude !!! I'm building some stuff with a small axle too :) Your design is pretty clever!

[HectorMB]

This is awesome! 

[keymaker]

I made some progress. Couple of parts are still missing (already ordered) but I think I am close to the end of designing. Any comments, advices, sugestion you have, please share them. Whatever can be improved, I will try to do it.

Guided by the game and what can be found in it for this truck I added some necessary additions useful in the wilderness. You can see bull guard, exterior roll cage, roof rack with lights and fuel canisters, tool box just under spare wheel and double snorkels. I also added cargo bed to complete the look.

I redesigned front lights to make them more solid and added black background, what you think? I looks better or worse than previous version of lights?

Front grill is also changed to be more transparent to let you see even more what is going inside of engine bay. I also added horizontal element to make grill looks more like in the real truck.

I changed hood a bit to be more sturdy and most of all not coliding with the grill like previous version.

Engine itself was also improved by many elements you can find located next to real engines. I am still waiting for some parts in better colours.

If you have some ideas what more can be done, please do not hesitate to point them out :)

Edited October 24, 2022 by keymaker

[Bluehose]

I love all the things about this build, and I particulary like in this configuration both geared side of the diff are necessary, in general the half of it look useless.

[keymaker]

4 minutes ago, Bluehose said:

I love all the things about this build, and I particulary like in this configuration both geared side of the diff are necessary, in general the half of it look useless.

Thank you, could you elaborate more about what you think is useless?

[Bluehose]

Nothing on your build obviously, sorry for my bad english 

But it's quite common that when this differential is used in other build, just the 24 teeth end is used or just the 16 teeth end is used.

This make this park look misadapted in general.

(But not on your build)

You need the 24 teeth end  / 24 teeth gear to have the good spacing with the motor (and less power loss annd less bulky than if you did 16 teeth end / 16 teeth gear / 16 teeth gear) 

And you need the 16 teeth end as a link between both differentials because you need gears without a cross hole and using the 24 teeth end with them would be more bulky.

In conclusion in this case the differential look like an optimal designed piece which make the whole look even more beautiful, LEGO itself never did that imo