Design process of a new motocross bike (Pursang)

Erick
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Erick
Edited Date/Time 4/23/2014 3:29pm
A very interesting website about the design of a new motocross bike with the old brand name Pursang.

Design Process

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Erick
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Erick 8/2/2011 10:12am
8/2/2011 10:12am Edited Date/Time 8/2/2011 10:12am
The frame is just beautiful if you ask me. Look at the castings, thats impressive for a single frame. These guys have serious manufacturing skills. I don't know if they did it themselves but they sure put in a very good effort.

DrSweden
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DrSweden 8/2/2011 10:30am
8/2/2011 10:30am
Erick wrote:
The frame is just beautiful if you ask me. Look at the castings, thats impressive for a single frame. These guys have serious manufacturing skills. I...
The frame is just beautiful if you ask me. Look at the castings, thats impressive for a single frame. These guys have serious manufacturing skills. I don't know if they did it themselves but they sure put in a very good effort.

In what way is that good casting? I'm clueless and I don't know what to look for other than the surface looks smooth?
Erick
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Erick 8/2/2011 10:54am
8/2/2011 10:54am Edited Date/Time 8/2/2011 10:56am
Erick wrote:
The frame is just beautiful if you ask me. Look at the castings, thats impressive for a single frame. These guys have serious manufacturing skills. I...
The frame is just beautiful if you ask me. Look at the castings, thats impressive for a single frame. These guys have serious manufacturing skills. I don't know if they did it themselves but they sure put in a very good effort.

DrSweden wrote:
In what way is that good casting? I'm clueless and I don't know what to look for other than the surface looks smooth?
Well, the castings are propably sand cast. With sand casting you get the same signature as sand. When you use coarse sand the texture will also be coarse. Since sand casting is pretty economical for low production units it is a suitable method for a prototype. If they plan to produce the frame in higher number you could consider a different method. But sand casting can also be done on a larger scale nevertheless.

Anyway, a rough surface finish is very common with these castings. Take a look at KTM engine cases and also forgings and castings from different aluminum examples. You will see similar textures.

There is also mold castings. Japanese bikes use mold castings for the engine cases. Mold castings produce a smoother and sometimes even shiny texture. The texture depends for instance for the type of aluminium used.

A rough finish is not a problem on relatively lightly loaded parts. The amount of aluminium in the frame is sufficient to lower stress levels to prevent crack propagation from the rough texture. When you have for instance the same roughness on a crackshaft it will definatly crack after only a few cycles because of the high dynamic loads.

I hope this makes things a bit clear. I can explain it further if you want Smile

The Shop

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DrSweden
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DrSweden 8/2/2011 12:48pm
8/2/2011 12:48pm
Erick wrote:
Well, the castings are propably sand cast. With sand casting you get the same signature as sand. When you use coarse sand the texture will also...
Well, the castings are propably sand cast. With sand casting you get the same signature as sand. When you use coarse sand the texture will also be coarse. Since sand casting is pretty economical for low production units it is a suitable method for a prototype. If they plan to produce the frame in higher number you could consider a different method. But sand casting can also be done on a larger scale nevertheless.

Anyway, a rough surface finish is very common with these castings. Take a look at KTM engine cases and also forgings and castings from different aluminum examples. You will see similar textures.

There is also mold castings. Japanese bikes use mold castings for the engine cases. Mold castings produce a smoother and sometimes even shiny texture. The texture depends for instance for the type of aluminium used.

A rough finish is not a problem on relatively lightly loaded parts. The amount of aluminium in the frame is sufficient to lower stress levels to prevent crack propagation from the rough texture. When you have for instance the same roughness on a crackshaft it will definatly crack after only a few cycles because of the high dynamic loads.

I hope this makes things a bit clear. I can explain it further if you want Smile
Cool, no that will do. But I wonder about the looks since earlier pictures shows a diff surface, and also that the frame is not single?

crashnburn11 8/2/2011 12:56pm
8/2/2011 12:56pm Edited Date/Time 8/2/2011 12:57pm
DrSweden wrote:
Cool, no that will do. But I wonder about the looks since earlier pictures shows a diff surface, and also that the frame is not single...
Cool, no that will do. But I wonder about the looks since earlier pictures shows a diff surface, and also that the frame is not single?

If by single, you mean one piece, then yes, it is welded together at the seams to create one piece, as seen in the picture in the first post.

If by single you are talking about single/twin spars, the no, it is not single.

Looks very nice for a prototype frame, I would have said a prototype would have been mode from more pieces than that and consolidated later
teggers
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teggers 8/2/2011 1:04pm
8/2/2011 1:04pm
Thanks for this.....very interesting.

About the aluminum casting.....I need some custom stuff done. Any suggestions on how to go about doing this....I need about 500 units.
Erick
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Erick 8/2/2011 2:12pm
8/2/2011 2:12pm
teggers wrote:
Thanks for this.....very interesting.

