Custom frame production reaserch... (updated on pg 1)

bzhwindtalker

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I am looking into starting a production of full suspention custom cro-mo & aluminium frames, I will in this thread post some CAD and prototype testing results.

I plan on making a first frame from scratch just to define geometry, that will be powered with either a Mac on 16s headway or a turnigy 80-85 with single stage #219 on 8s. The bike is designed with 24 or even 20 inch wheels, but will fit 26 too.

The bare frame will be made from 30x30x2 angle or 25x25x1.5 square cromo , then riveted side and top aluminium panels will make it rigid.
I will ty to make the frame fit 8 or 10 lipo bricks and wiring, wich equate to a 1kwh pack.

The first frame will be used to build a jig, then if test results are convincing I will make a first bach of them and sell them with no profit to select testers.

I am shooting for less than 400 euro for the frame without shock before shipping. I would like to provide customisation options like custom drops-out or alternate mounting otions for mid drives or RC motors.

The CAD is not done but the design is quite finished already, but i'm still open for sugestions, I want this to be perfect!

This is also for me some sort of test, and as an engenering student, this projetc will be a pretty nice learning curve.


drafts of what we are talking about :
early skech

adam bike cad.jpg

another vertion, I simplified the frame.

adam simpler vertion bike.jpg

last design to date, evrything is scale on the drawing, but the head tube angle is a bit too low rigth now (63° is quite extreme, 66-67 would be more suited)

DEB-0.1.jpg


now modified with sorter swingarm and 66° head tube angle :





feel free to comment ;)


Adam
 
Some bottom brackets I got from an english company that a forum member pointed out :
377441_10150546522459617_657019616_8736396_769990017_n.jpg


Received the head tube stock :

6766930683_285af08625_z.jpg


20 minutes on the lathe later :
head tube.jpg

the pivot tube was longer to make because I had to start of with round stock...
pivot.jpg

I Made a cardboard mock-up :
mock-up.jpg

Then I started building the frame for real :
cadre2.jpg
 
awsome project!

since i started this hobby i wanted to make my own frame, but i live in the city and have no room for a welding setup.
when ever i can i like to use laser cutting in my dayjob (3d cad engineer) because it is relatively cheap, and accurate.

when you are going to produce frames you might want to look in to getting some parts laser cut. (probably too expensive for prototyping)

if you are going to use CAD, and use it for profit, you need a legitimate edition of the cad program you used (no student edition, or pirated copies).
 
You are rigth about the cad software! I did not think about that... Also, I have acces to a water cutter machine at shool, i will probably get the parts for the prototype cut there.
actually after looking more into my design, I still have some major design challanges to solve, like head tube angle, rear suspention choices ext...
 
Subscibed!!! I've been wanting to do that for a future project. I will follow this closely.
 
You can borrow some good ideas from a few successful DH bike frames.

The seat post module can be bolted on, and adjustable with 3 mounting options. That will make your frame "one size fit all"
See the GT DHI for an example
post-8397-095775500%201283164483.jpg


The suspension could be designed to make the shock to push inside the frame with a deflected angle, and have 3 mounting options for adjustable travel. Mounting options for the link can make for adjustable progression.
See the Intense M9
Downhillbgimage2_3.jpg


The steer angle can be adjustable with a steer tube insert that can be rotated 180 deg, to have the option of + or - 1.5 deg angle. This makes the frame adjustable for stability or agility. Then, if the user add a Cane Creek angle set, this can give a full 3 deg + or - steer angle adjustment by 0.5 deg increment, from 64 to 70 deg to suit anyone's preference and need.
See the Scott Gambler

Many DH bikes have bolted on dropouts, making their wheelbase adjustable with a choice of longer or shorter dropouts.

When a frame has variable geometry settings, it can be tuned to ride road or dirt, for anyone size and riding style. It does make the frame more expansive, but the advantage is well worth the extra and the production complexity can be compensated by making only one frame size.
 
Thanks for the advice about adjustable geometry! I will make bolted drops, for HUB/RC drives. I think I will stick to a single pivot for now, desiging a good 4 link with no base would be difficult for me...

