# Advice needed: Adding Rear Suspension to CrazyBike2



## Amberwolf (May 29, 2009)

I've already started this experiment, but as usual, it isn't quite working as planned (I'm no engineer, and usually get by with just experiments, but in this case, not so much).

I have a thread on Endless Sphere about it, and another on FreakBikeNation, but I have a feeling there is more experience with suspension systems and physics here on DIYEC, so I'm asking for any input those with experience might have. Even if it doesn't seem relevant, it may give me ideas I can research or try out.

The basic limitations are that I am only going to be able to use recycled parts I happen to have laying around for this, and it needs to be as light as possible, as this monster bicycle is already at 150 pounds, and is expected to be at least 180 after installing this suspension plus an extra 15-pound SLA for more power/range. I would like to lessen that, but I doubt that I can. A further limitation is that I need to leave the original rear triangle intact enough to take this whole thing off the bike and put the wheel back into it to just use the bike as it was, should I need it urgently while I'm working out this suspension solution.

I can weld steel, and have quite a lot of various things around here I can cannibalize for the purpose, including a 1985 Ford LTD Crown Victoria in non-running condition. Most of it's parts are definitely too large or heavy but it is possible something on there I don't know about or haven't thought of may be usable for this.

I have a pair of what are probably Motorcross shocks with unknown spring and damping rates, and unknown load capability, from a thrift store find. They are what I am currently working with. In one experiment, using just one of these allowed me to get a nearly workable suspension but it pre-compressed the shock 2/3 of the way with me on the bike, leaving very little for bumps; just plopping my 150lb weight into the seat hard would slam it into the rubber stop on the shaft--I know it wouldn't take a big pothole very well. 

Using both of them side by side might help enough to work. 

One problem I have is that I am unsure of how to figure out what leverage points and angles would be best to use to get the most suspension with the least travel out of it, using the parts I already have. I know that this is heavily dependent on the spring rate and loading, but some of it has to do with the angles things are at; I'm just not sure I can quantify in words what I am seeing when I try it different ways.

The ES thread link above has pictures and a couple of diagrams, as well as details of what I have already tried. If it is preferred, I will copy all that here into a new post in this thread.


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## mxmtech (Apr 21, 2009)

Fact: Your Crazy Bike has been an unqualified success
Fact: You are exceeding the design specifications of bicycle wheels
Speculation: Based on my experience pedaling a bicycle that has shocks vs one without, the suspension system uses more power (comments please)
Are you towing a trailer to keep the weight off of that back tire as much as possible?
It is very clear that you have the skills, brains, and enough used stuff to build a tricycle that does not have a suspension system and you could carry up to 500 pounds safely with one. Plus you can still tow a trailer.
It might be easy for you to add a shock absorber to the seat for your comfort and a suspension system for your load later.

Good Luck


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## Amberwolf (May 29, 2009)

mxmtech said:


> Fact: Your Crazy Bike has been an unqualified success


Especially in being totally crazy, by a person unqualified to do most of this stuff.  




> Fact: You are exceeding the design specifications of bicycle wheels


Oh, _ABSOLUTELY_!  

I am exceeding the design specifications for pretty much every component on the bike, or else using it in some way the designers probably never even considered, like running my CFL headlight and taillight on DC from the traction pack.  I think maybe the wire and connectors might actually be *over* rated for what I'm using them for, but not much else is!

I'm honestly surprised at the end of every ride when I come back with a bike that hasn't broken in half yet, or something equally serious. 

I have an idea for a custom built wheel to take care of that, but the suspension system is more essential at this time, partly because I know I can work that out, and I am not certain of the wheel yet.  It's described in this blog post, with sketches coming to a future post once I work it out with the parts I have available to me.




> Speculation: Based on my experience pedaling a bicycle that has shocks vs one without, the suspension system uses more power (comments please)


Yes, with pedalling an upright especially with certain single-pivot-point URT designs, where the bottom bracket essentially *is* the pivot point, then every downstroke causes suspension bob, and that loses power in the downstroke. (it's not as much a problem in some other rear-suspension designs depending on where the pivot is and how it leverages for suspension).

