Battery box ideas and frame shapes

[spinningmagnets]

This is just a thread for me to park some ideas, so I can discuss some ideas with who ever might be interested, and I'll have something to point to. The user profile is a 30-mph full-suspension street commuter

First, here's a fuzzy thumbnail I had to enlarge because there were no full-sized pics of it. The specs are crap, Its a 24V SLA system with a small-diameter geared hub (brushed?). What caught my eye is it's a good example of what a form-fitted central plastic hard case for the batteries looks like, and I liked how the split-case wraps around the downtube. I think the "wrapping around the downtube" should be copied more frequently. You can even make them for sale with a large diameter lengthwise hole, and then 3D print tube-shims to fit the case to your model of bike frame.



Next, the area just in front of the BB is usually wasted space (in my humble opinion). Here is a frame (admittedly with no pedals) that uses that space for the battery:



Which brings me to the Tidalforce frame that wraps around that space (and I might copy as a battery pack support). The downtube is stressed in tension, so rectangular tubing (flat side horizontal) would not be a weakness (maybe add a small gusset at the prow?). Oh, and also the Mental Manno uses that space, too...

Anyways, fire away...warnings, suggestions, etc

 

[dogman dan]

On another thread, I suggested a slightly longer frame. Instead of a battery behind the seat, relocate the suspension parts to there.

The idea was to take the typical 4 bar rear shock setup, and locate it just behind the seat tube of the bike. In effect, you have two seat tubes, and sit on the front one. This leaves the full front triangle for a battery bag, or hard box.

pic of a crude sketch that shows what I mean. Likely there would be some bend in the top tube and a lower seat. As a commuter, you want a strong rack to carry stuff, so I include the rack as part of the frame. The sketch is crude, with stuff all proportioned wrong. It's just meant to show where I talk about locating the shock and rocker. About 4" longer wheelbase than a normal bike will make it like 30 mph street running better.

Bingo, now you have full suspension of the best type, And a big clean front triangle to locate batteries. We need Justin to get it built. And maybe do it with 20" rear wheel, and a non hub motor.

Some might say, sit on the rear seat tube, for a pedal forward. You could, but I'd prefer to carry that rear pannier load 4" further in front of the rear wheel. Assuming panniers, since a real commuter will carry extra clothes on the way home, and your dinner. To work, just lunch and your tablet.

 

[spinningmagnets]

I like it, thanks! I have been waffle-ing back and forth between having the shock horizontal and under the top tube (like the Mental Manno), or vertical and just in front of the seat-tube (when shopping for a used frame) to maximize triangle space. But your idea is better than either of them. That would leave enough room for one of cell_mans larger-sized triangle battery packs, and that's enough for me.

 

[amberwolf]

I altered Dogman's drawing a little for what should be a stronger rack and shock mount point:

 

[friendly1uk]

Great image host I used there. If you click it, you even get porn.

The taper of the triangle (or not so triangle) offers the opportunity to place a pack within it that lowers in to position. Two sides of this pack could be concave to wrap around the tubes meaning it couldn't fall off. It could also be fastened using bottle fixing points if it was a box that your cells could then be locked in to. Bit of velcro. Few options.
Not that hard to make. take some 1.5" waste pipe and cut it lengthways to make some small scale guttering. It should cup the tubes nicely after a bit of heat has been applied to reform it. Make the sides with pvc board and it could be solvent bonded together. Cheap enough to then test to destruction and see how it should really be made. Which may be the same technique but with some more glue poured in. How the flat sides meet the half round leaves a little valley that should aid construction.

I would go this route if I was a small scale manufacturer just converting walmart bikes. The battery box being the only thing I would actually be making. Although the above construction method would just be modelling for my plastics bloke to get his hands on.

 

[dogman dan]

Yup. Lots of variations possible. To do that change AW, I assume you mean two struts. Either way, it would have to clear the tire, which could come up at least 4-5 inches of travel.

That sketch was just to make clear what I meant by lengthening, and moving the shock back. It's far from fully realized. Make it from steel of course, with space for fat tires, 145 mm dropouts, etc etc. Or you could bolt on a stock bike swing arm for 135mm.

Another variation would be to simply support the rack with two conventional shocks, 60's motorcycle style. But I love the 4 bar shock mount, like the genesis, Konas, Mongoose blackcombs, etc. I keep eyeballing my old Mongoose Blackcomb's shock parts, and my wifes favorite steel mtb. I feel another frankenbike coming, but I dare not chop up my wifes favorite bike. The only other frame I have laying around is no good, too small a triangle for much battery.

