frame-build.md

frame-build.md

That's a smart move. The Detroit is the spiritual reference, but the Omera needs its own visual identity. A seat tube cutout is a strong signature — instantly recognizable and signals "this is a track-bred frame" without copying Dosnoventa's exact look.

What Makes Omera Visually Distinct from Detroit

Feature	Detroit	Omera
Seat tube	Standard round	Cutout wrapping rear wheel ✅
Down tube	Columbus Airplane ovalized	50mm round (battery inside)
Drive	Chain	Gates CDX belt (visible difference)
Brakes	None (track) or rim	Hydraulic disc
Rear dropout	120mm track	135mm horizontal/sliding
Motor	None	Bafang G020 (stealth hub)

The cutout + belt drive + disc brakes together give the Omera a completely different silhouette from the Detroit while keeping the same aggressive 74°/76° pursuit geometry. Someone who knows bikes would clock it immediately as its own thing. ppl-ai-file-upload.s3.amazonaws

Design Consideration for the Cutout

One thing to flag for the frame builder — the Omera has 135mm rear spacing (not 120mm track), so the seat tube cutout needs to be wider than a typical track frame cutout. The wheel sits in the same plane but the hub flanges and disc rotor are wider. Make sure the cutout clears:

• Tire (700×25c) + 3mm each side minimum
• Disc rotor on the non-drive side
• Belt on the drive side

This is doable but the frame builder needs to know upfront. Want me to add this to the frame fabrication brief?

Yes, you can absolutely design a cap/guard to protect that tiny exposed section at the dropout. That’s a good idea, and other systems do similar things.

What the cap does

• Covers the cable exit + connector area at the dropout.
• Shields it from side impacts, rocks, curbs, bike racks.
• Acts as strain relief, so any tug on the cable is absorbed by the guard, not the connector. reddit
• Visually cleans up the last exposed bit.

How others do it

• Bosch and Giant both sell small molded caps/covers to protect ebike cables and charge ports at frame exits. ebike24
• Some ebike owners 3D‑print rear hub wiring guards that wrap around the dropout area to protect the harness; these live right where your cable exits. facebook
• There are generic Bafang cable guards and caps in 3D print libraries you can copy or adapt. [printables](https://www.printables.com/tag/bafang)

How you could implement it on Omera

• Material: small steel or aluminum tab welded to the dropout, plus a snap‑on plastic or rubber cover; or a fully 3D‑printed nylon guard that bolts to a tiny boss.
• Shape: an “L” or “U” profile that wraps around the cable on the outside of the dropout, extending just past the connector.
• Mounting:
  • One M3/M4 boss on the dropout to screw the guard on, or
  • A slot in the dropout plate where a guard tongue slides in and is trapped when the axle is clamped.
• Serviceability: single screw (or clip) removal so the rear wheel can still come out easily.

So the final picture is:

• Cable fully internal through chainstay.
• Exits right at dropout.
• Immediately disappears under a small protective cap/guard, then into the hub.

That’s as clean and robust as it gets.

Yes — there are proven, buyable “frame split” solutions you can design around instead of inventing your own from scratch.

What Gates Requires

Gates explicitly says the frame must have a “frame break” in the rear triangle so the one‑piece belt can be slipped in. mi-tech
They don’t care where, as long as:

• You have at least 8 mm gap when it opens.
• You also have a belt tensioning system (sliding dropouts or eccentric BB). 2blua

You’re already planning horizontal/sliding dropouts, so you just need the frame split.

Off‑the‑shelf frame split hardware

You can buy CNC’d metal splitters and design your stays around them:

1. Paragon Machine Works belt splitters

   • Paragon sells stainless/ti splitters that go in a seat stay or chainstay (two plates bolted together).
   • Framebuilders use them for alloy/steel/titanium belt frames; they come with CAD/STEP files so you can integrate them cleanly into your jig and tubing. [bikeforums](https://www.bikeforums.net/framebuilders/1125177-belt-drive-alloy-frame-splitter.html)

2. Dropout‑integrated split (Tout Terrain / Olsen style)

   • The “RocknRollout Dropout” hides the split inside the dropout assembly itself. You undo 2–3 bolts, remove a splice plate, slide the belt through, then close it again. [olsenbicycles](https://olsenbicycles.com/blogs/olsen-blogs/the-rocknrollout-dropout)
   • Tout Terrain’s design similarly splits the right dropout in thickness: one half attached to chainstay, one to seat stay, clamped together by the axle. [bikeforums](https://www.bikeforums.net/framebuilders/1125177-belt-drive-alloy-frame-splitter.html)
   • This is the cleanest visually: from the side it just looks like a normal dropout.

