[MOC] Blue Mamba fast off-roader

[Daniel-99]

Hey, Eurobricks!

In this post I want to tell you about one of my latest MOCs, called Blue Mamba. It was made for outdoor King of the Hammers competition. Unlikely I was not able to participate in the competition this year, but I am not disappointed because it is very fun to drive this car.

 

Main features

1. 4-wheel drive

2. In-axe motors (one PF L-motor for each wheel)

3. 2 x Buwizz 3.0 units for power

4. RC tires 97 mm

 

 

 

Bodywork

The race vehicles used at the King of the Hammers are known as Ultra 4 vehicles. This Ultra4 class is unlimited 4400, and every vehicle is custom fabricated by each team. Most of the vehicle made with metal tubular frame and plastic body panels.

I tried to replicate the bodywork to match the real prototypes. Black pieces imitate a tubular frame of the car. Side panels and the hood are the structural elements of the chassis. The total weight of the car is about 1,280 grams.

Half of the weight (4x PF L-motors) is located in axes, this is not good for the dynamics of the car at big speeds, but helps a lot in trial. Steering motor and Buwizz units are located in the cockpit. It is possible to lower them, so there is a reason to revisit the chassis once again.

 

Suspension

The rial race combines desert racing and rock crawling. So the Lego version of the race combines high-speed and trial sections. For good performance in trial Blue Mamba has a free articulation of a rear axe. The string are placed on the middle link, so rear axe can suspend jumps. Front axe has a limited articulation for a good control at high speed.

 

Drivetrian

Ultra4 vehicles has both powerful engine and the gearbox which allows to drive fast on straight lines and slow on rock-crawling segments. But Lego gearboxes has a significant disadvantage - a huge loss of torque. So I decide to place the motors in axes. This gives nearly zero losses, but has it`s own disadvantage: an extremal load on the CV joints which connects front motors to the wheel hubs. There is no way to deal with in without widening the wheel base and adding the portal reduction.. I hope some day Lego will make a new hubs that connects to new CV joints (without planetary reduction).

In-axe motor placement provides some restrictions to the size of axes. I tried to maximize the ground clearance. Big wheels partially solve the problem. The resulting ground clearance in not big as one the cars with portal hubs has, but it is comparable to the ground clearance of cars with front independent suspension (there were several competitors with such configuration).

Also it is worth noting that front and rear axes does not stick out from the side profile of the wheels, so Blue Mamba has great approach and decent angles.

 

Control and Power

The car is powered by two Buwizz 3.0 units. Powerful lego cars usually have a big problem. They can not go on a full speed for a continuous time since the driving motors consume a lot of power. I build many cars powered Buwizz 3.0 units. And I noticed that 2 Buwizz motors or 4 PF L-motors consume more power then the battery can give   (in continuous drive). A good example of a car with 4 L-motors and 1 Buwizz unit is my Jeep Wrangler.

To deal this problem, I places two units in the Blue Mamba. This doubles the travel range of the car and allows to drive Blue Mamba on full speed  during the race. But multiple tests show that 1 Buwizz unit is enough for this car, since there are no losses in the transmission (in the first video car is powered by a single Buwizz unit).

For steering a C+ L-motor is used. It is placed in a cockpit in between Buwizz units. Small scrab-radius, positive caster angle and proportional steering provide a good control of a car.

 

Summary

The competition has passed, and I there is a video on youtube:

This allows me to compare my car with the other competitor cars. I would not win the race but perform good. I will look for the next King of the Hammers competition and prepare Blue Mamba to it.

The following changes will be made:

1. Buwizz units will be replaced with RC electrics
2. The cockpit will be lowered for few studs
3. The wheel base will be lengthened for 4-6 studs (to prevent the car from flips at high stairs in trial)

I made a 3D model of Blue Mamba, but I have no motivation for making PDF instructions since Rebrickable does not work for me nowadays... Hope everything will be changed soon! Now we can only wait and play Lego!

Edited April 27, 2022 by Daniel-99

[Alex Ilea]

I like the drive train and suspension a lot!

[gyenesvi]

I like the massive suspension on this one, and the in-axle motors, I want to try that once, though it needs a lot of space. Though I wonder whether it really needs to be raised that much, the real car seems to sit much lower. I mean I get that you want to maximize suspension travel, but does it actually use all that much? The bodywork is also a good start, I like the tubular/panel mix, but maybe missing some bits in the front?

[Daniel-99]

On 5/2/2022 at 4:39 PM, gyenesvi said:

I like the massive suspension on this one, and the in-axle motors, I want to try that once, though it needs a lot of space. Though I wonder whether it really needs to be raised that much, the real car seems to sit much lower. I mean I get that you want to maximize suspension travel, but does it actually use all that much? The bodywork is also a good start, I like the tubular/panel mix, but maybe missing some bits in the front?

Thank you! Honestly, I was waiting for your reply! I agree, that the whole car can be lowered down (see the very end of my summary). I am working on it right now.