PHANTOM Baja Truck [MOC]

[Daniel-99]

Hello everyone.

This is a story of my mid-scale RC baja truck called “Phantom”.

 

The beginning.

I always had a strong desire to go fast. For that reason I made my Red Roadster powered by Buwizz motors (See my Profile for dedicated post). But this sport car has one significant disadvantage - it requires a very smooth road! So I decided to build a trophy truck.

 

 

 

 

 

 

 

 

 

I learned a lot about trophy trucks made with Lego. Best of them had 2 Buggy motors for propulsion with a direct connection to the rear wheels. So I decided to build myself a similar setup. First trophy truck I designed in big scale (~1:10) but Buwizz motors were struggling with a load from big wheels (and that is not a problem of motors, but a problem of construction). So I made a portal reduction and the problem was solved.

 

After that I build an ultimate dune Buggy “Dragonfly” with independent suspension driven by couple of Buwizz motors. The result was great, Buwizz motors allowed to drive it very fast on 85 mm wheels. So I decided to build a trophy truck with them. Such wheel size is the smallest one which could be used outdoors. Smaller wheels does not provide enough of ground clearance to go full speed on bumpy terrain.

 

Photos.

 

Front axle.

I started the build with the front suspension. A technical task was the following:

  - to use big Lego wheel hubs

  - double steering rack

  - positive caster angle

  - ridged suspension arms

I took many ideas from the front suspension of my Dune buggy and tried to make it smaller. Dune buggy used 9,5 L shocks so I decided to change them to 7 L shocks. Also I was able to avoid ball connections, since they struggle a lot at bumpy roads. Here is the result.

The steering motors should get connected to the vertical black axe (on the first picture). The key idea was to place steering arms horizontally and in a slight diagonal way. Such placement caused some friction in the steering system, but from the other hand it reduced the wobbling to ZERO! Also there is a 3 studs distance from the connection of steering arms to the wheel hub and the pivot point of the hub (see picture 2). It reduces the maximal steering angle, but strengthen the steering system and make the control smoother!

 

Rear axle.

A technical task was the following:

  - direct mounting of Buwizz motors to the rear axle

  - Long suspension arms and long travel

  - Suspension with progressive hardness

I decided to make it simple without any articulation, though there was some provided by bending of plastic parts.

There are two sets of springs used. Small vibrations of the rear axle get absorbed by a soft 9.5 springs, while hard bumps compress the rear axle stronger, so the set of 7 L springs does their job. Finally, there is a couple of Lego rubber elements which play a role of fenders. So there are three stages of compression.

 

 

 

 

First stage. Soft settings.

 

 

 

 

 

 

 

 

 

 

 

Second stage. Hard settings.

 

 

 

 

 

 

 

 

 

 

 

Third stage. Rear axle touches the frame.

 

 

 

 

 

 

 

 

 

Frame of the car and bodywork.

A technical task was the following:

  - two layers of frame

  - use the roof of the car as structural element

  - minimalistic bodywork

The space frame of the car consist of two layers. Roof of the car tighten the upper layer in order to bear the load from the rear springs. The middle compartment is dedicated to power sources. The "new" cross-beams (15L and 11L) were very helped a lot.

The bodywork is made with several panels which can be easily detached for servicing the electronics.

 

Electronics.

On photos above you can see a custom Lego-compatible RC unit equipped with two high power cells 18650. It provides more power comparing to Buwizz 2.0, but it is not enough for two Buwizz motors. It get overheated quite fast (5-10 mins). 

One may ask me, why I use it. Actually, the first version of the Phantom was powered by two Buwizz 3.0 units, which provided a plenty of power to the car. But I managed to drown the car at first outdoor driving test! So I bought replacement for them since there was no possibility to purchase new Buwizz units in Russia. Here is the video of an accident: 

This month I bought a different Lego-compatible RC electronics from a Russian AFOL, it is called "Wixy". It plays a role of the controller for RC motors and allows to power my cars with 3S Lipos! WIth 3S Lipo I forgot about lack of power and was able to ride the Phantom for miles and miles...

