scratch steel frame for custom dirt bike

[Chaiti]

Hi guys

I'm a new user to endless sphere from India, I have taken inspiration from a couple of posts from here such as overclocker and trazor. I haven't started building the frame yet, but I did buy some material and I am planning to buy some more stuff after I complete my frame.

My part list:

• Qs138 70h kit with fardriver 72680 : Link to kit
• Molicell p42a, I think from mooch's test I would be able to run the cell cont at 30a compared to samsung 50s which he rated at 20a and its a little cheaper: mooch p42a test
• daly 300a bms, rated at 300a cont, max 450a : daly1 , daly2, Idk which one to choose because they both have same specs and price

I will be mainly be using parts from a adventure bike that is very popular here in india called the Xpulse 200/210, just because I don't want to pay the excessive price of shipping rims to india (I asked and shipping alone for a rear and front was 200$ with import tax)

• xpulse 17in spoked wheel: 49usd( One problem with this is that, the largest aftermarket rear sprocket I found was 49t)

• front tyre and suspension will be a mtb tyre and a random no-name dual crown suspension I found, it will probably break and I will replace with a better surron suspension such as rfloxa and I will also get 19in front moto

Rough frame sketch:




its a lil messy cuz I dont have that much experience with fusion 360. Also I am not sure of what rear shock I could use maybe the same rear shock from the xpulse but I think the the force or spring rate or whatever would be much higher.

Im going to be using a mig welder, haven't learnt how to but I have access to one

any advice on frame geometry or anything else, as I have very limited knowledge on this will be very helpful!

I plan to finish this project before my school starts in the end of july.

 

[ZeroEm]

practice on metal similar to the frame with the mig before. It would be good to use parts that you can get for lots of spares.
Cheers!

 

[amberwolf]

any advice on frame geometry

What bike rides the way you want under your actual riding conditions?

Use that geometry and basic frame layout, suspension, etc.

Im going to be using a mig welder, haven't learnt how to but I have access to one

I plan to finish this project before my school starts in the end of july.

~6 weeks or less seems like a very very short time to learn how to weld, design a frame for a dirt bike (which is usually intended for hard riding and will see a lot of stress), build it, test it, fix design / build problems, then get it all wired up and working....

I've done some projects in short time frames, but never that short (maybe I could if I didn't have to work a dayjob too, but probably not).

 

[Chaiti]

the tubes that I bought were made of stainless steel, So I look for some steel sheets to practice my welding. For the frame geometry, my riding conditions is just a lot of loose dirt trails, but I would want to the frame to be able handle small jumps. Today I will be going to practice my welding skill at a workshop where I have access to the welder and a grinder so I'm going to practice laying some beads and some 90* joints using the plates. I'll post these here.

I have summer vacation, So I'm pretty jobless but the only thing I am worried about is the total cost

also, Is there a way to fabricate my own dirt bike style seat?

 

[j bjork]

Stainless has its pros and cons. You don't have to paint it, a big pro on a dirtbike where the paint get scratched and worn off. But it is also special to weld and prone to crack.
When welding it moves a lot, so you have to plan well how to weld so it stays in place. It also oxidizes badly when in contact with air when welded, so you need "root gas" (probably not the right term i English..) in the inside of the tubes. I think there is a paste to brush on that can be used instead of gas.

There are probably several ways to build a seat, Dui on this forum printed one in TPU if I am not mistaken. Could be worth looking in to. Otherwise they are usually made from a tough plastic bottom, a stiff foam and a cover.
The covers are easy to find, there are plenty of aftermarket versions for dirtbikes. I dont know about the foam, but shouldn't be impossible. Maybe cut it out of one of those rock hard beds that are popular in south east Asia, if you have them too?
The hardest would be the bottom I think

 

[amberwolf]

also, Is there a way to fabricate my own dirt bike style seat?

websearching on your phrase finds a few pages that might help:
https://www.google.com/search?q=fabricate+my+own+dirt+bike+style+seat

 

[Overclocker]

hey! thanks for checking out my build here's a fairly recent pic that's mostly up-to-date except that it now has a 220mm 2.3mm thick rotor in front, and an o-ring chain (RK 428KLO)

i like your design w/ the battery centrally located. mine's way too much forward making it a bit front-heavy

i suggest you go w/ mild steel and do destructive tests (very important! you really don't want your head tube to come off LOL). don't waste your time like i did w/ flux core. go straight to gas shielded MIG. welding 1.2mm (wall) tube w/ gas is doable. it helps if you use 0.6mm MIG wire

check out my build thread for the anti-squat calculator. important

i wasted a lot of time/effort mucking around w/ non-sealed chains

only use 2-ply downhill tire in front. normal pedal bike tires probably aren't safe

have you considered using a smaller motor? you probably don't want to end up w/ a heavy bike (>50kg) if you're planning on using an MTB fork/tire