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I have read all sorts of complaints about Robot Inventor and by inference Spike Prime. Some are valid (eg poor documentation)... some are less so (eg colour scheme). One thing seems clear is that the hardware is well thought out (yes there are issues with cables). Now in robotics three elements stand out as being super important: being able to use multiple motors (motors are basic building blocks), multiple sensors plus having the computational brain (and software) to hold it all together. Unfortunately Lego only provide 6 ports on each hub and have 2 versions of software both of which initially appear limiting. Whereas wireless Inter-hub communication could be very helpful enabling models to use multiple hubs and access both software platforms this is not something that Lego have explicitly provided at the moment. There is however a very simple and seemingly reliable work around available immediately that could help in cases where high speed comms and high data volumes are less important. This is to use optical communication. The idea which I have tested is to use the distance sensor to signal light flashes to the colour sensor. The number of flashes in a fixed time frame thus delivers information from Transmitter to Receiver. As expected using downloaded compiled code speeds the process up though not massively. This process could be 2 way, could enable daisy chaining of hubs and could be expanded to longer instructions (again high speed not being a limitation). On the downside the process sacrifices at least one port on each of a pair of hubs (if the requirement is for one way communication between the pair). The sensors need to be carefully and firmly positioned for reliability although there is no other requirement for any connection between them. In this context a model containing the one hub could “launch” the second. As SP and RI software can be easily swapped on any hub the user has the choice of using SP/SP or SP/RI or RI/RI platforms. Unfortunately size limitations prevent me from uploading images of the set up and demo code at the moment.
Hello to all, It's been a long time since I was in the forum, therefore I do not know ( I did a research but couldn't find one) if a similar topic was opened before. Since the powerbanks have started to be able to give 9V outputs 2 amperes, Even 12V 1,5 amperes with a rated capacity of 12.000 mAh and a total capacity of 20.000 mAh or more, I started to think about using powerbanks instead of 1,5V*6 AA or AAA type batteries in powered and/or lit-up sets. These batteries clearly create a battery pollution after losing their full power or all of their power, thus needed to be replaced. This means money, toxic waste, corrosion of the hubs, unplayable/unusable sets. Corroded batteries create health problems, performance problems, usage problems. (i.e. Haunted House Set with "Powered Up". If the AAA batteries lose power, then the lift in the set immediately start to have problems. First of all, I believe the set's lift system using "Powered Up", has clear faults. Because the motor used to operate the lift is timed and its speed is also cleverly calculated. The lift's wheel system has problems. Many times, it is stuck, doesn't reset properly or because of the wheels slowing down the lift when falling do not act properly when the lift is going up, I tried taking off the side walls of lift, touching the wheels. This made the lift work properly but alas, when it did the panic fall, the wheels did not slow the lift down, so it had a "free-fall". Furthermore, if the batteries lose power, then the lift can not operate properly.) From what I see, at least in Turkey, LEGO is working with VARTA. VARTA has very durable and powerful powerbanks reaching up to 18.200 - 20.000 mAh. Yes, it is large but the technology is improving more and more. The price of the powerbanks? Well, even the VARTA ones are less expensive than the battery hubs sold by LEGO. The outputs can be various (USB-C, USB, micro-USB etc.) and they can simply be adapted to LEGO motors with some modifications. And after a 5-6 hour recharge after full depletion, voila! No waste, no power loss, no unnecessary battery buying/storage and thousands of reacharges only with a smart USB adapter. So? Why not? The powerbanks do not lose their full power at all until they are totally depleted. Because I am not an expert in battery hubs vs. powerbanks in means of generating power to the motors, kindly please warn me if I am talking nonsense. Best of health and Regards, Idris
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 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 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 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 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 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 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 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 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 These hubs are usually driven by the CV joint counterpart which pops inside Advantages: 1. Low steering pivot offset - usually at the edge of the tyre: 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 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 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 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 5. Built portal hubs 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 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 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 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. 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 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. 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 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 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 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 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: 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 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: 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: And example of good spring placement: When using multiple springs make sure to place them symmetrically centrred to the wheel hub: When attaching springs to torque tube suspension, you have to allow springs to tilt in two planes: You can also attach the springs to the suspension links to increase suspension travel. This technique is especially common on Trophy Trucks: 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: You can also attach springs inside the suspension arms: Or horizontally: As with the live axles make sure springs are in the center of the wishbones. Example of good placements: And an example of bad spring placement, which causes excessive friction and suspension binding: 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 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 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 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 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 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: 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. 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 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 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 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 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: 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 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: Use axles with stops to prevent them from sliding out of gears: Where possible always brace tooth gears from both sides: Transferring power at an angle Where pairs of U joints are used, make sure to align them to eliminate vibrations: Brick built CV joint which can transfer high torque at over 30 degrees angle Brick built cardan joint which can transfer extremely high torque up to 15 degrees angle Brick built flexible drive which can transfer medium high torque, extract and retract, suitable for low angles Transferring power perpendicularly The following perpendicular gearboxes are the best suitable for transferring high torque Avoid knob and worm gears, because they waste energy Gearboxes In my models I generally use the following gearboxes: 1:3 differential gearbox 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 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 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: 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: 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 Advantages: 1. High speed output 2. Smallest available motor 3. Cheap and available Disadvantages: 1. Low torque 2. Poor mounting options 2. PF-L Advantages: 1. High speed output 2. High torque 3. Cheap and available 4. Great mounting options Disadvantages: 1. Odd shape 3. PF-XL 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 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 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 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 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 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 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: 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.