My First Seat Bag...

[JReeves]

I've been browsing this site for a while, as well as spending a lot of time on the BPL Forum.  Fooled around with making my own gear in the past, but never anything for the bike aspect of camping.  Made a frame bag for my touring rig last week, and it came out decent, although I have a few changes I'd like to make on the second effort.  I'm waiting on some fabric that I ordered from Rockywoods.com, but figured I'd use some of the cheap material I have for a prototype.  I played around with some card-stock to get the shape and design I was looking for, then went from there.  I had a 7" diameter stuff sack that I designed it around, and then ordered the OR Dry Sack in the same diameter.  I wanted to do something "modular" as I knew it would be easier to achieve the waterproof aspect, and also eliminate some tough angles and curves when sewing it all. 
The "cone" that is mounted to the seat post is two layers with a thin semi-rigid plastic mesh sewn inside of it to give it some shape.  It's fully adjustable/compressible depending on what's in the dry sack.  It's shown here with my 20 degree down bag in it.  Hard to see all the strap locations for mounting: one velcro closure on seat post, one velcro strap over top of seat rail clamp, and then two separate straps around the seat rails.  Turns out to be pretty stable, with only some slight left-to-right sway(1"-2") when riding hard, but no up-and-down at all.  Clears the back of my legs perfectly also.  I'm very happy with the outcome and look forward to making some more gear!

[toosh]

  , what's capacity of bag?

[MattySF]

That is real cool. I like the modular concept.
Bag-bra?

[6thElement]

Really like that a lot!

[Village]

Brilliant! Well executed too. I'm really impressed by the lateral stability. I have to criss-cross my lifter straps to really stabilize the bag, and that's still not a complete fix.

[trebor]

Looks great!

[Bedrock]

Very Cool! I like your innovative approach with the modular concept. Smart. Nice job on the build as well. I'm inspired.

[Goatrak]

That is a very original piece of work and design, great attention to detail and sewing ability as well. The modular concept is a great idea.
For more stability had you thought of sewing in two side cinch straps with buckles that would mate with the roll up buckles on your bag, which would also give you another way to compress the bag from the side.

[caseygreene]

Whoa. I want one! 
Did you intend to use with different sized stuff sacks?

[JReeves]

-First off, thanks for the comments guys!!!
-The Dry Sack is 10L in capacity(7" x 14") although it will work with a few different sized bags, as the diameter and length are adjustable.  I built the "cone" based on a 7" diameter though, so that would limit the sizing a little bit. And more importantly it's load adjustable, so I can shorten or lengthen the main strap around the end of the bag depending on how full the dry sack is.
-Bag-Bra!  hahahaha...  That's perfect!
-In response to Goatrak, I had originally planned on doing two horizontal straps off of the corner of the "cone"(where the 1" webbing that goes through the actual seat is) that would wrap around the open end of the dry sack.  But after getting everything tacked together, I realized that wouldn't offer any real increase in the stability.  It's more a weakness/lack of true mounting to the seat post/seat that allows the movement, not the two modular pieces shifting independently.  So, while another strap would get the dry sack in there tighter, that wouldn't have made it move any less.  Still kicking around ideas of a way I can solidly attach the pack to a seat post or seat rails. 

[Solrider]

This is brilliant!  And you'll be making some for the rest of us, when exactly?? 

[Aslan]

Carousel and revelate better watch their backs!  Nice work.  When can I get one?

[Bedrock]

JReeves - my only question about your design is in regards to thigh room. Is the round bag at the base of the seatpost wide enough to rub against your legs when in the saddle? If this is not a problem your design seems superior to the standard seat bag design that is so common now.

[sherpaxc]

Excellent question.  I'd be interested to know the answer to that.  Honestly, this looks like the "next" step in seatpack evolution.  I would LOVE to test one of these suckers out. 
Man, what a simple and yet great design.

[JReeves]

Wow, I'm flattered!  Thanks guys. 
Greenwater, the bag itself is round, but I made a semi-rigid "cone"(for lack of a better word) built into the carrier system.  This acts as almost a funnel that forces the bag to a narrower shape the more you compress it.  Here's two of the pictures combined with some labeling.  It clears the thighs plenty.  It is very true to the shape/width of the seat for the first couple of inches off of the seat post.  And seeing as your leg is never perfectly perpendicular to the seat tube, it would be nearly impossible to get your thigh to touch any part of the bag while on the saddle.  The picture on the right was taken almost exactly in line with the seat tube looking down.

My materials should be here in a day or two, and I'll get around to tweaking a few little things, and seeing how it sews.  If I can get a good solid one made that I'm 100% confident in, I'd consider making a few for interested parties! 

[sherpaxc]

I am an interested party.  My CDW seat pack, going on close to 4 years now is quite used and in need of an update.  This thing get's me excited.  Please let me know when you're ready.

[bmike-vt]

I think you should consider flipping the design upside down. Fabric tends to work well in tension - so to tighten things up have a look at how Revelate and CDW attach under the saddle. If you flipped your design, maybe then adding a bit of the 'cone' part back under like you have it now @ the seat post, you'd be able to make a stronger connection under the saddle - using those straps and the top flap (which is now currently underneath) to stabilize and compress things further.

Here's a marked up shot of my Revelate:

[jeremy11]

looks good, and great mod idea.  that way you can bring different size stuff bags for different trips(?)
how easy is opening and closing compared to a "normal" big seatbag?  my first homemade seat bag was a little hard to get into, which with freezing hands looking for the extra mittens (to wear inside pogies) and extra puffy jacket, easy access makes all the difference.
keep it up!  these things take a number of prototypes to really get everything right at once.  I'm still not there yet

[DoctorRad]

This looks like a lighter alternative to pro_out's approach here:

http://www.bikepacking.net/forum/index.php/topic,605.msg14306.html#msg14306

The more I think about it, the more I think this is a great way to go, using a lightweight support for a drybag. Another approach here:

http://www.thecyclistsite.com/adventure/2010/10/3/dirtbagging-your-bags-making-your-own-seatbag.html

I thought those Quick Fist clamps looked particularly useful. I wonder what could be made from a couple of these mated to a cut-down 5-litre HDPE bottle...

[chrisx]

looks like a well designed seat bag