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Posted (edited)

I started this project because I wanted to share my experiences building various offroad models over the last decade.

This topic is meant to guide the builders with comparisments, suggestion and best building practices, It is however not a place to find already finished and perfected designs - that's up to you.

Various aspects of the design of the vehicles will be split into several subgroups and explained in details.

1. Number of wheels

First thing we need to know is how many wheels our design will have.

Most common setups are as following:

4x4 Setup

Advantages:

1. The simplest and most widely setup

2. Having only 4 wheels means lower weight and higher performance

3. Higher manoeuverability

4. Simple suspension and driveline design

Disadvantages:

1. With only 4 wheels the suspension has to be designed to be as flexible as possible to get the most out of the wheels

2. In a case of a mechanical failure of a single wheel, the whole model's performance is greatly affected

 

6x6 Setup with double rear axles

Advantages:

1. Two rear axle provide more traction area, especially when going uphill

2. Usually 6x6 vehicles are longer than 4x4 and therefore less likely to tip over

3. Since the front and second axle are usually closer than in 4x4 setup, there is less ground clearance needed between them

4. Greater redundancy in a case of a mechanical failure

Disadvantages:

1. Lower manoeuverability due to a longer wheelbase even with rear wheel steering

2. More complex driveline and suspension design is required

 

8x8 or more wheels setup

Advantages:

1. Having 8 or more allows for much greater traction area

2. Ability to drive over ditches

3. Because wheels are usually much closer there is much less chances of getting stuck on top of an obstacle

4. Excellent redundancy in a case of a mechanical failure

5. Better weight distribution

6. Less suspension travel required per each wheel as with 4x4 or 6x6 and hence better stability

Disadvantages:

1. Lower manoeuverability even with rear wheel steering

2. Powering 8 or more requires a very complex driveline

3. Depending on a driveline, combined torque required for powering all 8 wheels can destroy gears if a single wheel gets stuck

 

2. Type of wheels and tyres

Now that we decided on how many wheels we want for our offroad beast, we have to look into what type of tyres and wheels we want to use. I will hereby cover only the bigger types of tyres and wheels.

1. 94.8x44R

54120.png

Advantages:

1. Low weight

2. Good thread design

3. Low rolling resistance

Disadvantages:

1. Low traction, these tyres are prone to slip on the rim at high loads

2. Due to its rounded shape the tyres tend to slide off obstacles when crawling over them

 

2. 94.3x38R

92912.png

Advantages:

1. Low weight

2. Medium traction

3. Low rolling resistance

4. Realistic design and proportions

Disadvantages:

1. Shallow thread pattern

2. These tyres are very hard and don't adjust to the terrain

 

3. 107x44R

23798.png

Advantages:

1. Low weight

2. Medium traction

3. Very deep thread

4. Currently largest tyres by diameter

Disadvantages:

1. High rolling restistance and vibrations due to the thread pattern

2. These tyres are a bit hard and don't adjust to the terrain

 

4. Power Puller tyres

22969c01.png

Advantages:

1. High traction

2. Good thread

3. Largest Lego tyres ever produced

4. Deep wheel offset

Disadvantages:

1. High weight

2. Hard to use, they require complex hub assemblies

3. Very rare and expensive

 

5. Outdoor challenger wheels

47349c05.png

Advantages:

1. Very high traction

2. Very good thread pattern

3. Deep wheel offset

4. Over 7 studs of space inside the wheel

Disadvantages:

1. High weight

2. Hard to attach to the standard axles

3. They require a lot of torque to use them at their full potential.

 

6. Tumbler wheels

56908c03.png

Advantages:

1. Low weight

2. High traction

3. Very flexible

Disadvantages:

1. Low thread pattern

2. Small size

3. Expensive

 

For the 94.8x44R. 94.3x38R and 107x44R tyres we have a choice of two wheels:

1. Racing wheel large

15038.png

Advantages:

1. Good mounting option with axlehole and pinhole

2. Available in multiple colours

3. Cheap

Disadvantages:

1. No inside wheel offset means steering pivot point can't be placed inside the wheel.

 

1. Futuristic wheel

32077.png

Advantages:

1. Deep wheel offset allows us to place steering pivot point inside or closer to the wheel than racing wheel large

2. Slightly larger wheel size stops the 94.8x44R tyre from slipping on the rim

Disadvantages:

1. Limited mounting options, with only one axlehole

2. Hard to find

 

3. Hubs

Now that we have our wheels and tyres we need a way to mount and power them. Here are the most common currently available options:

