[MOC][WIP] John Deere 8RX model in 1:17 scale

[aniszek1]

Some time ago I started building John Deere 8RX model in 1:17 scale.  Unfortunately, due to the difficulty of the model, the scope of the work is very slow.

The project assumes rear and front three-point linkage, rear PTO driven by 2-3 m motors, one pneumatic output, 4x4 drive - XL or L motors ( if I have enough space), steering with servo motor, everything  controlled by 2 sbricks.

One of the biggest problems with this model that I encountered at the very beginning of the project was the drive of the tracks and the exact representation of all its moving elements. The second problem is the 8RX mask and its curvature. This is my 3rd mask concept. Now I'm waiting for the green bricks to finish the prototype of the mask.  And move on to body design .

 

DSC_3566 by Piotr Aniszewski, on Flickr

DSC_3567 by Piotr Aniszewski, on Flickr

DSC_3574 by Piotr Aniszewski, on Flickr

 

Sorry for ma bad english :(

[M_longer]

Links to the larger pictures do not work properly, check your privacy settings at flickr.

[aniszek1]

10 minutes ago, M_longer said:

Links to the larger pictures do not work properly, check your privacy settings at flickr.

I corrected

[1gor]

For 8 series mask you can use my solution on 7230R (mask is very similar)

https://brickshelf.com/cgi-bin/gallery.cgi?f=535335

The main complication for drivetrain is front axle to rear axle ratio. To make it work you have to get front and rear tracks extent (or rolling circumference) ratio.

Good luck

[M_longer]

12 hours ago, I_Igor said:

The main complication for drivetrain is front axle to rear axle ratio.

Central diff to the rescue!

 

 

[Jundis]

13 hours ago, I_Igor said:

The main complication for drivetrain is front axle to rear axle ratio. To make it work you have to get front and rear tracks extent (or rolling circumference) ratio.

Hmm as the driving gears are the large and the extra large sprockets, this should be fairly easy. Large sprocket has 10 teeth, extra large sprocket has 14 teeth, so the ratio is 5:7. Same ratio can be achieved with the 20 teeth bevel gear and the new 28 teeth bevel gear...? Circumference doesn't matter here.

Edited June 22, 2021 by Jundis

[1gor]

2 hours ago, M_longer said:

Central diff to the rescue!

 

 

I know that; I use it very often, but it can not compensate more than some 10%; on posted link I made rear tires with 123mm diameter and front is standard 94.8 but when I tried to motorize that solution I had much resistance...

1 hour ago, Jundis said:

Hmm as the driving gears are the large and the extra large sprockets, this should be fairly easy. Large sprocket has 10 teeth, extra large sprocket has 14 teeth, so the ratio is 5:7. Same ratio can be achieved with the 20 teeth bevel gear and the new 28 teeth bevel gear...? Circumference doesn't matter here.

 

Usually number of tracks segments are key for ratio between two tracks, but you need extent if you want combination with tires ... Like in terrarac CLAAS or Deere harvesters...

@aniszek1 sorry if I have confused you

[Jundis]

1 hour ago, I_Igor said:

Usually number of tracks segments are key for ratio between two tracks

I am really puzzled right now... number of track segments shouldn't affect the speed at all...?

What I forgot was the height of the track segment, which affects the speed and also the speed ratio.

1 hour ago, I_Igor said:

but you need extent if you want combination with tires ... Like in terrarac CLAAS or Deere harvesters...

Ah okay! I thought we were talking about his model here xD

Edited June 22, 2021 by Jundis

[1gor]

 @Jundis number of tracks segments determines rolling circumference (exact distance that tire or track travels with exactly one revolution) and original has smaller tracks at the front (with less segments if you want to represent it in LEGO MOC) so you need speed reduction to rear tracks to compromise front tracks overspeed...

I was trying to make general help for future movers since I plan when I build planned MOCS (both manial and RC) to stop this hobby; new control+ system is to much (in terms of price) for me

[Jundis]

@I_Igor This makes no sense to me. Imagine a flat track and one driving sprocket with constant rev. The track length doesn't affect the speed at all, no matter how long it is. Only the circumference and the rotation speed of the driving sprocket matters.

