Hill Climbing eBike

[Ianhill]

Im not having a pop im here to watch help and i got one question why use box section over round tube for a load bearing part ? The wall has to be thicker for same given load strength.

Box can be used but it would have been stronger facing the edge if the box metal upwards rsther than the face of the box theres more strength on its edge to downwards bending loads.

The arm will proberly be strong enough but theres room to make it stronger and lighter for later iterations, never have i got something to how i want it forst time so dont be disheartened your doing more than most.

 

[SafeDiscDancing]

Im not having a pop im here to watch help and i got one question why use box section over round tube for a load bearing part ? The wall has to be thicker for same given load strength.

Square tube is easier.

And I knew that before I started.

Square tube is easy to cut and can be "corrected" with heat causing shrinkage.

Just look at the sheer scale of these 1.5" square tubes compared to the skinny 1" fork tubes.

It just looks massive.

At this point the "concern trolling" about strength seems misguided.

This sucker is a monster.

-----------------------

A key strength factor is the orientation of the welds.

Look closely at the inside cross beam and how it has a 360 degree weld to the outer chain stays.

That is very important. It means you literally will need to bend the chain stay itself which at double the strength is beyond concern.

If there is a failure point it will be the lower shock mount which I need to build... so I might get creative there.

 

[SafeDiscDancing]

The Shock Mount that will be adjustable is "getting there".

4 and a half hours to get this far.

Once I get this completed I'll begin to be able to actually sit on the bike and bounce the suspension to get a feel what it will be like.

At a little over three inches wide it should spread the shock impact around a bit.

The four bolts will act as a clamp.

It will be possible to slide this clamp forward and backward to test different shock loading.

 

[SafeDiscDancing]

Shock mount in place.

Set to "neutral". (same length to both shock pivot points)

First reaction.... WAY TOO SOFT.

So cranked the pre-load all the way to maximum and it's better, but it still bottoms just from me jumping up and down on it.

The next step is the air. It's a dual air and spring shock so if I can get some significant air pressure it should start to be usable. It came with no pressure.

And I own a regular bicycle pump and I even bought what was supposed to be a high pressure pump which is such junk it's hardly useful at all.

What this means is I need to figure out what is possible.

But enough for today.

This is good point to take a break and just think about it a little.

Might be buying a new pump soon or really what I need is a quick release so all the air I pump into the shock does not leak through the valve when I disconnect. The pump seems to generate good pressure but it's just the screw on attachment which allows the air to leak.

 

[SafeDiscDancing]

The bike stand is not actually finish yet... but it looks nice.

Just thought I'd throw it out there.

 

[DogDipstick]

I would set it up so that you have ample travel at loaded sag.

A lever is a linkage. Remove the spring and check the articulation for binding. Check damping action vs travel. Adjust. Consider different spring rates available for the strut. A harder spring rate is a given, however it reduces compliance, in the trade.
....good luck.

So cranked the pre-load all the way to maximum and it's
The next step is th
It's a dual air and spring shock so if I can get some signifi

https://en.wikipedia.org/wiki/Lever
https://en.wikipedia.org/wiki/Linkage_(mechanical)

I would reconsider linkage mooring. If you can. Perhaps a, heavy rate, shorter, spring, and /or a rocker linkage to reposition the load transfer on the upper eye, on the swingarm (rocker linkage on the swingarm mooring, and the strut attached to that: A second mooring on the same rocker attached to the original mooring of the bicycle: To keep the rocker in orientation: You can decrease strut travel like this while retaining articulation with careful tuning... A "compound lever" of sorts... ).

That shock is very-o-long, I understand you want the travel. To give it a degree of freedom. Or move the fancy strut closer to the vertical (SHORTER LEVER ARM TO ACT ON STRUT, UNLOADED SAG SITS HIGHER, SWINGARM AT GREATER ANGLE, HARDER SPRING CONTROLS ARTICULATION). IF you can. Given weight bias, and the length of the swingarm this may not be practical.