1. New standard ungeared CV hubs

23801c01.png11950c01.png

These hubs are usually driven by the CV joint counterpart which pops inside

32494.png

Advantages:

1. Low steering pivot offset - usually at the edge of the tyre:

Normal%20hub%20pivot%20point.png

2. Firm wheel mounting

3. Readily available, easy to use and to build on.

Disadvantages:

1. Low operating angle - the CV joint can operate to a maximum of about 30 degrees, which limits steering angle.

2. Very low torque transfer - the CV joints are prone to deforming and popping out even with low torque applies to them

3. Low ground clearance

 

2. Old ungeared CV hubs

x873c01.png

Advantages:

1. Low steering pivot offset - usually at the edge of the tyre

2. Firm wheel mounting

3. Better ground clearance than newer hubs

Disadvantages:

1. Very low operating angle - the CV joint can operate to a maximum of about 25 degrees, which limits steering angle.

2. Very low torque transfer - the CV joints are prone to deforming and popping out even with low torque applies to them

3. Hard to find and expensive

4. No other mounting points than 4 ball joints

 

3. Built cardan ungeared hubs

U%20joint%20built%20hub.png

Example of a hub using a cardan joint to directly transfer the power to the wheel

Advantages:

1. Low steering pivot offset - usually at the edge of the tyre

2. Easy to build

3. Can transfer higher torque than a CV joint

4. Higher steering angle

Disadvantages:

1. Mounting relies only on the axle and is not as firm as standard hubs

2. Not capable of transferring high torque to the wheels

3. Low ground clearance

 

4. Standard portal hubs

92908c01.png

Advantages:

1. Easy to use and to build on.

2. Can transfer very high torque to the wheels when using 8z and 24Z gear combination

3. High steering angle

4. High ground clearance

5. Firm wheel mounting

Disadvantages:

1. Very high steering pivot offset - requires stronger steering mechanisms and more fender space for wheel to swing

Portal%20hub%20pivot%20point.png

 

5. Built portal hubs

640x632.jpg

 

Advantages:

1. Easy to build.

2. Can transfer very high torque to the wheels when using 8z and 24Z gear combination

3. High steering angle

4. Higher ground clearance than standard portal hubs

5. Low steering pivot offset when using futuristic wheels

Disadvantages:

1. Wheels are mounted and held only by one axle, not as firm as standard hubs

2. Hub relies on friction of the components to keep it together, which can slide apart after prolonged use

 

6. Built planetary hub

640x693.jpg

Advantages:

1. Highest gear ratio of all other hubs, 1:4

2. Firm wheel mounting when using futuristic of power puller wheels

3. High steering angle

4. Lower steering offset than standard portal hubs

Disadvantages:

1. Requires old turntable, futuristic or power puller wheels for best results - all are hard to find

2. High number of moving gears

3. Least efficient due to the high friction caused by the large surface contact area and number of moving gears

 

4. Suspension

Suspension is the mechanism that will keep our model's wheels in contact to the ground and will be supporting most of its weight.

Most of the designs cover 4x4's

Following factors determine the type of suspension system we will use:

1. Weight of the model - The heavier the model, the stronger the suspension components have to be

2. Speed - Faster models require more responsive suspension systems with low unsprung weight

3. Flexibility - The higher the obstacles you want to climb over the more flex and/or wheel travel suspension has to provide

 

1. No suspension

I have yet to see and offroad vehicle without any type of suspension (except for maybe 42070,  42081 and 42082), but I will list my opinion regardless:

Advantages:

1. Simple design - having no suspension simplifies our design...and that's about it

Disadvantages:

1. No flex over terrain means, there are only 3 wheels at once touching the ground

2. Low stability

3. Poor weight distribution

4. No shock absorption at high speeds

 

2. Pendular suspension

 

640x416.jpg

This is the simplest suspension you can put on your vehicle. It basically means one or more of your axles are free to swing about.

When using this suspension I suggest using the small turntable where drive axle enters the axle. This will keep the drive axle from carrying the weight of the model, which causes unnecessary friction.

42030 is a typical example of this suspension system.

Advantages:

1. Simple, robust design

2. Using this suspension on both axles can give the model very high flexibility

3. If there are no springs used, the model can have perfect weight distribution on left and right wheel

Disadvantages:

1. Large unsprung weight, poor responsivness at high speeds

2. No shock absorption means this suspension is not suitable for high speeds

2. When using on one axle, the stability of the whole model relies on the unsuspended axle.

3. When using pendular suspension on both axles springs or a transfer mechanism are required to keep the model upright

 

3. Single torque tube suspension

640x407.jpg

This suspension became available with the release of the 8110 Unimog. Best examples of this suspension are 8110, 9398 and 41999.

