A new frame

I have been working on a new frame design for a while, progress has not been as fast as I would have liked but I have now got one together. My thinking behind this frame is to produce and make available to others a frame that people could move their own cycle parts over to from an existing ebike conversion or use it for a new build. I have spent a lot of time trying to ensure the compatibility of most cycle parts and hub motors. It is still a way from production, I have the components for 5 frames and my intention is to build them all very different to test and hopefully show the versatility. There may have to be some small alterations as the frame matures to a production design.

The rear suspension has a ride height adjuster independent of the spring preload, this will allow the fitment of a variety of different fork lengths and still allow the builder to choose the fork angle, or use a bigger front wheel than rear wheel and still be able to tailor the geometry to their needs.

The cad drawing is drawn with my 17" moped rims with 17x2.75 Heidenau K46 tyres (22.75" dia). It has an HT3525 rear hub motor, the drawing doesn't show this, that is the disc brake you can see on the front wheel. There are no chain tugs, the hub motor axle fits in clamps and the chain tension when not fitted with a derailleur can be adjusted by a tandem eccentric bottom bracket. My own motor has square axle ends, the clamping drop outs on this frame are specific to my motor, the others accept std 10mm flat axles.
The seat post mounting is going to be on the battery box lid (not made that yet!) This battery compartment will house 20 4s hard packs with ease for 84v 20ah.

Here is the drawing I have worked from;



I am off to fit some forks and wheels, while you wait for those pics have a look at a few pics of the frame I have put together today.

But the real question is..

Can it fit a Cromotor?

Not in this frame but the next one I am putting together will be having a Cro in it. When I get around to jigging it up for manufacture the ability to build the swingarm with extra width will be catered for. I still have to jig up for the fitting of the rear caliper mounts too, I will get that done on next session in the shed.

This battery box arrangement with end entry was chosen so I could build in aluminium, I felt a side entry frame with a large removable panel would not be strong enough. The benefit is extra stealth, this one will be well hidden by the rider legs!

I have estimated the complete frame with no forks or shock will weigh in under 6kg.

Two of these are mine. The craftsmanship Simon demonstrates time and time again is second to none. Absolutely amazing. I like his work that much I'm selling them built up with top spec components. Can't wait si. Hurry up. Oh and the cro frame is mine haha.

Beautiful metal work as always. You don't show the inside of the battery box to see how it is reinforced in the area where the 3 tubes connect near the saddle, but the lines on the side in the drawing seem to indicate an extra layer for more strength at both ends. The down tubes are less concern since the loads are transferred to the corners of the box. Maybe I'm just over analyzing it, since there are 3 tubes, but aluminum always makes me nervous as an ebike frame material.

I had similar thoughts about the fastening points for the top tubes. There is a lot of flat area there to take compression from the top tubes. You seem to have gone after the down tube reinforcement with that square gusset, but it's arguably the least attractive part of your design.

I was wondering if a couple of split tubes crossways side-to-side on the battery box as boxed reinforcing members might be worth considering.
Something like this:


I re-shaped the side reinforcing plates (?) as external and serving duty as end caps for the cross-tubes...

Anyhow - just a thought...

I like Teklektik's idea, especially since it introduces another, which would be to make the entire battery box removable. Then fitting the battery exactly is even easier, or using a different material.

This area of the design has occupied my thoughts a lot, this is the first incarnation. Allthough the drawing isn't clear in this area it does have a gusset folded over the top tube connecting the 3 points of attachment to the battery box to spread the load further, not too dissimilar to Tek's idea, which is why you cannot see the bottom of that tube where it attaches to the box, non of the shown gussets have been fitted yet.

I have considered all sorts of reinforcement of the box sides to better withstand the compression force in that area. At least all the rear sus forces are contained within the plate structure. I didn't want to rivet or weld additional plating to the outside of the box.

My plan for this first frame is to have a snug slide in short internal box with an integral bulk head under the area of the highest tube which will also secure the battery from movement. The box lid will also over lap outside an inch bolting through holes on all sides into captive fixings in the slipped in bulk head box. All easy parts to fabricate and will add substantial rigidity to the structure while keeping the external look clean and the internal faces free of any intrusion that would hinder battery installation.

Then go ride it and try to break it!!

The bike is on its wheels now, I will take some pics in the daylight tomorrow.

A few more pics;







A few more parts have arrived so more pics to follow as they get fitted.

The fork and wheels pull things together quite nicely. I like it more than initially, though I still am up in the air about whether it seems just a bit forced in trying to be different from the more common orientation of the batteries (lengthwise, head tube to BB). The battery will feel heavier in that orientation, but that effect will be be small and more than offset by the better access to batteries. Everything below the battery box has a strong elegant look with even the rear shock looking more like it belongs there than the majority of dual susp pedal bikes. I think it all comes down to the part that's probably been keeping you up at night...how to fit the saddle and seat tube. A small concern in that regard is how the upper corners of the battery box play along with thigh clearance while pedaling.