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

[Marxpek]

9 hours ago, TechnicSummse said:

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

The axle bending was never in the front, only in the rear. but yes i tried them on the bikelane track, with and without suspension, they roll great but steering is nearly impossible they just lack the grip.

4 hours ago, TechnicSummse said:

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 :)

This is the key, testing, we can never determine every variable so we have to test, up to a certain point theorycrafting works, but in real conditions we might find different results.

Yesterday i have done some tweaks one of the issues with my new racer was that it was lifting the front under its acceleration (back-heavy), so i had to shift the COG. which made me think: weight distribution can help with reducing friction/pressure on the bearings (halfbeams), in my case this meant: 6 bearings total, 4 in the back, 2 in the front, so i would guess a 67% rear and 33% back weight distribution might help, so i'll try that, (not taking into account how rpm of an axle influences friction)

With some luck i can do some tests later today. 

[Marxpek]

Todays tests barely exceeded 35km/h, the 4 wheel system gives problems with steering, it wants to roll over when steering, (don't worry i did not use the motor cross tires ;D) so i stopped using it quickly

I brought the old steering which now has a return to center hockey spring built in as well (with the small glued ZR wheel) and got similar speeds, but way more stable steering, I managed to do a 290 meter run (35,1 kmh) without a crash for the first time, and another of 200 meter (34,9) with a crash into the grass, but both with over 150m of acceleration, strangely in both occasions the gps curve shows a sudden drop in acceleration, i see 2 options here: i was too far out of range with the controller, twice in a similar fashion, which i find unlikely (i have it all on video and was not exceptionally far from the racer), or: this was the actual top speed and the motors just work at their top. 

most likely the weight distribution thing that i tried (put both rc units in the middle) did not work and causes it to slow down, or the longer wires are bad for results, either way, the 2nd rc unit has to be in the back again for further testing.

Back to the build!

Edited July 5, 2017 by Marxpek

[nicjasno]

The car needs all 4 wheels with suspension. This will make it a lot more stable. The front needs caster and kingpin inclination.

[Marxpek]

I have found the problem to my speed issues, while taking my car apart i decided to test all 4 buggy motors and it seems one of the buggy motors has met an early retirement, at least until revision, if possible..., it has a clicking sound... i hope i can save it....

But for now the racer has been rebuilt the exact same way as it was with the units in the center but the motor was replaced of course, since my current design was not fully tested (and who knows how many of my other tests...)

11 minutes ago, nicjasno said:

The car needs all 4 wheels with suspension. This will make it a lot more stable. The front needs caster and kingpin inclination.

I have had this in previous setups, it helps with steering, but not with speed, so suspension was ditched, we do not aim to make a well steering car, we aim to make a car capable of minor adjustments, a good track is certainly needed here.

And my current setup has caster by the way.

[nicjasno]

Have you tried to use silicone spray lubricant, to reduce friction on the axles and gears?

[Marxpek]

 

1 minute ago, nicjasno said:

Have you tried to use silicone spray lubricant, to reduce friction on the axles and gears?

hmm no..  it is a good idea yeah..

@TechnicSummse @mocbuild101 do you use this? shall we allow it? i kind of feel it could help save on Lego, these racers eat axles and halfbeams...i vote yes, but only when you agree.

[nicjasno]

It's not really a modification. And with such high speeds a necessity. Lego also uses grease in the motors. Speeds should increase.

Would be interesting to see if lubrication alone can make up the missing 5kmh.

Edited July 5, 2017 by nicjasno

[Marxpek]

On 3-7-2017 at 11:04 PM, Marxpek said:

sorry for reposting but looking into my own posts i found this: the picture shows there already was an issue before testing, the red bushing inside the buggy motor on the top left is cracked, that is gonna  need some fancy glue if possible at all, it will probably never run like it did before sadly...

Just now, nicjasno said:

Would be interesting to see if lubrication alone can make up the missing 5kmh.

I think fixing this might do the trick.. but i guess we will discuss this.

[TechnicSummse]

1 hour ago, Marxpek said:

 

hmm no..  it is a good idea yeah..

@TechnicSummse @mocbuild101 do you use this? shall we allow it? i kind of feel it could help save on Lego, these racers eat axles and halfbeams...i vote yes, but only when you agree.

I tried this at an early stage of my car, like 2 month ago... with not really a good result... except it sucks dirt like hell, producing even more friction, and scratching trenches into the pinholes, and the axles.