It is the simplest suspension which also allows for vertical suspension movement.

Advantages:

1. Simple, robust design

2. Universal joints can be placed inside the ball joint, allowing power to be transferred to the axle

3. Easy to implement

Disadvantages:

1. Large unsprung weight, poor responsivness at high speeds

2. Axle requires a some kind of a linkage system to keep it cenetred (panhard or parallel links as seen above).

3. Using this suspension on the front axle usually results in negative caster angle which causes higher rolling resistance

4. When used on rear drive axle, the suspension has the tendency to cause oscillate, especially with soft suspension and high power

4. Hard to connect springs to the chassis

 

4. Double torque tube suspension

This is an evolution of the single torque tube suspension, which uses two ball joints to drive each wheel side respectively.

It is my own original idea.

640x394.jpg

 

Advantages:

1. Simple, robust design

2. Universal joints can be placed inside the ball joint, allowing power to be transferred to the axle

3. Easy to implement

4. Self-cenetring, since axles are connected in the center there is no need for linkages to center it

5. Can carry power to each wheel side independently

6. Drive torque compensation

Disadvantages:

1. Large unsprung weight, poor responsivness at high speeds

2. Using this suspension on the front axle usually results in negative caster angle which causes higher rolling resistance

3. When used on rear drive axle, the suspension has the tendency to cause oscillate, especially with soft suspension and high power

4. Hard to connect springs to the chassis

 

5. Parallel floating axle

640x352.jpg

This suspension uses linkages which keep the axle parallel to the chassis of the model.

For best functionality and reliability the lengths of all links and that of the double cardan joint should be equal. Also all the linkages and drive axles should be parallel.

Advantages:

1. Keeping the axle parallel to the chassis reduces the oscillations effect

2. Better responsivness compared to the torque tubes

3. Neutral caster angle when used on front axles.

4. Self cenetring when using A arm as upper link or 4 link setup

5. Can be configured to carry power to each wheel side independently

6. If configured to carry power to each wheel side independently the drive torque can be compensated.

7. Easy to connect spring to the chassis

Disadvantages:

1. High unsprung weight, less responsive at high speeds

2. Increased mechanical complexity, double cardan joints required to carry the power to the axle

 

6. Half axle independent suspension

This is the simplest independent suspension you can build. Best example of such suspension are Tatra and Pinzgauer trucks.

640x281.jpg

 

Advantages:

1. Independent suspension with low unspring weight, suitable for high speed

2. Robust design with low number of moving parts

3. Easy to connect spring to the chassis

Disadvantages:

1. Changes of the caster angle as the wheels travel up and down

2. Hard to implement a drive system that does not carry the weight of the vehicle

3. Hard to implement steering system

4. Wheels tend to drag sideways on the ground when suspension travels up and down, reducing efficiency

 

7. Trailing arm parallel independent suspension

640x305.jpg

Personally I have not used this suspension yet, but I did use a normal trailing arm suspension which does not keep the hubs parallel.

Normal trailing arm suspension which does not keep the hubs parallel acts similarly to torque tube suspension.

For the prallel version of the trailing suspension I imagine the following:

Advantages:

1. Independent suspension with low unspring weight, suitable for high speed

2. Robust design with low number of moving parts

3. Long links allow for high suspension travel

4. Very easy to connect spring to the chassis

5. Can be configured to carry power to each wheel side independently

Disadvantages:

1. Hard to keep the wheels from sagging under the weight of the model.

2. Difficult to transfer power to the wheels

 

8. Double wishbone suspension

640x327.jpg

This suspension uses two A-shaped arms to keep the wheel hubs in place. As of late it's my favourite suspension system due to:

Advantages:

1. Independent suspension with low unspring weight, suitable for high speed

2. Very customizable design with lots of adjustable characteristics (suspension arm lengths, caster angle, camber angle, steering geometries)

3. When build correctly it is far more robust than live axle suspension

4. Increased ground clearance compared to live axle suspension, especially when used with portal hubs

5. Can be configured to carry power to each wheel side independently

6. Extremely easy mounting of springs

7. Very stable compared to live axles

8. Frame holding the suspension can be part of the chassis, therebye lowering the center of gravity

Disadvantages:

