The caster line needs to run through the center of the wheel. And the trolley cart wheels show how unstable they are the moment they loose contact with the ground. Which at high speeds without suspension, your wheel absolutely does. Mount a gopro to it and film while running.

  On 9/4/2017 at 7:08 AM, PorkyMonster said:

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.

I was checking this again... basicly caster is the angle of the steering axle compared to the wheel-standing-point, and trail is the distance between those both points (axles hitting the ground).

But here also the caster angle is just used to reach a trail, with the steering-point being behind the frontwheel.

So again... i am at the point, that my front-setup is pretty ok.

 

  On 9/4/2017 at 11:31 AM, nicjasno said:

The caster line needs to run through the center of the wheel. And the trolley cart wheels show how unstable they are the moment they loose contact with the ground. Which at high speeds without suspension, your wheel absolutely does. Mount a gopro to it and film while running.

  On 4.9.2017 at 9:08 AM, PorkyMonster said:

all depending on where the two lines intersect, which need not be the center of the wheel

@nicjasno 

As @PorkyMonster said again... the steering-axle does not have to run trough the center of the wheel.

 

Take a look at the following video, wich shows the "regular" bike-setup as unstable as mine while not in motion... you should also "shake" the trike in your video like you did it with my setup ;)

But thank you for the ideas.

There is another problem on those tests you build. The wheels need to be whithin a casing... they may not be at the end of the axle, because this produces axle-bending, and like this friction, wich reduces speed. So a front-setup with 2 wheels would only work, if you place them on one fixed axle, or if you house the wheels from both sides, but this again will need a really complicated construction and lead to 4 bearing points at the front.

 

  On 4.9.2017 at 9:08 AM, PorkyMonster said:

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? 

Look at the text above 

 

@nicjasno

I was bored a bit, since i could not testdrive today (bad weather)... so i build just for you something like you was thinking about (i think) .

Caster like in real bikes, huge suspension travel and so on... it looks nice... works ok... but results in a really high center of gravity. Everything would need to be a bit more reinforced here... especially the steering part, but it is just a prototype.

This setup could be really nice for a offroad-trike-racer :D 

But it would need a wide and stable rear-axle. Maybe i will build somethin like this for fun in the future.

 

 

Suspension travel:

10-3= 7 studs

 

Having the wheel supported on both sides is not necessary.

The friction and rolling resistance are the least of your problems.

And as you can see in the video i made, the cartwheel has the problem, that it is inherently unstable. Every slight difference between the rear wheels will immediatelly affect it, because the whole vehicle from the rear wheels forward acts as a giant lever on it.

Your soft bike suspension is also not good, because there are gigantic caster changes during the suspension travel, making the whole thing unpredictable and unstable.

Also, the center of gravity is not really important here, since the battery pack makes is pretty low. If i would be building such a vehicle, i'd use the double wishbone front, and have a single wheel as the drive wheel in the back, like a morgan 3 wheeler (if small rolling resistance is what you're after).

Ultimately, i'd make a baja truck like chasis, with soft suspension and the proper front geometry. This would make it all very stable at high speeds over rough terrain.

Edited September 9, 20177 yr by nicjasno

  On 9/9/2017 at 8:13 PM, nicjasno said:

Having the wheel supported on both sides is not necessary.

The friction and rolling resistance are the least of your problems.

Well they are, since i want to go as fast as possible... you can see the difference of wheels supported at the outside and wheels not supportet, if you look at @mocbuild101's speed car, and compare it to my 2-motor-record-car.

His car is lighter then mine, but still ~2kph slower, using the same gearing as i used. The difference is... he put the wheels at the end of the axles... i supported them at the outsides.

I made tests with exact same setup... one time supportet at the outside, and the second time without support... the result was ~1,5 kph less.

If you want to use double wishbone with the Lego-wheel-hubs it will be even worse... they will produce a horrible friction at higher speed.

  3 minutes ago, nicjasno said:

Your soft bike suspension is also not good, because there are gigantic caster changes during the suspension travel, making the whole thing unpredictable and unstable.

There is a big caster change... yes thats right... but even fully compressed, there is still a positive caster ;)

  3 minutes ago, nicjasno said:

If i would be building such a vehicle, i'd use the double wishbone front, and have a single wheel as the drive wheel in the back, like a morgan 3 wheeler (if small rolling resistance is what you're after).

I would do this, if i wanted to build a fast fun-car being able to run on rough terrain, like this one:

But that's not what i am aiming for...