Right now you have a Class 3 lever. The "effort arm" is smaller than the "load arm". Mechanical advantage is always less than 1. Wherever you place the lower mooring, close, or far away, from the wheel. Less than 1. The length of the initial ( primary) lever arm is the swingarm length (AKA load). The shock placement, denotes the length of the "effort arm".

Obviously, the swingarm is nothing more than a lever that applies a multiplied force to your shock. Make that lever longer, and the multiplication gets higher…effectively making your rear suspension softer.

Perhaps you want to move the lower shock mount, more, toward the rear wheel. However, you will lose travel with this scenario. With a long swingarm, you increased the leverage of the swingarm. I think you need a harder spring.

Good luck. I do not know what would be best. Just some suggestions.

 

[SafeDiscDancing]

I would reconsider linkage mooring. If you can.

Agreed. I'm thinking I can get another inch or two extension at the upper shock mount.

That moves my baseline loads closer to where I need to be.

Adding air pressure to the shock could achieve what is needed but I'd rather start a little closer to what it needs to be at.

I'm kind of surprised because this shock seemed really stiff but once you add the leverage it gets soft.

We will see. Enough work for today.

Oh... and it was fun sort of coasting around a bit and getting a feel for the wheelbase. Even at 55" it still feels like you can move around without the wheelbase being totally wrong.

Climbing a steep hill should be very stable.

One last thing... I had assumed this shock would be very stiff and so I had planned on the motor being located behind the lower shock mount.

At this point I'm even thinking of a middle location for the motor. (and I might cannibalize the work I just did and repurpose it for the motor mount)

This is one of those points in the process where you sit back and just ponder for a while... see where your mind goes with it.

Let me add that the swingarm seems really rigid. I sense no flex at all.

This is the "chaos stage" of invention where no madness is too absurd. 8)

 

[99t4]

And I own a regular bicycle pump and I even bought what was supposed to be a high pressure pump which is such junk it's hardly useful at all...

...Might be buying a new pump soon or really what I need is a quick release so all the air I pump into the shock does not leak through the valve when I disconnect. The pump seems to generate good pressure but it's just the screw on attachment which allows the air to leak.

What you are looking for is a shock pump:
https://brainybiker.com/do-i-really-need-a-shock-pump-for-my-mtb/

 

[SafeDiscDancing]

I'm thinking of just moving the shock back a bit.

The top mount can go back a few inches pretty easily.

The bottom mount could actually act as an addition brace for the cross member.

Then the motor gets moved forward ahead of the shock.

 

[99t4]

Won't that limit the amount of travel?

Maybe that is what you are after.

 

[gogo]

You suggested earlier that this is all an effort to be able to get past one steep area. If longer wheelbase ruins the rest of the riding, maybe consider something like an electric winch to get past that one point, and leave the wheelbase at a more enjoyable length?

 

[SafeDiscDancing]

Okay, so this is an increase from 12.5" to 14.5".

Still too soft.

And I did get some air into the shock but I don't think it's intended as much more than a fine trim.

I'm going to need to push everything out to 16" at minimum and see.

Obviously the shock will need an extension... and I anticipated this problem and if you look at the base it has a screw to adjust the length. It only does about an inch so I'll need to add more.

Think of an equilateral triangle... 16", 16" and the shock is 13" so I'm going to need an extra 3".

And I don't mind having less suspension travel because the forks only have about 2". If I got a really perfect 4" in the back that's plenty.

It's all very unexpected because the shock seemed really stiff just playing with it before I started.

You suggested earlier that this is all an effort to be able to get past one steep area. If longer wheelbase ruins the rest of the riding, maybe consider something like an electric winch to get past that one point, and leave the wheelbase at a more enjoyable length?

No. The whole point is to win the difficult struggle.

Galaxy Quest "Never Surrender".

 

[Ianhill]

The air is the damper the spring carrys the load so to adjust stiffness you got increase the spring rate, in turn bigger spring rates need stronger damping to stop it feeling like a rocking horse after big impacts.

If you wound the spring up and its still soft try finding a higher lbs spring you may be too much of a big boy for its liking.

 

[SafeDiscDancing]

If you wound the spring up and its still soft try finding a higher lbs spring you may be too much of a big boy for its liking.

