New serious Offroad bike : The Chainer

[bzhwindtalker]

Thanks for those links! I like the first one, I remember seeing pics of it in the interweb before !

I got my tubes, seems like good enough stuff and relatively lightweight. I started on the swingarm parts too, but as I am not 100% sure of the dimensions yet I can't get much further than cutting the tubes and get the dropouts done. anyway It seems like I will have a 100% straight swing arm with parallel box sections, meaning I will have something ~155mm wide right below the seat between my legs. I will use a 135mm wide BB, I hope it wont't require bow-legged pedaling!

While searching back through my stuff I discovered I could have saved 100-120€ in machined parts with cutting away some old frame experiments. Well like that I'll have some spare in case I break something...

 

[bzhwindtalker]

I plan on having most of the frame tack welded this weekend.
This design is what I will aim for :

 

[sigimem]

Wish you good luck with your build hope it comes together as you planed it.

Can you tell what tubes you will use and where you got that 135mm BB from?

Why do you want to use these two Seat tubes above the BB ? You don´t want to bend the tube?
You might consider that notching the short tube becomes more difficult with less angle between the tubes.

 

[bzhwindtalker]

I wanted this triangle shape to get two tubes joining at the pivot point, to incrase rigidity.

I made a lot of progress today, pulling out most of the frame. I followed my drawing up to a point where I just tried to copy my previous alum frame. The frame work worked out OK, It now needs quite a lot of MIG work to fill some bad cutouts. It is heavy, but still about half less than the pit bike front half I planned on using some time ago. I confused myself and made the BB tube 4cm short, but as the frame looks really close to the old alum frame i'm not to concerned by this issue.




However I discovered a major design bug : the pedals are not clearing the 190mm wide swingarm (140+2x25mm) How did'nt I think about that?

View attachment 1

I scratched my head for some time trying to find a solution. I figured that I could use my jackshraft another way, with the swingarm being the middle part and the external bearings on the two down tubes. This would allow me to make the swingarm clear the pedals, with a less massive look. the main drawback is that I won't be able to get the motor as far into the frame as I had hoped, but anyway I need the frame space for the battery...



In the end It seems like I can pull something great from this, a little on the heavy side but at least easy to weld. I'm glad I did'nt go with more expensive Cro-Mo tubing for this first trial, as the thick mild steel allows welding/grinding/cuting away/weld again.

 

[ejay]

You can get a 206mm long BB from sickbikeparts, I may use this on my mid-drive to clear the HPM5000/Mars/MiniMonster rocket

Love this build btw and Mild steel (at least on the first 'draft' of a frame for the win!)

Jay

 

[bzhwindtalker]

I made some progress and received my new motor and some goodies from bms-battery (along with 40 euros of tax...)
I solved some issues, the pedals are now clearing the frame perfectly, the 51t chainring fits. But I found some new issues : I will need to make room for the left side chain, the tube is in the way right now, and the shock placement will be complicated..

I ordered a flux core MIG to weld this up, I found a model (made in italy) that does 35-95amp for 220€. I never welded flux core but I assume it is easier than stick, and it's still way cheaper than a decent GAz MIG. My tubes are 2mm thick so it should be quite easy.

The BPM motor looks great and well built, apart from the axle that looks plain ridiculous, i'm glad I have this one in a mid drive and not in-wheel I fitted a 7speed freewheel with all cogs removed apart from the lowest one, 14t. If I keep the 51t, I will be able to keep up with the motor pretty nicely! But 51t looks a bit too big on this small frame :/

Overnight charger, not bad for 17$... if it does not blow up in the next 2 weeks.

 

[renago]

looks to me that the pivot point is a "bit" too high .
mt personal impression .

Renago

 

[bzhwindtalker]

Yeah I must adimit it's quite extreme, but there are other bikes with a similar geometry, exemple :

Not a race-wining bike, but a bike someone spent a lot of money making...

 

[toolman2]

yep, but that is never going to have huge drive loads, and if it did, it would jack up real bad under acceleration.
-anyway a lower pivot would prolly be better :wink:

 

[wildharemtbkr]

The pivot point and the jackshaft are the same point. There won't be any chain pull in his design. His pivot point is just about perfect. It will also make his wheel path follow the same lines as the front wheel does.
The bottom bracket does look pretty high though. I really like this bike.

