[MOC] Rock Bouncer - Tim Cameron's Tyrant

[gyenesvi]

Hi Guys!

This is a rock bouncer model I built a while back last year for the off-road competition in the Buwizz Camp in 2022 and ended up in 3rd place with it. I have been postponing publishing here as I wanted to make a version with a more realistic livery (stickers) and also make more testing / filming. Well the livery project is also being postponed for various reasons, but finally as the weather is getting better I could finally take it out again for more testing at least, so I decided to make a writeup.

But I believe a video tells more than a lot of words, so let's start with that :)

 

So the build is meant to be an accurate model (as much as possible) of Tim Cameron's rock bouncer buggy named Tyrant. Here's a short video showing around the real thing. It's a monster.

 

If you follow rock bouncer races a bit, you might agree that this guy is probably the best builder out there, and his 2022 model is not only very capable, but also a very cool one among these often raw looking hand built rock bouncers. This is one of the reasons I decided to build this one. Another reason is that it has a suspension geometry that was possible to closely mimic in lego form and results in an amazingly smooth responsive and flexible suspension.

Rock bouncers are different from rock crawlers in that they don't just crawl up rocks slowly by precise manoeuvring, rather they use sheer power to bounce up the rocks and steep walls. Such a build was definitely calling for the use of Buwizz motors, which I had been wanting to test, and also this way it was an ideal entry for the competition. Another goal with this model was to build something with a really massive and realistic 4-link suspension both front and rear, and buggies are ideal material for that. And one more thing to test was if it is possible to build a sleek tubular body that's also solid at the same time.

Features

- Long travel, highly articulated, bouncy live axle semi-triangulated 4-link suspension both front and rear
- 4-wheel drive, driven by 2 Buwizz motors
- Steered by a PU L motor
- Powered by a single Buwizz 3 unit
- Good weight distribution, low center of gravity, very stable against rolling over
- Working V6 engine at the front
- Fully tubular exterior with a few side panels, but very sturdy due to inner beam structure
- Realistic cockpit with detailed racing seat

Suspension

I have previously built rear 4-link suspensions on a medium scale, but I was never completely satisfied with the realism of the geometry. There are all sorts of factors in real suspension geometry, but one thing that I realized was that I was never able to position the upper links realistically, so this time I dig into how it's really supposed to be. It turned out that the best geometry varies with the purpose of the vehicle, but in case of these kind of buggies, the upper links usually start out quite low, which makes things quite difficult in terms of avoiding collision with other things. This is especially true for the front, where the links need to go around the whole engine. Other interesting factors are the nature of triangulation and where the shock absorbers are mounted. A setup used in some of these rock bouncers is a semi-triangulated 4-link, meaning that the lower links are parallel, and the upper ones form a wide and pointy triangle. This allows for a shock absorber to be mounted onto the lower link itself at around half of its length, effectively doubling the travel at the end of the link. For this to work, the lower links must be mounted to the body in such a way that the link only tilts minimally (so that it doesn't twist the shock absorber), and there's a lot of tilting at the axle end. This is something really easy to replicate in lego form; the link at the body end is mounted to frictionless pins or axles, while the axle end is mounted on towball pins, resulting in exactly what is done in reality. I also managed to add the imitation of sway bars as on the real buggy, but those are only for aesthetic purpose.

Here are renders of both front and rear axles. The rear one has a very long lower link (15L beam with a towball arm on the end).

Drivetrain

As the model is driven by 2 Buwizz motors, and the form factor of those motors makes them hard to integrate into live axle off-roaders, I had to apply some trickery when building the drivetrain. There were two problems with the motors. First, I wanted to make the drivetrain efficient with minimal gearing to minimize wear on the components, but at the same time I wanted to leave the middle of the model for the cockpit. So the only place to put the motors was in the back behind the seat (which is already quite far back in the real buggy), in a vertical position. The idea was that hard coupling the two motors further in front would make space in the middle for the double CV-joint drivetrain going to the rear axle, which had to be long enough to enable the new 5L sliding male part to be used, necessary to follow the movement of the massive suspension. However, that brings another problem; the two motors cannot be placed close enough for a simple 16T gear-train to hard couple them, only further apart. First I tried 1 stud wider setup, coupling the motors with 24T gears, but those took up too much space. So I ended up experimenting with placing them on a half stud offset and coupling them with 20T gears, and that worked out quite well from a rigidity point of view as well, I was also able to use the motors as structural elements. Besides the basic drivetrain, I later also added a working fake engine with a fan, because there was this big empty space in the front right where the engine is in the real car, so I could not miss that opportunity :) But it's very impractical in a high performance model, and those motors even generated plastic powder inside the pistons! so I ended up disconnecting the drive from it when I was playing the model..