 

  3 minutes ago, nicjasno said:

Ultimately, i'd make a baja truck like chasis, with soft suspension and the proper front geometry. This would make it all very stable at high speeds over rough terrain.

Well again... i am not aiming for rough terrain... i am trying to reach highest possible speed on a as smoth as possible surface.

  Quote

Also, the center of gravity is not really important here, since the battery pack makes is pretty low.

The battery-pack have to be mounted (suspensiontravel+ groundclearance)= 7+2= 9 studs above the ground in the example. This is verry high, as you can see below... i need some ideas/help

___________________________________________________________________________________________________________________________________

 

Here i could need help:

 

As i wrote last week, i had/have some steering problems:

  On 9/3/2017 at 10:50 AM, TechnicSummse said:

When steering the car tilts a bit to the side... this causes one of the rear wheels to lift from ground, and the supporting wheel to contact with the ground. 

Furthermore the supporting-wheel acts as lever, and also lifts a bit the second rear-wheel, to also loose grip.

What i did...:

- i removed the supporting wheels

- i set center of gravity ~1 stud deeper again

- i made the rear axle even wider as you can see in the following picture:

But, as you can see in the picture above, my "motor-protection-beams" are damaged after the first testrun again.

The follwing happens:

I am driving ~30kph, and at some point i need to do small steering corrections. Up to this speed everything goes pretty ok... but at 30+kph i do just little corrections, and the car tilts to the opposite side ...

...once the car tilts, it hits the ground with the "motor-protection-beams" and the rear part lifts, looses traction and does a 180° turn... like you would use the handbrake in your car while driving a curve.

 

Any idea what i could do?

- Wider rear-axle does not work, because there is no differential, and it will bring problems to the steering. Also this would add air resistance, axle-bending and so on.

- Shorten the wheelbase? Should result in less tilting, but a more instable car at all. Also this would require to move the battery-box at the end of the car, what will change the balance of the car... not sure if in a good way...

- any other ideas? I am open to all, since i want to test this gearing at its full potential... i have allready the next idea, and want to build it... but at first i need to know what this one could do... so please help 

As i suggest the whole time, you need a different front suspension. The trolley cart wheel that you have now is the worst possible option.

I guess I should put my thoughts into the mix...

 

  On 9/3/2017 at 4:02 PM, TechnicSummse said:

  Quote

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".

This happens in cars only... did you see any parking bike with a straight frontwheel? 

Well there are some other things you need to consider:

• The weight of the rider
• The angle of the whole bike (which is tilted when parked)
• The gyroscopic affect of the wheels (when moving)

  On 9/9/2017 at 6:04 PM, TechnicSummse said:

the steering-axle does not have to run trough the center of the wheel.

Yes, and no... The center of the wheel just needs to be in line with the turning point of the steering.

  On 9/9/2017 at 8:13 PM, nicjasno said:

Your soft bike suspension is also not good, because there are gigantic caster changes during the suspension travel, making the whole thing unpredictable and unstable.

Yes, but it's not the softness that is the problem, it's the way it was made - real bikes have the wheel attached directly inline with the shock absorber - which means the angel wouldn't change.

  On 9/9/2017 at 9:02 PM, TechnicSummse said:

His car is lighter then mine, but still ~2kph slower, using the same gearing as i used. The difference is... he put the wheels at the end of the axles... i supported them at the outsides.

The other difference was acceleration time - you had more time to accelerate. (also, are you using standard 1.5v alkaline batteries? Because I'm using 1.2v NIMH batteries)

  On 9/9/2017 at 9:02 PM, TechnicSummse said:

Any idea what i could do?

Think about the triangle of contact with the ground, and were the weight is positioned over it.  The way you have it at the moment puts quite a bit of weight outside the triangle of contact.

  On 9/9/2017 at 6:04 PM, TechnicSummse said:

So again... i am at the point, that my front-setup is pretty ok.

 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).

  On 9/9/2017 at 9:02 PM, TechnicSummse said:

The follwing happens:

I am driving ~30kph, and at some point i need to do small steering corrections. Up to this speed everything goes pretty ok... but at 30+kph i do just little corrections, and the car tilts to the opposite side ...

...once the car tilts, it hits the ground with the "motor-protection-beams" and the rear part lifts, looses traction and does a 180° turn... like you would use the handbrake in your car while driving a curve.

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.

 

 

  On 9/10/2017 at 5:34 AM, PorkyMonster said:

reduce your steering angle (to really really small) to avoid drastic direction change..

Yeah, that affects it a lot too. (I forgot to mention that...)