About the aluminum casting.....I need some custom stuff done. Any suggestions on how to go about doing this....I need about 500 units.
You can do it yourself, if you have the knowledge and tooling ($$$). What do you want to be cast? What material? How big? What are your tolerances?

If it is moto related you should post it here. I would like to elaborate
OriolMassot
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OriolMassot 8/2/2011 2:42pm
8/2/2011 2:42pm
I wonder if the descendants (and owners of Bultaco rights) have something to say about the name. Long time ago a bunch of french enthusiasts bought the rights to use the name Bultaco. Then, they had problems with the family (i guess it was much more about money or not fulfilling the conditions).

Nowadays Bultaco is only a brand for jerseys and casual wear, nothing about bikes. Someone thought it was "cool" to wear the logo anywhere, but being realistic, it was sad not to see the re-born of the mitical brand as Ossa did a couple of years ago.

So the french enterprise decided to rename his bikes with the: "SHERpa + bultaCO" = SHERCO name.

And yes, Bultaco Pursang's name belongs to the original idea of thoroughbred, because in catalan, thoroughbred means "Pura sang", and also in spanish is called: "Purasangre".

Those past days, catalan brands named its bikes with translations (let alone the OSSA Phantom or the OSSA Enduro), but as an example, the beautiful Montesa CAPPRA had the name because of: "CABRA MONTESA" which translated is "Cabra = Goat" and Montesa a kind of goat.
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OriolMassot 8/2/2011 3:01pm
8/2/2011 3:01pm
Heck! Glad people is keeping alive our motorcycle history! Thumbs up for that adventure! (And sure I want one of those when they'll be on the market!) We still want more things like that: OSSA, Pursang... Come on!
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teggers 8/2/2011 3:26pm
8/2/2011 3:26pm
teggers wrote:
Thanks for this.....very interesting.

About the aluminum casting.....I need some custom stuff done. Any suggestions on how to go about doing this....I need about 500 units.
Erick wrote:
You can do it yourself, if you have the knowledge and tooling ($$$). What do you want to be cast? What material? How big? What are...
You can do it yourself, if you have the knowledge and tooling ($$$). What do you want to be cast? What material? How big? What are your tolerances?

If it is moto related you should post it here. I would like to elaborate
Not Moto....could you send me an email with your number, I will call you with the project. teggersmx@yahoo.com
Erick
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Erick 8/2/2011 3:30pm
8/2/2011 3:30pm
You are absolutely right, we need as much brands as possible. The more choices, the better Smile
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stillwelding 8/2/2011 3:40pm
8/2/2011 3:40pm
teggers wrote:
Thanks for this.....very interesting.

About the aluminum casting.....I need some custom stuff done. Any suggestions on how to go about doing this....I need about 500 units.
Try http://www.laaluminum.com/,They're actually in Idaho.
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Tiki 8/2/2011 4:05pm
8/2/2011 4:05pm
I think the seat height should be even taller. Just go for the record so you have to be 6'3" to ride the bike.
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Spartacus 8/2/2011 4:14pm
8/2/2011 4:14pm
The MK4 rocked with its fiberglass box fenders.

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mjskier 8/2/2011 4:25pm
8/2/2011 4:25pm
Tiki wrote:
I think the seat height should be even taller. Just go for the record so you have to be 6'3" to ride the bike.
I'd be fine with that (6'3.5"). It would save me from buying a tall seat like I have to do on all my bikes.
imoto316
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imoto316 8/2/2011 4:39pm
8/2/2011 4:39pm
I've always loved the look of the gas tanks on the pursangs.

I had a clapped out Bultaco but unfortunately it had a plastic tank. Boy, was it easy to push out the back end and "flat track" a corner on that thing. It was the loudest thing I've had because there was no "pickle" with the exhaust.

I hope this bike ends up looking a lot like the old pursang.
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imoto316 8/2/2011 4:44pm
8/2/2011 4:44pm
Oops, should have clicked on the link. I like the looks of the old one better.

Pit Row

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ns503
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ns503 8/2/2011 5:00pm
8/2/2011 5:00pm
teggers wrote:
Thanks for this.....very interesting.

About the aluminum casting.....I need some custom stuff done. Any suggestions on how to go about doing this....I need about 500 units.
Erick wrote:
You can do it yourself, if you have the knowledge and tooling ($$$). What do you want to be cast? What material? How big? What are...
You can do it yourself, if you have the knowledge and tooling ($$$). What do you want to be cast? What material? How big? What are your tolerances?