Fortunately, pedalling isn't the primary drive means on this bike, the constant-smooth-power motor is, *and* any pedalling I do has much more power in forward-stroke component than down-stroke, pretty much eliminating the bob problem. Plus the suspension pivot point is far behind the pedals, which helps as well.

Bob isn't the only reason for power loss, but it is probably the most easily noticed. It can also come from the motion absorbed by the suspension as it travels over bumps; for instance almost any front fork suspension will push the bike backwards a bit for every bump you hit, the taller the bump and the faster it is hit, the more "negative motion" you'll get. Depending on the rear suspension's pivot point and swivel direction in reaction to bump, it could do the opposite, and push you forward a little, but it might not do anything at all; I'm not sure if it could push you back or not--probably would. (these are off the top of my head as I visualize the shocks working--they may not be how it really works).



> Are you towing a trailer to keep the weight off of that back tire as much as possible?


Only for really big and heavy cargo (like multiple bags of dog food, large freecycle.org items, etc). It's not practical in city traffic to tow a trailer with a bike this long, nor really safe, unless I haven't got a choice, and there's no room on sidewalks for one in most places I have to go even if there were no pedestrians. Even on my much-shorter upright bike, with the shorter trailer I have for it, it's not that safe or practical to use on the streets. People around here drive, ride, or walk in a less-than-sane manner a fair amount of the time. 



> It is very clear that you have the skills, brains, and enough used stuff to build a tricycle that does not have a suspension system and you could carry up to 500 pounds safely with one. Plus you can still tow a trailer.


Yes, but given conditions on roads here, especially where bicycles must ride to not become roadkill (especially with the 20MPH speed limit on ebikes), I need the suspension to prevent destroying wheels and eventually damaging frames, not to mention comfort (suspending just the seat isn't enough, even if it was comfort I was worried about).

So I've been holding off on building the trike (a tadpole) until I can do it with suspension, and I want (need, really) to get some experience with doing that on the bike first. 

I also don't have enough components to build the trike without taking things off the bike, so I need to prove more systems on the bike before starting the trike project, or collect more components (especially drivetrain parts). Or come up with completely different ways of driving the trike that I know will work.



> It might be easy for you to add a shock absorber to the seat for your comfort and a suspension system for your load later.


Well, comfort isn't an issue on this bike--with the webbed sling-seat I use, it is it's own suspension system. It's as comfortable as most of the chairs in my house, for as long as I care to ride. 

The suspension system for the bike is the priority, so it doesn't keep destroying things because of the potholes and rocks and other road debris that traffic and other conditions occasionally prevent me from avoiding. 

I rarely carry cargo that is fragile enough to worry about breaking without the suspension, but I certainly freguently carry cargo that's heavy enough to break the bike without a full suspension given the road conditions I have to deal with.


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## mxmtech (Apr 21, 2009)

Well, you were talking about hitting a pothole about an inch deep, which doesn't sound like much of a pothole here in Canada.
My bike plus myself weigh 130 kilograms or 280 pounds. I pull a trailer which weighs around a hundred pounds and I hit potholes all the time. I haven't broken any spokes yet.
Thank you for showing me that it is a danger by the way.
If you weren't breaking spokes you wouldn't need the suspension system?
If you weren't exceeding the design specs you wouldn't break spokes?
Granted that you want to design a suspension system but if your cargo box were independantly springed and shock absorbed from the vehicle frame wouldn't it amount to the same thing?
I have a gut feeling that adding a suspension system won't solve your spoke breakage problem anyway, it'll probably make it worse.


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## Amberwolf (May 29, 2009)

mxmtech said:


> Well, you were talking about hitting a pothole about an inch deep, which doesn't sound like much of a pothole here in Canada.


It's not much of a pothole here, either, compared to some. I'm not sure what the average size is. 

The problem here is that the asphalt melts in summer, and when cars brake or accelerate at the intersections (primarily, but also along the road near driveways or other entrances/exits to the road), it pushes it up like super-slow-motion slosh at the edge of the road, where it meets the concrete gutters or curbs/sidewalk edges. There are places where these "waves" are as almost as high as the average curb, and they are not a gentle wave either--it's usually around 4 to 8 inches "wide" as it goes around the curve of corner curb, peaking in height and narrowing in width right about where I'm forced to ride over it if traffic is bad enough, and that's like running over someone's lower leg, only made of road. 

