[MOC] Hornet 4x4 Baja Buggy

[Daniel-99]

Hello Eurobricks! 
A few months passed since I shared with you my creations. Well, I was working hard on two RC projects and now I am proud to introduce you one of them! It is called "Hornet" and it is an Ultimate 4x4 Baja Buggy. 

Technical specs:

1. 4-wheel drive, open differentials
2. Full independed suspension 
3. Brushless motor, 3S Li-Po, GeekServo
4. Custom wheel hubs with metal bearings
5. Carbon-fiber axes, metal U-joints
6. Transmission sits on the metal bearings
7. Positive caster angle, kingpin inclination, Ackerman
8. Anti-rowbar at the front axel
9. 98 mm RC wheels
10. understeering
11. Light tubular frame

A story behind the build.

Half a year ago I bought myself a Brushless setup adapted to Lego. It can provide a strong and stabled stream of power to my RC Lego cars. In two days after the motor arrived I build a first project with it to test its capabilities. 
Of course, this was a buggy! The main goal was achieved, I was able to test the new system and it performed greatly! Though I was not happy with the car itself. It had technical problems with both front and rear suspension, steering, overview and proportions... 

 

During the winter holidays I found a great set of RC wheels on AliExpress. They looked ten times better then all the other RC wheels I had, so I bought them and at once started a new 4-wheel drive project (which will be revealed in my next post). All I will say now, it has solid axle suspension and no planetary wheel hubs. So it appeared to be quite fast and somewhat unstable due to the soft suspension and high center of gravity. 
I decided to postpone that project and build a fast and more stable Baja truck with the front in-depended suspension and the solid rear axle. The fist prototype can be seen of the picture below (half-way dismantled) and it looks totally weird, especially the placement of the Brushless motor! With such layout I tried to load the rear wheels,
but did not succeeded. Despite a completely failed project, I get two important ideas from it. 
1) My custom wheel hubs allows to build an advanced front suspension and steering with king-pin inclination, positive caster angle and Ackerman geometry. Also I learned how to use a half stud off-set for the attachment points of the lower suspension arm.
2) The placement of the Brushless motor behind the rear axle greatly load the rear wheels.

I was not ready to give up, and decided go bigger next time and use my favourite 98 mm RC wheels. By widening the wheel base significantly I decided to solve the front wheel drive problem! It is well-know that steering rack is usually interact with a differential. Also the steering rack must be placed behind the front axle to achieve the Ackerman geometry. So I decided to move the front differential one stud to the front. The first sketch of the front axle looked very promising, so I decided to "copy" it for the rear axle. Well, to keep the same wheel base as at the front i needed to use the half-stud off set once again and this time on both lower and upper suspension arms. That is why the rear differential is covered with a mess of connectors and beams...

Solving all problems with axles, I connected them together via central driveshaft and had to decide how I should place the Brushless motor.
The problem is that the motor has a size of a PF XL motor, and so it requires a 24 to 24 tooth gear combination to connect it to the central driveshaft (and place the motor on a side or on top of the driveshaft). I was not happy with it because big gears would stick out from the flat bottom of the chassis. The brilliant idea came right in time! I decided to place the motor behind the rear axle and place the another driveshaft over the rear differential. This allowed me to use a 12 to 20 tooth gear combination! In addition it loaded the rear axle to achieve the understeering feature. 

It took me another day to finish up the first prototype, and I took the Buggy to an extensive driving tests. These tests took me over a month to complete, since they were interrupted with a melting of the snow. The following improvements were made (one by one):

1. Reinforcement of the upper suspension arm. First version of the front suspension was falling apart on each big bump.
2. Lowering of the suspension by one stud. This was made to increase the stability on the straight line and make the overview of the buggy closer to references. Also I widened the tubular frame for the same reason.
3. Playing with gear ratios: differential swap and swap from 12:20 to 16:16 gear combination in between the driveshafts.
4. Adding an Anti-rowbar with a carbon-fiber axe to the front axle. It was added to increase the stability on the fast corners.
5. Making 3.5 L axes to solve the problem of the front U-joints falling off from the differential.

 

 

The results.

