Marxpek

[WIP] trying to break 40km/h with only Lego "2 new designs, -steering advice needed"

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8 hours ago, TechnicSummse said:

Seems like you have every part wich you need... just grabbing into your chest and pulling it out :D

How i wish this was true, I've spent about 4 hours searching for the pulley wheels, i was certain i had them somewhere, but i could not find them, it turns out they were in the box of the 8412 with the rest of it's spare parts (the b-model uses them)

I have sorted my Lego, but not everything, sometimes making it hard to find (older) pieces

8 hours ago, TechnicSummse said:

Why you dont put the pulleys directly together on the axle? I think its way more fragile, the way you have done it now.

Putting them together will make it harder to "push away" rocks since they will be pushed into the next wheel, or even wedging it in between them. it also needs more construction as they do not run smoothly when mounted in a 1 stud wide opening, the tires rub the curved halfbeams, however i do agree it should improve a bit further to get the wheels braced from the outside.

 

8 hours ago, TechnicSummse said:

but what are you doing with the bikers?

wait for the right moment, the raised center is a good thing for this, incoming bikes can never get to my half and since the car is going way faster then anyone is cycling there; bikers behind me will never keep up, so i just need the road ahead to be clean, but here is always the danger of running my own bike over it, i still consider that the most dangerous. But yesterday it took me 1 hour to do 4 runs.

The bent antennas do give a little bit less range, but not 80% less, but i do notice some lag on the steering when its far ahead me, i'll see into it.

The weight with the new suspended front comes in at 1029 grams, and with the ZR frontwheel it comes in at 1030 grams, ready to run, including the 40 gram gps device.

20 minutes ago, Epic Technic said:

As a man of science, I'm here to tell you that you're using the wrong front wheel!:grin:

Since this wheel is not powered, we want the largest front tire to reduce friction. Plus you want to use the skinniest tire possible, to lower friction even more, but this does come at the cost of worsening your steering.

I am aware that a bigger wheel will give less resistance to rolling and bumps, but the size will also increase the construction and thus the weight, but i would love to hear your suggestions, but i cannot see how i can get a skinnier tire then i have now, larger yes, but more skinny? no

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On 7/1/2017 at 9:09 AM, Marxpek said:

I am aware that a bigger wheel will give less resistance to rolling and bumps, but the size will also increase the construction and thus the weight, but i would love to hear your suggestions, but i cannot see how i can get a skinnier tire then i have now, larger yes, but more skinny? no

I was sort of thinking of another motorcycle tire, but that is going to make your car way heavier, so your current wheel is still probably your best bet. You guys are going to get some more competition! :grin: I've got my car up to 32 km/h so I still have a ways to go, but in my defence I only have a v2 LPE and a super short track. :laugh:  

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Update on the progress / rebuild

mayor rebuild, 2 studs more narrow design and more earodynamic profile

No tests done, just pictures for now.

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4 halfbeams of friction in the back (3x5 curved halfbeam), 2 halfbeams of friction in the front. still some minor tweaks need to be done, this is the heaviest one yet at a whopping 1128 gram! (i added a few more pieces after the pictures) but i have high hopes!

Sadly i will not be able to do runs today or tomorrow, more soon!

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49 minutes ago, Epic Technic said:

I was sort of thinking of another motorcycle tire, but that is going to make your car way heavier, so your current wheel is still probably your best bet. You guys are going to get some more competition! :grin: I've got my car up to 32 km/h so I still have a ways to go, but in my defence I only have a v2 LPE and a super short track. :laugh:  

32km/h on air? how? launch it like an air powered rocket or something? i'm impressed!! can we get some pictures please? 

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5 hours ago, Epic Technic said:

I was sort of thinking of another motorcycle tire, but that is going to make your car way heavier, so your current wheel is still probably your best bet. You guys are going to get some more competition! :grin: I've got my car up to 32 km/h so I still have a ways to go, but in my defence I only have a v2 LPE and a super short track. :laugh:  

Is the lpe cylinder modified? If so, it does not count technically. But I would be fine with that type of competition.

