crossbreak
1 MW
there has to be someone around here who has a good 2-linker. Just PM people
Switched to a GNG style "big block" swingarm coming soon!!
- Thread starter Whiplash
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Whiplash said:
That's a CAD model (cardboard aided design).
Hard to beat for visualizing things. I use it extensively.
Whiplash
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I've been staring at the motor trying to get a mount figured out and I think I'm good but I'm torn about mounting both chains onone side or doing it like cross suggested. His looks better and would be easier to package but requires you to push the motor if pedaled without power...
bØb
1 W
Whiplash said:
The sprag clutch in the motor disengages everything in the motor. It should be very easy to turn the shaft in the direction of rotation with your fingers. If you can't, you have got something wrong. I can spin mine with my fingers and it will spin about one additional turn. It would turn more but the shaft has very little inertia. My old clutch does drag more than the new on does though.
bØb
bØb
1 W
Sometimes it can be hard to wrap you head around 
When you convert the motor to shaft output the brake side becomes your new right side.
This is the beginnings of an adapter to hold 2 chainrings and a FW on the brake (new right) side of the motor. I will post a picture of the completed item later.
bØb
When you convert the motor to shaft output the brake side becomes your new right side.This is the beginnings of an adapter to hold 2 chainrings and a FW on the brake (new right) side of the motor. I will post a picture of the completed item later.
bØb
2moto
100 W
That's not really the swinging arm position you're going to use, is it?
Lebowski
10 MW
Whiplash said:
Cardboard Aided Design ?
bandaro
10 kW
dont knock the cardboard, it is a very common (and successful) prototyping method, fast, cheap and easy.
So here is what I have, way to close to it and pulling some blanks now, so opinions? Thinking brushed anodised aluminium tubes for the frame, and inside it a carbon box that holds the batts. latest image shows how the motor could get it's airflow via vents from the bottom, geometry follows a similar layout as other bikes, both high end DH, moto's and current electrics, so ergonomics should work nicely.
So here is what I have, way to close to it and pulling some blanks now, so opinions? Thinking brushed anodised aluminium tubes for the frame, and inside it a carbon box that holds the batts. latest image shows how the motor could get it's airflow via vents from the bottom, geometry follows a similar layout as other bikes, both high end DH, moto's and current electrics, so ergonomics should work nicely.
I agree with 2moto.2moto said:
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2moto
100 W
bandaro said:
That looks pretty good. There are really two critical issues you have to get as best you can when designing two-wheeled suspension vehicles. One is chain tension variations. While a rear deraileur will accomodate chain length variations it will feel strange pedalling. If a motor drives it you will feel torque variations at the wheel due to chain tensions. Either way, it won't be nice and you WILL feel it when riding. The ideal solution to this is to locate the sprocket of the final drive chain concentric with the swinging arm pivot. If that is physically not possible, make it as close as possible. Given you'll probably need two chains, one connecting the BB to the motor, and the second to connect whichever one to the rear wheel, this should easily be possible.
The other what's called motion ratio. This it the ratio of the motion at the rear axle and the travel in the shock absorber. I would try for a ratio of no more than 4:1. This will give you a much nicer damping on the shock and allow to run a lighter spring. This is the major reason that cheap suspension bikes don't work very well and have to run massive spring rates. Good suspension design gets actually quite a bit more complicated as you need to consider progressiveness. That is, how does the spring rate vary over the total travel?
To ignore these issue and forge ahead with building a frame will almost certainly end in disappointment.
Looking at your sketch, bandaro, I calculate a motion ratio of about 6:1. If you can move the bottom mounting location of the shock further back on the swinging arm, you'll improve this.
As an example, Orange makes some of the best downhill racing bikes available. As you can see below, the swinging arm pivot is very close to (and critically aheado of) the bottom bracket. The motion ratio is approximately 3:1, and progression almost linear. All important reasons why it works well. BTW, I have no affiliation with Orange whatsoever. There are plenty of other examples, including bad ones!
2moto
100 W
Here is another example of a cheap 20" kids bike that I converted to an e-bike for my 8-year old son. As you'll see in the before and after pictures, I relocate the rear shock and it made a huge improvement to the feel of the rear suspension. It actually works now while still using a cheap shock. I didn't bother trying to relocate the swinging arm pivot as it doesn't have a chain anymore. The crank has been replaced with footpegs. 
The front suspension is woeful, though.
Before:
After:
The front suspension is woeful, though.Before:
After:
Whiplash
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All great input guys THX! I need to say that the bottom bracket has nothing to do with driving the rear wheel. I am coming straight off the motor to the rear cluster so the pivot albeit a little high looking at it now will be much closer to the drive sprocket. I DO intend to play with all the locations I.e. motor mount location and swing arm pivot and shape. As much as I LOVE the sketches for ease of construction and cost I need to stick to a design from sheet/plate aluminum. Its far easier to work with and requires MUUCH less time to build once the design is figured out. If all works well I plan on trying to sell complete bikes so I want to be able to have a local shop cnc plasma cut the plates and I'll simply weld em up! My goal is a 2000+watt selectable gear bike I can sell for under 3k so I need to save labor/costs anywhere I can. I am really going to give this a go and take the demo bikes to downhill races and such to let people try them! I appreciate all the hep keep it coming!