A tremendous efforts had been applied to finish this Buggy. A lot of hard work, tricky decisions and big regrets... Does the Hornet worth it? - NO!
As a result I build myself a balanced RC car with a precise control, decent speed (about 15 km/h), enduring transmission and good-looking bodywork. But I would not suggest anyone to follow my way, because it will cost you a lot! If you want to get a good driving experience you would better buy an RC car! LOL.  

[gyenesvi]

Nice project, I like the suspension design, all the geometric details that has gone into it. Do I understand correctly that both the caster and the kingpin angle is achieved by half-stud offsets of the suspension arms? If I see properly, the lower arms are half a stud out (kingpin) and half a stud front (caster)?

I also like the bodywork, it has clean lines :) And nice idea with the motor placement!

[Daniel-99]

29 minutes ago, gyenesvi said:

Do I understand correctly that both the caster and the kingpin angle is achieved by half-stud offsets of the suspension arms? If I see properly, the lower arms are half a stud out (kingpin) and half a stud front (caster)?

As I saw in several projects one achieve a caster angle with lego hubs by moving lower suspension arm half a stud forward. This works with Lego hubs due to an admissible wobbling of plastic parts, but my custom hubs are designed for such off-set. And the kingpin is also achieved by a half stud off-set of the lower ball-joint. All together this allows me to achieve a good geometry easily. On the other hand, this wheels hubs are not than "universal" as Lego`s one. (Foe example, I would not use them in the solid axles).

29 minutes ago, gyenesvi said:

I also like the bodywork, it has clean lines :) And nice idea with the motor placement!

Thank you! 

[Krxlion]

I already saw your video and was waiting for some more details to be shown and here they are!
Great placement of the motor and it suits baja buggy models a lot! I like usage of sturdiest, new differential gears in both axles, are those from aliexpress or Lego? I would just cover the working gears using Technic panels, it shouldn't be that hard.

[Daniel-99]

4 hours ago, Krxlion said:

I already saw your video and was waiting for some more details to be shown and here they are!
Great placement of the motor and it suits baja buggy models a lot! I like usage of sturdiest, new differential gears in both axles, are those from aliexpress or Lego? I would just cover the working gears using Technic panels, it shouldn't be that hard.

Thanks! I used Lego`s differentials in the Hornet, but also I tested Chinese clones. They have too much friction, but the problem can be solved by using Lego`s 12 gears.

I will definitely protect the working gears in the near future.

[Daniel-99]

On 4/12/2023 at 5:30 PM, Krxlion said:

 I would just cover the working gears using Technic panels, it shouldn't be that hard.

Well, I made few attempts with lego panels but did not succeeded. The whole construction looked very bulky and it was hard to attach pannels to the bottom of the car since there is a half stud off-set under the differentials.. Also I did not liked how this panels stepped over the flat bottom...

That is why i used plastic bottle to make a custom protection! NO GLUE is used, panels hold on the car by the inner tension of a plastic (bottle has a natural curve, and I used it in a smart way).

As a result, bottom is almost flat, differentials are well-protected and no extra weight added! Who can do better? ;-)

 

[gyenesvi]

That is neat :) I use duct tape for similar purposes.

[Daniel-99]

I made a short introductory video !

 

[Krxlion]

Now this is what I am talking about! Great stuff Daniel! I really like the way you are aiming your models to have around 15km/h max speed which is honestly enough. I have found btw. one cool way to make our A2212 Brushless motors drive front and back axles at the same time without gearing. I might show it up in the weekend. I also really like the idea of driveable front axle with positive caster. This is something I am currently trying to achieve and I am looking for ideas. :) I do not know what yet what king-pin solution put into our models but I might get into it deeper. Ackerman geometry looks sick, the steering angle looks so great that I cannot even believe you manage to do front axle driveable. Your plastic bottle solution gets better, it is more clean, though I still I am not a fan of but hey as long as it does it job it is okay. One thing that In my mind could be done better is body and maybe cable management, but those are really not the things you should concern about. Great stuff and keep us posted on further projects or modification of the current model!