3. Custom seat‑stay splitter services (Bike Knack, Ti Cycles)

   • Shops like Bike Knack and Ti Cycles retrofit Gates frames by cutting the seat stay and installing a machined splitter matched to the stay diameter. bikeknack.com
   • Their parts are basically a tube connector with two bolts. Good reference geometry if you want to mill your own.

4. Veer split belt (no frame split)

   • Alternative approach: a belt that splits and re‑rivets, so the frame doesn’t need a break at all. [bikeradar](https://www.bikeradar.com/news/add-a-belt-drive-to-any-bike-with-veers-belt-drive)
   • But you lose the standard Gates CDX ecosystem; for Omera that’s a no‑go.

What makes sense for Omera

Given your goals (stealth, clean BB, CNC dropouts, 135 mm belt hub + disc):

• Use a dropout‑integrated split on the right side, like the Olsen RocknRollout / Tout Terrain pattern. olsenbicycles

  • Chainstay and seat stay both bolt into a two‑piece dropout.
  • Loosen 2 bolts, remove the outer piece, slide belt through, bolt back up.
  • Visually, it just looks like a chunky CNC dropout, which you already want.

• Keep no cuts in the seat stay or chainstay tubes themselves — all the complexity is in a replaceable dropout block.

So the answer: yes, you can absolutely base your design on existing hardware. Look at Paragon’s belt‑drive splitters and the RocknRollout/Tout Terrain split dropout concepts as references, then have your own 135 mm disc‑compatible CNC dropout machined around a similar interface. bikeforums

Would you like me to sketch a right‑side dropout concept (135 mm, flat‑mount disc, belt split) you can hand to a machinist?

okay so you sanwitch the dropout module to chain stay and seat stay and lock it with screwbolts. unscrew the bolts. the gap for belt is there

Got it — then we just mirror the function, not the look.

On the non‑drive side:

• Same axle slot height and length as drive side, so tensioning and wheel position behave identically.
• One solid 6 mm plate (no split), with: axle slot, brake mount (if rotor that side), and a small hole/feature for hose exit if needed. bikecad
• Overall 135 mm O.L.D. preserved by making this plate the same thickness as the inner plate on the drive side, so dish stays simple and hub sits centered. alibaba

If you like, I can now define just the critical numbers you need to send your machinist for that non‑drive plate (slot position, thickness, axle center to stay junction, etc.) in plain text.

Beyond the 6% space saving, there are several strong arguments for the oval:

Directional Stiffness

An oval tube lets you put stiffness where you need it. The downtube's biggest load is lateral flex from pedaling — orient the wide axis horizontally and you get far more resistance there, while allowing slight vertical compliance for comfort. A round tube gives equal stiffness in all directions, which means you're over-built vertically and under-built laterally for the same wall thickness.bikeforums+1

Columbus MAX tubesets used exactly this principle: elliptical cross-sections oriented so the major axis opposes the highest active stresses.[astrocycloalpine.weebly]​

Aerodynamics

An oval profile with the narrow axis facing forward cuts wind drag compared to a circle of equivalent area. At city speeds (25 km/h) it's marginal, but it's free — you're already oval for other reasons.unionsteel+1

Better Stress Distribution

Oval tubes have no corners (unlike square/rectangular) but also distribute stress more evenly than circles under directional loads. This improves fatigue life under repeated loading. For an e-bike frame that vibrates from motor + road input, that matters.ytdrintl+1

Frame Joint Geometry

An oval downtube meets the head tube and BB shell with a wider, flatter weld interface on the lateral axis. This gives more weld surface area and a stiffer junction compared to a round tube of the same cross-section area.pailian-aluminium+1

Visual Proportions

Subjectively, oval downtubes look more "designed" and premium — almost every modern performance frame (Pinarello, Liv, etc.) uses ovalized tubes specifically because they signal intentional engineering.pinarello+1

Summary

Advantage | Oval | Circle -- | -- | -- Space efficiency | ✅ 6% smaller | — Lateral stiffness (per gram) | ✅ Higher | Equal all directions Aerodynamics | ✅ Better | Neutral Fatigue / stress distribution | ✅ Slightly better | Good Weld/joint interface | ✅ More surface | Less surface Manufacturing simplicity | — | ✅ Simpler

The only real pro-circle argument is manufacturing ease (standard round tube stock, simpler jigging). For Omera, oval wins on every axis that matters.