There are other places where those "waves" have broken off, leaving holes in the pavement as deep as they were tall, of varying widths.

Then there's the just generally crumbly road edges, which "repaving" here means they put a new coat of tar and pebbles over the top, not that they actually remove the breaking-up bits and replace them with fresh. So after a very short time, the road edges just break up again, with the coating doing nothing to hold it together. 

Patches for holes, on the rare occasions they actually bother (usually when they are deep enough to cause *cars* problems), are just pouring chunky asphalt into the hole and flattening the top a little, leaving at least an inch or two of plug sticking out that I then have to ride over. After a few months, it might flatten out at the edges so it's not so harsh but it's still a fairly big bump.

If the hole was caused (as is common) by water from sprinklers and whatnot pooling under the road edge and keeping asphalt from sticking together, then the plug will just break up and come out in a few weeks to perhaps a few months, and then the hole is usually worse than it was before. This is probably one of the worst problems on the roads where they have patched them.

They sometimes dribble sealer asphalt in liquid form as lines over cracks, and that can help but when they do it on crumbling areas it doesn't work for very long, and it makes things worse when it does come off, as it takes chunks with it. 

If I could always just take the lane it wouldn't be a big deal, but there are too many places where I have to ride to the side to stay out of dangerously stupid traffic, or traffic that has too much of a difference in speed to my legal limit where I know many vehicles will not use the other lanes available and go around me. 





> My bike plus myself weigh 130 kilograms or 280 pounds. I pull a trailer which weighs around a hundred pounds and I hit potholes all the time. I haven't broken any spokes yet.


My first guess is that you have higher quality parts than I do, and/or a better-designed bike, even if it has no suspension at all. I know that mine is almost certainly poorly-designed, since the only real criteria I meet with it is that it is built from the parts I have on hand and with as little reworking of them as possible, yet still perform the functions I designate at the time of building it. This certainly makes it less efficient, heavier, and less-well-designed in general.

I know that some of my broken spokes are caused by stress from the motor pulling them, as those are on the drive side and are the pull spokes. But some are not, and I know the bent rims and such are not motor-caused, but are from potholes. If an impact can bend a rim, it can certainly break spokes, so I know that some of them must be from potholes/bumps, perhaps in addition to the motor stress.

The motor stress isn't going to go away, but at least it will become the primary problem, which I can predict maintenance on, rather than having to take the wheel off after every ride to recheck the whole thing. 




> Thank you for showing me that it is a danger by the way.


I'd say that for most people, the danger is of breaking the drive-side pull spokes, for any motor that goes thru the bike drivetrain. For hub motors, it is less of a worry, as the torque is distributed thru the whole set of pull spokes more evenly, and there is less worry about dishing and different tensions on either side of the wheel (I think). Any motor that goes thru the left side of the wheel puts more stress on *those* pull spokes. 



> If you weren't breaking spokes you wouldn't need the suspension system?


No, I'd still want the suspension even if I weren't breaking spokes, just to gain experience with doing it (and to see if I can), but it's primary purpose at this point is to help minimize damage to the rear wheel from stuff the suspension can help with, including bent rims, which are a separate issue from the spokes. 



> If you weren't exceeding the design specs you wouldn't break spokes?


Possibly, but so far haven't had a way to test that. I've been looking for spoked motorcycle wheels, or very light one-piece motorcycle wheels, but so far none have turned up on Freecycle.org or the other places I frequent, except for on some whole motorcycles that I wasn't picked as the recipient for, or couldn't afford.

That's part of why I'd like to build a custom wheel with double rims and double the amount of spokes, to distribute the load better and see what happens. It'd be similar to having a trike rear end except that both wheels would be right next to each other, and I could still get the bike thru places and into buildings that a trike mightn't fit thru. 

There is a very narrow delta trike design I have considered that would be no wider than my bike, simply putting the rear wheels at the edges of what are now the cargo pods, and the pods together in the center. But this would not be (in theory) very stable in turns, especially tighter higher speed turns at 16-17MPH that I must fairly often do to get out of the way of traffic that isn't turning and isn't even slowing down, at right turns at intersections. 