Question : how to make a good single pivot suspention?

Also, would multiples swing-arm pivot points would be a good feature?

I started building the jig too, and I will make adjustements using a k2 alum frame as reference, and found stock for the head tubes. I still need to find the tubing for the frame themselves and the pivot bearings holder.
 
I talked to a guy who's a pro frame builder/welder last week. we were discussing welding and he said that there is a special sequence to weld all your pieces together to prevent the materail from warping wich is inevitable. You can minimise this tendancy by respecting this sequence. When we started discussing this, some customers walked in so we left it at that. But this little detail is something that needs consideration.
 
More pivot points means more lube joints, complexity, and weakness if done wrong. I'm no frame builder, but the best design is usually the simplest. Good luck.
Brian L.
 
bzhwindtalker said:
Question : how to make a good single pivot suspention?
If you stick to monopivot, it has to be strong, to make it very stiff laterally. Your swingarm will also need to be stronger, to keep it from flexing without the guiding aid of a link.

Very few monopivot suspensions have the stiffness required for DH.

Santa Cruz super 8
super8.jpg


Most that have built monopivots in the past, have added a 2nd anchor point that, even if very short, is a prevention to swingarm twisting in landing or hard cornering.

The Commencal Supreme have a pivoting swingarm shock mount that makes a connection with the frame. Technically it is a monopivot, but the shock mount is a link by itself.
commencal-supreme-dh-racing-2010-mountain-bike.jpg


Note that all good DH frames have a suspension design that transfers the shock pressure into the frame. Many configurations have been explored, and you will see some with various force deflections. Some will push in the direction of the head tube, others will be pushing toward the ground, but none today are pushing up in the direction of the seat. We don't want the suspension kick reaction in the frame to be vertical, but we want the swingarm action as vertical as can be.
 
Allrigth, but based on a super 8 geometry, making a frame that fits a lot of battery will be hard. What do you think of the Bomber geometry? It seems like a quite sucessfull e-moto platform...



stelth_bomber_.jpg



also, check out the figther, it has the bb on the swingarm itself making the whole things WAY simpler!


_____3968670.jpg
 
Yep, the Stealth and Bomber have a good geometry, and carry alot of batteries. I don't like the suspension design though, it is good for dirt but I wouldn't like to ride it DH. When you are down a slope with bumps and hard corners, you don't want the shock to push up and make the tail buck. That is why the suspension design of DH bikes, and many dirt motorcycles too, is made so the shock is pushing forward, with progressive action.
 
I look forward to seeing where you take this..

you should take a look at this program for designing the frame. http://www.bikechecker.com/home.phtml

also, if you haven't already, you should take into account how the battery weight and position (as well as hub motor?) will affect the handling and flexing of the frame. Most production frames (non-electric) have geometries to only work with rider weight and positioning. I'm not sure how Stealth designed their e-bikes but once you add weight in the rear and upfront things change.

hope you can make something awesome. maybe some frame building experts can offer you some good advice to make this the best frame for our e-biking needs.
 
I guess MOST people on this board would be prety satisfied with a strong and simple dirt-E-bike, even if it does not win downhill races. Actually, I would be quite incapable to design and build a DH race worthy bike, but I can build a good electric dirt bike frame to suit people's need of a strong and relyable frame to build upon.

The figther's suspention has the shock going forward towards head tube, do you recon something along thoses lines will probably be fine? One of my mates is semi pro downhill racer, and I will probably get him to test the crap out of the prototype bike :twisted:




I decided for 6001 bearings (12x28x8) with a tigth press fit rigth into the frame, with 64mm center to center distance for rigidity. The bb will be on the swing-arm, just under the pivot point, a la Stleath figther.
402152_325138054184055_154742641223598_1115489_2058173345_n.jpg

320783_258669360830925_154742641223598_906906_1011295044_n.jpg

The jig is mostly done, I just need some metal cones to get a nice positioning of the headtube and pivot holder.

