April 07, 2020, 02:13:55 pm

## News:

GP Bikes beta17 available!

## Modding tools and documentation

Started by PiBoSo, January 03, 2014, 10:16:07 pm

#### HornetMaX

##### January 08, 2014, 03:18:56 pm #15
Quote from: neoraptor on January 08, 2014, 03:11:28 pm
Is that right?

That was exactly my question #2 above. BTW, in your formula, the "Radius" is the Torus Radius and not the overall tyre radius, which is called ... Radius.

MaX.

#### neoraptor

##### January 08, 2014, 03:30:56 pm #16 Last Edit: January 08, 2014, 03:45:48 pm by neoraptor
I just changed it, so there is no confusion.
What is a bit strange, is that we don't find 17" or 16.5" rim diameter. So I wonder if the model is not :

<-------->
><=====   : 1/2 Tyre
^^
Torus

With this "model", we have:
500 soft front : (28.75-7)*2/2.54=17.12"
500 soft rear : (30.5-11)*2/2.54=15.35"
1000 soft front : (29.5-7)*2/2.54=17.72"
1000 soft rear : (32.5-13)*2/2.54=15.35"

The other possibility is that we don't care about the rim diameter, but only about the tyre diameter.

Edit: I just had a look to the Scooter tyres, and to have the 10" wheel size, they are also based on this model (Tyre Radius - Torus Radius/2)*2/2.54 = 10"
Our greatest glory is not in never falling, but in rising every time we fall. Confucius
>> Wiki to help modders <<

#### HornetMaX

##### January 08, 2014, 06:05:40 pm #17
Quote from: neoraptor on January 08, 2014, 03:30:56 pm
The other possibility is that we don't care about the rim diameter, but only about the tyre diameter.

I think that's the case: the model used seems to be outer tyre radius + torus radius + tread arc (half) angle.

Quote from: neoraptor on January 08, 2014, 03:30:56 pm
Edit: I just had a look to the Scooter tyres, and to have the 10" wheel size, they are also based on this model (Tyre Radius - Torus Radius/2)*2/2.54 = 10"

Don't bother, I've already discussed with oDi, ALEAle and Buggi and they don't know how the model works exactly

MaX.

#### neoraptor

##### January 09, 2014, 11:05:03 am #18
OK. Thanks

Could someone confirmed which model is used for the physic?

Or is it more like this one ?

Also where are the references for each part of the model?
Thanks for the help ;=
Our greatest glory is not in never falling, but in rising every time we fall. Confucius
>> Wiki to help modders <<

#### HornetMaX

##### January 09, 2014, 11:52:30 am #19 Last Edit: January 09, 2014, 11:55:06 am by HornetMaX
Quote from: neoraptor on January 09, 2014, 11:05:03 am
Could someone confirmed which model is used for the physic?

The high level model of GPB (Piboso briefly described it once on the old forum) is:

• 1 front wheel

• 1 chassis

• 1 swingarm

• 1 rear wheel

Joint-wise you have:

• a revolute  ("rotational") joint between the front wheel and the lower front fork

• a prismatic ("translational") joint between  the lower front fork and the steering head (front upper fork)

• a revolute joint between the steering head and the chassis

• a revolute joint between the chassis and the swingarm

• a revolute joint between the swingarm and the rear wheel

The front suspension is a spring + damper between lower and upper front fork.
The rear suspension is a torsional spring + damper between swingarm and chassis. The fact it's torsional is just a technical detail for our purposes, as in-game it is presented as an equivalent "linear" spring+damper. Using a torsional one instead of a "linear" one is just more convenient in terms of model simulation.

MaX.

#### neoraptor

##### January 09, 2014, 12:07:29 pm #20
Thank you very much for these info Max ! It is very useful.

Question 1
?1>Do you also know where are the reference point (ie 0,0,0) for each part?
The 0,0,0 from the chassis is already in the scooter schematic, but what about the other parts? It would be really helpful.

Question 2&3
Suppose I want to calculate the wheelbase of the bike (before adjusting it).
?2>Is it measure with the suspension fully compressed? uncompressed?
?3>I need to do some trigo to retrieve the complete wheelbase (from rake angle + fork length / the same for rear suspension) Correct?
Our greatest glory is not in never falling, but in rising every time we fall. Confucius
>> Wiki to help modders <<

#### HornetMaX

##### January 09, 2014, 01:28:07 pm #21 Last Edit: January 09, 2014, 01:30:22 pm by HornetMaX
Quote from: neoraptor on January 09, 2014, 12:07:29 pm
Thank you very much for these info Max ! It is very useful.