Chassis

As I knew I wanted to build the outer body from tubular elements, which would not really going to be holding anything structurally, I wanted to design sort of a back-bone inside the chassis to hold everything together. This is mainly achieved by a couple of beams running through the center of the chassis. The two Buwizz motors are also used to hold the back of the body. Also I had to place the remaining electronics. I did not want to place the steering motor on the front axle to minimize the unsprung weight, so I thought it could go under the seat and steer through two CV joints. As the real buggy has only one seat on the left, I could use the right side to place the Buwizz unit; it is placed very low on the floor giving a quite low center of gravity. This way the whole front section remained empty and available for the fake engine.

Here's a render of the inner chassis that serves as the load-bearing structure:

A note about the drivetrain: it really requires lubrication to be able to take the abuse without serious damage. I have been using silicone grease, which seems to work so far.

Bodywork

So as the inner structure of the chassis is rigid, I was able to put a tubular bodywork on it with tubes going in all angles. Obviously, it is impossible to reproduce the rich and dense tube structure of the real buggy, but I tried to mimic the main lines at least. It turned out to be quite complex especially at the front, but I am really satisfied with the end result.

Here are renders of the complete chassis with the tubular outer structure on it.

On top of the tubular structure, the buggy has minimal paneling on the side, and luckily it was possible to fit a few panels of the right size and shape between those tubes. Unfortunately, the model cannot be built with green panels / wheels as some key parts are missing from the lego lineup. I was able to build it first in orange, that went well with the yellow springs and wheel hubs. It would also be possible in red, and later I built a version in blue using 3rd party parts for the large wing panels on the side as that's the only one missing in blue. I think this colors works really well here. Of course black would also be a viable option, but that did not look so cool on renders.

Here are a few more renders and pictures from various angles:

More images are available on Bricksafe.

Building instructions are available on Rebrickable.

Since the race in the Buwizz camp, where other models were visibly faster than mine, I rebuilt the drivetrain with older differentials (as I originally built it with new ones) resulting in a 1.5x speed increase, and it still has plenty of torque to go uphill. Unfortunately, the Buwizz unit is prone to shutting down this way..

I must also note that the model is hard to control with a touchscreen, it is even challenging with a physical controller when going on rough terrain and trying to avoid bumping into things and scratching it all over the place. Although, with an appropriate skid plate (duct tape at the bottom :) ) I worry about that less, and sometimes just give it full throttle, and it really goes through everything that I throw at it, really smoothes out the terrain amazingly. That's really satisfying, I really feel like playing with a real RC car. I'm trying to prepare another video showcasing that, hope it will actually be able to show that aspect nicely.

Let me know how you like it!

Cheers!

Viktor

Edited March 27, 2023 by gyenesvi

[Daniel-99]

Hey, Viktor! Your Bouncer is a great example of technicality and RC performance which I miss with a current technic lineup. Your B-models are great, but they bring certain limitation both in bodywork design and technical solutions. So this creation reveals your hidden powers ;-) Well done!

[nerdsforprez]

Fun model and great build.  I do follow rock bouncer's and agree Cameron's builds rank among the best.  Also, it is worth mentioning they are different than rock crawlers.  Crawlers, as the name suggests, are slow, geared with tons of torque but also high power.  Bouncers need bursts of speed so they can "bounce" in a situation that they can not crawl up. Bouncing can sometimes hurdle over otherwise unclimbable obstacles.   

This is a great and very capable bouncer.  Still think perhaps they best bouncer was built by PTNYC, his "wasp crawler" but your model has a realistic suspension, details such as an engine, etc. so they are not really comparable.  Great build and thanks for sharing!

[gyenesvi]

On 3/28/2023 at 2:33 PM, Daniel-99 said:

Hey, Viktor! Your Bouncer is a great example of technicality and RC performance which I miss with a current technic lineup. Your B-models are great, but they bring certain limitation both in bodywork design and technical solutions. So this creation reveals your hidden powers ;-) Well done!

Thanks, glad you think so, indeed B-modelling can be restrictive, though often it's less restrictive than one would think if the model is well chosen for the available parts :) But true that for really fine builds a wide selection of parts can be required..

On 3/29/2023 at 11:53 AM, nerdsforprez said:

This is a great and very capable bouncer.  Still think perhaps they best bouncer was built by PTNYC, his "wasp crawler" but your model has a realistic suspension, details such as an engine, etc. so they are not really comparable.  Great build and thanks for sharing!