Edited by Aventador2004

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8 hours ago, Epic Technic said:

I was sort of thinking of another motorcycle tire, but that is going to make your car way heavier, so your current wheel is still probably your best bet. You guys are going to get some more competition! :grin: I've got my car up to 32 km/h so I still have a ways to go, but in my defence I only have a v2 LPE and a super short track. :laugh:  

That's very fast for a LPE, but it isn't really competition - because it's completely different from using motors.

8 hours ago, Marxpek said:

Update on the progress / rebuild

mayor rebuild, 2 studs more narrow design and more earodynamic profile

No tests done, just pictures for now.

Have you got steering, or is it just that I can't see it?

8 hours ago, Marxpek said:

still some minor tweaks need to be done, this is the heaviest one yet at a whopping 1128 gram!

I think you are going the wrong way... :laugh:

And my car is getting lighter every day! (currently 660gm, or 615gm without the watch)

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9 hours ago, Marxpek said:

Update on the progress / rebuild

mayor rebuild, 2 studs more narrow design and more earodynamic profile

No tests done, just pictures for now.

4 halfbeams of friction in the back (3x5 curved halfbeam), 2 halfbeams of friction in the front. still some minor tweaks need to be done, this is the heaviest one yet at a whopping 1128 gram! (i added a few more pieces after the pictures) but i have high hopes!

Sadly i will not be able to do runs today or tomorrow, more soon!

You are using my wished gearing...basicly the same then my first 38+ setup... but with bigger gears... but sadly i own just one 36 teeth-gear.

I ordered another one yesterday... hope it will arrive until the weekend..

 

Narrow design sounds good... but i think 2 frontwheels, and the rear-wheels profile will brake way too much. Did you try to exchange the outer support at the frontwheels vs the pulley as stabilization?

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11 hours ago, Marxpek said:

32km/h on air? how? launch it like an air powered rocket or something? i'm impressed!! can we get some pictures please? 

All it is, is a good old fashion V2, some wheels, a chassis and 6 Bar of  air pressure. I'll start a topic soon...

7 hours ago, Aventador2004 said:

Is the lpe cylinder modified? If so, it does not count technically. But I would be fine with that type of competition.

Yes, the cylinders are drilled and oiled, switches are stock though. I personally think it still counts as modified pneumatics are rather quite accepted in the LEGO Technic community. Also, the current record uses modified pieces, so I though it would only be fair if I used some too, but I see where you're coming from.

3 hours ago, mocbuild101 said:

That's very fast for a LPE, but it isn't really competition - because it's completely different from using motors.

Yeah, I know it's not actual "competition" :wink: I just wanted to see how fast I could get LEGO to go.

 

 

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1 hour ago, Epic Technic said:

Yes, the cylinders are drilled and oiled, switches are stock though. I personally think it still counts as modified pneumatics are rather quite accepted in the LEGO Technic community. Also, the current record uses modified pieces, so I though it would only be fair if I used some too, but I see where you're coming from.

I wouldn't mind competing against a lpe car, but I am currently not part of this, so we shall see about the last fact.

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1 hour ago, Epic Technic said:

All it is, is a good old fashion V2, some wheels, a chassis and 6 Bar of  air pressure. I'll start a topic soon...

I guess the airpressure is stored in LEGO-Air-tanks? And pumped by a LEGO-compressor? ;)

1 hour ago, Epic Technic said:

Yes, the cylinders are drilled and oiled, switches are stock though. I personally think it still counts as modified pneumatics are rather quite accepted in the LEGO Technic community. Also, the current record uses modified pieces, so I though it would only be fair if I used some too, but I see where you're coming from.

I think this is pretty much the same, then removing the current-limit from battery-boxes, or to modify the motors.

But... sure... if others are using the same method, you can compare with them, on the same level ;)

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14 hours ago, Marxpek said:

this is the heaviest one yet at a whopping 1128 gram!

5 hours ago, mocbuild101 said:

I think you are going the wrong way... :laugh:

its a balance between power and weight... heavier models can go faster if it has the necessary power... which comes to my point - is there a limit on the max number of motors in this competition? 