@aniszek1 : Sry for the misuse of you thread for this :D

[1gor]

5 minutes ago, Jundis said:

@I_Igor This makes no sense to me. Imagine a flat track and one driving sprocket with constant rev. The track length doesn't affect the speed at all, no matter how long it is. Only the circumference and the rotation speed of the driving sprocket matters.

@aniszek1 : Sry for the misuse of you thread for this :D

Ok, then when you decide to build something like this, perhaps you will think about it 

[Andman]

2 hours ago, I_Igor said:

Usually number of tracks segments are key for ratio between two tracks, but you need extent if you want combination with tires ... Like in terrarac CLAAS or Deere harvesters...

Doesn't make sense to me too. Why should the number of track segments should matter? I very much agree with @Jundis' statement:

14 minutes ago, Jundis said:

Only the circumference and the rotation speed of the driving sprocket matters.

 

[1gor]

33 minutes ago, Andman said:

Doesn't make sense to me too. Why should the number of track segments should matter? I very much agree with @Jundis' statement:

 

Because bigger sprocket has more teeth and you need more segments on tracks...I have tried that and like on tires the same thing is with tracks more tracks means more length and more length means bigger rolling circumference, but let @aniszek1 test it. Real 8RX has longer tracks at the rear in the first place 

 

 

 

 

 

Edited June 22, 2021 by I_Igor

[Andman]

2 hours ago, I_Igor said:

Because bigger sprocket has more teeth and you need more segments on tracks...I have tried that and like on tires the same thing is with tracks more tracks means more length and more length means bigger rolling circumference, but let @aniszek1 test it. Real 8RX has longer tracks at the rear in the first place 

 

 

 

 

 

I'm afraid you are fundamentally wrong. The circumference of the rubber track has no influence on the ratio between the front and rear tracks. The only thing which has influence, is the driving sprocket wheel. You can extend the ancathete and the counter ankath as much as you like and the tractor would still run at the same speed and the tracks would still have the same ratio.

3 hours ago, I_Igor said:

more length means bigger rolling circumference

That's were you are wrong. The track is not rolling. It's is driven by the sprocket wheel. The only thing which is rolling, is the sprocket wheel and no matter how long the rubber track is, the sprocket wheel has still the same circumference.

Edited June 22, 2021 by Andman

[1gor]

24 minutes ago, Andman said:

I'm afraid you are fundamentally wrong. The circumference of the rubber track has no influence on the ratio between the front and rear tracks. The only thing which has influence, is the driving sprocket wheel. You can extend the ancathete and the counter ankath as much as you like and the tractor would still run at the same speed and the tracks would still have the same ratio.

That's were you are wrong. The track is not rolling. It's is driven by the sprocket wheel. The only thing which is rolling, is the sprocket wheel and no matter how long the rubber track is, the sprocket wheel has still the same circumference.

You are free to demonstrate your possibility

[Jundis]

31 minutes ago, I_Igor said:

You are free to demonstrate your possibility

Imagine a track openly laying on the ground. Then the sprocket just rolls over it with the speed given by it's rotation and circumference. When the track touches the ground (like it should), there is no relative speed difference between the ground and the track. The sprocket rolls just over it. It's like a gear rolling over a gear rack. Doesn't matter how long the gear rack is ;-)

[Andman]

38 minutes ago, I_Igor said:

You are free to demonstrate your possibility

https://bricksafe.com/files/andman/prototypes/IMG_20210622_194426.MP4

Different number of tread links. Same speed at the idler gear (24z). So the length of the track has no influence to the speed at which it is driven.

Edited June 22, 2021 by Andman

[1gor]

8 minutes ago, Jundis said:

Imagine a track openly laying on the ground. Then the sprocket just rolls over it with the speed given by it's rotation and circumference. When the track touches the ground (like it should), there is no relative speed difference between the ground and the track. The sprocket rolls just over it. It's like a gear rolling over a gear rack. Doesn't matter how long the gear rack is ;-)

Then there is other issue with PF motor? Too much gears, reduction 8:24 and 12:20? Or perhaps bad PF motor?

[Andman]

1 minute ago, I_Igor said:

Then there is other issue with PF motor? Too much gears, reduction 8:24 and 12:20? Or perhaps bad PF motor?

Could be. Do you happen to have a video showing the issue?