  On 9/10/2017 at 5:34 AM, PorkyMonster said:

Another thing you could try is to move more weight to the rear...

...As long as you keep the weight mostly inside the contact area.

 

Edited September 10, 20177 yr by mocbuild101
er... why did it post automatically??

This guy has the right idea, but the concept has a few fatal flaws, like the huge bump steer in the front suspension setup, and you have the better drivetrain setup.

 

  On 9/10/2017 at 5:03 AM, mocbuild101 said:

I guess I should put my thoughts into the mix...

Yes, and no... The center of the wheel just needs to be in line with the turning point of the steering.

Hmm where is the difference to "it has to be in the center of the wheel"? :D

The center of the wheel basicly has nothing to do with the caster... it is sometimes on this line... but not allways...and does not have to be there...as you can see at the following pictures:

  2 hours ago, mocbuild101 said:

Yes, but it's not the softness that is the problem, it's the way it was made - real bikes have the wheel attached directly inline with the shock absorber - which means the angel wouldn't change.

Hmm... it seems i work in the wrong garage :D

Never seen something like this?

  2 hours ago, mocbuild101 said:

Think about the triangle of contact with the ground, and were the weight is positioned over it.  The way you have it at the moment puts quite a bit of weight outside the triangle of contact.

Yes... it seems this is my problem... that's why i made the rear-axle wider in the last step. But the way i made my gearing (36:16), i can not put the motors to the middle of the car.

But i had an idea this morning... while using my smaller frontwheel it seemed to work without that much tilting. The biggest difference to the big frontwheel now is the wheelbase i guess. I think it's about 5-6 Studs bigger now. I think i will change this at first now.

  On 9/10/2017 at 5:34 AM, PorkyMonster said:

Like what @Marxpek and @mocbuild101 have done - reduce your steering angle (to really really small) to avoid drastic direction change... 

Hmm... i would need to change the steering-lever to 0,5 studs then :D

  1 hour ago, PorkyMonster said:

Another thing you could try is to move more weight to the rear.

The balance point now is right between the motors and the PF-battery-box, i am afraid, i will loose contact with the frontwheel, if i put the weight more at the rear.

But i will also try this.

 

Thank you for the suggestions so far... any other ideas? :D

  On 9/10/2017 at 7:13 AM, nicjasno said:

This guy has the right idea, but the concept has a few fatal flaws, like the huge bump steer in the front suspension setup, and you have the better drivetrain setup.

I know this one... it is really nice. But i dont see, why to suspend the front axle, if 80% of the weight rest on the rear wheel, wich is not suspended :D

But i can not use such a long-travel suspension on my car... 

It is like you would compare a dragster (my car) vs a dune buggy (your suspension thaughts/ the cars in the videos).

I like THIS suspension the most :D

Most of your weight is inbetween the axles, and a dragster is designed to lift the front wheels of the ground. Something whch your car will not do.

As far as the bike suspension goes that you made, it is very different from the real life forks that you posted in the previous post. The real life example has very small changes in caster, yours has huge ones, and is tilted too much actually.

  On 9/10/2017 at 7:36 AM, TechnicSummse said:

Hmm where is the difference to "it has to be in the center of the wheel"?

What I meant is, the direction of travel, the wheel, and the steering all need to be in the same line, otherwise it will affect the steering of the vehicle. (I know, it was kind of a useless comment...)

  On 9/10/2017 at 7:36 AM, TechnicSummse said:

Never seen something like this?

Well, no...  (but it is still closer to the shocks than in your example)

  On 9/10/2017 at 7:36 AM, TechnicSummse said:

i will loose contact with the frontwheel, if i put the weight more at the rear.

But you still should have enough traction for steering...

  On 9/10/2017 at 9:00 AM, nicjasno said:

Most of your weight is inbetween the axles, and a dragster is designed to lift the front wheels of the ground. Something whch your car will not do.

I wanted to change the wheelbase.... but currently i decided to follow a new idea. The battery-box will be behind the rear-wheels i think, and like this i will have a 20:80 weight ratio i guess.

Hope i can show you some pictures soon :)

 

  Quote

As far as the bike suspension goes that you made, it is very different from the real life forks that you posted in the previous post. The real life example has very small changes in caster, yours has huge ones, and is tilted too much actually.

  On 9/10/2017 at 10:19 AM, mocbuild101 said:

Well, no...  (but it is still closer to the shocks than in your example)

 

I never said its a 1:1 copy of the real life thing... but it's similar to it... but still the caster stays positive with fully compressed springs... so everything should be fine :)

And at the end, this was just a protype to see what i maybe could use.

