PorkyMonster

LOL why did u bother to reveal your age? After all, people here won't care if you don't act like a kid. You and I belong to the same breed... from one of the endangered species... so to me, your idea is perfectly normal! I have similar ideas, only that I plan to include Arduino for transmission control (i.e. automatic transmission) and I'm targeting for perfect steering geometry, in my next build. Don't give it up if you still have the passion... just do it slowly, like I'm doing now (not just budget, but also the need for time to figure out how to solve certain issues to do with high rpm). Granted, not many appreciate our ideas and ideals, but we do it to challenge ourselves!

Distance between each parallel sides is 17mm, while diameter (as in your qn) is 19.63mm. Note that the round hole through the middle is about 12mm diameter.

I'm bored, and I want to go into something that can evolve/modified/rebuilt over time.

Nah... can't conclude whether he has used the full potential of his motor without the KV figure and the Lego gears he used in the entire drive train. Your motor looks OLD... and should be brushed... and if it fits well within Lego's XL motor casing, i would say just go ahead and hook up and test... after all most motors can take higher voltages than what Lego battery box can supply.

Chanced upon this video while browsing youtube just now... I'm not in any way promoting the use of 3rd party parts () here (it's individuals' tastes after all), but I thought this video pretty much gives a rough gauge to all of us what pure Lego, when combined with brushless motor (i.e. no lubrication, no bearings, no other metallic 3rd party hobby-grade RC structural/mechanical components), can do... how Lego parts (especially differentials and universal joints) survived at such speed, for a roughly 1 kg model (my own model weighs 3 kg and if I accelerate it hard, the rear-front-middle differential and universal joints will complain)... and the control range to be expected using rc-grade transmitter/receiver. and if the speed claimed is accurate, the 68.8 mm wheels would have to be spinning at close to 6k rpm - depending on weather conditions this is probably the top limit before Lego axles melts (this limit will go down the heavier the model is).

"faster" is a relative and subjective term, much like the word "purism". end of the day it is our very individual definition of playability, and our willingness to "venture out" as opposed to working with familiar stuff, that really matters... So it would help if you could state down your comfort level in terms of using non-lego parts. having said that, based on what you said, this might interest you: here (in particular, the part on changing out the motor).

Oh my... how freaky?!

On second thought, I think Buwizz IS easier to integrate THAN SBrick & pure PF... so here's the revised chart, with price estimation added...

Looks like there is a solution to suit people of different tastes , each with its own pros and cons.

This is by far the strongest solution I've come across that still fit the 1x1 cross-sectional size. But I don't quite like the amount of drillings and cuttings . So far, I've tried larger solutions - either with Lego pulley wheels, or with brass-joints measuring 12x24 mm (and 5mm holes that fits an axle nicely). With the brass-joints, I would do what @z3_2drive did - made use of the tiny screws, but applying glue additionally, to make sure they don't unscrew themselves out over time. What I've experienced so far is that Lego axles are VERY STRONG, so long as you take care of their rpm and friction - make sure they turn freely, and limit rpm to below 4k (max 5k), so that they don't get the chance to heat up and turn soft.

To most of us, Lego-ing is just a hobby, and hobby changes over time as we grow up or age. However, with the pieces lying around, we can always get back when the interest returns .

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Right... for off-road, and at 7kph, its fine that there is slight toe-out and little caster. In fact, one can easily get away even with negative caster (like so many Lego MOCs before... LOL). I actually thought you were gunning for higher speed and on-road when you used 4 motors, queried about Buwizz, included caster, and so on... haha... my bad.

IMHO, its a pity that the design does not allow for a gearbox, and there is no space for gearing up the wheels individually... because, based on my calculation, it can only go up to 7 kmh , based on wheels of 94.8 mm diameter, and the maximum 390 rpm that PF-L motor can do at 9 volts (slightly more for buwizz at 10 volts)... One real issue I see is that of the toe-out - because you don't have other geometries like caster (ok, you have 5 degrees... which is rather negligible and can easily be canceled out by your toe-out) and kpi as well... so driving this buggy in a straight line may be challenging.

As mentioned by @TechnicSummse, I was only referring to the doubling of propeller just to achieve redundancy in case one of them drop off far from shore... unless you're thinking of something like this (then you'll have no problem with space and buoyancy):

The water helps a lot, I think... it cools down most of your moving parts, and offers rather good cushioning to your boat's body. However, given the rpm and propeller size, have you considered doubling - Use two (or even more) propellers to move even more water in the same time...? Serves as backup too, in case one of the propellers drop off far from shore...

LOL... same here. Anyway I just went through the pictures again, I think @DugaldIC's stepper seems to require intense listening/observation for it to stop advancing to the next gear as well... correct me if I'm wrong.

This looks interesting... not sure about its performance though... Otherwise, I'm sure that @Didumos69's stepper PLUS servo works flawlessly... no need for any slipper/clutch - I know, because I've tried .