In the most ideal variation of this design, both top and bottom tubes would be two pipes, to better support a battery box, and provide insane lateral stiffness. Two tubes extending past the seat tubes would be strong enough with no diagonal bracing. Maybe just a gusset would be needed.

 

[friendly1uk]

I altered Dogman's drawing a little for what should be a stronger rack and shock mount point:

Would that be a better mounting point for the shock? You have taken the triangle away and loaded up the trailing arms pivot point. It looks more stressed to me.

There is a box of tubing around the shock that also has no triangulation. I would not of moved the original brace, but instead lengthened it through the box to the seat tube to strengthen the bike. Taking it away has removed another triangle that was mutually helping both the rack and the post the suspension link is loading laterally.

 

[dogman dan]

Nothing some gussets won't cure. Or, extend the diagonal tube supporting the rear deck through to the front tube, if it won't interfere with the shocks motion.

Again, the drawing is just a quick sketch, to illustrate the idea of lengthening the frame 4", to relocate the 4 bar type shock linkage to behind the seat tube and crank. It's nowhere near an engineered final design.

In prototyping, you'd start with it as light as possible, ride it, see where it flexes, add braces, etc. You could just make the shock mounts part of a truss web. Definitely, the idea is to minimize flex. Not a frame a road biker would like, but a FS cargo bike concept. Designed for a pounding for sure, not for carrying up steps.

The idea came from the cheap china ebikes that had a battery tray between the seat tube and the rear tire. Some had shocks, but cheap sucky suspension with 50mm travel. I want 200mm. But looking at those cheap frames, it dawned on me that 4 bar suspension would fit in a similar space.

Ideally, the bike would just barely fit on the bus bike racks, for getting home broke down some day. Not a full blown longtail, just long enough to fit a nice battery in the front.

 

[dogman dan]

For example, add two webs to the square.

Lots of variations possible within the basic concept, lengthen the bike enough to fit the shock behind the seat, instead of in front.

You could us the rear swing arm and shock linkage from a Specialized FSR for example, but mount it on a steel frame that has the swing arm bottom pivot relocated 4" further back. In that case, you would have only the one seat tube.

But for a cheaper frankenbike, the 4 bar shock linkage is available on a much cheaper bike, like the genesis.

 

[amberwolf]

To do that change AW, I assume you mean two struts. Either way, it would have to clear the tire, which could come up at least 4-5 inches of travel.

Yes, two struts. I redid the drawing to show it better, and fixed some other stuff I didn't bother with in the original modded drawing, pointed out by Friendly1uk.

I altered Dogman's drawing a little for what should be a stronger rack and shock mount point:

Would that be a better mounting point for the shock? You have taken the triangle away and loaded up the trailing arms pivot point. It looks more stressed to me.

Well, I didn't take any triangles away in my mod of the drawing that I know of--are you talking about the original drawing by Dogman or did I miss something?

There is a box of tubing around the shock that also has no triangulation. I would not of moved the original brace, but instead lengthened it through the box to the seat tube to strengthen the bike. Taking it away has removed another triangle that was mutually helping both the rack and the post the suspension link is loading laterally.

I think i see what you mean there, but the main reason I moved the rack triangulation supports is that they push into a vertical bar that has little support for it at that point, and that if they connect down at the intersection of chainstay and "rear post" they triangulate that section and make it all stiffer, and should decrease the sway of the rack itself at it's rear end. If it werent' for the suspension I'd also add a cross-triangulation at the rear of the rack, but the wheel travel would probably prevent doing that wihtout moving the rack upwards significantly.

If no heavy loads (>10lbs?) are ever put on the rack, then all of that stuff probably doesn't matter. But over time evne that much load will break racks off on bumpy roads, suspension or not, cuz of side-sway on the rack causing fatigue of the supports.

I've made new drawings that might work better, based on Dogman's original one. Light green is hte frame itself, dark green is the suspension and forks, pink is the pivots of the 4-bar, black is tires pedals seat, yellow for a couple gussets up at the headtube. I left the bottom shock pivot/mount where it started out, since now at that point it's inside a tiny triangle and shouldn't matter about spreading load down into the frame. All the horizontal frame is pairs of tubes spreading outward toward the rear from the headtube where they join, with seattube and shock mount tube all single tubes between the pairs, kinda like how a mixte frame is built. Should make a stronger frame that is easier ot mount a battery in?