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7 minutes ago, PorkyMonster said:

its a balance between power and weight... heavier models can go faster if it has the necessary power... which comes to my point - is there a limit on the max number of motors in this competition? 

Well theoretically not... but physically...

As you may notice... i could run a 2-motor car with 34,8 kph.... adding 2 motors was an increasement of ~4 kph so far. Maybe you can get 40kph from 4 motors... 

But i think you can see, how this diagram would look like...

-> 2 Motors -> 0-35kph                +35kph

-> 4 Motors -> 35-40kph              + 5 kph

-> 6 Motors -> 40-41,5??? kph?  + 1,5 kph?

I think this will even end with lower speed at some point...

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1 hour ago, TechnicSummse said:

As you may notice... i could run a 2-motor car with 34,8 kph.... adding 2 motors was an increasement of ~4 kph so far. Maybe you can get 40kph from 4 motors... 

But i think you can see, how this diagram would look like...

-> 2 Motors -> 0-35kph                +35kph

-> 4 Motors -> 35-40kph              + 5 kph

-> 6 Motors -> 40-41,5??? kph?  + 1,5 kph?

Did you gear up further as you add more motors? You need to gear up each time you add motors, because otherwise you won't benefit much (speed-wise) from the added torque.

Edit: Let's see... assuming that with 2 motors, you model weighs W, and you get torque T and top speed S using gear-up ratio of G. Now, when you double the motors, you get 2T, your model won't weight more than 2W (hence your top speed definitely won't be lower than S given the same G), and if you double your gear-up to 2G, you'll be able to get 2S!!! And you'll be able to break 40 kph - no sweat :laugh:.  And after that someone will definitely raise the need to limit the number of motors...

Edited by PorkyMonster

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1 hour ago, TechnicSummse said:

I guess the airpressure is stored in LEGO-Air-tanks? And pumped by a LEGO-compressor? ;)

No air tanks, just one big compressor (not lego) :wink: However, I see the compressor as the type of batteries you would put in your car, you could go with Alkalines, NiMH, Li Ion, or NiCd, and I choose to use a big compressor instead of a lego one.

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2 hours ago, PorkyMonster said:

Edit: Let's see... assuming that with 2 motors, you model weighs W, and you get torque T and top speed S using gear-up ratio of G. Now, when you double the motors, you get 2T, your model won't weight more than 2W (hence your top speed definitely won't be lower than S given the same G), and if you double your gear-up to 2G, you'll be able to get 2S!!! And you'll be able to break 40 kph - no sweat :laugh:.  And after that someone will definitely raise the need to limit the number of motors...

You have forgotten two things: A- acceleration time & L- length of track

With 2 motors you get 2T, but when you gear it up 2G, you only end up with 1T - which means the car will need 2A, which means 2L.

So in other words, you need to double everything!

But you do have a point, because it would be possible to get close to double the speed, you would just need something like 300m+ of track - and a way to keep the remote in range of the car!

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10 hours ago, mocbuild101 said:

Have you got steering, or is it just that I can't see it?

You probably are missing it, there is steering, exactly the same as before, just the axle was raised over the black liftarms now.

10 hours ago, mocbuild101 said:

And my car is getting lighter every day! (currently 660gm, or 615gm without the watch)

Still.. my power to weight ratio is better, and one of the "tweaks" might save about 100 grams ;)

10 hours ago, TechnicSummse said:

Narrow design sounds good... but i think 2 frontwheels, and the rear-wheels profile will brake way too much

One of the tweaks might be loosing the double front wheel, but i haven't worked it out yet, i might tonight.

4 hours ago, PorkyMonster said:

is there a limit on the max number of motors in this competition? 

First of all this is not a real competition, just our personal need to break the speed records ;) but for me: the only rule is: go as fast as you can by any means, but with 100% unmodified Lego and be able to stop, start and steering. i still have more buggy motors lying around (but no more rc units) so i could easily try technicsummse's 3 motors on 1 rc unit and double that..., but i don't know about that yet... i don't want to risk the electrics (yet).