[1gor]

3 minutes ago, Andman said:

Could be. Do you happen to have a video showing the issue?

My mobile phone is an old timer so it is difficult to make it, but after I finish some chassis mods to my Fastrac, I'll go to work in Jaguar terrarrac and post some progress in my topic...manual version works but it could be to much for PF motors...(3 differentials, portal axles on tracked module...)...and steering with m-motor on rear axle...but I think that should not be in this topic, any discussion feel free to post in my topic ( https://www.eurobricks.com/forum/index.php?/forums/topic/161934-systems-tractors-and-other-machinery/&page=18)

[aniszek1]

27 minutes ago, Andman said:

https://bricksafe.com/files/andman/prototypes/IMG_20210622_194426.MP4

Different number of tread links. Same speed at the idler gear (24z). So the length of the track has no influence to the speed at which it is driven.

thanks for the video, for a moment I was not sure myself reading the comments whether the length of the tracks affects the speed or not. I see two solutions or will use a central differential as in my MOC URSUS 1604 which I am slowly finishing. Or I will align the speed of the front and the rear through the gear ratio.

 

10 hours ago, M_longer said:

Central diff to the rescue!

The central differential is a good solution but it takes up a lot of space when connecting, I did it in URSUS. There is another downside to the central differnity. If the front or rear gets stuck (slips), the tractor will not move with this solution. all propulsion will go to the axle that is lighter and skidded. I know that this is only a model and it will not work anywhere in the field ;) But on a slippery surface, Lego tracks without rubber pin ( or whatever they are called ) skid very easily.

[1gor]

1 minute ago, aniszek1 said:

 There is another downside to the central differnity. If the front or rear gets stuck (slips), the tractor will not move with this solution. all propulsion will go to the axle that is lighter and skidded. I know that this is only a model and it will not work anywhere in the field ;) But on a slippery surface, Lego tracks without rubber pin ( or whatever they are called ) skid very easily.

I think you give me idea how to solve my problem 

Thanks 

[Andman]

1 minute ago, aniszek1 said:

thanks for the video, for a moment I was not sure myself reading the comments whether the length of the tracks affects the speed or not. I see two solutions or will use a central differential as in my MOC URSUS 1604 which I am slowly finishing. Or I will align the speed of the front and the rear through the gear ratio.

My gut feeling tells me that it could be wise to get the gear ratio at the diff as close as possible to the ratio between front drive and rear drive, so the diff turns as little as possible when you are driving. In the best case it does not turn at all, when you are driving although front and back tires have different diameters. That way you lower the total friction because the internal gears of the diff do not turn under normal circumstances. Does that make sense?

[TeamThrifty]

20 hours ago, Andman said:

The circumference of the rubber track has no influence on the ratio between the front and rear tracks. The only thing which has influence, is the driving sprocket wheel.

Agreed.. Only the driving sprocket is relevant.

 

On 6/21/2021 at 10:43 PM, I_Igor said:

or 8 series mask you can use my solution on 7230R (mask is very similar)

I'd forgotten about this excellent moc! I love tractors, so i'm bound to love this.. but what i like about the bodywork (mask as its being referred to), is that its technic - not a thousand bricks used to close every gap. 

8RX is an excellent concept. (I've been looking at the Claas Axion terra trac... ). Central diff is an option, depends on how faithful to the original you want to be. It doesn't use a central diff, very few tractors do - one exception is the Xerion due to its steering modes.

[1gor]

3 minutes ago, TeamThrifty said:

Agreed.. Only the driving sprocket is relevant.

 

I'd forgotten about this excellent moc! I love tractors, so i'm bound to love this.. but what i like about the bodywork (mask as its being referred to), is that its technic - not a thousand bricks used to close every gap. 

8RX is an excellent concept. (I've been looking at the Claas Axion terra trac... ). Central diff is an option, depends on how faithful to the original you want to be. It doesn't use a central diff, very few tractors do - one exception is the Xerion due to its steering modes.

I have managed curved JCB Fastrac bonnet with technic parts, but drivetrain problem I had mainly due to PF XL motor inconsistent power output. Thanks for Deere praise (it is still assembled)...usually real tractors have cvt transmission that compensate front tires overspeed, but it depends on front wheel to rear wheel ratio...