 

[madin88]

i very like how the battery is mounted on the EMX-bike. I looks like it could be mounted to any frames with straight lower frametube.
EMX bikes are made in austria.

 

[melodious]

i very like how the battery is mounted on the EMX-bike. I looks like it could be mounted to any frames with straight lower frametube.
EMX bikes are made in austria.

+1 I think that area is the sweet spot but you need to focus on weatherproofing & impact resistance for a legit build. Also, you'd need more power to make it wheelie if that's your style.

 

[madin88]

+1 I think that area is the sweet spot but you need to focus on weatherproofing & impact resistance for a legit build. Also, you'd need more power to make it wheelie if that's your style.

as far as i have read the details on their homepage, the battery box should be watertight. It contains about 1400Wh with 50V nominal, so there should be lot of space in there.

The EMX hub motor and controller is new and special made by the company. It's too bad they only sale the complete bike and not the separate components

Link: http://www.emx-bike.com/index.php/details_en.html

 

[dogman dan]

Nice rework of the design AW. Looks much stronger. I still think though, that a small diagonal brace on the rear rack is fine, provided you did brace it to a section of tube with some additional support, like some truss webbing in the rectangle. I was thinking commuter loads, like 20 pounds of groceries, but not a 50 pound bag of dog food. We both have larger bikes that can do that with ease.

Hell yeah, the EMX is one really good design. Definitely one of the winners for a trail bike. But it lacks the slightly longer wheelbase you come to love in a street ride, particularly if you will travel 30 mph or more.

I just had a different thought process, now that so many good triangle carry designs are out there, ready to go on any bike with a decent size triangle. To me, the problem was just how to get that, and retain the entire triangle space for battery.

I solved it already for my grocery getter. But I sure can understand that not everybody wants to ride this. It's got full suspension, and I ride it off curbs at 20 mph with no hesitations.

The frame I used to build the front half is an old Currie electric bike. It has a longer than usual frame.

It now sports an EM3ev bag, that holds 48v 15 ah of RC lico easily. But notice I had an extra 3" in the frame for the bag.

 

[dogman dan]

Since there seems to be some interest in this idea, I did a full redraw. This is all to scale now, with the frame angles traced from the picture above of the frankenbike. So you get the same longer than usual front triangle, and head angles for 150mm travel front shocks.

This frame has a fairly low top bar, easy to straddle for a 5-10 tall man. So that meant the rear rack had to change a lot. The shock mount positioning is much more realistic than in the first crude sketch. Pivot points on the rear swing arm are indicated with a dot. Note that 4 bar suspension needs a pivot near the rear dropout.

The rack would be built from smaller tube than the main frame, and include side pieces to support large pannier bags, baskets, etc. With the diagonal supports, I see no reason it could not support 50 pounds easy, but ride quality will of course diminish when more than 20 pounds was carried. It has plenty of height, so the tire won't contact the cargo deck on a big bump. The diagonal braces would be placed so they don't interfere with tire movement either, allowing that small space to be used to carry the controller.

If you have a wire feed welder, you could just about scale this drawing up, and build it. It would ride fine, as does my frankenbike. The key thing as you build, is to maintain the bb height off the ground the same as it was on the original donor front frame. This keeps your head angles the same, and avoids pedal strike, or having a too high bottom bracket. You'd want to build the bike, make all changes if needed to shock mount positions, then work out how to add the rack. It would work to just add a seatpost pannier rack, such as the axxiom, and then bolt on the diagonal brace. More could be carried if it was built into the frame though.



Last commuter oriented details are not shown in the picture. A front fender of course, and a rear fender is made by attaching a sheet of something to the diagonal rack supports. You'd want a nice CA mount, like the headset mount rather than the bar mount, and of course some good lights. Weld some mounts for head and tail lights to the frame rather than clutter the handlebars.

Also bear in mind, the donor bike could be anything steel. It could be a beach cruiser for example, with it's large frame space. But, most likely the best donor bike remains a steel MTB, because a cruiser frame will not have the right head angles for front shocks, and might have 1" headset. In my experience, once you have good rear suspension, you can live with no front suspension pretty well for street commute riding. Look at piles of old junk bikes. You have 50 straight front wheels, and 50 bent rear ones. So a rear suspension and a hard front fork is not that bad an idea for street.