 

Conclusion.

The car Is made for outdoor driving. It has a decent speed and a good control. Though there are several weak places of Phantom which can not be fixed with plastic Lego parts. The dust is very annoying, especially on county roads! It fills all holes of the car, most importantly plastic wheel hubs. I destroyed all the wheel hubs I own and there is no way of fixing the problem... Also the car has slight problems with ground clearance - it is acceptable for city roads but too small for stony surfaces. Finally, the Truck can not go trough the tall grass with such small wheels and RWD. 

 

 

[2GodBDGlory]

Nice work! You made a good presentation, and have some well-thought-out engineering in there. The dual-stage rear suspension is quite cool!

I'm also intrigued with that control hub you're using. You said that it uses two 18650 cells, but also that it can be a 3S battery. Those can't be true at the same time (I don't think), so are those different options? Where could I learn more about it?

[Daniel-99]

13 hours ago, 2GodBDGlory said:

Nice work! You made a good presentation, and have some well-thought-out engineering in there. The dual-stage rear suspension is quite cool!

I'm also intrigued with that control hub you're using. You said that it uses two 18650 cells, but also that it can be a 3S battery. Those can't be true at the same time (I don't think), so are those different options? Where could I learn more about it?

Thank you!

Speaking about control hubs... Well, after my Buwizz units drowned I bought myself TWO different Lego-compatible systems from Russian AFOLs.

1. "Leshy 2" - the one you can see installed in the car. It is an analog of Buwizz 2.0 with inverter power supply from two 18650 sells. If one installs high power cells in it, it could convert them into high voltage output.
2. "Wixy" - the one is not widely presented in my cars yet. It is a custom RC controller for PF motors (analog of a controller for RC models), so it can be powered by any RC power supply, in particular with 3S Lipo. With 3S Lipo the whole system became an analog of Buwizz 3.0 but way more powerful (it can supply up to 10 Buggy motors if you get enough controllers).

Both systems has it`s strong and weak sides.

 

Speaking about "Leshy 2", strong sides:

1. electronics is hidden inside;
2. you can change the voltage of output from 8 to 12 volts;
3. easy change of batteries and easy to find new one (18650 cells);
4. It has more power comparing to Buwizz 2.0;
5. Precise physical control with RC transmitter;
6. Low price ("Leshy 2" + batteries + RC transmitter (cheap) ~ buwizz 2.0).
7. Great control range (over 50 m);
8. On-off switch;
9. PF outputs and RC outputs in one unit;
10. special controller for lights (see the video with my Phantom);

"Leshy 2", weak sides:

1. Big size, comparing to Buwizz units (the size of big PF battery box);
2. It is not as powerfull as 3S Lipo, and get overheated after 5-10 mins of heavy load;
3. Batteries are heavy and can not be 100% fixed inside the unit, so it is not appropriate for fast driving on bumpy roads...

 

Speaking about "Wixy"... It is a small white piece which has PF contacts both on top and bottom and an RC connector on one side. You need to connect the unit to a PF power source (to the bottom connector), plug motors to the top connector and connect RC output to the receiver (to the channel which is going to control connected motors). "Wixy" allows to transmit power from a power source to connected motors form a signal of receiver. It provides a proportional control as well as "Leshy 2".

"Wixy", strong sides:

1. All the wirings could be distributed in various pars of the car, so you do not need a big amount of space incide;
2. you can power the car with any RC power source (a special cable from RC battery output to PF connectors included);
3. easy change of batteries and easy to find new one;
4. NO LIMITATIONS IN POWER (for each Buggy motor you need one "Wixy" controller which could be connected to one channel);
5. Precise physical control with RC transmitter;
6. Low price (2 x "Wixy" + battery box + all necessarily cables + mid-price RC transmitter ~ Buwizz 3.0).
7. Great control range (over 50 m);
8. You can use both PF and RC outputs.

