Project: Adding passenger seat to FS bike

[cwah]

Hello,

I've finally decided to add a seat to my bike:

I've already prepared anchor for the side of the bikes that would allow to put M6 bolts:

The principe would be similar to Thebikeseat, but with working for 20" wheel, with bigger box capability and working for full suspension bike:

Here's what I'd like to achieve:

Key requirement:
Able to support 75kg passenger and small potholes vibrations


So there are 4 things I need to make sure are right:
- The pillar tube that needs to hold on passenger weight + box weight. I'm thinking to get 6mm thick * 20mm width bar for each side:
http://www.ebay.co.uk/itm/304-Stainless-Steel-Flat-Bar-Strip-10-15-20-25-30-35-40mm-x-3-4-5-6mm-thick-/252123870089?var=550966013650&hash=item3ab3c0f389:m:mKmAXQgsaPVW-Hva8fNkPig
It will be fixed by 1 stainless steel M6 bolt:
http://www.ebay.co.uk/itm/M4-M5-M6-M8-M10-A2-STAINLESS-STEEL-COUNTERSUNK-BOLT-CSK-ALLEN-SOCKET-SCREW-/181276846436?var=480302297717&hash=item2a34f12964:m:mgpaglHKBfZXoxcL7wueiFw

- The top of the box will use the same 6mm thick * 20mm width bar. The rest will use 2mm thick 20mm width bar.

- The hinge... I don't know what to get. Any idea?


What do you think about this plan?

 

[Alan Quay]

I don't think 6mm bolt will be strong enough. I think you should aim to use the rear wheel axle as your support, say by cutting a 12mm slot into the bottom of your support, then clamping back in place with wheel nut.

 

[craiggor]

 

[cwah]

I don't think 6mm bolt will be strong enough. I think you should aim to use the rear wheel axle as your support, say by cutting a 12mm slot into the bottom of your support, then clamping back in place with wheel nut.

I'm using 10mm torque arm on it, it's very thick and I was thinking with longer bolt it could hold?

Otherwise, is this what you mean for the support?

 

[anotherkiwi]

A design school first year we had a project:

- Build a suspension bridge capable of supporting a brick between two other bricks
- Material allowed are balsa wood, paper and thread

You learn a lot about triangulation and how structure is just as, if not more, important than material strength. So after doing a bit of research on Eiffel and whatnot I got away with a single stick (of carefully chosen) balsa and compression struts at the ends. It exploded after the ten minute reglementary time period - I passed

Your seat and box needs to be attached to a carefully triangulated structure that is balance by a hinged parallelogram attaching it to the frame at the top. If I were to build it I would use plywood, which is light and strong, attached with aluminium mounting plates. You use epoxy to protect the ply from the weather. If I was feeling arty and creative I would probably chuck in a bit of carbon fibre to make the structure look ridiculously unsafe to sit on but even stronger.

 

[cwah]

A design school first year we had a project:

- Build a suspension bridge capable of supporting a brick between two other bricks
- Material allowed are balsa wood, paper and thread

You learn a lot about triangulation and how structure is just as, if not more, important than material strength. So after doing a bit of research on Eiffel and whatnot I got away with a single stick (of carefully chosen) balsa and compression struts at the ends. It exploded after the ten minute reglementary time period - I passed

Your seat and box needs to be attached to a carefully triangulated structure that is balance by a hinged parallelogram attaching it to the frame at the top. If I were to build it I would use plywood, which is light and strong, attached with aluminium mounting plates. You use epoxy to protect the ply from the weather. If I was feeling arty and creative I would probably chuck in a bit of carbon fibre to make the structure look ridiculously unsafe to sit on but even stronger.

I have done some additional research, and from what you say on triangulation maybe the simplest way would be to buy a ready rack and adapt it for my needs?

This one is cheap and is supposed to be rated to 70kg:
http://www.tredz.co.uk/.Axiom-Journey-Rear-Rack_54655.htm

Or this one supposed to be extra strong at 60kg:
https://www.sjscycles.co.uk/carriers-racks/thorn-expedition-steel-rear-cycle-pannier-rack-seconds/

I assume if I avoid lateral weight and place it correctly, then I it should be a winning combination?

 

[Wicky]

and somehow incorprate some rear passenger footpegs / chain-guard before they end up as bloody stumps...

On that note what's the law on carrying passengers? otherwise you'll need to consider Martin-Baker's designs

 

[anotherkiwi]

I have done some additional research, and from what you say on triangulation maybe the simplest way would be to buy a ready rack and adapt it for my needs?

This one is cheap and is supposed to be rated to 70kg:
http://www.tredz.co.uk/.Axiom-Journey-Rear-Rack_54655.htm

Or this one supposed to be extra strong at 60kg:
https://www.sjscycles.co.uk/carriers-racks/thorn-expedition-steel-rear-cycle-pannier-rack-seconds/

I assume if I avoid lateral weight and place it correctly, then I it should be a winning combination?

I would say you are good for a 20% safety margin on those racks. That is what I would do rather than build.

@Wicky when your government finally sells you down the river to China here is what will be on the streets

 

[cwah]

and somehow incorprate some rear passenger footpegs / chain-guard before they end up as bloody stumps...

On that note what's the law on carrying passengers? otherwise you'll need to consider Martin-Baker's designs

If you check the pictures... there are already footpegs on it

 

[Wicky]

http://www.ebay.co.uk/itm/55466-Honda-CBR900-1996-Foot-Peg-Hanger-Guards-/301233365629?hash=item4622e8627d:g:pQAAAOSw0vBUgA8X ;-)

 

[cwah]

http://www.ebay.co.uk/itm/55466-Honda-CBR900-1996-Foot-Peg-Hanger-Guards-/301233365629?hash=item4622e8627d:g:pQAAAOSw0vBUgA8X ;-)

What are these for?

 

[Alan Quay]

I'm using 10mm torque arm on it, it's very thick and I was thinking with longer bolt it could hold?

Otherwise, is this what you mean for the support?

Roughly, but I'd just use the axle bolt to hold it in place, and the torque arm to stop the axle from spinning in the drop outs (as it is now)