Newbie Seeks Guidance From Experienced E-Bike Motor Engineer

[Chalo]

The "brand new" aluminums you're probably talking about date from the age of Zeppelins up to the jet age.

Most, as I've already said, are not weldable. That includes 7075, 7050, 7040, 7068, and 7178. 2024 aluminum is sorta-kinda weldable with special techniques and inspection methods-- so, not weldable for the purposes of your project. 2014 and 2017, not weldable.

Scandium aluminum alloy was a flash in the pan in the bike business a handful of years ago. That's the real deal-- a high strength, weldable aluminum-- but good luck finding tubing diameters and lengths that are relevant to your project. You'll only find precut butted tubesets for stupid-light diamond frames.

 

[Film_Director_Mark]

Hi Chalo:

The "brand new" aluminums you're probably talking about date from the age of Zeppelins up to the jet age.

Most, as I've already said, are not weldable. That includes 7075, 7050, 7040, 7068, and 7178. 2024 aluminum is sorta-kinda weldable with special techniques and inspection methods-- so, not weldable for the purposes of your project. 2014 and 2017, not weldable.

Scandium aluminum alloy was a flash in the pan in the bike business a handful of years ago. That's the real deal-- a high strength, weldable aluminum-- but good luck finding tubing diameters and lengths that are relevant to your project. You'll only find precut butted tubesets for stupid-light diamond frames.

....I was told that some newer aluminium required special welding rods and flux. I will speak with my buddy Terry the welder and see what he has to say about this too.

That's the real deal-- a high strength, weldable aluminum-- but good luck finding tubing diameters and lengths that are relevant to your project. You'll only find precut butted tubesets for stupid-light diamond frames.

....I was initially looking for solid aluminium stock. I was quite prepared to use non-tubular aluminium stock to fabricate the main part of my E-Trike frame to compensate for not using the stronger tubular steel for framing. I was thinking the minor weight gain from using solid stock would be a reasonable compromise in the equation, if I could, in exchange for this have a slightly stronger aluminium frame for the main part of my design. I also think it's time I took up my drafting pencil and began to sketch out the E-Trike frame design I have in my head

Scandium aluminum alloy

....Hmmmmm ? Let me make some calls. It's the weekend now, so I will get back to you.

 

[Film_Director_Mark]

Hi Chalo:
Ok. I think I found at least one of the reasons this Scandium Aluminium Alloy is difficult to get. Follow this link http://www.dunand.northwestern.edu/refs/files/JOM-0302-35.pdf

Mark

 

[Chalo]

I was initially looking for solid aluminium stock. I was quite prepared to use non-tubular aluminium stock to fabricate the main part of my E-Trike frame to compensate for not using the stronger tubular steel for framing. I was thinking the minor weight gain from using solid stock would be a reasonable compromise in the equation, if I could, in exchange for this have a slightly stronger aluminium frame for the main part of my design.

If you think you can have "minor" weight gain while still having a "slightly stronger" frame by using solid aluminum bars instead of steel tubes, you're waaaaaaay over your head design-wise.

If you take a steel tube with a wall thickness of 1/20 of its diameter, and compare it to a solid aluminum bar of the same diameter, you'll find that the steel tube has the same stiffness as the aluminum bar, but the aluminum bar weighs almost twice what the steel tube does. That's ignoring technical details like the fact that the heat affected zones in an aluminum frame made of solid bars would be huge compared to those in a steel frame, and welding it would be much more of an ordeal requiring many, many times more heat and power.

The only way aluminum exercises ANY advantage over steel tubing is by using larger structural unit sizes. Its strength to weight ratio and specific stiffness is the same as steel. Only by using larger, hollower shapes can it gain an advantage over steel.

I think you're being seduced by the perceived glamour of certain materials, without having any idea whatsoever how to make their special properties work for you. And you're not acknowledging why other people who successfully finish projects like yours generally don't use those materials.

 

[Film_Director_Mark]

Hi Chalo:

If you think you can have "minor" weight gain while still having a "slightly stronger" frame by using solid aluminum bars instead of steel tubes, you're waaaaaaay over your head design-wise.

..... I never claimed to be an engineer Chalo. I haven't got the faintest idea what are the various metals do to whatever. I'm not stupid. I'm merely a newbie to E-Trike design. I've never made a bike from scratch before. Did you have a look at that white paper I put a link on this thread to for all to read yet ? It was very enlightening.

That's ignoring technical details like the fact that the heat affected zones in an aluminum frame made of solid bars would be huge compared to those in a steel frame, and welding it would be much more of an ordeal requiring many, many times more heat and power.