Having 3 rc units might be very problematic, i never mentioned this before but this is a real issue when using 2 units: the units interfere with each other, sometimes when both units are on and i do nothing, it can steer or drive on its own, something is giving it a rc input, most likely the other unit on the same channel is causing the interference, having 3 units will most likely cause 3x more interference.  

But i found that building a car with 2 motors is fairly easy, but with 4 motors, the construction increases also, and with every added motor you will add more weight and construction, there is a point where its not viable to add more motors i think, and i think we are close to it.

@Epic Technic i'm very interested in your LPE record racer, but i feel it has a lot of non-lego or modified parts, even if it is accepted in the community, it is "the easy way" and i think it would be a more fun record with 100% unmodified Lego which is more accessible to people and easier to compare to others since it is not about how you modified the parts but how you used them.

10 hours ago, TechnicSummse said:

Did you try to exchange the outer support at the frontwheels vs the pulley as stabilization?

sorry i don't understand, what do you exactly mean?

Edited by Marxpek

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Out of boredom, I did some calculations to determine the acceleration gain (if any) from adding motors (here, each pair of Lego RC motor is assumed to consist of the weight equivalent of 1 RC unit, 2 RC motors and 6 AA Alkaline batteries - ~450 grams including slight overheads) for models of different overall weight (when using 1 pair). And the higher the acceleration gain, the more likely that gearing up will give better max speed.

Here's the result:

Lego%20RC%20Motor%202.png

The chart indicates that the heavier a model is, the more it stands to gain (in relative terms) from adding motors... however, adding motors will not allow them to accelerate any faster than the lighter ones. However, playing with momentum, wheel sizes and gearing, its hard to tell whether they can reach greater max speed though...

Also, does look like most of the models here fall within the orange and yellow weight range... and adding 2nd to 3rd pairs of motors can be useful, but the gain from adding 4th or more pairs will be negligible...

 

Edited by PorkyMonster

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1 hour ago, PorkyMonster said:

Out of boredom, I did some calculations to determine the acceleration gain (if any) from adding motors (here, each pair of Lego RC motor is assumed to consist of the weight equivalent of 1 RC unit, 2 RC motors and 6 AA Alkaline batteries - ~450 grams including slight overheads) for models of different overall weight (when using 1 pair). And the higher the acceleration gain, the more likely that gearing up will give better max speed.

Here's the result:

Lego%20RC%20Motor%202.png

The chart indicates that the heavier a model is, the more it stands to gain (in relative terms) from adding motors... however, adding motors will not allow them to accelerate any faster than the lighter ones. However, playing with momentum, wheel sizes and gearing, its hard to tell whether they can reach greater max speed though...

Also, does look like most of the models here fall within the orange and yellow weight range... and adding 2nd to 3rd pairs of motors can be useful, but the gain from adding 4th or more pairs will be negligible...

 

Thats what i wrote yesterday :)

Nice chart :)

17 hours ago, PorkyMonster said:

Did you gear up further as you add more motors? You need to gear up each time you add motors, because otherwise you won't benefit much (speed-wise) from the added torque.

Edit: Let's see... assuming that with 2 motors, you model weighs W, and you get torque T and top speed S using gear-up ratio of G. Now, when you double the motors, you get 2T, your model won't weight more than 2W (hence your top speed definitely won't be lower than S given the same G), and if you double your gear-up to 2G, you'll be able to get 2S!!! And you'll be able to break 40 kph - no sweat :laugh:.  And after that someone will definitely raise the need to limit the number of motors...

What you forgot here is... rolling resistance and air resistance wich will grow extremely at higher speed.

To give you a simple example... lets say you own a car with 50hp, it can drive ~150 kph.

-> did you ever see a 100hp -car wich could drive 300 kph? :O 

And there is not even the weight doubled in this sample... both cars will use the pretty much same weight.

14 hours ago, Marxpek said:

sorry i don't understand, what do you exactly mean?

Well... did you add these : 8b493b4018d3c43cd6ba5ed46e646190.jpg

to you front-setup, to compensate the not existing outer bearings?