Thank you, indeed this is not such extreme build in terms of flex for example, but the goal was to have it more realistic. And I think it becomes quite a bit more difficult if you want to keep motors off the axles and have an actual clean cabin.

[langko]

So my only experience with RC lego models is the 42129 Zetros... My curiosity got the better of me and I bought it for a heavy discount about a year ago. The experience was underwhelming to say the least. So slow and heavy with rubbish ground clearance meant it got scrapped for parts pretty quickly. Out of the blue though some family members chipped in and got me a Buwizz 3.0 + 2 buggy motors for a birthday present. I thought about designing some electric supercar like a Rimac Nevera, but in the end I wanted something with more ground clearance/playability. I saw your model on rebrickable and it was exactly the type of model I was looking for! Thankfully I had most of the parts lying around already, so it wasn't too hard to get what I was missing. 

I settled with a DBG colour scheme for the body, with a black and yellow seat to match the shocks.

Overall, this model is amazing! For me its way better than the Zetros is every way.

Its fast enough to be fun, but not too fast that plastic starts exploding. Great ground clearance and suspension, good climbing ability and looks great (I love the tubular structure to the bodywork). Haven't had a chance to test it on super rocky terrain like your video yet, but it tears through all sorts of grass, bark and challenging terrain in the estate I live in. It's got the ground clearance to easily come down the square curbs in my street as well.

The biggest weak link is the fake engine, the motors are way too powerful for it. The instructions even suggest to leave it disconnected if you plan on pushing the model, which is good advice. However it seems like a wasted opportunity for a RC model, especially when the Buwizz has extra ports. I realised you can sacrifice some of the engine detail and fit a medium motor in the snout. This only required some minor structure changes and could easily be routed to the Buwizz unit. Much more satisfying as it can now be turned on/off seperate from the drivetrain, and one can run it at less power. 

I also tweaked the structure just in front of the large steering motor... There is just enough room to add a mechanical limiter/block, when means it can be calibrated in the Buwizz app now. I can make a small render if you are interested. 

Thanks so much for sharing this model! I appreciate the effort put into the detailed write up as well 

 

 

 

 

[gyenesvi]

@langko, thanks for building this and posting pictures; it looks really cool in DBG :) Glad you like the result!

I have to say the idea with the M motor for the fake engine is pretty neat! At first I thought that you threw out the piston engine and just use kotor to spin the fan, but now I see that you actually managed to keep the pistons underneath, right? That's pretty practical indeed, it can be run independently.

As for the calibration, what was wrong for you? Did it push the mechanism aprt somewhere? As far as I remember it calibrated okay for me with the Buwizz app as well when I tried once to control it with a tablet, but it was pretty uncontrollable that way, so most of the time I was using the BC2 app, and that could not do autocalibration for the Buwizz at the time, only manual. The physical limiter right at the motor seems like a good idea for that case if it does jot decrease the steering angle.

I still have this one built so I might try these mods. Curious about the engine especially!

[langko]

9 hours ago, gyenesvi said:

I have to say the idea with the M motor for the fake engine is pretty neat! At first I thought that you threw out the piston engine and just use kotor to spin the fan, but now I see that you actually managed to keep the pistons underneath, right? That's pretty practical indeed, it can be run independently.

Yes the piston engine is still in the same position as the original. So the axle out of the motor runs straight into the fan but the original gears run to the motor underneath. 

I tweaked the original structure to this: (the M motor can be attached upside down to the 3 black pins)

A few pieces hidden for clarity.

Then the area where the piston engine connects to the chassis was tweaked to this.

9 hours ago, gyenesvi said:

As for the calibration, what was wrong for you? Did it push the mechanism aprt somewhere? As far as I remember it calibrated okay for me with the Buwizz app as well when I tried once to control it with a tablet, but it was pretty uncontrollable that way, so most of the time I was using the BC2 app, and that could not do autocalibration for the Buwizz at the time, only manual. The physical limiter right at the motor seems like a good idea for that case if it does jot decrease the steering angle.

Well, to be honest I didn't actually try the original way... I read what you wrote on rebrickable "However, the gearing in the steering system must be built centered such that the servo motor is at a 90 degree angle (in fact at it's zero position, which is not marked unfortunately), because proper steering calibration is lacking in the app for the Buwizz unit at the moment."  So I presumed it wouldn't work, but know I see that was a misunderstanding on my part and you were talking about using the brick controller 2 app and not the Buwizz app. I presume the steering calibration works with the   you have in the front?, but I didn't see that at the time haha. Anyways I changed the section in the front of the motor to this: Which works really well in the app. I found the model is actually pretty smooth to drive, even with the touchscreen controls.