[gyenesvi]

That's some serious performance, and cool video! The more I think about it the more I get convinced that by swapping only the motor and drivetrain parts to metal ones and adding a few frames with ball bearing it is possible to build a durable high performance vehicle. And then all the rest can be genuine lego to do the suspension and body shaping as one wishes..

[Daniel-99]

On 4/21/2023 at 12:09 AM, Krxlion said:

Now this is what I am talking about! Great stuff Daniel! I really like the way you are aiming your models to have around 15km/h max speed which is honestly enough. I have found btw. one cool way to make our A2212 Brushless motors drive front and back axles at the same time without gearing. I might show it up in the weekend. I also really like the idea of driveable front axle with positive caster. This is something I am currently trying to achieve and I am looking for ideas. :) I do not know what yet what king-pin solution put into our models but I might get into it deeper. Ackerman geometry looks sick, the steering angle looks so great that I cannot even believe you manage to do front axle driveable. Your plastic bottle solution gets better, it is more clean, though I still I am not a fan of but hey as long as it does it job it is okay. One thing that In my mind could be done better is body and maybe cable management, but those are really not the things you should concern about. Great stuff and keep us posted on further projects or modification of the current model!

Thank you! I will look forward to see your ideas about the drivetrain!

With a FWD I cheated a lot by using custom hubs, which provide all suspension and steering geometry. Though I have another project in mind with independent suspension and planetary hubs, and there will be no way for me to cheat ;-)

I understand why you would prefer not to use any custom parts, and I try to keep my solutions Lego-ish as well, but in some situation I have to use custom parts due to the practical purposes.

I will definitely keep my Hornet in the garage for the future improvements. I agree, that both cable management and bodywork can be done better and I will work on in! 

 

18 hours ago, gyenesvi said:

That's some serious performance, and cool video! The more I think about it the more I get convinced that by swapping only the motor and drivetrain parts to metal ones and adding a few frames with ball bearing it is possible to build a durable high performance vehicle. And then all the rest can be genuine lego to do the suspension and body shaping as one wishes..

Thank you! Exactly! Though they wont be able to compete with RC cars both in speed and durability. If I would need the driving experience only, I would have swapped from Lego to RC. But I really enjoy the development process, so I use Lego bricks but add some necessarily 3-d party components to make my cars alive.

Edited April 22, 2023 by Daniel-99

[gyenesvi]

I started looking at RC components and trying to find a good transmitter that is a bit better than the most basic ones, with extra channels to control some more advanced stuff as well. I'm kind of converging on FlySky FS-GT5, and I saw your image in this thread @Daniel-99. Is that what you are using? If so, how is it for you?

[Krxlion]

8 minutes ago, gyenesvi said:

I started looking at RC components and trying to find a good transmitter that is a bit better than the most basic ones, with extra channels to control some more advanced stuff as well. I'm kind of converging on FlySky FS-GT5, and I saw your image in this thread @Daniel-99. Is that what you are using? If so, how is it for you?

I have no experience with FlySky FS-GT5, but the DumboRC is actually pretty good starting point (be sure to go check if it is dumborc x6fg - it comes with gyro receiver that will help you stabilise your model). The receiver also features 6-channels and in my case I use one of those channels to control gearbox with another geek-servo.

[vergogneless]

I confirm that the Dumbo RC is definitely up to the task. In fact, I can highly recommend the latest model X6PM-350 with the X6FG receiver. It's smaller and more compact (about half the size), lighter, and has a better finishing quality.

The fact that it's really small might bother some people, but it becomes incredibly portable, and it's a true pleasure to take it everywhere. The feeling is excellent, and I wouldn't go back to the old one for anything; it's a real evolution.

It has exactly the same features as its big sister, with the only difference being that it offers "only" 350 meters of range (instead of 500+).

Regarding the receivers, always go for the X6 "FG" for the gyro, as specified by Krxlion. You have the choice between a standard version or a mini version. I use both, and the mini can be useful for very small models, but I don't think it's necessary to insist on using the mini version when the standard one works just fine.

It's important to note that the mini version has a small antenna, and I sometimes experience signal loss beyond 100 meters because this antenna is inside the car body.

For the gyro, there are a few procedures to follow for pairing, activating the gyro, and especially changing its direction, but you'll figure that out in due time.