Beyond the 6% space saving, there are several strong arguments for the oval:

Directional Stiffness

An oval tube lets you put stiffness where you need it. The downtube's biggest load is lateral flex from pedaling — orient the wide axis horizontally and you get far more resistance there, while allowing slight vertical compliance for comfort. A round tube gives equal stiffness in all directions, which means you're over-built vertically and under-built laterally for the same wall thickness. bikeforums

Columbus MAX tubesets used exactly this principle: elliptical cross-sections oriented so the major axis opposes the highest active stresses. [astrocycloalpine.weebly](https://astrocycloalpine.weebly.com/columbus-steel-tubesets.html)

Aerodynamics

An oval profile with the narrow axis facing forward cuts wind drag compared to a circle of equivalent area. At city speeds (25 km/h) it's marginal, but it's free — you're already oval for other reasons. unionsteel.co

Better Stress Distribution

Oval tubes have no corners (unlike square/rectangular) but also distribute stress more evenly than circles under directional loads. This improves fatigue life under repeated loading. For an e-bike frame that vibrates from motor + road input, that matters. ytdrintl

Frame Joint Geometry

An oval downtube meets the head tube and BB shell with a wider, flatter weld interface on the lateral axis. This gives more weld surface area and a stiffer junction compared to a round tube of the same cross-section area. pinarello

Visual Proportions

Subjectively, oval downtubes look more "designed" and premium — almost every modern performance frame (Pinarello, Liv, etc.) uses ovalized tubes specifically because they signal intentional engineering. velo.outsideonline

Summary

Advantage	Oval	Circle
Space efficiency	✅ 6% smaller	—
Lateral stiffness (per gram)	✅ Higher	Equal all directions
Aerodynamics	✅ Better	Neutral
Fatigue / stress distribution	✅ Slightly better	Good
Weld/joint interface	✅ More surface	Less surface
Manufacturing simplicity	—	✅ Simpler

The only real pro-circle argument is manufacturing ease (standard round tube stock, simpler jigging). For Omera, oval wins on every axis that matters.

Right — 43 mm wide, 59 mm tall. The narrow dimension faces sideways to keep the downtube slim between your knees.

That flips the stiffness story: the tall axis gives you high stiffness in the frame plane (resisting braking loads and vertical flex from rider weight), while the narrow axis keeps it laterally compliant — which on a steel e-bike actually helps ride comfort rather than hurting it. Lateral pedaling stiffness on Omera comes from the motor, not your legs, so you don't need a wide downtube fighting that axis. bikeforums

It also means better standover clearance and a slimmer visual profile from the rider's perspective — the frame looks clean and narrow, hiding the fact there are 20 cells inside. [unionsteel.co](https://www.unionsteel.co.uk/the-benefits-and-challenges-of-oval-tubing/)

Here's v2 . Two changes:

1. Fins gone — those were leftover thin walls between the individual board pockets (BMS, boost, PD trigger cavities overlapping awkwardly). Now the interior is just one clean hollow cavity. You drop all three boards in there and secure them with standoffs or adhesive. Much simpler.

2. USB-C goes through the side — the port hole is on the Y+ wall of the bay, positioned at 15mm up from the bottom. When assembled, this aligns with a matching hole drilled/CNC'd in the alu cover. So the charging workflow is:

• Battery in bike → USB-C port hidden inside the downtube, not exposed to weather.
• Pull battery out → USB-C port on the side of the alu shell, plug in your MacBook charger, done.

The alu cover just needs a 12×9mm cutout in the right spot to let the USB-C receptacle poke through or sit flush.

Render it and let me know how it looks — should be a clean box with no weird internals this time.

You're right — Omera is aluminium, not steel. Noted permanently.

The stiffness argument still holds for alu: the tall oval orientation gives high rigidity in the frame plane (braking and vertical loads), while the narrow 43 mm width keeps the profile slim between your knees. Aluminium is already stiffer than steel for a given tube size, so the lateral compliance from the narrow axis won't make it feel noodly — it's a net positive for comfort without sacrificing structural integrity. bikeforums