Also, I visited a small mecanical fab company that will probably end up doing the welding and the machining of head tubes and bearing holders, should be quite cheap, but it looks like they can't source cromo or even good steel so i'll have to look further... I will probably end up building the prototype from s335 or even s235 :? Wrong, but it will help me to get the geometry dialed. I an waiting for the head tubes stock to start building.
 
from the pinkbike thread, this is looking pretty good with small wheels :
p4pb328366.jpg


The suspention is quite simple, but as we discussed, pointing up wich seems to be problematic, by causing a lot of suspention bounce and un-progressive travel.
 
Wasn't there a big thread on someone trying to make and sell a custom frame. He was taking deposits, you might want to look at that thread, there was a lot of chat about strength of aluminium and considerations for battery placement etc anybody know where that thread is?

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I recently had an interesting discussion with Hangdog98 via PM on the subject of rear suspension deigns. He is a pro in this field and has designed bike suspensions for major manufacturers. I thought I would share what he told me on this thread :

« Hi fractal. MTB suspension is often shrouded in myth and mystery and the best designs all have one thing in common. That is, to isolate pedalling forces from the suspension forces. One design did it in the 80's and has been protected by a rock solid patent which is licensed to Specialized. They call it the FSR Link and it was patented by a man in Laguna Beach called Horst Leitner who created AMP Research and it is also known as the "Horst Link". Pretty much every other design seeks to emulate the Horst link or find a way to achieve the same result and that is, to stop the suspension bobbing as you pedal and stop the rear brake from grabbing as you go over bumps and to allow the wheel to follow the ground without being affected by those other forces.

There are two main things to know about swingarms.
1. The path of the rear axel.
2. The position of the pivot.

Before I discuss those, it is important to note that motorcycles don't suffer from pedalling induced bobbing and you'll notice that their swingarm design is pretty much standard across each discipline of motorcycle design. If your desire is to have an E-Bike that behaves well under power, then the design process is much easier.

I should also dispell a myth about swingarms. Having the pivot close to, or even around the BB shell doesn't isolate the swingarm from pedal forces. The pedal forces come from the chain pulling a line across the top of the chainring to the rear sprocket. A line drawn from where the chain joins the chainring (at the top) to the pivot point center, is the lever that acts on the swingarm. This leverage changes with each gear change. If you run multiple fron chainrings then the leverage over swingarm action changes even more. The most effective pivot position to reduce pedalling forces is to have the pivot point behind the chain at the top of the front sprocket.

If you imagine the swingarm as a radius, the path of the rear axel is part of a circle. The longer the swingarm, the easier the curve (arc). The ideal situation is to have a long swingarm and as straight an axel path as you can manage. The vertical axel path should be vertical when the bike is on level ground and not pointing down a hill as some designers have tried (and failed). The purpose of this is to stop the wheelbase changes as the swingarm moves through its arc. On downhill bikes there was a school of thought that wanted to lengthen the wheelbase under compression, and/or to make the axel follow a vertical path (relative to level ground) when the bike was pointing downhill. This meant moving the pivot up quite high which necessitated the use of a jack-shaft to bring the chain up to the pivot point. They weren't very successful. Balfa is an example. They were supple in a straight line but weird and wobbly around the corners because the wheelbase kept changing which affects the steering.

The 2nd thing about the axel path and wheelbase changes is that when the wheelbase changes, the wheel must either speed up or slow down to keep up with the changes. If it speeds up because the wheelbase has shortened then the tire has greater traction demands placed on it. This causes it to break traction. If you are also applying the brake, the brake rotor changes speed with every bump and causes brake chatter (hopping and skidding). This is why I advocate a floating brake caliper which seperates the brake action from suspension action. (MadRhino has never heard of this and confused something like a Hope floating disc as being a floating brake system) I have attached a picture to illustrate the floating brake. The idea is that the brake caliper is not fixed to the swingarm, but fixed to a bracket that is free to rotate around the axel. It is then secured by a torque arm to a position on the frame to create a parrallelogram action. As the swingarm moves through an arc, the brake caliper stays constant with the rotor and matches the wheel speed, thus isolating the braking from the suspension. 99% of performance motorcycles have this.

