Project Shoestring

Chambers

Chambers

100 W
Joined
Nov 11, 2011
Messages
298
Location
Brisbane
Hey All,

So Covid-19 has put a halt on my elaborate e-bike plans.
I find myself in a position with less money but more time - Enter project shoestring

Goals:

- Use what I have available
- Up-gradable easily when the time comes
- Concentric (to pivot) mid-drive
- Linkage suspension at the rear
- Removable battery
- As cheap as humanly possible without being s#!t

Things I have:

- Original GNG Motor/controller/throttle (Big block style motor + Nuc' controller upgrade when possible)
- Steel SHS in 13x13mm and 25x25mm
- Old broken pit-bike frame (will probably use the head-tube from this)
- Bunch of old milk bottles - May recycle the HDPE into something
- Some scrap aluminium checker plate (probably won't use this - But you never know)


Here's the design so far...
Frame8.jpg
Frame7.jpg

I was going for a little bit of Sintesi Bazooka with some Old school FSR and Turner DHR thrown in the mix.
The frame is made from steel SHS which I have on hand.

I have an original GNG motor and controller which will be used initially - When possible these will be upgraded.

To those with a keen eye - Yes the linkage fixing points aren't modeled yet.
 
That top truss structure ?

Make it big enough so a big battery pack fits inside, and ideally designed so it can get easily be swapped in and out.

Then the bigger cubic space below can just be optionally filled for extending range.
 
@john61ct

I get where you're coming from - but the frame ends up wider than I'd like doing it that way.

Cheers.
 
OK,

So I've been thinking about suspension.
A dual crown downhill fork in Australia starts at about $500 AUD - More than I'd like to spend.

Pit-bike forks are cheaper at around $200 AUD for a full set-up - But would be heavier and probably not as good

I'm thinking about building a girder style fork - I figure I could use a downhill shock - Would work out cheaper than the downhill fork and lighter than the pit-bike fork.

Has anyone done this?

Or thoughts/possible pitfalls?
 
what wheel diameter is the pitbike fork designed for?? using small diameter pitbike wheels will reduce your ground clearance for off-road.. would like to see the suspension design but telescopic is hard to beat for strong design.. (and maybe cheaper than r&d or fork failure under hard use?)..
 
girvin was junk.. and test rider for amp research broke his face and other body parts testing there linkage fork.. so how will the bike be used and what can you afford to break for novelty suspension design??
 
Are you sure the frame will be strong enough? My guess is there will be a lot of stress concentrated where the frame is narrow right at the top inner corner of the battery box.
 
Yes I agree that will be the weak point.

I will probably add some extra strength to that area.
I also plan to make the battery box a structural element.

Cheers
 
So I finally managed to string a few hours together today between kids schooling from home and zoom meetings!

I gathered some parts together and liberated the head tube from the pit-bike frame

pitbike frame.jpgbits.jpgliberated.jpgquick clean up.jpg

Then I set to cutting the SHS (square hollow section) to the desired angles - I find the easiest way is to notch 3 sides and leave one attached as below
mark out.jpgnot cut through.jpghaving a look.jpg

Once that was 'good enough' I cut a few spacers and tacked the lot together 6mm ply spacer.jpgGetting closer 2.jpg

That's all for today - Hopefully I'll find some more time tomorrow
 

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  • Getting closer.jpg
    Getting closer.jpg
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efMX Trials Electric Freeride said:
girvin was junk.. and test rider for amp research broke his face and other body parts testing there linkage fork.. so how will the bike be used and what can you afford to break for novelty suspension design??
Click to expand...

Novelty? Girder forks were established state of the art for motorcycles long before telescopic forks became workable, and for some time after. There’s no reason they can’t work well for this project. Failed girder forks of the past mean no more than failed telescopic forks of the past (of which there have been many).

1920px-VINCENT_Black_Lightning.jpg


Leading link is another front suspension layout that is proven, and feasible to construct from scratch:

CLASSIC-1967-GREEVESjpg.jpg
 
linkage forks are not used on modern motocross or competition downhill bikes, and there are likely good reasons for that.. so why use outdated, likely inferior suspension (except as a novelty, not due to superior performance or strength) designs for a new build intended for hard off-road use.. if you value riding hard with trust in the bike and parts, over reinventing the wheel (or suspension)..
if building a retro style street cruiser bike, then please build a linkage fork.. I would like to see that:).. but if building a bike for serious off-road use, please use modern suspension with performance and strength for the task.. :banana:
 
I find myself drawn to anything thats different - hence ebikes - and also linkage forks.

I suspect the most likely case that telescopic are the most common is that the are 'good enough' and 'cheap enough' for 99% of use cases - Why redesign something if you don't have to.

I'm sure girders could be used in the same circumstances as teles but much more engineering would be required for each bike.

Tony Foale and Norman Hossack had some interesting designs if anyones interested.

But for this build - I'm going with what I know works. Telescopic
 
efMX Trials Electric Freeride said:
linkage forks are not used on modern motocross or competition downhill bikes, and there are likely good reasons for that..
Click to expand...

I’d be willing to bet it’s because telescopics are cheaper to make on a commercial scale. But I know (from making things) that linkage forks are most likely easier for a DIY builder to make.

I’m sure you can make one as modern and functional as you please.

leading-link-fork-8-web.jpg
 
I decided I would start work on the swing-arm today.

Started with a piece of tubeIn the beginning there was tube.jpg

Marked, cut, bent and welded.

2 halves.jpg

Starting to look like something, The bearing mount and dropouts will be made from plate.

Swingarm placement.jpg
 
Balmorhea said:
efMX Trials Electric Freeride said:
linkage forks are not used on modern motocross or competition downhill bikes, and there are likely good reasons for that..
Click to expand...

I’d be willing to bet it’s because telescopics are cheaper to make on a commercial scale. But I know (from making things) that linkage forks are most likely easier for a DIY builder to make.

I’m sure you can make one as modern and functional as you please.

leading-link-fork-8-web.jpg
Click to expand...

I'd bet that linkage forks were never as competitive for off-road motocross or dh bike racing and therefore were never widely adopted for those uses.. race teams will spend big bucks for any competitive advantage, so if linkage forks had significant advantages over telescopic then we would see more of them on contemporary race and consumer bikes.. in most cases linkage forks are a solution to problems that barely exist or don't matter much, or they create other problems while only solving minor ones.. imo linkage forks are the rube goldbergs of suspension design.. of course ppl will keep building them, and they will continue to be a novelty, not better or mainstream.. example, in the picture above, looks like exposed shock and linkage could easily become caked with mud, compromising the performance or requiring more frequent maintenance;)..
 
Not a huge amount done in the last couple of days.

I made a couple of gussets (more to come) they double as one part of the battery mount.
gusset 1.jpggusset 1 tacked.jpggusset 1 welded.jpg

Then I got curious about the weight.
scales.jpg

Obviously the frame isn't finished but it just goes to show that you can build something reasonably light with steel.

Out of interest - Does anybody know the size of the tube used in the Vector/EBB frames?

Oh and in case anyone is interested cost so far $0.00
Of course I already had the steel and I own a welder.
 
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