Another reason to explore suspension systems is so that I can learn to work out the challenge of making a more leaning-style trike rear end that will turn more like a bike, putting more weight on the inside of the turn to keep the trike stable and not flip. Most of the weight is already low on the bike in the center with the batteries, but if it is loaded with cargo that may not be the case, depending on what I have to carry.




> Granted that you want to design a suspension system but if your cargo box were independantly springed and shock absorbed from the vehicle frame wouldn't it amount to the same thing?


No, because the bike itself plus me weigh more than the cargo and pods are likely to ever do (~275 pounds, leaving out the estimeated weight of wheels and the unsprung part of the front fork). So that will still not help the rear wheel from having to *be* the suspension for most of the otherwise-unsprung weight, and thus take far more abuse than it is capable of. For most of my riding, there is less than 10 pounds of stuff in the cargo pods, and the pods themselves don't weigh that much in total. Any suspension I add that could hold up the 80+ pounds I do have to carry in them sometimes would itself add more weight than the pods and stuff I usually carry, and put that much more stress on the rear wheel via unsprung weight.




> I have a gut feeling that adding a suspension system won't solve your spoke breakage problem anyway, it'll probably make it worse.


I won't know until I try. 

FWIW, it helps a lot in front, as I don't even have much in the way of truing problems with the front wheel, and certainly no spoke or rim damage. Even though there is less load on the front there is still quite a bit, and even the overloaded simple department-store bike shock fork it has works well enough to keep even the biggest potholes and bumps from destroying that wheel, so far.

It *should* help the back wheel at least a little, since the shock and spring will be taking the brunt of the compression forces, and not the rim and spokes. The spokes and rim will still bear the instantaneous impact and then have to transfer that force to the axle and then the frame and suspension, but instead of the weak flex point being the rim and spokes (because of the rigid frame), the suspension will be the "weak" point and do the flexing, as it is intended to.

It's possible I've totally misunderstood how suspensions operate and what they do, but I'm pretty sure this is part of what they are meant for, or at least capable of. If so, having a suspension will help at least some, despite the extra weight it adds (perhaps another 5% of overall vehicle+rider weight; somewhat less than that with cargo added into the picture).


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## Amberwolf (May 29, 2009)

I am about to start the repair of the bike frame from my stupid mistake, and at the same time replace the insufficiently-strong metal plate I started with in the first concept with some of that 1/4" steel plate, which should fix the main problem I had with it. I'll also be taking off my not-so-great adjuster idea with the Razor fork, and just putting 1/4" thick pivot points there.

I'll also be shortening the rear triangle that pivots, so that the entire shock should stay below the cargo pod tops even during bottom-out. 

Then I will use the seatpost portion of DrunkSkunk's idea to make a slightly-adjustable ride-height, but with a twist.

I'll weld the removed portion of the seatpost (or other tubing to do the same job) horizontally in front of the seatstays, so that I can still adjust the shock length/ride height per his idea.

I will have to use both shocks; one of them simply can't handle the weight of this thing, no matter which way I try it.


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## mxmtech (Apr 21, 2009)

My bicycle is a factory designed electric bicycle from a Canadian box store (Canadian Tire) and I have added accessories to it without modifying the original design. It could be restored to near original condition easily.
When I began this experiment I wanted to learn how the professional engineers did it before I began designing my own electric vehicle.
There is a lot to learn about battery technologies, controllers, gearing and torque, etc and I can practice on this bike from a valid start point.
Plus, I believe that the bike has paid for itself in fuel savings.
I believe that I am now ready to begin my own project from scratch (used bicycles) and build a tricycle.
The motor will be chain drive to the gear cassette on the left wheel so I shouldn't have a problem with breaking spokes from the torque should I?
How big is your motor? From the pictures it looks like you have one chain drive and your pedals always turn.
My right wheel will be pedal powered.
I will have to make parking arrangements with the people I work for as the tricycle won't be able to go inside like the bike does. (I am a maintenance man for 2 hotels)
Here is my thought for suspension for a tricycle


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## Amberwolf (May 29, 2009)

mxmtech said:


> My bicycle is a factory designed electric bicycle from a Canadian box store (Canadian Tire) and I have added accessories to it without modifying the original design. It could be restored to near original condition easily.