Here is a pic of an excellent floating brake on a long travel e-bike
014_1.jpg

This is an excellent set-up for motive power adapted to an existing swingarm. If you had the freedom to fabricate the swingarm you would simplify the shock linkage system. The four bar system employed by Kona in this bike is nothing more than a designers attempt to make it look like a Horst link without infringing patents. The links and bars and shock linkages do nothing special nor isolate the pedalling action, but they're fine for motive power.

Now on the subject of frame mounted engines and hub motors. Because both legs and frame mounted engines apply torque along the chain which affects the forces on the swingarm, they are very very different from the forces exerted by a hub motor. The hub motor will drive forward and cause the frame to pitch upwards. This is a desireable trait as the end result is to improve traction by forcing the tire into the ground, and during cornering under power, will steepen the head angle and help keep the front tire planted. Tyring to isolate this action would be a mistake.

Finally, the weight of the swingarm, wheel brake and shock linkages is all unsprung weight. The difference between a cro-mo home-made swingarm with a heavy DD hub motor, 12g spokes, fat rim and heavy duty tire/tube, derailleur, linkages etc etc will probably weigh much more than a modern 125cc motorcross bike rear end anyway.

An e-bike with a powerful motor is a motorbike. Try to be inspired by how the motocycle guys do it rather than the pedal pushers. There's less BS in motorcycle suspension designs because they're designed by engineers and not graphic artists.»

«The spring calculation method is loosely based on the weight on that wheel (front or rear including rider, use bathroom scales under the wheel). Divide axel travel by shock shaft travel and multiply that by the reading on the rear scales. The shock will need to be attached to the swingarm for this measurement. This will give you the ball park figure. Test ride with an O ring or cable tie tight around the shock shaft to see how much travel you're using and go up or down from there. You want to use about 80% in normal off road riding saving the last 20% for unplanned big hits. Remember, despite what many people think, winding up the pre-load adjuster doesn't change the spring rate, only a spring change will do that.»
 
This seemed like a quite popular design back in the days, and it actually won races :

GT_DHiDrive.jpg


It still use the I drive system for the BB, but it is a simple single pivot frame with about the same angles for shock as my lastest draft, I can replicate something like that.
 
Hi Bzhwindtalker,

Your design on page 1 (more definite draft) is correct and well done for me. Even if you want to pedal this power full ebike you can do it with not losses in the pedaling effort (fractal post).

Stealth ebike use a pit bike shock on their Bomber so you can use the same shock with this design, those shocks are cheaper and can handle allot of stress (unsprung weight).

My only "recommendation" is about the battery compartment, you need to open it on the opposite side of "the crankset and chain" I have done this mistake on my Black Arrow so please don't do the sam.

Good day!
Black Arrow
 
Thanks for input Fractal! That's what I have been thinking too, complicated bikes suspentions designs are BS for 2kw+ ebikes, where pedaling starts to be anecdotic.

exemple : this is so complicated!
2010-specialized-demo-8-downhill.jpg


On the floating brake part, would it be usefull or needed on a single-pivot motorcross-like rear susp design?
I understand how the wheel's relative speed is changing when braking power is applied and suspention is moving, but the thing I don't see is how a single pivot frame benefict from this, isnt the floating brake ting about getting the brake assembly always perpendicular to suspention axis? I guess I could have 4 bar like linkage for the brake, with the brake axis parallel to a line going from the two rear axle cinematic extremums, but i'm not too sure if it works like that!


Black Arrow : I will probably use pit bike shocks, that's what I have on my bike rigth now and I like it! still quite ligthweigth and really cheap, with the option of nicer units for a quite reasonable price. Would you mind posting a photo of your design? I don't get what you are explaining about frame opening around crankset? Do you mean to check cleerance?
 
Just saw the thread in your sig ;) really nice! It seems heavy though :roll: I hope to get the frame with side panels and swingarm at around 10kg and complete bike at less than 35kg with 1kwh of lipo and a geared hubbie.

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