 

@Marxpek i hope you can save your motor :(

Edited July 5, 2017 by TechnicSummse

[PorkyMonster]

On 6/28/2017 at 5:45 AM, Marxpek said:

The steering setup resembles a shopping cart wheel setup, with the pivot point way in front of the wheel so it wants to go straight by itself, but it allows for accurate and low drag corrections. I might try to reduce its weight a bit more.

2 hours ago, Marxpek said:

And my current setup has caster by the way.

I've been thinking about this... while I agree that it allows for very low drag correction, I seriously doubt the shopping cart caster works the same way as a car's caster... because when direction changes, the shopping cart has absolutely no self-desire to revert back to its original (straight) direction, unlike a car with caster.

Here's what I found from wikipedia - One major disadvantage of casters is flutter. A common example of caster flutter is on a supermarket shopping cart, when one caster rapidly swings side-to-side. This oscillation, which is also known as shimmy, occurs naturally at certain speeds, and is similar to speed wobble that occurs in other wheeled vehicles. The speed at which caster flutter occurs is based on the weight borne by the caster and the distance between the wheel axle and steering axis. This distance is known as trailing distance, and increasing this distance can eliminate flutter at moderate speeds. Generally, flutter occurs at high speeds.

Edited July 5, 2017 by PorkyMonster

[mocbuild101]

8 hours ago, Marxpek said:

 

hmm no..  it is a good idea yeah..

@TechnicSummse @mocbuild101 do you use this? shall we allow it? i kind of feel it could help save on Lego, these racers eat axles and halfbeams...i vote yes, but only when you agree.

I vote no, mainly because of these reasons:

• lubrication is non-Lego
• I never use lubrication on Lego parts (except inside motors and pneumatic parts)
• I haven't experienced wear on axles and beams on my car (yet)

8 hours ago, Marxpek said:

sorry for reposting but looking into my own posts i found this: the picture shows there already was an issue before testing, the red bushing inside the buggy motor on the top left is cracked, that is gonna  need some fancy glue if possible at all, it will probably never run like it did before sadly...

I actually noticed that - and was going to mention it - but I wasn't sure how to explain it. (so I glad you noticed it)

Hope you find a way to save it...

[Marxpek]

21 hours ago, TechnicSummse said:

except it sucks dirt like hell, producing even more friction, and scratching trenches into the pinholes, and the axles.

this is reason enough for me to change my vote to no. but the reasons @mocbuild101 mentions (except the axle wear here..) are solid also,  so no lubes.

20 hours ago, PorkyMonster said:

Here's what I found from wikipedia - One major disadvantage of casters is flutter. A common example of caster flutter is on a supermarket shopping cart, when one caster rapidly swings side-to-side. This oscillation, which is also known as shimmy, occurs naturally at certain speeds, and is similar to speed wobble that occurs in other wheeled vehicles. The speed at which caster flutter occurs is based on the weight borne by the caster and the distance between the wheel axle and steering axis. This distance is known as trailing distance, and increasing this distance can eliminate flutter at moderate speeds. Generally, flutter occurs at high speeds.

This is a problem in caster in general i think, just the shopping cart is the best example, it has to easily steer so it need a small trailing distance, i want to barely steer so i use a large trailing distance.

My steering currently works very well, besides the caster i have added a return-to-center hockey-spring in the front, and it really works well, this not too great track has a big bump in it (0:20 in the vid) and it managed to survive that bump and dodge grandpa on the roadside right after. this is a 35,1km/h run with 1 broken buggy motor.

 

However i do need to work on the front.. the axles and bearing start to melt and/or eat into the halfbeams after only 1 or 2 runs..

[TechnicSummse]

44 minutes ago, Marxpek said:

However i do need to work on the front.. the axles and bearing start to melt and/or eat into the halfbeams after only 1 or 2 runs..

I would love to have such a track... BUT, and thats a big BUT... are you not afraid of running too far to the left side, to the street and loose your car under a real cars wheels?

This would be a to dangerous track for me :O

[Marxpek]

13 minutes ago, TechnicSummse said:

This would be a to dangerous track for me :O

This track is about a 2 minute bike ride from home and it is the access road to my old track, i always considered it too dangerous for this exact reason, there is about 30 cm of grass, then some moderately dense bushes (the racer could slip through at certain points though) then a hardcore busy road as you can see, landing there would indeed mean total destruction.