It's pretty likely that being a factory-designed ebike, it is already made of stronger components for spokes and such simply because of the torque the motor exerts on them, so it's probably one reason you don't see problems with them whereas I do (since mine is made from random recycled parts whose history I do not even know). 




> When I began this experiment I wanted to learn how the professional engineers did it before I began designing my own electric vehicle.
> There is a lot to learn about battery technologies, controllers, gearing and torque, etc and I can practice on this bike from a valid start point.


There sure is.  I learn as I go, often the hard way.  I do as much research as I can about whatever subject is at hand, but at some point I must actually *do* something in order to really understand it. Just reading about it or looking at others' work doesn't do enough for me without really getting hands-on with it. But I am also not normal, in any sense of the word. 




> Plus, I believe that the bike has paid for itself in fuel savings.
> I believe that I am now ready to begin my own project from scratch (used bicycles) and build a tricycle.


It is in theory not that difficult, but it depends on how much you will save from the original bikes and how little you want to change their frames. Much of my bike ended up as it did simply because I did not want to change much so I could return to a previous point if necessary (though I've committed many changes permanently since then).




> The motor will be chain drive to the gear cassette on the left wheel so I shouldn't have a problem with breaking spokes from the torque should I?


Depends on the motor torque. If it's high enough and applied suddenly enough with a big enough load on the rim/wheel, then sure, you could still stretch or break spokes. Also depends on the quality of the spokes themselves, as there are some of good stainless steel, some of milder, and some of just plain old drawn-wire steel (which is probably what mine are). And many gradations between those.




> How big is your motor?


It is a nominally 650W powerchair/wheelchair motor, from one of two powered wheels. The chair it normally goes on is capable of easily hauling 400lbs of rider, plus the chair's weight, which including 24V of SLA batteries can itself be over 100lbs easily. I think the max speed of that chair is 8MPH, but it also is direct drive of the wheels from the gearbox output shaft (which is the wheel axle). 



> From the pictures it looks like you have one chain drive and your pedals always turn.


There are two chain drives on the left that feed into the main rear chain drive on the right (which is just a standard complete bike drivetrain including derailers). The first is the pedal chain, which is ~1:1 (43:44) from the pedal chainring to the innermost (smaller) receiver chainring. The motor chain which is about 0.54:1 (28:52) inputs to the outermost (largest) receiver chainring. The motor is already geared down by it's internal gearbox to something around 200RPM at full throttle (which I don't use much).

The only reason the pedals and motor are both on the left is because I had no other easy way to make the regular rear bike drivetrain shiftable unless I left it on the right side. Then the simplest way to input power into that was to use another front chainring set on the left, and just work out chainring ratios as needed for the pedals and motor to input to that, so the bike drivetrain would operate the same way as if it was only being pedalled on a regular bike. It's not the most efficient, but it was easiest with the limited parts I had.




> My right wheel will be pedal powered.


You may have issues with steering if you use different power sources for different wheels, unless you have some kind of mechanism that will feed power back from one wheel into the other. When one side wheel pushes (delta trike) or pulls (tadpole) more than the other, it is going to tend to turn the bike in a circle, which you will have to "fight" by steering off-center all the time. 

If you have not already looked into it and verified it will not do this with your design, you might want to instead run both power sources to a differential that then feeds both wheels the power necessary to go straight. Differentials can be as simple as two freewheeling sprockets, one on each axle end, fed by sprockets on the flanges of a hub mounted just in front of the freewheels. then when one wheel turns faster than the other due to a turn, it will allow it to freewheel while the other is still driven by either power source. 

If the hub in front of the freewheels is also freewheeled on either side, then you can feed in power from each source independently, neither affecting the other. If it is an internally-geared hub, then you can even shift gears for either power source, so that you can stay in the optimal power band for either power source for the speed, terrain or conditions you are in. Just beware that many internally-geared hubs arent' strong enough to take the torque motors put out, and can be destroyed, based on reports I've seen browsing the web, and on the ES forums.