I do that all the time for my wheels From your photos, I have a feeling that you'll need to build strong wheels... here's one possibility (click on image for the lxf file if you want more details):

You have huge trail + negligible caster, coupled with the fact that your steering axis does not even cut the wheel - perfect recipe for fluttering (which increases with speed). Like what @Marxpek and @mocbuild101 have done - reduce your steering angle (to really really small) to avoid drastic direction change... well, if this is what you think that good caster (something that you have implemented) still requires, so be it . Another thing you could try is to move more weight to the rear.

That's rather surprising ... my understanding is that both caster and trails mean very different and independent things. Caster defines the angle between the (1) steering axis and the (2) vertical line that cuts through the rotating axle of the wheel, and trail defines the distance between the point where the lines cut the ground. Huge caster does not necessarily imply huge trail, and vice versa, (all depending on where the two lines intersect, which need not be the center of the wheel) and varying each of them separately can lead to different straight-line performance. Note that this is only true for single, thin, wheels... when you have a wider, more squarish cross-sectioned wheel, or even better - two wheels with KPI, you can avoid such problem. So... time to consider having two front wheels?

My bad I forgot that tyre width and a squarish cross-section matters a lot when it comes to wheel self-straightening while stationary. Without width and a squarish cross-section, KPI will be necessary (as @nicjasno already mentioned) and therefore 2 wheels are needed. Once in motion, the trail (i.e. the distance between the point where the steering axis touches the ground and the tyre's contact point with the ground - hope we have the same definition) contributes to the straight-line behavior. Great, so we're at the same point so far. That's due to your trail - there is reason why the steering axis hits the ground in front of the tyre's contact point with the ground. However, this fluttering effect is much reduced for cars with wider and more squarish cross-section tyres. I believe you have huge trail, but almost negligible caster angle (although contributed by the body tilt, but front weight tends to go down as speed goes up). Coupled with thin tyre, you have near zero wheel self-centering desire. What your huge trail allows is for the front wheel to follow wherever the movement takes the vehicle. Much like a trolley with 4 caster wheels - you can push it in any direction and the wheels will all follow happily without any desire to revert back to any particular direction - that's what trails contribute. Whereas with caster angle and wider and squarish cross-section tyre, the wheel itself will resist any attempt to change its direction, thereby contribute to greater stability. So imagine a 3-wheel vehicle like yours - when any wheel hits a bump, you really need the remaining two to stay on-course... but implementing the front this way, you've relieved your front wheel from this duty. You do have a point here, but it depends on where the force originates from - if its a bump sustained by the front wheel, yes, you're right that it won't dis-orient the wheel easily due to the big lever effect... but if its a bump to one of the rear wheels, the entire vehicle will dis-orient pretty easily (again, due to lever effect from the other direction which renders the self-centering ability of the front wheel useless).

LOL you're absolutely right that its crazy!!! why do you think your caster is right when there are tonnes of literature all over the web on that topic? For a car, or a bike, with proper caster, there is tendency for the front wheel(s) to center even while stationary... this property does not exist in your "caster". What you see as centering behavior is caused by the rear wheels being fixed in forward direction - so when your front wheel hits a bump, you're relying on your rear wheels to prevent your racer from deviating from straight line, and this may place more stress on the rear axle and slow down the racer (and of course, caster should not be tested on flat/smooth surface). In contrast, proper caster will self-align, relieving the rear axles to focus on its main purpose - to propel the racer forward.

I've tried to bring across the point that a "caster wheel" is NOT a wheel with "caster angle" to @Marxpek, in his thread before, but failed ... Let me try again here . First, what we want, in a fast vehicle, are wheels that can self-align to the vehicle, NOT to the direction of movement - and this behavior should be more apparent the higher your speed is. Second, we want more steering efforts the higher the speed - so we'll need to send more power to the servo, or we'll need bigger bumps, in order to change the direction of the vehicle. Caster wheels, the same kind used in shopping trolleys, and as implemented in your models, DO NOT exhibit the above properties. You need wheels that have their steering axle properly angled in order to achieve high speed stability. Regarding suspension - I agree with @nicjasno that you need proper suspension (yes, there might not be significant effect on speed due to lost traction (possible reasons mentioned in my earlier post), but suspension will affect steering and that will prevent you from staying the course and reaching the highest possible speed). For proper suspension to work, the unsprung weight must be much less than the sprung weight (target less than 10%, even lower if possible). If the ratio is not significant enough, the wheels (being part of the unsprung weight) will send vibration up onto the rest of the vehicle and cause the entire racer to rock and you'll lose traction as a result. As for hardness/travel of suspension, that really depends on your speed and track surface - something to be experimented (in general, harder+shorter for flat surface, softer+longer for rough surface...).

This is the kind of models I like - BIG , and good looking. Is fine if it cannot move well, afterall it really depends on your focus. Nope, not going to criticize you as I have no issue with using 3rd party parts... However, there are ways to handle high torque / heavy models without resorting to non Lego parts - the key is proper bracing and gearing. I've built heavy models and even run them with 3rd-party brushless motors, and I've never felt the need to use 3rd party differential ever since I learnt how to brace and gear properly.