 

[bzhwindtalker]

Yeah the BB is a bit too high, I messed up my measurements when building..
You are right, as the jackshaft and suspension pivot are at the same place, so chain pull should not interfere with the suspension.
The pivot point only changes the rear wheel trajectory rigth? Having it close to the front foks action does not seem like a bad thing to me but i'm not a suspention expert, I'm actually really far from understanding what makes a good suspention
There is a number of things that are not perfect in this build, but I never said I wanted to make something perfect

I received the velosolo ISO Disc brake mount sproket, money well spent, this thing is beef !

 

[wildharemtbkr]

Maybe not perfect, but you are making it! I think it will be quite good. A lot of us can sit here and critique your work, in the meantime you've built and ridden 3 or 4 bikes and learned something from each one. This one may not be perfect, but you will be that much closer to knowing what works. So keep up the good work!

 

[bzhwindtalker]

Received my JS! feels like being a kid with a new lego kit, I like that feeling

There will be some parts to modify to reduce the width because it is 10-15mm too wide at the moment, I wish I had a lathe... It's stuff I can do with my hacksaw but it sucks to cut those beautifully machined parts!

The whole setup weigths a consequent 1300g. Oh well

 

[bzhwindtalker]

This is how I will get it to the right size. I will need to find a way to keep the freewheel adapter from moving if I cut the part with those set screws... I can only reduce the width on this side because otherwise the swingarm would be off center.

 

[bzhwindtalker]

I managed to get the FW adapter from 29,55mm down to 22,5 with two M5 set screws, I will just have to cut the 20mm axle to size and re-thread the 12mm one. Easy game!

 

[bzhwindtalker]

I only have to make the M6 threads deeper on the FW side and call it a success! The outer bearing supports will be cut too to only keep a 1mm flange on the outside to keep the bearing from moving.

One thing I fear is the torsional loads (when crashing for exemple ) bending the frame to the point where the bearings jump away from their supports... It would be better to have the flanges on the inside but space is tigth :?

 

[Phoebus]

Subscribed.

 

[bzhwindtalker]

I did some very good progress today, I decided to use a 15t FW instead of the 10t sproket that would have provided too much reduction! I should have used screw on track cogs instead of freewheels, I would have saved a lot of weigth... I will be able to do it later.

 

[AussieJester]

Loving it..subscribed

KiM

 

[bzhwindtalker]

Da frock!! I have no idea what the hell is happening. I just properly ripped off 50mm² of weld on the frame while trying to get one of the bearing supports straigth, the weld seems to be SOOO weak betwen the frame (mild steel) and the machined bearing supports (unknown steel...)

I need to call the machine service

 

[bzhwindtalker]

I got a reply from the machine shop, it appears that they machined those bearing supports from 316L Inox! That's why I couldn't weld it with my regular stick rods... I used the parts I machined before in s235, I welded those instead!

 

[bzhwindtalker]

Actually they machined ALL my parts in stainless They are giving me a very low price on an updated version in regular mechanical steel (XC38 probably). I changed some measurements in the process to ease assembly. This means that I will need to cut away the threaded part on the old 20MM axle and weld it again on the new one :/
I received my flux core MIG, I went trougth the included 600g of wire way too fast The results are quite good but there is a LOT of splatter. I started on the frame and it's doing the job nicely, it just needs a lot of cleanup. At least the welds are good even in tricky positions and places, which was my problem with stick (Arc) : I could pull a almost perfect weld in some position and do the shitiest job in other ones!

 

[bzhwindtalker]

I almost finished the main frame, I only have to make a cutout to gain a little more clearance under the 15t sprocket but most of the welding is done. The flux core does quite well on 2MM thick steel, it's just messy. After cleanup, the welds look decent
My front half is very heavy :| like 4kg by itself!

 

[Memran]

Looking very good!
This is the kind of build I want to do, but just don't have the skills.

 

[jateureka]

subscribed!