1. More moving parts as live axle suspension, increased mechanical complexity

2. Limited wheel travel - Lego wishbones allow a max. of around 25 degrees of suspension angle

 

9. Multi-link suspension

To be updated when I build my first multi-link offroad suspension. I can assume the following characteristics:

1. Independent suspension with low unspuing weight, suitable for high speed

2. Extremely customizable design with lots of adjustable charactersitics (suspension arm lengths, caster angle, camber angle, steering geometries, virtual pivot point)

3. Large steering pivot point compensation

4. Increased ground clearance compared to live axle suspension, especially when used with portal hubs

5. Can be configured to carry power to each wheel side independently

6. Very stable compared to live axles

7. Frame holding the suspension can be part of the chassis, thereby lowering the center of gravity

Disadvantages:

1. Very high amount of moving parts, increased mechanical complexity

2. Limited wheel travel - Lego wishbones allow a max. of around 25 degrees of suspension angle

3. Hard to connect springs to the chassis

 

10. Spring types

Listed below are the most common types of springs available:

6.5L Soft shock absorber

731c06.png

Advantages:

1. Small, easy to implement

Disadvantages:

1. One stud of suspension travel

2. Low spring rate, can't support heavy models

 

6.5L Hard shock absorber

731c04.png

1. Small, easy to implement

2. High spring rate, can support heavy models

Disadvantages:

1. One stud of suspension travel

 

9L soft shock absorber

When using 9L shock absorbers I suggest you do not use the default offset upper attachment point, but use an in-line attachment point instead.

This will reduce the friction and allow for better high speed performance

Example:

640x1413.jpg

2909c03.png
Advantages:

1. Two studs of suspension travel

2. More attachment possibilities than 6.5 L shock absorber

Disadvantages:

1. Default attachment points create friction

2. Low spring rate, can't support heavy models

 

9L hard shock absorber

95292c01.png

Advantages:

1. Two studs of suspension travel

2. More attachment possibilities than 6.5 L shock absorber

3. High spring rate, can support heavy models

Disadvantages:

1. Default attachment points create friction

2. Rare and expensive

 

11. Attaching springs to live axles

If we start with basics, the first things we have to check is how position of springs affects suspension of live axles.

The closer you place the springs together, the more flex the suspension will have, but it will also be less stable:

640x548.jpg640x519.jpg640x478.jpg

 

 

 

I suggest you to keep springs at a distance of around 1/2 of the total model width.

When placing springs you should keep them in-line with the wheel bearing in order to reduce friction.

First example of bad spring placements:

640x1437.jpg640x448.jpg

And example of good spring placement:

640x1175.jpg640x531.jpg

When using multiple springs make sure to place them symmetrically centrred to the wheel hub:

640x447.jpg

 

When attaching springs to torque tube suspension, you have to allow springs to tilt in two planes:

 

640x512.jpg

You can also attach the springs to the suspension links to increase suspension travel. This technique is especially common on Trophy Trucks:

640x517.jpg

 

12. Attaching springs to independent suspension

Independent suspension allows for much more flexible spring placement. Generally the closer you attach the spring to the main suspension arm pivot, the higher spring travel you get, but lower suspension force.

Examples going from the hardest suspension with low travel to the softest with high travel:

640x553.jpg640x502.jpg640x551.jpg

You can also attach springs inside the suspension arms:

640x389.jpg

Or horizontally:

640x333.jpg

As with the live axles make sure springs are in the center of the wishbones. Example of good placements:

640x476.jpg

640x748.jpg

And an example of bad spring placement, which causes excessive friction and suspension binding:

640x626.jpg

 

5. Steering

Steering is the system which allows our model to change direction. Generally there are two types of steering system used:

1. Skid steering

Advantages:

1. Very simple to implement and control with two separate motors for left and right sided wheels.

2. Does not require a dedicated steering motor

Disadvantages:

1. Not efficient, since wheels have to skid to steer

2. Power had to be reduced or even reversed in order to steer.

3. Not very accurate

4. Not very effective offroad

 

2. Classical steering with steerable wheels

Advantages:

1. Efficient, with minimum loss of speed

2. Accurate

3. Does not reduce the power of the drive motors

4. Can be used in front, rear or all axles for tight steering radius or crab steering

5. Effective offroad

Disadvantages:

1. Requires more complex hub assemblies

2. For best steering accuracy you need a dedicated servo motor.

 

Examples of a simple classical steering system for live axles

1. Parallel steering system for live axles

640x574.jpg

Here both hubs are always parallel. Position of the steering in the front or rear rack has no affect on the steering.