I will have to make parking arrangements with the people I work for as the tricycle won't be able to go inside like the bike does. (I am a maintenance man for 2 hotels)
That's one of the problems with trikes; unless you make some way for the suspension system to also allow you to fold it up to make it narrower, which I'd like to integrate into my tadpole. 



> Here is my thought for suspension for a tricycle
> 
> ms paint picture goes here
> 
> Wait a minute, how are you putting the ms paint drawings in your post?


I host the images usually on my blog, which uses the free Picasa web service from google to host the actual images. Sometimes I have forgotten and ended up only having it hosted on another forum, like the ES forum (which allows and encourages images to be uploaded directly rather than externally linked). Then I copy the URL for the image itself, and paste that into my post. I select the URL, and click the little yellowish postcard with mountains on it in the message editor toolbar, which puts IMG tags around it. 

One could insert the tags first, then paste the URL to the image between them, and that works too.


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## order99 (Sep 8, 2008)

First of all-that Crazybike really lives up to its name, I can't believe that you've done so much with so little and made it work so well. I shudder to think of the bikes you could turn out if somebody handed you $3000-4000 and commissioned a design...

Before you turn the Crazybike into a softtail-have you noticed any structural problems cropping up from the 'diet' you put the bike on awhile back? Because I honestly don't know whether your rear triangle would have less stress placed on it due to the shocks taking up the stress, or more due to the constant movement? Also...given the derailer setup you have, aren't you a little apprehensive about hitting a pothole and flexing the rear while under power? If the chain tensioner lags behind the flex even a bit, you'll probably be tossing chains on a regular basis.

Just in case those Motocross shocks are clapped out-are you within range of a decent, cheap salvage yard? Lord only knows i'd never have started my own fumbling project without the fruits of LKQ salvage ($2 to get in, bring your own tools, pay roughly 20-25% on what you grab-I love it!). Some of the alternates I might try on your budget-

1) A coiled chassis spring from a sub-compact car like my Festiva-the flex would be stiff but it would take the strain off the rear frame and rim without bouncing all over the place.
2) Another motorcycle shock if you're lucky.
3) A leaf spring, fastened vertically. By taking individual leaves out you can adjust the flex anywhere you want it-and since you can adjust them you could probably use anything from a riding mower spring all the way up to one from a light truck. And if anyone thinks it looks too strange, well...Crazybike, right? 

As far as the strain on your rims and spokes-I got nuthin'. Just keep your eyes open and maybe some heavy duty wheels will pop up. Lord knows if my Mom can find a Worksman Trike for $50 at a church sale (going rate of $800+ new) then you should run across something...


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## Amberwolf (May 29, 2009)

order99 said:


> First of all-that Crazybike really lives up to its name, I can't believe that you've done so much with so little and made it work so well. I shudder to think of the bikes you could turn out if somebody handed you $3000-4000 and commissioned a design...


Well, I dunno about that. I'm kinda good at repurposing things but I don't know how well I could actually do if I had to use things for what they were designed for. :lol:




> Before you turn the Crazybike into a softtail-have you noticed any structural problems cropping up from the 'diet' you put the bike on awhile back?


Not so far. It does twist a bit more if I am turning it over for working on it, or laying it on it's side, but during riding this is not noticeable, so I don't think it is happening during a ride--the forces on it are not the same. 

Given how much extra stress I am putting it under with the newer motor (which ripped out of it's mounting plate once), I guess it is pretty sturdy even as it is. 




> Because I honestly don't know whether your rear triangle would have less stress placed on it due to the shocks taking up the stress, or more due to the constant movement?


I don't know either, but I know the *wheel* will have less stress, and that is the part that keeps breaking. 




> Also...given the derailer setup you have, aren't you a little apprehensive about hitting a pothole and flexing the rear while under power? If the chain tensioner lags behind the flex even a bit, you'll probably be tossing chains on a regular basis.


I am a bit worried about that, as I am not so good with the chainline thing, anyway. If stuff doesnt' just work, I dont' seem all that good at making it work in a way that isn't too noisy or with other side-effects. 

All I can do is to test it for these conditions before I go on non-test trips, and see what happens. If it has a problem but it doesnt' happen if the motor isn't running, then I can for now simply learn to cut power just before a bump or hole and then continue. I already have to do this for severe bumps especially during turns so that the pedal chain doesn't get jammed. (none of the tensioners I have tried so far work well enough to be worth the constant noise they make). 