The lego shocks do not allow to work like regular bike shock absorbers do. They only work at relativly small angles... if they are tilted to much... like they would be in a regular motorcycle fork... there will be to much friction, and they wont compress.

Edited September 10, 20177 yr by TechnicSummse

Good to see your progress, i have been away from the site for a while, so a lot to catch up, and did not read all here but i noticed this:

I see you took my "shopping cart steering" and have some issues with it, i can tell you your steering should be reduced, maybe try a fake engine crank shaft, that helped me to reduce steering, one drawback is that under 30km/h you will not be able to steer very effective, but that is not really interesting to us..

I hope I will find more time to break my current max speed of 39.5km/h on the "bumpier old 35km/h racer track".. soo close...and my redesign has been untested yet, but is a more promising build! (bluffing to keep you on your toes?!?) 

Good luck!

 

Welcome back @Marxpek, I was wondering what happened to you...

  On 9/10/2017 at 7:11 PM, Marxpek said:

...my current max speed of 39.5km/h

Wow, you're so close to 40km/h! When did you get to that speed, and with what design?

@Marxpek nice to see you again... no time right now... gonna write some more later...

 

here the promised pictures:

 

  On 9/11/2017 at 6:31 AM, TechnicSummse said:

here the promised pictures:

It looks better, but it looks like the contact area has gotten even smaller...

  On 9/11/2017 at 7:03 AM, mocbuild101 said:

It looks better, but it looks like the contact area has gotten even smaller...

from 10 to 8 studs between the wheels... yes :(

But 8 studs is what i had all the time before and worked well...

  On 9/11/2017 at 4:53 AM, mocbuild101 said:

Wow, you're so close to 40km/h! When did you get to that speed, and with what design?

2 weeks ago, of course on video and recorded with gps, not sure if i took detailed pictures of that design, but there is always video.

@TechnicSummse i see you took the suspension advice... i'm pretty sure you will remove it soon, I did... But it is kind of fun to see you do all the tests i have done a few months back (never documented, i was not on the forum). Althought the scale of the bumps is a valid arguement, i do not believe in suspension, mainly because we cannot make  good suspension, just springs is no great suspension (only makes it bounce longer, since they do not have dampeners). My very first speed record actually had suspension, but when I took it out i got way better results with the same design on a rough test track.

  On 9/11/2017 at 3:38 PM, Marxpek said:

2 weeks ago, of course on video and recorded with gps, not sure if i took detailed pictures of that design, but there is always video.

@TechnicSummse i see you took the suspension advice... i'm pretty sure you will remove it soon, I did... But it is kind of fun to see you do all the tests i have done a few months back (never documented, i was not on the forum). Althought the scale of the bumps is a valid arguement, i do not believe in suspension, mainly because we cannot make  good suspension, just springs is no great suspension (only makes it bounce longer, since they do not have dampeners). My very first speed record actually had suspension, but when I took it out i got way better results with the same design on a rough test track.

Basicly its just building for fun, since i could not test anything in the last days. The point of having no dampers i have in mind, since i startet with lego again, but ... these builds are just to do something

And i really hate it, to do nothing :(

If everthing goes fine, my 3rd 8366 will arrive soon, then i will have 8 motors and 3 units... so i can build two 4-motor-cars at the same time, if the weather stays that bad.

I know... one day i did not want to buy even a second one... but sorry... 30€ including shipping... i could not say no 

 

I had a 40+ run last week, but i was not 100% sure, if there maybe was some slipping at the rear wheel... that's also the reason, why i mounted the speedcomputer at the front wheel now... especially for you :D

Edited September 11, 20177 yr by TechnicSummse

  On 9/11/2017 at 4:22 PM, TechnicSummse said:

If everthing goes fine, my 3rd 8366 will arrive soon, then i will have 8 motors and 3 units... so i can build two 4-motor-cars at the same time, if the weather stays that bad.

I know... one day i did not want to buy even a second one... but sorry... 30€ including shipping... i could not say no 

that's either a scam or you are very very lucky! i wish you the last of course!

  On 9/11/2017 at 4:22 PM, TechnicSummse said:

I had a 40+ run last week, but i was not 100% sure, if there maybe was some slipping at the rear wheel... that's also the reason, why i mounted the speedcomputer at the front wheel now... especially for you :D

just get a GPS device.. but good you took the speed computer to the non-driven wheel, but the GPS device will eliminate all the non-believers since it shows more then just speed (altitude, acceleration, ect.)