Hope everything I tried to explain makes sense 

 

[vergogneless]

Incredible construction, well done!

Have you ever considered switching to brushless? You would have at least three times the power, no electronic cuts, and the maneuverability that this kind of vehicle truly deserves!

[gyenesvi]

On 6/24/2023 at 2:28 AM, langko said:

Yes the piston engine is still in the same position as the original. So the axle out of the motor runs straight into the fan but the original gears run to the motor underneath. 

Sounds great, thanks for showing the tweaked structure.

On 6/24/2023 at 2:28 AM, langko said:

Well, to be honest I didn't actually try the original way... I read what you wrote on rebrickable "However, the gearing in the steering system must be built centered such that the servo motor is at a 90 degree angle (in fact at it's zero position, which is not marked unfortunately), because proper steering calibration is lacking in the app for the Buwizz unit at the moment."  So I presumed it wouldn't work, but know I see that was a misunderstanding on my part and you were talking about using the brick controller 2 app and not the Buwizz app. I presume the steering calibration works with the   you have in the front?, but I didn't see that at the time haha.

Oh, okay, indeed, that was about BC2's inability to do auto calibration at the time. Not sure if it has been fixed already since then.. And yes, those black towball pins are there to limit the steering exactly where it needs to be, to allow good steering angle, while not oversteering. The physical stopper you built could allow a tiny pit of oversteer, as it allows a bit more steer than mine. The CVs could take it at slow speeds, but since this is a faster one, I did not want to risk wear on the joints, and it already has quite good steering angle at this point.

On 6/24/2023 at 9:00 AM, vergogneless said:

Incredible construction, well done!

Have you ever considered switching to brushless? You would have at least three times the power, no electronic cuts, and the maneuverability that this kind of vehicle truly deserves!

Thanks, glad you like it! Sure, I am always looking for such possibilities, though I have not gotten there yet. I do have geekservos for steering, but I don't have yet a drive motor, I'd prefer something that has some custom (maybe printed) housing and axle output to make it possible to build it into the model properly, and maybe something that's a bit slower, or otherwise I'd really have to upgrade the whole drivetrain with metal joints, shafts, ball beared O-frames, differentials, wheel hubs, etc.. I guess it works okay in small scale, RWD without all these, but when you want to have a larger model and full drivetrain, I guess that changes many things.

[langko]

2 hours ago, gyenesvi said:

Sounds great, thanks for showing the tweaked structure.

You're welcome!

2 hours ago, gyenesvi said:

Oh, okay, indeed, that was about BC2's inability to do auto calibration at the time. Not sure if it has been fixed already since then.. And yes, those black towball pins are there to limit the steering exactly where it needs to be, to allow good steering angle, while not oversteering. The physical stopper you built could allow a tiny pit of oversteer, as it allows a bit more steer than mine. The CVs could take it at slow speeds, but since this is a faster one, I did not want to risk wear on the joints, and it already has quite good steering angle at this point.

You can tweak the settings in the app to adjust the degrees of the steering angle. So you can remove that little bit of oversteer. Here is an example screenshot of the settings from the app.

 

[gyenesvi]

4 hours ago, langko said:

So you can remove that little bit of oversteer.

Sure you can tweak and limit things a bit in the controller as well (and I do that too in order not to put stress on parts), but for best effect, you really need physical stoppers, and it's best to have them close to the wheel hub somewhere for precision. On one had, you want to max out the turning of the wheels in response to the motor movement. On the other hand, you also want to minimize unwanted steering movement due to bumps hitting the wheel and pushing it to hit the chassis / fender or whatever you have there. That's why what I usually do is limit the steering rack precisely, and sometimes even limit the wheel hub on the other side of the rack. But yeah, I also do sometimes limit the movement right at the motor as well, so that it does not even try to rip things apart, though that limit needs to be a bit more loose to allow for enough movement even when taking lag in the steering joints into account.

[langko]

@gyenesvi makes sense! Thanks for the explanation 

[vergogneless]

On 6/26/2023 at 11:04 AM, gyenesvi said:

Thanks, glad you like it! Sure, I am always looking for such possibilities, though I have not gotten there yet. I do have geekservos for steering, but I don't have yet a drive motor, I'd prefer something that has some custom (maybe printed) housing and axle output to make it possible to build it into the model properly, and maybe something that's a bit slower, or otherwise I'd really have to upgrade the whole drivetrain with metal joints, shafts, ball beared O-frames, differentials, wheel hubs, etc.. I guess it works okay in small scale, RWD without all these, but when you want to have a larger model and full drivetrain, I guess that changes many things.