But this is how much faith i have in my new steering now ;D today i did new tests on the same track with ,despite the replaced buggy motor, only slightly better results.

but the track further away from home with the raised edge in the middle but with the same surface, will give better results most likely, its much cleaner and more straight/flat, but i still think i need to solve the front, the axle just has to spin too fast, maybe your double bearing front wheel will has to be applied here, but i really do not like the tire and its off center hub, i would rather decrease the axle speed with a motorcycle wheel.

I also have a rigorous new idea in which i can use a big wheel for the steering, but bracing the wheel still proves difficult which is kind of vital to steering..

[TechnicSummse]

8 minutes ago, Marxpek said:

This track is about a 2 minute bike ride from home and it is the access road to my old track, i always considered it too dangerous for this exact reason, there is about 30 cm of grass, then some moderately dense bushes (the racer could slip through at certain points though) then a hardcore busy road as you can see, landing there would indeed mean total destruction.

But this is how much faith i have in my new steering now ;D today i did new tests on the same track with ,despite the replaced buggy motor, only slightly better results.

 

I also trust my steering... but i dont trust me... especially i wouldnt, if i had to cycle at the same time :D

8 minutes ago, Marxpek said:

i still think i need to solve the front, the axle just has to spin too fast, maybe your double bearing front wheel will has to be applied here, but i really do not like the tire and its off center hub, i would rather decrease the axle speed with a motorcycle wheel.

I also have a rigorous new idea in which i can use a big wheel for the steering, but bracing the wheel still proves difficult which is kind of vital to steering..

I ordered some new parts, to have more options soon ;) Using a bigger front-wheel is also planned... but i still did not found a usable solution to steer with a big wheel.

Your current frontwheel is also included in my order... so we maybe gonna exchange the frontwheels to each other? :D

I also wanted to order a few of those, because i dont own them :( But i didnt find a seller who sells all my wanted parts together

[PorkyMonster]

2 hours ago, Marxpek said:

This is a problem in caster in general i think, just the shopping cart is the best example, it has to easily steer so it need a small trailing distance, i want to barely steer so i use a large trailing distance.

This problem pertains to "caster wheels" - those used by shopping carts, wheelchairs, office-chairs, for e.g. rather than "wheels with caster angle" - car front wheels, for e.g. Here's another quote from the wikipedia site on "Caster Angle":

...The shopping trolley/cart setup has a great deal of trail, but (somewhat confusingly) no caster... 

"Wheels with caster angle" has a tendency to align with the vehicle's body even without forward movement, so when the wheels are turned, they naturally want to return to the straight position.  This behavior is very different from "caster wheels" - which simply follows the direction you push (regardless where the vehicle is facing - you can experiment by pushing a shopping cart at an angle while facing the front), and is why you require additional return-to-center mechanism (the fact that your rear wheels are fixed in one direction helps a bit).

[Marxpek]

14 hours ago, PorkyMonster said:

and is why you require additional return-to-center mechanism

My setup does not require one on a perfect track, it will self-center without a return to center spring purely from it caster setup, without any wobble at high speed. (35+)

Just when i hit a rock or something, the center position is found way faster, making it easier to steer, so the return to center spring helps, but i can work just as well without (on a perfect track)

[Marxpek]

So it has been a while since there was an update, here is what has been changed.

- running on 3 motorcycle 94.2mm tires now.

- 2 driven front wheels

- caster steering setup in the rear 

- weight reduction, totaling 1083 gram including speed computer.

- more narrow and aerodynamic design 

Some pictures:

 

This racer is the longest design yet but it still is only 1083 grams as shown on the pictures, the rear steering setup is still based on caster, the steering was made for small corrections and besides the caster helping it to return to center, there is also a "hockey-spring" installed to give more stable steering. 

The more narrow and more aerodynamic design should also help a bit.

For now the gearing remains 1:3 from the slow output, which i might change again soon, but i want to test and compare this to the small steering wheels setup from earlier ("just 36.2" with that).

And that is where the story ends for now: waiting for a good day with some spare time to do some test runs, as always: high hopes!

 

[TechnicSummse]

Nice design idea :D

I had a rear steering once... worked fine up to ~15 kph any faster speed resulted in heavy oversteering, causing crashes. But i used tiny wheels on this model... maybe yours works better with the big wheel.