 

"Wixy", weak sides:

1. A "slight" mess with wires;
2. nothing else... 

 

 

 

 

 

 

 

 

Hope my comment was helpful to you! 

P.S. Next week I will snow you my new car with "Wixy" controllers!

 

[gyenesvi]

Nice truck and presentation, I like how clean and simple the whole frame is! Though the drivetrain and suspension is also somewhat simpler, and it helps keep things clean :) I also like the use of the Geekservo for steering, I'd like to try that myself. Is that strong enough to steer a model of this size on rough terrain as well? Does it also steer comfortably when the model is stationary?

That Wixy controller also sounds interesting, as I'm looking for something simple that could be used to control that Geekservo. Is that little white connector thing and RC to PF plug converter? Can that be used to connect the Geekservo to a PF reveiver or a Buwizz for example? Or does that need some other control unit to actually work? It will be helpful if you present the whole system with Wixy controllers next week! Thanks!

[Daniel-99]

1 hour ago, gyenesvi said:

Nice truck and presentation, I like how clean and simple the whole frame is! Though the drivetrain and suspension is also somewhat simpler, and it helps keep things clean :) I also like the use of the Geekservo for steering, I'd like to try that myself. Is that strong enough to steer a model of this size on rough terrain as well? Does it also steer comfortably when the model is stationary?

That Wixy controller also sounds interesting, as I'm looking for something simple that could be used to control that Geekservo. Is that little white connector thing and RC to PF plug converter? Can that be used to connect the Geekservo to a PF reveiver or a Buwizz for example? Or does that need some other control unit to actually work? It will be helpful if you present the whole system with Wixy controllers next week! Thanks!

Thank you! I am trying to get to the "perfection" in the definition your have on your Eurobricks page ;-) 

Speaking about GeekServo, it is strong enough to steer this 85 mm wheels both in stationary position and on a bumpy road on full speed. Though It is not that fast, comparing to C+ L-motor, and nearly not as powerful (I will present you another car next week with wider and bigger wheels there Geek Servo is not enough...  ). So it`s usage in fast car is quite arguable, but after many tests I could say, that It really works for Phantom. On high speed RWD car needs a smooth control without fast oversteering (otherwise it is easy to loose the control!).

Also I tested GeekServos in my trial truck (which I am going to present a few weeks later), I increased the steering arm so GeekServo had enough power to steer 105 mm  fat RC tires. Such solution reduced the speed of the steering process, but it could be overplayed with two steering axles, as I did. 

Fast and big Lego cars requires coupled GeekServos per steering axle... Probably I will build such project a autumn.

P.S. I see you have an interest to Wixy setup... I will try to make a presentation next week, so do not miss it!

[2GodBDGlory]

Thanks for the extra detail, and I'll look forward to seeing your more complete post of those electronics! You Russians sure seem to make a lot of high-powered Lego RC systems, between these two and the older RCBricks (or something). I don't suppose either of those are really available for sale in the West?

[Daniel-99]

On 8/13/2022 at 7:25 AM, 2GodBDGlory said:

You Russians sure seem to make a lot of high-powered Lego RC systems, between these two and the older RCBricks (or something). I don't suppose either of those are really available for sale in the West?

Yes, there was an RCBricks in the older days and many Lego technic builders in Russia use RC units and controllers to power their cars, since they are cheaper and more affordable in Russia, especially nowadays. The major problem is that their developers can not afford to make a real business of their products yet. All the amazing units and controllers we have for now being made by a single man with a great amount of enthusiasm... I hope we will get ourself a new company such as Buwizz in Russia in the future, but there are no plans about it yet. So there are no products available for sale in the West these days .

All I know is that SBrick could be powered by 3S Lipo, if you make a custom connector.