Advantages:

1. Very simple and robust

2. Easy to build

Disadvantages:

1. No Ackermann steering geometry

2. Steering rack moves inwards as it steers, requiring more space.

 

2. Ackermann steering system for live axles

640x599.jpg

This system allows the hubs to steer at different rates. The steering arms are offset inside so they form a virtual steering point where at the point where lines meet.

Advantages:

1. Better steering performance

Disadvantages:

1. More complex assembly

2. Steering rack moves inwards as it steers, requiring more space.

 

3. Steering system with diagonal linkages

640x600.jpg640x347.jpg

This system acts similar as Ackermann steering system by using diagonal steering links.

Advantages:

1. Better steering performance

2. Steering rack only has to move in one direction without sideways movements

3. Can be configured to be used in front or the rear of the axle.

Disadvantages:

1. More complex assembly

 

4. Simple steering system for independent suspension

640x1267.jpg640x1333.jpg

1. Very simple and robust

2. Easy to build

3. Can be even more robust when using double steering racks and links

4. Steering rack only has to move in one direction without sideways movements

Disadvantages:

1. No Ackermann steering geometry

 

5. Ackermann steering system for independent suspension

640x796.jpg

Advantages:

1. Better steering performance

2. Steering rack only has to move in one direction without sideways movements

Disadvantages:

1. More complex assembly, less robust.

 

3. General steering tips

1. When using independent suspension always make sure your links are paralel to the suspension arms, otherwise you may end up with wheels which are not parallel and are causing excessive friction:

640x338.jpg

2. When using standard portal hubs make sure your steering system is robust enough to deal with the forces generated by wheel driving into obstacles.

3. If possible use servo motors which allow for high steering precision and return to center. They are especially useful at high speed models.

4. Most efficient way to steer the wheels is using the steering racks.

5. Build axles in such way they have positive caster angle, example for direction of travel from right to left. This will self-center your wheels and reduce rolling resistance.

Positive%20caster%20angle.png

 

6. Drivelines

Drivelines are the responsible for transferring the power from the motors to the wheels.

There are various drivelines you can build, here I listed few with their characteristics:

Driveline types

1. Permanent 4x4

640x377.jpg

Advantages:

1. Simple, centralized, low mechanical complexity

2. Wheels are always powered, great offroad performance

3. Light weight

Disadvantages:

1. Poor steering radius

2. Tyres have to skid when steering, lowering efficiency of the model

 

2. 4x4 with open differentials

640x383.jpg

 

Typical example of this driveline is 42070

Advantages:

1. Differentials allow the wheels to so spin at different rates when steering

2. Very efficient since wheels don't have to skid when steering

Disadvantages:

1. If one wheel loses traction, all the power is transfereed to it, poor offroad performance

 

3. 4x4 with lockable differentials

640x342.jpg

Advantages:

1. Differentials allow the wheels to so spin at different rates when steering

2. Very efficient since wheels don't have to skid when steering

3. All differentials can be locked, so wheels are powered for great offroad performance

Disadvantages:

1. Higher mechanical complexity

2. Dedicated motor is required to actuate differential locks, higher weight

 

4. Axle mounted motors

640x345.jpg

Typical example of this driveline are 9398 and 41999.

Advantages:

1. Differentials allow the wheels to so spin at different rates when steering

2. Very efficient since wheels don't have to skid when steering

3. If one wheel gets off the ground the second axle can still pull/push the model.

Disadvantages:

1. Higher mechanical complexity

2. Usually the rear axle motor is more loaded than the front, especially when climbing uphill, the motors can't "help" each other.

3. Worse offroad performance than permanent 4x4

 

5. H drive:

640x456.jpg

This is my favourite driveline due to the following reasons:

Advantages:

1. Motors allow the wheels to so spin at different rates when steering

2. Model can skid steer

3. Very efficient since wheels don't have to skid when steering normally

4. Having 2 drivelines allows you to carry more torque to the wheels

5. Redundancy, even if one drive fails the model can still move

6. Wheels are always powered, great offroad performance

Disadvantages:

1. Higher mechanical complexity

2. Slightly higher weight

 

6. Wheel motor drive

640x297.jpg

Each motor powers a wheel independently.