.....Uhhh, I don't know how to break this to you, but I don't know how to weld either

I think you're being seduced by the perceived glamour of certain materials, without having any idea whatsoever how to make their special properties work for you.

.....I was hoping I could find this lighter Scandium Aluminium alloy you were talking about, and this would possibly compensate for the extra weight being lighter, much stronger, and weldable ?? I don't know what I don't know, but if I admit that I don't know, then that's a good place to start

 

[Chalo]

If you don't know what you're doing, follow the lead of those who've come before. That means using proven materials and techniques that are available and appropriate to the homebuilder.

 

[Film_Director_Mark]

Hi Chalo:

If you don't know what you're doing, follow the lead of those who've come before

.....This is why I am on here.

That means using proven materials and techniques that are available and appropriate to the homebuilder.

....Appropriate ? Dude, you really need to stop breathing down my neck ! I Frankly, I don't like your tone, or the way you talk down to me on my thread, and I would appreciate a little more respect, please. Just because I'm new to something doesn't give you a licence to give me so much attitude, and treat me like a child. I understand you are a very experienced builder, but please respect the fact this is still my project. You are not my boss, and I don't work for you. A little humility would look good on you Sir

Respectfully.

Mark Job

 

[Chalo]

You should solicit experienced local help with both design and materials.

Normal design and materials are normal because they work. Most novel and/or exciting designs and materials are novel not because nobody else thought of them, but because they simply don't work (or because they don't work at a feasible cost).

 

[e-beach]

Hey Mark, try not to get mad at Chalo, he is really just trying to help you out. The man speaks his mind and sometimes people don't know how to take it. If you hang around long enough, you, like most others around here learn to appreciate his brilliance in engineering perspectives. Over time you might even become a Chalo fan like I am. :wink:

Take his suggestions to heart, and think about building a frame/motor setup that is more in line with what are standard materials. The reason they are standard materials and designs is because the are known to work. Consider building your first trike a more standardized build style and then see what you can change to make it a lighter more exotic in it's build.


I ride daily on an aluminum frame and IMO the weigh savings over chromoly is not enough to consider in my overall weight/power/distance ratios.

 

[Film_Director_Mark]

Hi e-beach:
Ok. Thanks for the heads up on Chalo. I don't know the guy and I was starting to feel really pressured by him I can certainly see the guy is knowledgeable I need my E-Trike to be as light as possible. I would like to keep it to 60 lbs, but I think the size of my huge honking batteries will quickly sink that idea.

Mark

 

[e-beach]

My mountain bike with 14lbs of 36v 15ah batters rolls around at about 80lbs. That is a fairly normal around here.

A 60lb bike with long range capacity and high speed motor setup is unlikely. I don't think it is possible.

 

[Film_Director_Mark]

Hi e-beach:

A 60lb bike with long range capacity and high speed motor setup is unlikely. I don't think it is possible.

.....It is one of my goals in this build. I also want to greatly shorten the overall wheel base from front to back, but not necessarily from side to side.

 

[e-beach]

Have you ever ridden a bike with a shout wheel base?

Edit: If you haven't checked out these pages, they are worth a look...

https://www.electricbike.com/astro/

http://www.atomiczombie.com/DIY Plans.aspx

 

[e-beach]

If you really want to get exotic.......consider this build

http://www.trekbikes.com/us/en_US/bikes/road/performance-race/émonda/c/B211

Of course, considering it and building it for heavy loads are worlds apart.

 

[kdog]

I'm not sure having an ultra light frame is necessary or desirable. Once you add the power you are talking about, gram saving is irrelevant even kilograms are less important.
This about this.... You are flying down the road @ 80+kph...that's going to be minimum of 200 kg.
now you have to stop really fast. You grab a handful of disc brake on motorcycle wheels. The forces on your frame are huge! and that's irrespective of the bumps , any loss of traction causing shuddering vectoring etc.
you want to be sitting on an exceptionality strong frame. As in motorbike like strength. Scrimping grams here and there is going get you killed.
I smashed an incredibly light xc chromoly mtb frame ( team Marin circa 94) once jumping it and landing badly. Small jump didn't hurt myself. When I picked up my shattered frame, it had snapped into three razor sharp jagged ended tubes. I used to smash down the local hills on this frame (no suspension ) - I wouldn't have if I knew how weak it was, but damn it was a light bike. Too light, everything kept breaking on it. Nipples, rims, chain rings, and ultimately the frame...all too light.
Just painting a picture...
Build yourself a sweet trike, but forget the gram saving.
K

 

[Film_Director_Mark]

Hi kdog:
True enough. What good is it to have an ultra-light frame if that frame can't take the pressures and weight vectors required to be safe for my height and weight on the road ??