Question 1
?1>Do you also know where are the reference point (ie 0,0,0) for each part?
The 0,0,0 from the chassis is already in the scooter schematic, but what about the other parts? It would be really helpful.

It shouldn't be to hard to figure out using the data of an existing bike. I'll have a look when I start the modding guide.

Quote from: neoraptor on January 09, 2014, 12:07:29 pm
Question 2&3
Suppose I want to calculate the wheelbase of the bike (before adjusting it).
?2>Is it measure with the suspension fully compressed? uncompressed?
?3>I need to do some trigo to retrieve the complete wheelbase (from rake angle + fork length / the same for rear suspension) Correct?

Yeah, you will have to compute it with some trivial trig. The day modtools are out, this would be done by them.

I'm tempted to say the wheelbase is measured with the susp (front and rear) fully uncompressed, because otherwise it will depend on the weight you put on the bike (with/without oil, fuel, rider etc) and on the suspension stiffness and preload. But I'm not sure.

MaX.

P.S.

#### C21

##### January 09, 2014, 02:52:42 pm #22 Last Edit: January 09, 2014, 02:55:50 pm by C21
Max youÂ´re my hero for today
Great explanation!!
# Member of the CAWS Racing Team #

#### neoraptor

##### January 09, 2014, 03:04:17 pm #23 Last Edit: January 09, 2014, 03:29:48 pm by neoraptor
Thanks a lot Max ! This is some really good and useful info !!
I will try to split the parts in the geom file into these categories and display their references in a schematic

The 3D model doesn't use the same reference system? This might also be a point to document.

?> What is the influence of the "footpeg_left/right" parameter?
I noticed the position was wrong in the scooter model. Is it actually used?

?> Is the parameter "rear_length" the length of the shock travel?
?> Are "rear_upper" and "rear_lower" offset from a point? For what are they used?
Our greatest glory is not in never falling, but in rising every time we fall. Confucius
>> Wiki to help modders <<

#### neoraptor

##### January 10, 2014, 11:55:07 am #24 Last Edit: January 10, 2014, 11:57:17 am by neoraptor
I made a first "dynamic" model with some parameters available.
This is only temporary, until the bike tool is released, but at least we have a tool to see the influence of the parameters.

It still needs some works, but all points from the 500 bike are in this model.

For the moment, I have 3 references:
* classic 0,0,0
* chassisRsuspMinMax
* chassisSteer

As well, the rake angle is defined from the chassisSteer point, but I am not sure if this is the correct point.

Todo:
* animate rear suspension
* animate fork travel
* display other information (trail, swingarm length, ...)

Can someone review this model?
I attached the file with this post. Just go to http://www.geogebra.org/webstart/geogebra.html and open it
You can change the points coordinate by right clicking it

@Piboso: if you send me some additional info, we could have a temporary bike tool while waiting for yours

Our greatest glory is not in never falling, but in rising every time we fall. Confucius
>> Wiki to help modders <<

#### Hawk

##### January 10, 2014, 03:45:30 pm #25
You guys are doing fantastic work here!

Brilliant! Keep it up guys!

#### neoraptor

##### January 10, 2014, 05:35:41 pm #26
Thanks Hawk
I have almost finished the tool. The only thing left is the fork !!
So I have a few question :

> How is the fork offset processed?

Our greatest glory is not in never falling, but in rising every time we fall. Confucius
>> Wiki to help modders <<

#### Hawk

##### January 10, 2014, 08:08:30 pm #27
Hi neoraptor.

I noticed your tool above is in French? Will there be an English version?

#### neoraptor

##### January 10, 2014, 08:26:23 pm #28
Yes, of course. The tool is multilingual and at the end you will only push sliders and move some coordinates.

But for the moment I need to complete the fork model !!!
Our greatest glory is not in never falling, but in rising every time we fall. Confucius
>> Wiki to help modders <<

#### C21

##### January 10, 2014, 09:02:15 pm #29

QuoteHow is the fork offset processed

Do you mean how to find in the geom. File?
# Member of the CAWS Racing Team #