> Just in case those Motocross shocks are clapped out-are you within range of a decent, cheap salvage yard? Lord only knows i'd never have started my own fumbling project without the fruits of LKQ salvage ($2 to get in, bring your own tools, pay roughly 20-25% on what you grab-I love it!).


There are none really close to me. I got the radiator fan motors for my DayGlo Avenger bike's friction drive from a PickAPart or PullAPart (forgot which) about 20-something miles away. I do have a non-running 1985 Ford LTD Crown Victoria in the driveway, usable for parts, if you think anything off of that would help. 




> Some of the alternates I might try on your budget-
> 
> 1) A coiled chassis spring from a sub-compact car like my Festiva-the flex would be stiff but it would take the strain off the rear frame and rim without bouncing all over the place.
> 2) Another motorcycle shock if you're lucky.
> 3) A leaf spring, fastened vertically. By taking individual leaves out you can adjust the flex anywhere you want it-and since you can adjust them you could probably use anything from a riding mower spring all the way up to one from a light truck. And if anyone thinks it looks too strange, well...Crazybike, right?


Hey, I was going to use a leaf spring off the Ford LTD *as* the rear swingarm on one bike design. That would have taken care of suspension and swingarm all in one swell foop. I can't find the blog post with the design info, but one of the sketches is here:








which shows a curved tube as the bottom swingarm and the leaf spring curved above it.




> As far as the strain on your rims and spokes-I got nuthin'. Just keep your eyes open and maybe some heavy duty wheels will pop up. Lord knows if my Mom can find a Worksman Trike for $50 at a church sale (going rate of $800+ new) then you should run across something...


I keep hoping, and looking on the Freecycle.org posts, because anything on that list is free, which makes it at least twice as good as anywhere else.  I just don't see much in the way of these kinds of parts offered there. Sometimes, though....


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## Amberwolf (May 29, 2009)

I had to go somewhere today, so I had to revert to the original bike and do the repair mentioned previously, so I didn't get any other versions worked out or tested yet. So in lieu of that, here's a post about the repair itself:

Here's the broken stay:
















On the righthand stay is the prior attempt, which was not long enough; I decided to try one a little farther forward and longer, but being farther forward it had zero support from the dropouts and just crushed the tube as soon as I put the suspension together and let the bike's weight on it, and pushed down just a little.

The repair required replacing some of the tubing. Fortunately I had a frame already being parted out with some tubing just larger than what I had to replace, so it could be slipped over the damaged area and welded on.








I cut out the damaged area first, then straightened the dropouts and other stays.








Then I cut off a piece from the other frame large enough to completely cover the removed area plus as much as I could get from it. I left the curved end on because it comes close to matching the curve on the back of the stay to be fixed.








I left the brake stud on there as a way to manipulate the tubing while I did the repair; it will be removed later once I am sure I'm done.

I slipped it over the front of the stay first, then aligned the stays and slipped it over the back end.








so it ends up like this:








Once alignment was certain, with a wheel in the dropouts instead of the triangle above, I welded it in place. It seems as strong as ever, but I am sure it is not quite as good as it used to be.

Now I have a better plan for doing this, based on this idea:








but modified to be adjustable, based on Drunkskunk's seatpost idea:








So that the cut-off part of the seattube will end up rewelded pointing forward, so a shortened seatpost can be clamped in as an adjuster for the ride height. 

Now, I still have to work out the chainline issues, as the chain currently wants to pass directly thru the space the pivot BB occupies. I must install something to force it to go around that, yet still shift across it for gear changes. 

I have a nylon or teflon cutting board that I may try to cut a strip from that will be used to deflect the chain across, and clamp it to the BB. It will wear, and it will add noise, but it should let me test the feasibility of the suspension while I think up other ways to get the chain around it (eventually redesigning the rear end to eliminate the problem).


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## Amberwolf (May 29, 2009)

Right now this is on hold until I get more info on how to do it; I am working out some stuff from this PDF here:
http://www.wind-water.nl/rec_build_booklet.pdf
which tells me how to work out what my springs already do, and how to use them to get the suspension I need.


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