Advantages:

1. Motors allow the wheels to so spin at different rates when steering

2. Model can skid steer

3. Very efficient since wheels don't have to skid when steering normally

4. Redundancy, even if one or more motors fails the model can still move

6. Lower mechanical complexity

Disadvantages:

1. Motors can't "help" each other

2. Higher weight due to a higher motor count

Transferring power axially

When transferring power via axles, you can reduce the flex by using connectors instead of simple "bare" axle:

640x601.jpg

Use axles with stops to prevent them from sliding out of gears:

24316.png87083.png99008.png32209.png32209.png

 

Where possible always brace tooth gears from both sides:

640x465.jpg

 

Transferring power at an angle

Where pairs of U joints are used, make sure to align them to eliminate vibrations:

640x199.jpg

 

Brick built CV joint which can transfer high torque at over 30 degrees angle

640x429.jpg

Brick built cardan joint which can transfer extremely high torque up to 15 degrees angle

640x213.jpg

Brick built flexible drive which can transfer medium high torque, extract and retract, suitable for low angles

640x269.jpg

Transferring power perpendicularly

The following perpendicular gearboxes are the best suitable for transferring high torque

 

 

640x532.jpg640x424.jpg640x502.jpg

Avoid knob and worm gears, because they waste energy

32072.png32905.png

 

Gearboxes

In my models I generally use the following gearboxes:

1:3 differential gearbox

640x409.jpg

Advantages:

1. Very high gear ratio between low and high gear, 1:3

2. Capable of transferring high torque

3. Very efficient since only 2 gears are used at any time

Disadvantages:

1. Takes a lot of space

2. This gearbox requires a good housing to brace the gears properly

 

Compact two speed gearbox

800x600.jpg

Advantages:

1. High gear ratio between low and high gear, 1:2,77

2. Capable of transferring high torque

3. Very efficient since only 2 gears are used at any time

4. Very compact design

Disadvantages:

1. Requires two of the rare 20 tooth clutch gears

2. More complex shifter assembly.

 

Diagonal gearbox

640x183.jpg

Advantages:

1. High number of gears

2. High gear ratio possible, over 4:1

2. Capable of transferring high torque

3. Very efficient since only 2 gears are used at any time

Disadvantages:

1. Takes a lot of space

2. Input and output axles are not parallel.

3. A complex shifting assembly is required for sequential operation.

 

Driveline effect on suspension

Transferring torque on the wheels can affect the suspension, especially when live axles are used.

The following photo shows how the torque causes one side of the axle to push down and the other to lift up:

640x454.jpg

In order to minimize this effect I suggest the following:

1. Make sure to have most if not all the downgearing inside the axles, so you do not need high torque going to the axles.

2. Make sure your models have a low center of gravity

3. You can eliminate this effect by using two counte rotating axles which cancel each other's torque, example below:

640x434.jpg

7. Motors and control

Following are the most common types of motors used for Lego models. You can find more info here: http://www.philohome.com/motors/motorcomp.htm

My personal favourites are L and RC motors due to the balanced output speed to torque ration and great mounting options.

1. PF-M

58120c01.png

Advantages:

1. High speed output

2. Smallest available motor

3. Cheap and available

Disadvantages:

1. Low torque

2. Poor mounting options

 

2. PF-L

99499c01.png

Advantages:

1. High speed output

2. High torque

3. Cheap and available

4. Great mounting options

Disadvantages:

1. Odd shape

 

3. PF-XL
58121c01.png

Advantages:

1. Very high torque

3. Cheap and available

4. Good mounting options

Disadvantages:

1. Slow speed output

2. Large form factor

 

4. PF-Servo

99498c01.png

Advantages:

1. Very high torque

2. Very precise output with 15 positions

3. Good mounting options

Disadvantages:

1. Slow speed output

2. Output axle can move a max of 180 degrees

3. Large form factor

4. Hard to find

 

5. 9V-RC motor

5292.png

Advantages:

1. Most oowerful Lego motor

2. Very high speed output

3. Good mounting options

4. Two output axles with different gearing ratios

5. Drive axles can pass through the motor

Disadvantages:

1. Low output torque

2. Low efficiency

3. Power hungry

4. Odd form factor

5. Hard to find and expensive

 

Power options

1. PF - AA battery box

59510c01.png

 

Advantages:

1. High capacity

2. Good mounting options

3. Works with rechargeable batteries, but with lower performance

4. Cheap and easy to find

 

Disadvantages:

1. 750mA current limit - not enough to fully power RC motor

2. Heavy

3. Has to be removed and opened to replace batteries

4. Wasteful

5. Odd form factor

 

2. PF - LiPo battery box

84599.png

Advantages:

1. Small form factor

2. Light weight

3. Easy to recharge

 

Disadvantages:

1. 750mA current limit - not enough to fully power RC motor

2. Low capacity

3. Studded design

4. Expensive and hard to find

 

3. RC control unit

6272c01.png

Advantages:

1. No current limit - can power 2RC motors at once

2. 3 Power levels

3. Has integrated steering output with 7 positions

4. Good mounting options

5. Easy battery replacement

6. Radio based control

 

Disadvantages:

1. Poor quality, prone to breaking

2. Limited angle (45 degrees) and torque from the steering output

3. Has to be removed and opened to replace batteries

4. Very large form factor

5. Expensive and hard to find

6. Heavy

7. Required dedicated antennas and remote

 

Control options

1. PF receiver and controller

58123bc01.png58122c01.png8879-1.png

Advantages:

1. Receiver is easy to integrate into the model

2. Controllers have physical feedback

3. Cheap and easy to find

Disadvantages:

1. IR based, low range, useless outside

2. Lack of PWM motor control, unless using train controller which is awkward to use

3. Odd form factor for use with steering

 

2. RC control unit

See above

 

3. Third party options such as BuWizz and Sbrick

Advantages:

1. Smaller form factors, easy to integrate into model

2. More outputs than PF system

3. Smooth control of motors

4. High range thanks to Bluetooth control

5. Higher power available with BuWizz

6. Customizable profiles

Disadvantages:

1. Smart device is required

2. No physical feedback

3. Sbrick is limited by PF battery box

4. Price

 

8. Chassis

Chasis is the backbone of your model which olds everything together.

For chassis I suggest you to use the following components in order to make it strong and robust enough to deal with the stresses involved when crawling or driving at high speed:

15100.png14720.png15458.png64782.png64179.png64178.png

Some flex in the chassis might be a good thing to improve offroad capability, but only if id does not affect the driveline and cause friction on the drive axles.

Remeember to use diagonal support, since triangles are the strongest shapes.

You can also use panels and motors as structural support.

Interlocking your chassis will keep it from slipping apart.

For good examples of chassis designs I suggest you check the instructions for 9398 and 42083.

Edited by Zerobricks
Correction of typing errors

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Very well done and much needed, I really wish there would have been a thread like this when I first got into Technic a couple of years ago. It would have saved me a lot of researching but it was fun. 

I look forward to rereading this and checking out any added content, a must read for those just getting started or anybody that is just looking for some ideas. 

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Posted (edited)

Great recap; I can just suggest that people put one 94.8x44 R balloon tire inside CLASS tire if they want use futuristic wheels because wheel is 6 mm more narrow than racing wheel medium.

I look at this like Old Testimony, New will be with New Hub from 42099 set :grin:

Edited by I_Igor

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Thank you @Zerobricks for this informative thread. I will be revisiting my latest MOC to apply some of your solutions. The use of simple builds to illustrate your points is particularly helpful :thumbup:

 

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Wow, I am very impressed with this write-up. A lot of great knowledge has been shared here.

Though, I would like to see a revision on the typos, there is quite a few of them, still not so bad that I can't understand it.

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I also say this should be pinned. a great explanation of lots of info. I found axles frustratingly very hard to build for steered sprung driven that actually work well with proper vehicle characteristics, so this should help guide indeed :thumbup:

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2 hours ago, Carsten Svendsen said:

Wow, I am very impressed with this write-up. A lot of great knowledge has been shared here.

Though, I would like to see a revision on the typos, there is quite a few of them, still not so bad that I can't understand it.

Thank you. I took time today to correct all the typos.

1 hour ago, Maaboo35 said:

Very cool stuff @Zerobricks! I wonder if TLG's official portal hubs will bear any resemblance to your design.

You mean planetary gear hubs? As soon as I get them, I will add them to the bible.

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5 minutes ago, Zerobricks said:

You mean planetary gear hubs? As soon as I get them, I will add them to the bible.

Damn, that is what I meant. :grin: It'll be interesting to see how they compare.

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9 hours ago, Zerobricks said:

Control options

1. PF receiver and controller

Disadvantages:

1. IR based, low range, useless outside

Very interesting, although I do have one issue with it. IR doesn't have that bad a range considering it's IR and is not "useless" outside. My system works fine outside in bright sunlight, I got almost 43ft during one test in an open carpark at like 2:30pm last summer even with half used batteries. I have tested the range with both my remotes and the speed controller. The speed controller has the worst range of about 30ft but both normal controllers had about the same range. And yes I'm a purest, I have not modified the remotes or the receivers in any way, I've only ever changed batteries.