If it is moto related you should post it here. I would like to elaborate
teggers wrote:
Not Moto....could you send me an email with your number, I will call you with the project. teggersmx@yahoo.com
Too bad you weren't a bit closer to here - I do business with a fellow who has a foundry business. He's casting & machining all different kinds of aluminum stuff.
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andymoto 8/2/2011 7:30pm
8/2/2011 7:30pm
imoto316 wrote:
Oops, should have clicked on the link. I like the looks of the old one better.
Admire the fellas for the effort, but nothing replaces those original Bultaco Pursangs character.
DrSweden
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DrSweden 8/2/2011 10:34pm
8/2/2011 10:34pm
crashnburn11 wrote:
If by single, you mean one piece, then yes, it is welded together at the seams to create one piece, as seen in the picture in...
If by single, you mean one piece, then yes, it is welded together at the seams to create one piece, as seen in the picture in the first post.

If by single you are talking about single/twin spars, the no, it is not single.

Looks very nice for a prototype frame, I would have said a prototype would have been mode from more pieces than that and consolidated later
Crap, he meant single as in one frame only, I though he meant one single piece...

I don't get how these guys could find the motivation to do it, and only one bike? I think it's one of those things one just needs to applaud and be impressed by. There's no negative in this what so ever and if they can do it, I guess others can as well. I love to see more prototypes running around! Smile
Jim Palau-Ribes 8/3/2011 1:14am
8/3/2011 1:14am
Hi guys,

I´m the guy who builded the Pursang. I´ve never had the time to reply and write in forums like Vitalmx because just building the bike during my free time was enought to fullfill day and night. Better late than never so within the next days I can explain more about the project and some details of the process and brand as well. It´s really interesting to see your comments and see that the passion that moved me to do the project is shared by lots of people around.
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montesagold 8/3/2011 11:44am
8/3/2011 11:44am
I know that Hughe's Bultaco in New York has the rights to the namesake, at least Bultaco.com. I wonder if there is any connection between the two?
andymoto
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andymoto 8/3/2011 12:03pm
8/3/2011 12:03pm
In 1998, rights to the Bultaco name were purchased by Marc Tessier who used it to help launch a range of purpose-built trials motorcycles from his company Sherco Moto S.A.R.L. The bikes were initially named Bultaco Sherco's, then in 2000 the bikes became 'Sherco by Bultaco' and in 2001 the Bultaco name was dropped altogether. The US trademark is now owned by HDW Enterprises, parent company of a parts and repair specialist for old Bultacos.

http://www.findownersearch.com/bultaco-cemoto-3278387-brand.html
motogeezer
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motogeezer 8/3/2011 12:15pm
8/3/2011 12:15pm
andymoto wrote:
Admire the fellas for the effort, but nothing replaces those original Bultaco Pursangs character.
Maybe if they put the shifter on the right and the brake on the left...
Erick
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Erick 8/3/2011 2:39pm
8/3/2011 2:39pm Edited Date/Time 8/3/2011 2:52pm
Jim Palau-Ribes wrote:
Hi guys, I´m the guy who builded the Pursang. I´ve never had the time to reply and write in forums like Vitalmx because just building the...
Hi guys,

I´m the guy who builded the Pursang. I´ve never had the time to reply and write in forums like Vitalmx because just building the bike during my free time was enought to fullfill day and night. Better late than never so within the next days I can explain more about the project and some details of the process and brand as well. It´s really interesting to see your comments and see that the passion that moved me to do the project is shared by lots of people around.
Congratulations with the work you have done this far. I am very impressed with the professionalism of your work.

I have a few engineering related questions:

- Did you design the steering geometry (wheelbase, trail, swingarm length, swingarm location, fork offset and head angle) to replicate in someway the steering geometry of the original model? If not, on what data did you decide steering geometry?
- There is a picture where you analyse the rigidity of the frame, how do you know what kind of rigidity is good? Did you compare it to other similar models?
- Did you consider welds in the simulation?
- What kind of aluminium did you use for the different frame components? Did it require heat treatment?
- Are you planning to mass produce this model, or is it just a show/study model for further development?
- How about a two stroke? Wink
Tiki
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Tiki 8/3/2011 4:47pm
8/3/2011 4:47pm
Jim Palau-Ribes wrote:
Hi guys, I´m the guy who builded the Pursang. I´ve never had the time to reply and write in forums like Vitalmx because just building the...
Hi guys,

I´m the guy who builded the Pursang. I´ve never had the time to reply and write in forums like Vitalmx because just building the bike during my free time was enought to fullfill day and night. Better late than never so within the next days I can explain more about the project and some details of the process and brand as well. It´s really interesting to see your comments and see that the passion that moved me to do the project is shared by lots of people around.
Can you make one for short people? What is the seat height? 96cm?
machine
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machine 8/3/2011 4:54pm
8/3/2011 4:54pm
You guys honestly think this is a good looking bike?....Sick


I guess beauty is in the eye of the beer holder. Tongue



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