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Created March 12, 2026 20:26
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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?

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eonist commented Mar 12, 2026

You're right — the brake hose doesn't go all the way down the seat tube. It enters the ST briefly at the TT/ST junction, then immediately crosses into the seat stay and rides that all the way down to the caliper.

Corrected Route A:

text
HT hole → through TT → into ST (just the junction, ~20mm) → into seat stay → down seat stay → exit hole → rear caliper

The seat tube is basically just a junction box at the top — the hose passes through it for a centimeter or two to get from the TT into the seat stay. It never goes down the ST toward the BB. That keeps the ST cable void free for the motor cable (Route B) and rear light wire (Route D) which actually need to travel the full length of the seat tube.

Updated Route Table

Route | Path -- | -- A Rear brake | HT → TT → brief ST junction → seat stay → exit → caliper B Motor power | DT → overlap → short ST → chainstay → dropout → hub C Torque sensor | BB → 10mm hole → DT D Rear light | DT → overlap → up full ST → seatpost → saddle light E Front light | DT → up DT → exit HT → user's problem F Front brake | External down fork

Good catch — the ST only handles Route B and D long-distance. Route A just clips through the top junction. I'll correct the SVG if you want an updated drawing.

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eonist commented Mar 12, 2026

Yes. With the current plan everything except the front brake hose is fully internal.

  • Rear brake hose: head tube → top tube → brief seat-tube junction → inside seat stay → out at caliper.
  • Motor cable: inside down tube → overlap into seat tube → inside chainstay → out at dropout into hub.
  • Torque sensor: inside BB → 10 mm hole → straight into down tube electronics zone.
  • Rear light wire: inside down tube → overlap into seat tube → up seat tube → into seatpost → out under saddle.
  • Front light wire + display/control wiring: inside down tube → out at head tube → user routes to cockpit.
  • Only external line: front brake hose down the fork, which is normal even on high‑end road bikes. [bikeradar](https://www.bikeradar.com/advice/buyers-guides/bike-tyre-sizes)

Do you want to keep that external front hose (simpler fork) or explore an internally-routed fork as a stretch goal?

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eonist commented Mar 12, 2026

Yes. Everything can be fully internal with the layout you’ve described.

What’s Internal vs External

  • Rear disc brake hose:
    Internal from head tube → top tube → seat tube → left seatstay → exits only right at the caliper.

  • Motor cable:
    Internal from controller in down tube → through DT/BB/chainstay overlap port → inside right chainstay → exits only at rear dropout into hub.

  • Torque sensor wire:
    Internal from BB shell → tiny 4mm hole into down tube → up to controller.

  • Battery power + all electronics (controller, BMS, GPS/BLE):
    Entirely inside the down tube.

  • Front light wire:
    Internal in down tube → exits at head tube. (User handles cockpit routing.)

  • Rear light wire:
    Internal DT → overlap → up seat tube → exits near seatpost or through a hollow seatpost.

Externally you only see:

  • The rear brake caliper hose at the caliper itself.
  • The motor cable at the dropout–hub interface.
  • The headlight and taillight fixtures and their short exposed pigtails.

Everything else lives inside the tubes.

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eonist commented Mar 12, 2026

Yes. Fully internal. No temporary exits. Let’s lock this in very explicitly.

Final Motor Cable Path (Only Exit Is At Hub)

Motor cable (8mm 3‑phase + signal) route:

  1. Inside down tube

    • Starts at the controller/BMS block in the free 130mm space above the BB.
    • Runs inside the down tube, below the battery pack, toward the BB area.

  2. Inside DT/BB/chainstay overlap zone

    • Passes through an internal brazed passage in the junction where down tube, BB shell, seat tube, and chainstay meet.
    • This is designed as a built‑in channel during framebuilding, not an external hack. pedelecs.co

  3. Inside right chainstay

    • Enters the right chainstay interior at the BB junction.
    • Runs fully inside the chainstay tube to the rear dropout.

  4. Exit at dropout → into hub

    • Only here does it exit the frame, at a small port right by the dropout.
    • Immediately plugs into the hub motor connector.

So:

  • No external run under the BB.
  • No exposed section along the stays.
  • Only visible section is the last few centimeters right at the dropout into the motor, just like on clean OEM ebikes. bigforestframeworks

Everything else for the motor cable is inside steel tubes, from controller to dropout.

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eonist commented Mar 12, 2026

Your plan (fully internal motor cable, only visible at the dropout → hub) is exactly the clean, “OEM” way to do it. There isn’t a better alternative that avoids that last short exposed section.

How rear hub motors are normally wired

On essentially all decent rear‑hub ebikes:

  • The motor cable exits the motor axle right at the dropout (short exposed pigtail).
  • From there it immediately enters the chainstay, runs inside the stay, and then inside the frame to the controller. macfoxbike
  • The only unavoidable external bit is that few‑cm section right at the axle, which also needs strain relief for safety. macfoxbike

Hiding the entire cable path inside the frame up to the dropout, as you’re planning, is actually cleaner than many production bikes, which often zip‑tie the cable along the outside of the chainstay. forums.electricbikereview

Why there isn’t a “more internal” option

The motor connector physically sits at the end of the axle or just outside it. You cannot:

So the cleanest, structurally safe pattern is exactly:

  1. Internal: controller in DT → internal DT/BB overlap passage → internal right chainstay.
  2. External only for the last 3–5cm: exit at dropout → plug into hub.

You’re already designing to that best practice. The cable is inside the frame all the way until it has no choice but to appear at the axle.

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eonist commented Mar 12, 2026

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.

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eonist commented Mar 12, 2026

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

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

  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)

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?

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eonist commented Mar 12, 2026

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

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eonist commented Mar 12, 2026

omera_split_dropout

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eonist commented Mar 13, 2026

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.

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