I plan to push the limits first... I have room for 17.5" on the swingarm.

If that is not enough then yeah... I'll have to spend money.

The reason I bought this shock (which normally sells for near $100) is because it had been scratched up and the seller couldn't claim it was new because it had been installed on a bike.

So I paid $25 for it. (which was probably dealer cost)

Less suspension travel is not a negative. The front forks have only an inch and a half to two inches of travel.

An added bonus with a far rearward shock mount is there is less stress on the swingarm.

It will force the motor forward ahead of the shock so it's juggling things around a bit.

This type of thread is helpful for people new to DIY projects to let people learn that these things have a way of guiding themselves.

You start with an idea and then adapt as things turn out differently than expected.

This is the DIY way... no computer software running simulations which is obviously faster, but takes the hobby out of it.

It's funny that if the 17.5" position works that will be a full 5" off from what I thought it would be. (off by 30%)

 

[SafeDiscDancing]

A more direct approach would look like this.

By stretching the upper frame mount way backwards I actually get the shock further back and don't need to increase it's length drastically.

I was staring at it a bit and realized if I simply creep up the seat post that most of that distance is at such an angle that it's not actually changing the leverage very much.

Basically you change the leverage by going directly away from the pivot point... and it's an absolute value not related to the distance from pivot to shock mount.

In other worlds if the two shock mounts are at 90 degrees apart then an inch outward ends up some amount less of a true shock pivot increase which is directed outwards at the midpoint (45 degrees) between the shock mounts.

Hopefully that makes sense.

 

[SafeDiscDancing]

A sneak peak.

I'm adding new ideas into this upper shock mount to be certain it can handle it's new role as an extension far back in the bike.

Just getting started.

The "hint" is to look at the "original" shock mount for the stock bike.

 

[99t4]

Rear shock placement starting to look closer and closer to that of the Honda 305 Scrambler I rode in high school.

It wasn't so great offroad actually but:::::::::::::::::::: Fond memories.

 

[SafeDiscDancing]

It wasn't so great offroad actually but:::::::::::::::::::: Fond memories.

It's still one shock... this Hill Climbing eBike.

So the problems with the old dual shocks were that one might have been just slightly different than the other and that introduced twisting motions into the swingarm.

But the big difference now is that all the stress which I was expecting to be concentrated into the forward half of the swingarm is now entirely gone. (one source of failure entirely ruled out)

The lower shock mount will be a full 17" back... about as far as you can go.

And the plan is to place the upper shock mount also at 17".

Then the last part is the shock itself at 13"... so my work will try to hit that spot as perfectly as possible.

My "guess" is that the upper shock mount will be roughly 10" rearward compared to the image.

I'm not expecting major troubles in this adjustment.

Frankly I knew that getting the shock loading right was going to be tricky but expected a much stiffer spring.

The suspension travel could drop to as little as 4" which would be fine.

What would be the last potential nightmare would be to push everything out to their maximums and that STILL not make a stiff enough suspension. It's unlikely that will be the case, but not impossible.

If that nightmare happens then I go to using linkages which would be a fun direction to play in.

One last thing... that area of extended frame kind of looks like it could be a rack. Which is another wildcard idea to actually build in some utilitarian features as I go. Have to play that that idea some too.

Pack up a picnic basket and climb up some insane hill and eat lunch.

It's also a nice place to stick the controller.

 

[calab]

That is a lot of weight in the back wheel, will you use a bump stop or limit straps?
I do not know if bump stops are used on motorcycles, limit straps arent but are on four wheelers.
Hill climbing can involve air time.
https://www.youtube.com/results?search_query=motorcycle+hill+climbing

 

[SafeDiscDancing]

That is a lot of weight in the back wheel, will you use a bump stop or limit straps?

Actually no... it's really light.

I was very careful about grinding down the hub and I switched to a hollow aluminum axle.

Not only that but I even ground the aluminum rim significantly and got it to a more perfect true along the way.

It weighs not much more than a standard 26" wheel with a dozen cogs in a cassette.