 

  On 9/11/2017 at 4:22 PM, TechnicSummse said:

Basicly its just building for fun, since i could not test anything in the last days. The point of having no dampers i have in mind, since i startet with lego again, but ... these builds are just to do something

And i really hate it, to do nothing :(

agreed sitting still is no fun, (will you enter the tc12 contest for fun?) but i hate redesigning before i can test... and that remains a problem here as well.. bad bad weather.. but when you double up you can double up your testing speed, good thinking! ;)

I hope i can test mine this weekend, let's both pray to the weather gods..

  On 9/11/2017 at 5:41 PM, Marxpek said:

that's either a scam or you are very very lucky! i wish you the last of course!

It was just announced as "lego rc car"... in the description he wrote, it's a toy from the late 80's or early 90's. Well... it has been sold as non working... but at the end...just one working motor would be worth the price... so i could not do anything wrong here i think :D

  2 minutes ago, Marxpek said:

just get a GPS device.. but good you took the speed computer to the non-driven wheel, but the GPS device will eliminate all the non-believers since it shows more then just speed (altitude, acceleration, ect.)

Maybe i will get a gopro in the next month... i heared they have included gps in some versions...

  2 minutes ago, Marxpek said:

agreed sitting still is no fun, (will you enter the tc12 contest for fun?)

I will not enter TC12... i think i don't have the modeling skills for such things... i am more technically... looking for working solutions wich seem not possible to solve...

  2 minutes ago, Marxpek said:

but i hate redesigning before i can test... and that remains a problem here as well.. bad bad weather.. but when you double up you can double up your testing speed, good thinking! ;)

I don't know how many versions i disassembled before they were tested, just because of the weather...

  2 minutes ago, Marxpek said:

I hope i can test mine this weekend, let's both pray to the weather gods..

I wish you good luck :)

Any chance to see some of you progres in the last months?

  On 9/11/2017 at 5:50 PM, TechnicSummse said:

Maybe i will get a gopro in the next month... i heared they have included gps in some versions...

Those are pretty expensive, great equipment, but i would not dare to strap a 500 euro camera on my racer.. besides that i think that they are heavier and bulkier then cycling computers. I bought them separate, a 1080p@60fps (or 4k@30fps) action cam for 60 euro and gps cycling computer for 60 euro. I use them on separate occasions and should one get destroyed it is "only" 60 euro compared to a gopro5 (400-500?)

  On 9/11/2017 at 5:50 PM, TechnicSummse said:

Any chance to see some of you progres in the last months?

Well any run i do gets filmed with my action cam mounted to my bike so yes, but i do not recall if i took pictures of all the designs i made (4 or 5), i have a habit to forget taking pictures... i will have to dig through my photos a bit.

I did drive over one of my designs... had to happen someday, it cut me off the road while it was overtaking me, loose parts in the steering ... luckily it went into the grass and i drove over it there. damage was minimal: just a 15L liftarm went to heaven, nothing else. luckily... Sadly not in the shot of the camera.

 

  On 9/11/2017 at 7:22 PM, Marxpek said:

Those are pretty expensive, great equipment, but i would not dare to strap a 500 euro camera on my racer.. besides that i think that they are heavier and bulkier then cycling

i didnt know that 

 

Well... to my latest 8366... im pretty happy at the end.  This is how it arrived...dirty and NOT working :(

 

First i cleaned the RC-units battery-contacts, and tested it with a pair of pf leds.

The steering seemed to work, but the 3rd power-step (full power) did not work... the leds were like: glowing a bit, brighter, dark...

When testing them at the auxilary output, everything was fine. So i made the same test with my old remote... and HEY... everthing worked fine :)

 

So i took a look into the remote... and i found a broken cable at the drive potentiometer. I soldered it and glued it to the circiut board.

And... again... Yeah! ... it works. 

At the end i removed the leds... and tested it with the motors, you can see the result in the video below:

 

So... 32€ and the last two days of free-time to work on it... and i am a happy guy 

Oh... is this still unmodifed lego now? :D

 

 

To Topic:

I was testing my suspended version 2 days ago at the evening... with the result of a big crash again (it was dark, and the street still wet... not a good combination) :(

Steering was still sh**... so i started rebuilding again... but last 2 days went to the new 8366 repairing... 

Also the weather is so f***ing bad... its raining for about 1 week now... and it seems the weather will stay like that for the next few days :(

 

Edited September 13, 20177 yr by TechnicSummse