I mean did you hope to prevent the axle-bending with these... and did it help? :D

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39 minutes ago, TechnicSummse said:

What you forgot here is... rolling resistance and air resistance wich will grow extremely at higher speed.

That's true :grin:. I did some googling and found this chart:

fuel1.jpg

Apparently air resistance is the biggest culprit... So to break the next frontier - looks like its either adding paneling or to build loooooong and narrow... now i see why dragsters are built that way :laugh:

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59 minutes ago, PorkyMonster said:

That's true :grin:. I did some googling and found this chart:

fuel1.jpg

Apparently air resistance is the biggest culprit... So to break the next frontier - looks like its either adding paneling or to build loooooong and narrow... now i see why dragsters are built that way :laugh:

air resistance only overtakes rolling resistance in that chart at 60 km/h, at 40 the rolling resistance is twice as large as drag. Now i think that chart is not universal, as in, both curves will depend on some constants, such as the drag coefficient and the hardness of the tires for rolling resistance, so the actual graph for these record mobiles might turn out different, with the crossover at a different speed.

Id be more interested in seeing a torque/power chart for the buggy motors, sort of like a dyno chart, because you want to make sure the peak in the power graph is at your target top speed, provided the graph isnt crazy, that should give you the best chance at hitting your target.

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15 minutes ago, vectormatic said:

air resistance only overtakes rolling resistance in that chart at 60 km/h, at 40 the rolling resistance is twice as large as drag. Now i think that chart is not universal, as in, both curves will depend on some constants, such as the drag coefficient and the hardness of the tires for rolling resistance, so the actual graph for these record mobiles might turn out different, with the crossover at a different speed.

Oops!! :grin: u'r right, this chart is based on other unknown set of factors. Can't take short cuts... :tongue:

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7 minutes ago, mocbuild101 said:

You might want to check out @Philo's motor characteristics page.

I'm not sure if it has what you are after, but it's worth a look...

The info there is in slightly different charts then im used to, but there probably is enough info there to find the optimum RPM for extraction the most mechanical power out of a buggy motor

I know a gearbox probably isnt attractive due to transmission losses, but i think it might very well be worth it to make a two speed gearbox in these record breakers, a low-ish gear to take it up to 20-25, then a higher ratio to deliver the highest output power at slightly over 40

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1 hour ago, vectormatic said:

The info there is in slightly different charts then im used to, but there probably is enough info there to find the optimum RPM for extraction the most mechanical power out of a buggy motor

You will need this "point" a little bit earlier then your wished top-speed. 

But thats exactly what i did, while comparing all "so far"-speed records. The motor-rpm at top speed was between 900 and 1100 at all of them.

1 hour ago, vectormatic said:

I know a gearbox probably isnt attractive due to transmission losses, but i think it might very well be worth it to make a two speed gearbox in these record breakers, a low-ish gear to take it up to 20-25, then a higher ratio to deliver the highest output power at slightly over 40

 

This will only help, to shorten the required track, but this would mean additional gear-friction, additional axle/beam-friction (because you need at least 1 additional axle for that) and some additional weight.

Also this comes in here:

19 hours ago, Marxpek said:

But i found that building a car with 2 motors is fairly easy, but with 4 motors, the construction increases also, and with every added motor you will add more weight and construction, there is a point where its not viable to add more motors i think, and i think we are close to it.

Construction will give some problems here.

 

But... as long as you dont know exactly your rolling resistance, and all other friction-factors, there is no sense of knowing exact dynographs. Because you can only calculate a usefull gearing, if you calculate with all those numbers.

Lets say you have a total friction of "X"... and you can reach 38kph with a 2:1 gearing.

Now you double the friction to "2*X" and your topspeed will be, lets say.... 29 kph.

But if you take the same "2*X" friction and gear is 1,66666:1, you will be able to reach 34 kph.

 

You cannot define one perfect fact (for example gearing) without knowing all the other facts.

In our case this means testing, testing, testing, and even more testing... with different wheels, axle-constructions, gearings... and so on.

We are pretty close to the limits, since we testet allmost every possible setup :)

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