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Great topic, Zerobricks!

10 hours ago, Zerobricks said:

Axle mounted motors

3. Worse offroad performance than permanent 4x4

To be honest, this is one of the most effective setups I've tested, especially on 6x6 and 8x8 trucks. Pros: very good weight distribution between axles, short drive chains.

You are not mentioning articulated steering. Personally I like it very much, since it eliminates a lot of typical troubles for offroad vehicles such as bending and tumbling of links, you can make straight axles with no 90 degree power transfer (which you also haven't mentioned I believe, that it is a very weak point for high weight models). The only minus I can see is that it usually has huge turning radius.

 

It is also pretty important to fix any gearbox or just gears not only vertically, but also horizontally if that makes any sense. 

These should be your best friends 6536.jpg63869.jpg41678.jpg15100.jpgas well as liftarms. High torque models destroy gearboxes, so ideally I suggest making vehicles with hard coupled gearboxes or without them at all.

Can't really quote every little thing you have mentioned, which I came across once and made a note for myself, very useful information!

Since I also like offroad technic direction most of all - BIG thanks for your work on this topic, hopefully it will grow and get attached.

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Posted (edited)

Very original ideas and great info..  The best quick info guide and its very helpful and should be pinned!! You should write a book!!! @Zerobricks

Edited by sirslayer

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Posted (edited)
27 minutes ago, gate said:

Great topic, Zerobricks!

To be honest, this is one of the most effective setups I've tested, especially on 6x6 and 8x8 trucks. Pros: very good weight distribution between axles, short drive chains.

You are not mentioning articulated steering. Personally I like it very much, since it eliminates a lot of typical troubles for offroad vehicles such as bending and tumbling of links, you can make straight axles with no 90 degree power transfer (which you also haven't mentioned I believe, that it is a very weak point for high weight models). The only minus I can see is that it usually has huge turning radius.

Yes, I might add articulated steering to the list, though I see lots of disadvantages:

- requires strong actuators to steer the model

- hard to pass multiple drivlines through the joint

- steering changes the weight distribution of the model

90 degree power transfers are mentioned under drivelines (perpendicular gearboxes).

Edited by Zerobricks

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15 hours ago, Zerobricks said:

Yes, I might add articulated steering to the list, though I see lots of disadvantages:

- requires strong actuators to steer the model

- hard to pass multiple drivlines through the joint

- steering changes the weight distribution of the model

90 degree power transfers are mentioned under drivelines (perpendicular gearboxes).

The best solution for articulated steering is obviously pendular suspension, and in this case it is pretty easy to make a straight driveline.

I have seen you wrote about 90 degrees. I think it is worth a separate mention for new builders that any technic 90 degree connection is pretty weak all by itself for it can slip and grind gears easily.

P.s. the worm gears are ineffective, but knob gears are pretty good, except some twitching movement of the model (with high reduction ratio) and the sound it makes. Both reasons are not really strong enough for not using knobs completely. Interesting what you think about it, Zerobricks.

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19 hours ago, Zerobricks said:

You mean planetary gear hubs? As soon as I get them, I will add them to the bible.

I hope that it will enable us to use portal axle hub from Unimog too, so we can have pivot point closer to center; by my perception maximum one stud... but I know that you'll inform us asap

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Really useful, thanks a lot.

would you share some idea of steering system with Old ungeared CV hubs(X873)?

 

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On 4/28/2019 at 8:12 AM, efferman said:

This thread has to be pinned on top of the technic forum

Completely agree! This is a very thoughtful and useful sharing of knowledge that many (such as myself) don't have. Many thanks :wub:

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Posted (edited)

Very interesting, I always wanted to do something similar about structural reinforcements but it was a lot of work even in my own languaje. I think it will be like a dictionary, impossible to finish but very useful.

Edited by jorgeopesi

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Respect, @Zerobricks, I wish you've done it about 7 years back in time. Was gonna save me a lot of experiments. Another layer of respect for sharing it free. (lately it isn't that obvious sadly)

One little question on the tatra suspension. Didn't you mean camber, instead of caster?

And +1 vote to be pinned!

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Posted (edited)

For Power Puller tires, I would suggest including in the cons that the tires are quite soft, resulting in a really high rolling resistance. Also, with Sbrick you can use a PS4 gaming pad and get physical feedback.

Edited by Sariel

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