I like the inverted shovel :D 

When i tried some aerodynamics, i used this:

I wanted to try this on one of my newer versions again, and see if aerodynamics help or not :)

[Marxpek]

3 minutes ago, TechnicSummse said:

worked fine up to ~15 kph any faster speed resulted in heavy oversteering

to compensate for this; the steering movement is so little that under 15 km/h you barely notice it steering, but it will have to prove itself over 30 km/h yet (i have done a 25 km/h+ test run in the street with this setup but with the motorcross tire in the rear)

8 minutes ago, TechnicSummse said:

I like the inverted shovel :D 

When i tried some aerodynamics, i used this:

i saw that ramp in one of your videos i think, it is a play ramp for pullback cars? seems a bit to big, but i guess it is very light? but worth a try, would at least to be fun/easy to compare results on a car, the bucket also acts as a bumper here, protecting the rc unit in a frontal crash, i do not think i dare to drive it without the bucket, since the rc will be fully exposed in the front without it.

[TechnicSummse]

7 minutes ago, Marxpek said:

i saw that ramp in one of your videos i think, it is a play ramp for pullback cars? seems a bit to big, but i guess it is very light? but worth a try, would at least to be fun/easy to compare results on a car, the bucket also acts as a bumper here, protecting the rc unit in a frontal crash, i do not think i dare to drive it without the bucket, since the rc will be fully exposed in the front without it.

Yep, its a pullback-racer-ramp... and it is not as light as i thaugt :D 

It weights 9g, and you need some construction underneath it, to get it to the right angle, and hold it on place. When i tried it the last time, it added like ~25g in total to my model.

But i like its size... its as wide as the rc- unit, and its length is nice, to cover a pretty big area of the car.

[Marxpek]

here is a small update:

On 16-7-2017 at 7:30 PM, TechnicSummse said:

Nice design idea :D

I had a rear steering once... worked fine up to ~15 kph any faster speed resulted in heavy oversteering, causing crashes.

correct!

 

On 16-7-2017 at 7:49 PM, Marxpek said:

to compensate for this; the steering movement is so little that under 15 km/h you barely notice it steering, but it will have to prove itself over 30 km/h yet (i have done a 25 km/h+ test run in the street with this setup but with the motorcross tire in the rear)

did not work... crashed twice, gave up the steering setup, but turned it around and drove the other way with relatively decent results, but i did not dare to go full speed on a inverted caster setup. so i had to redesign the front again to brace the wheel properly and give it the correct caster.

I also found what could be a game changer on my part, i found that there are 2 different types of rubber used in the 94.2 motorcycle tires, hard black ones and a bit softer grey ones. The grey ones were the ones I used all the time, but i think the harder black ones I just received via bricklink have more potential, since they don't show any ballooning at all, the grey ones did, at max rpm without load. So now there are 2 black tire for drive and a grey tire for steering in the front. You can clearly see the difference in the photos here, the black ones also have a bit of a shine to them, the grey ones do not, but the grey ones do seem to have a bit more traction, but i think the harder black tires will run better because they have less "bounce" to them.

pictures:

Do i dare to keep the gps computer there? it sits perfectly there, but it is very close the the ground...

Steering relies on caster and a return to center spring, which in this case is also the (only) pivot point on the frame, the wheelbracket houses the wheel, and can only move half a beam width right or left. Steering is very limited now but can be easily changed to give it a slightly smaller turning radius. It now weights 1075 gram total, maybe i'll add the bucket again to see if it creates lift :D

And of course as always, terrible weather, but i'll be running outside once i get the chance.. with high hopes as always!

[TechnicSummse]

1 hour ago, Marxpek said:

correct!

I hoped something else ... but i thaught it would be the same then by me.

1 hour ago, Marxpek said:

I also found what could be a game changer on my part, i found that there are 2 different types of rubber used in the 94.2 motorcycle tires, hard black ones and a bit softer grey ones.

Hmm.. how can i see wich ones i have... or how can i be sure to get the right one, if i will buy one?

I also wanted to order a 3rd one for my steering... but now im not sure how to get the right version. I think what i actually have are the "grey" ones?

[Marxpek]

5 hours ago, TechnicSummse said:

I think what i actually have are the "grey" ones?

looks like you have the black, yours have a bit of a shine to them in the pictures and they look black to me.

5 hours ago, TechnicSummse said:

or how can i be sure to get the right one, if i will buy one?

I have no idea, maybe ask the seller? But i doubt many people are aware of this difference..

[mocbuild101]

8 hours ago, Marxpek said:

I also found what could be a game changer on my part, i found that there are 2 different types of rubber used in the 94.2 motorcycle tires, hard black ones and a bit softer grey ones.

I think the difference is age, the softer ones are older and the harder ones are newer. (or is it the other way round...)