That was one of my main things to focus on early in the project which went on for a few months before I even started posting about it.

The primary concept is "Light Weight Hill Climbing eBike".

I'm expecting the whole bike to weigh in around 60 lbs when done.

Remember the motor is only about three pounds and it puts out three horsepower.

https://endless-sphere.com/forums/viewtopic.php?f=30&t=114604

It will be one of these motors.

And the modifications I'm looking to do to get the shock placement correct should end up about neutral as far as weight gain.

I'm dropping the adjustable sliding clamp in favor of a direct weld on mount.

But... I'm thinking I'll recycle the clamp as a motor mount. So it won't go to waste.

 

[99t4]

So the problems with the old dual shocks were that one might have been just slightly different than the other and that introduced twisting motions into the swingarm.

Sure but mostly the short travel (less than 4"?)(guessing) was what mainly hampered its offroad performance.

 

[calab]

Its not like he will be needing the suspension for big jumps, just little moguls or kids skate ramp park.
"Hill Climbing" is what I linked to, steep long hills that may include air going up the steep long hill or big air after the steep hill.

 

[SafeDiscDancing]

Its not like he will be needing the suspension for big jumps, just little moguls or kids skate ramp park.
"Hill Climbing" is what I linked to, steep long hills that may include air going up the steep long hill or big air after the steep hill.

I think people are imagining a 100 horsepower motorcycle radically bouncing up an insanely steep hill.

This is a very light weight Hill Climbing eBike with just three horsepower and a designed peak speed for power of about 18 mph.

On the Grin Motor Simulator I expect a 15% slope and up to 5 miles range going straight uphill. (20 miles on flat)

By comparision my other eBike can barely get up a 10% slope. (same motor, but a bigger rear wheel)

So at no point am I going to be doing aerobatic tricks on this.

The idea is to slowly plod up plowed fire roads which can be deeply loose in some areas and then hard packed sandstone in others.

Everything has been focused on low gearing and peak vertical climbing capability by being light weight.

The suspension is just to do something other than a rigid rear end that actually would have worked fine.

---------------------

Another area to talk about is rear brakes... so far that is still in the imaginary stage.

My ideas are going towards using the big 94 tooth #219 aluminum sprocket as a disc and applying brake pads used on rims as the contact which will prevent the aluminum from grinding away.

This means designing a very unique rear brake mechanism which has gone through several design outlines so far.

You can see that region outside the larger drilled holes and inside the actual teeth which is enough for brake pads.

Since the chain lube tends to fly off outwards the brake pads will be mostly clean in that middle region.

By reusing the large sprocket I get brakes without much extra weight added.

Not sure of the exact diameter but it's bigger than 203 mm so around 215 mm or so at the pad contact area.

Oh... I have thought of using an actual disc brake on it but the pads would ruin the aluminum really quickly so I'm backing off from that and I don't want the weight of adding a proper disc so that idea is out too.

 

[Ianhill]

Stop crazy bad idea.

The chain grease makes it onto the sprocket all my spockets are stinking and the brake pads will be cleaning through crud all the time contaminated with grease squealing away proberly.

The chani would have to be dry as a desert to get any use from the pads, think nw fella theres a reason for it been seperated and all the times its been flirted by emgineers to this day none them pulles it off even a belt drive throws of debris over time specially when banging it through boggy puddles etc.

Why you feel the need to go that route rather than traditional separation?

Plus the discs are heat treated specialised steel for the task the sprocket will be mince meat in no time and warp with the heat, ive never seen a caliper that can slot on a sprocket to begin with even my 219 kart sprocket is like 5mm thick, ill check now.

Edit
4mm thick sprocket, mtb disc brakes are 1.8 to 2.2mm thick not sure on pitbike etc

 

[99t4]

So at no point am I going to be doing aerobatic tricks on this.

The idea is to slowly plod up plowed fire roads which can be deeply loose in some areas and then hard packed sandstone in others.

OK, I get you now. I was imagining something different.

For rear brakes, if you don't want to add a disc setup (you stated weight considerations?) that leaves you with (cantilever?) rim brakes.