You are absolutely right, building a large brushless model is a whole different story compared to smaller scales!

But there are solutions that work quite well (for example):

https://www.avito.ru/moskva/tovary_dlya_detey_i_igrushki/motor_dlya_lego_technic_-_beskolektornyy_a2212_2310818883

It is an investment, for sure, but it's worth knowing that it ends up being much cheaper than a BuWizz 3 with all the motors. Even if you add metal parts, ball bearings, or 3D-printed components.

Brushless motor + servo + ESC + receiver/radio control + battery = about 70€.
With that budget, you can easily fill your shopping cart with additional parts :D

[gyenesvi]

On 6/30/2023 at 9:02 AM, vergogneless said:

You are absolutely right, building a large brushless model is a whole different story compared to smaller scales!

But there are solutions that work quite well (for example):

https://www.avito.ru/moskva/tovary_dlya_detey_i_igrushki/motor_dlya_lego_technic_-_beskolektornyy_a2212_2310818883

It is an investment, for sure, but it's worth knowing that it ends up being much cheaper than a BuWizz 3 with all the motors. Even if you add metal parts, ball bearings, or 3D-printed components.

Brushless motor + servo + ESC + receiver/radio control + battery = about 70€.
With that budget, you can easily fill your shopping cart with additional parts :D

Thanks, I have been following those solutions and they look quite nice, but I was always lost in all those russian sites. I can translate some of the text to understand the products on sale, but it's really hard to buy something there, it seems you need to register first and then you can buy stuff hopefully, and that's quite difficult when you don't understand a word there.. and then in the end it may turn out that it's impossible to pay due to current political situation. So that's a bit of a hard path now.. But yeah, the cost seems pretty okay.

[vergogneless]

Yes, it's true that I may not have given the best example, considering the current situation.

But there are other solutions that you should know about, such as:

• Effermans parts for 3D printing: https://www.shapeways.com/shops/effermans-technical-parts
• TF-Engineering for ball bearings: https://tf-engineering.at/products/
• And also MTP for metal parts: https://metal-technic-parts.com/

By the way, MTP is currently developing a mount for brushless motors.

If you happen to know any other suppliers, I'm open to suggestions!

Edited July 8, 2023 by vergogneless

[gyenesvi]

5 hours ago, vergogneless said:

Yes, it's true that I may not have given the best example, considering the current situation.

But there are other solutions that you should know about, such as:

• Effermans parts for 3D printing: https://www.shapeways.com/shops/effermans-technical-parts
• TF-Engineering for ball bearings: https://tf-engineering.at/products/
• And also MTP for metal parts: https://metal-technic-parts.com/

By the way, MTP is currently developing a mount for brushless motors.

If you happen to know any other suppliers, I'm open to suggestions!

Thanks, I have seen all of these solutions, but so far only tried some of efferman's printed parts. The mount for the brushless motor seems like an interesting thing for sure!

[langko]

So after pushing this model at a wide variety of places (skate parks, mountain bike tracks, various hiking spots and even the beach) I finally dismantled the model to use the buwizz components for something else. The only bad thing after everything would be the rather exposed diffs (difficult to cover without compromising ground clearance) Blades of grass or the like would get tangled up there more than I would've liked, or a stick would some times jam it. Most of the times this would cause the buwizz unit to shut down and it's game over until you can plug it back into power. 
After pulling everything apart there is surprisingly very little damage to any of the parts. The only exception being the lower tow balls at the front hubs are quite worn (I'm guessing due to the tighter fit with the way the lower section is angled up a stud)
Overall though this model was a great experience and I had a lot of fun/learnt a lot from it. Thanks again for sharing!

 

[gyenesvi]

Thanks for all the feedback!

5 hours ago, langko said:

The only bad thing after everything would be the rather exposed diffs (difficult to cover without compromising ground clearance)

Indeed, that is a tradeoff, and I choose the ground clearance :)

5 hours ago, langko said:

After pulling everything apart there is surprisingly very little damage to any of the parts. The only exception being the lower tow balls at the front hubs are quite worn (I'm guessing due to the tighter fit with the way the lower section is angled up a stud)

Glad to hear that there's little damage! I also observed some wear on ball joints, not just on the hubs but also on steering links. Maybe some greasing there could also help..

5 hours ago, langko said:

Overall though this model was a great experience and I had a lot of fun/learnt a lot from it. Thanks again for sharing!

Thanks a lot, happy to hear that you enjoyed it!