Whiplash
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After staring at it a bit, I think Im going to shorten the main frame at the back by an inch or two and open up the angle on the swin arm to get the rear tire farther away from the frame, it looks like it might hit in compression if I have any real travel and I am hoping to get at least 6-8" for a nice trail/moderate downhill ride...
crossbreak
1 MW
Whiplash said:
Yeah, that's the way I would prefer too, go for it!! Plz post your final design before welding, so we can grizzle a bit till it will LAST
this one would be fine, but a bit conservative IMO with ~65° steering angle it's more like a low rider and does not feel good driving around corners, does it?
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crossbreak
1 MW
this really would be a large frame.. with wheels one can better emagine. I'll make a CAD model for you whisplash, just to show the difference. How about a chat so we can figure out how this can be displayed on your computer ????
????
Whiplash
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I'm on my phone so it opened good. I like it but I'm not sure if its "nimble" enough of a look for me. I want to keep it as light looking as possible. I think it will be better received by the masses that way and 20ah of 12s is PLENTY of range for a shift motor bike..
crossbreak
1 MW
with 44.4V/20ah you get 888Wh you could loose 10% effciency and add 88.8wh (which would weight 0.124kg) and would still get equal 
If you really want to gain a benefit of the increased efficiency of your bike over a a single speed high power build, you have to add ENERGY to your battery. Otherwise a competitor could be as lightweight and hillclimbing as you are, doing a lower weight build
you could loose 10% effciency and add 88.8wh (which would weight 0.124kg) and would still get equal If you really want to gain a benefit of the increased efficiency of your bike over a a single speed high power build, you have to add ENERGY to your battery. Otherwise a competitor could be as lightweight and hillclimbing as you are, doing a lower weight build
crossbreak
1 MW
we have to compare each other in racing standard, otherwise this whole thing here in the sphere wont lead to nothing IMO (a bit more competitive, plz)
and reach the top earlier btw...
bandaro
10 kW
2moto said:
Yup, I see what you mean, whiplash had specified he wanted it driven from the motor so I just took a guess as the diameter of the motor, but either way the front drive sprockets can't be any closer to the hinge than the motor's radius. Would you be able to reduce the bob by having it along the axis of the rear swing arm? if so then having the motor at the front base would be better, but also leave the motor more exposed to rocks and logs.
As for the ratio, you got me there, in my trace-offs the 26" wheels were bigger than in the images from crossbreak, so I guess I was drawing a smaller frame or something, but I did base it off several different frames size/wheel size ratio's (as in, layed images on top of each other in photoshop to get an "average" location of bb, handlebars, seat, front sweep, etc). So what I'm saying is I would move the pivot point on the frame forward, rather than the spring mount back, as there is no room before it would hit the tyre.
As for the sweep/size/etc, it's similar to proven angles, so it *should* be alright, but I'll do some layups to show you what I mean. As for construction, well, I entirely agree, this model would probably require custom tubes and all, but to be honest I don't like the look of the sheetmetal design whiplash has, primarily for aesthetic reasons but a man can dream right? I make carbon longboards, and had to change design to a finish I could consistently get, so while I hate compromises, they are needed in some cases...
Edit: ok, the layups done, the sweep should have been the same as the sheetmetal design I posted in page 2, but it seems it got distorted a little when I chucked it into a page with other frames, so I adjusted it to fit the original scan. But it could be slightly too steep still, more oriented to the moto/fast riding than technical trials type stuff. Hope it makes more sense with the layups. Also noticed you took the original open frame sketch, with the external lines, the bb area can't be that long without being broken up by a strong feature, such and tube of the frame, so the length will need to be shortened if it is going to be sheetmetal or it will just look like an empty expanse, the battery box was a feature designed to stick out of the frame.
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crossbreak
1 MW
sry but i'm too lazy to finish your CAD model atm... i've run into some unforeseen obstacles..hope i'll find time for this next week.
Whiplash
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crossbreak said:with 44.4V/20ah you get 888Wh
If you really want to gain a benefit of the increased efficiency of your bike over a a single speed high power build, you have to add ENERGY to your battery. Otherwise a competitor could be as lightweight and hillclimbing as you are, doing a lower weight build
Well my current MAC powered mid drive bike only has 666wh at 44.4v and its PLENTY of range for most riding. I just want to add the extra bit to increase range a little for the really long off road rides. I am sure this new arrangement with the converted motor will be far more efficient than my current mid drive as well since it does not have to step the gearing down for the pedals then back up again to the wheel so with those two things combined I should be quite happy with range on this build if I can get 888wh in there!