The receiver must be securely fixed for the gyro to function properly. It should also be as straight as possible (parallel or perpendicular to the chassis, it doesn't matter), with the cables facing upward.

 

Glad you're joining the brushless club !

 

EDIT: 

Edited July 1, 2023 by vergogneless

[gyenesvi]

On 6/30/2023 at 11:40 PM, Krxlion said:

I have no experience with FlySky FS-GT5, but the DumboRC is actually pretty good starting point (be sure to go check if it is dumborc x6fg - it comes with gyro receiver that will help you stabilise your model). The receiver also features 6-channels and in my case I use one of those channels to control gearbox with another geek-servo.

On 7/1/2023 at 8:09 AM, vergogneless said:

I confirm that the Dumbo RC is definitely up to the task. In fact, I can highly recommend the latest model X6PM-350 with the X6FG receiver. It's smaller and more compact (about half the size), lighter, and has a better finishing quality.

Thanks for the info guys! I did look at the DumboRC as well, indeed, that's also a good looking cheaper option, though the ones I found here in stores does not have the X6FG receiver, only X6F. The gyro function definitely seems useful, I have seen videos of those. That mini DumboRC also looks nice, but seems to have less output channels / controls.

The FlySky FS-GT5 is somewhat more expensive mid-range one I guess, it does have the gyro, and it has a ton of detailed settings (for example counter steering gains, 4-wheel steering modes, and a lot more). Furthermore, I like that it has two turnable knobs on top that don't return to center (like that bigger DumboRC on the picture), I want to use those for rear steering.

On 7/1/2023 at 8:09 AM, vergogneless said:

Glad you're joining the brushless club !

I am not yet ready to go brushless, I just want to control the regular brushed lego DC motors, along with GeekServos. I want to use multiple GeekServos for steering / gearbox / diff-locking, in crawlers. Going brushless for faster buggies will be the next step. For that I'd prefer to have a way to mount a brushless motor properly. The ideal would be if the inside of an L motor could be swapped out to a brushless one. Has anyone seen that done? (I did find a video doing that with an M motor though).

[Daniel-99]

2 hours ago, gyenesvi said:

Thanks for the info guys! I did look at the DumboRC as well, indeed, that's also a good looking cheaper option, though the ones I found here in stores does not have the X6FG receiver, only X6F. The gyro function definitely seems useful, I have seen videos of those. That mini DumboRC also looks nice, but seems to have less output channels / controls.

The FlySky FS-GT5 is somewhat more expensive mid-range one I guess, it does have the gyro, and it has a ton of detailed settings (for example counter steering gains, 4-wheel steering modes, and a lot more). Furthermore, I like that it has two turnable knobs on top that don't return to center (like that bigger DumboRC on the picture), I want to use those for rear steering.

I am not yet ready to go brushless, I just want to control the regular brushed lego DC motors, along with GeekServos. I want to use multiple GeekServos for steering / gearbox / diff-locking, in crawlers. Going brushless for faster buggies will be the next step. For that I'd prefer to have a way to mount a brushless motor properly. The ideal would be if the inside of an L motor could be swapped out to a brushless one. Has anyone seen that done? (I did find a video doing that with an M motor though).

Hi! I am using  FlySky FS-GT5. It has a Gyro and CRAWL mode for 4-wheel steering (it uses channel 3 for second servo). In addition, one can set the center position and the maximal steering angle at each channel separately (which is quite handy for building SUVs with rear steering wheels). Also It is small enough for me to use it with one hand. On my opinion, this transmitter fit well to Lego. 

[vergogneless]

@gyenesvi 

The X6PM version has the same functions as its big sister (literally identical).

But I understand that you need even more specific functions, in that case, upgrading to the next range is the best thing to do.

I'm excited to see what you're going to do with all of this!

[Lixander]

Nice model!, you inspired me to start another project.

And with those centered pieces (the ” axle and pin connector perpendicular double”), I could obtain the closest position a Lego car can have for its suspension arms, which, if I manage to do this well until the end and to actually test-build it, it will have a extremely good suspension.

Edited July 18, 2023 by Lixander