slickginger

Thank you for the suggestion on increased strain... totally agreed and I'm actually already all over this using FEA to make sure my material can take it. It looks like I have plenty of headroom right now, but I want to test in fatigue in real life to make sure this thing can take the abuse. It's worth noting that the Brompton carrier block itself is made of PA 6 which is polyamide nylon. Not a very strong material, so the bar isn't exactly high!

Got my Brompton block in! There is a LOT of geometry that I was missing here, it gives me some great ideas for how to transmit the loads more effectively. Stay tuned for more in the coming days (man I love holiday break... I get so much DONE!)

Good to know about the bags. I was thinking I only had room for a S bag, but I'm glad I can go bigger. I want to commute with this thing, so it's got to have some room.

slickginger

I've responded to you badmother several times, not sure why mods are blocking. Must be because I'm new. Anyway, let's give this a try:

Thank you for the suggestion on increased strain... totally agreed and I'm actually already all over this using FEA to make sure my material can take it. It looks like I have plenty of headroom right now, but I want to test in fatigue in real life to make sure this thing can take the abuse. It's worth noting that the Brompton carrier block itself is made of PA 6 which is polyamide nylon. Not a very strong material, so the bar isn't exactly high!

Got my Brompton block in! There is a LOT of geometry that I was missing here, it gives me some great ideas for how to transmit the loads more effectively. Stay tuned for more in the coming days (man I love holiday break... I get so much DONE!)

Good to know about the bags. I was thinking I only had room for a S bag, but I'm glad I can go bigger. I want to commute with this thing, so it's got to have some room.

badmother

It is a good thing you did not give up on responding It is possible that you was trying to respond with a PM (personal message) that is not visible for the forum. You need to have 50 postings to be allowed to do that.

After playing with the B luggagesystem (on different bikes) and reading about other peopels experiences I have realised the strength of the system is closely linked to the design and materials. Make a small change and you can get a huge change in strength. Peopel who modify The B block to be used on a Dahon use 6mm bolts and that does to some extent compensate for the longer distance from headtube to bag mount and/or the weaker B block if it is carved out to fit close to the Dahon head tube.

I am not sure if you intend to glue your B block to the piece you make yourself or if you rely on the screws to hold it together. Plse keep us updated.

You may know there is several aftermarket luggageblocks for Brompton for sale, you find them on ebay but also available from other sites. Alu and titanium is used. Also several front racks for B, steel and titanium.

There was a forum member that had two "B blocks for Dahon" made as a prototype. We are still waiting to hear from him about that one..

I used to dedicate a lot of time to bikes in the end of December and beginning of January. This year we are renovating an old house so working 12 hour days and are frustrated over peopel who just disappear.. (have anybody seen our missing electrician? )

Keep us updated- and give us some pix plse.

slickginger

I seems that certain posts just don't go through. Weird.

Anyhow, I've not been able able to find any adapters for putting Brompton stuff on the Dahon/Tern. Most I've seen is the CNC aluminum carrier blocks that look cool but are 4 times the price ($100 vs $25) and about the same weight (50 grams is the lowest I've seen vs 75 stock). My solution will be easily available to anyone online, light (I'm at 7 grams right now), and reversible. Hopefully more than just myself will be interested in it...

Understood about the old house woes... I grew up in a 1901, and now I'm renting a 1915 house that just needs constant work. I will say the more care you put in now the easier it'll be in the long run!

Rick Imby

I will say the more care you put in now the easier it'll be in the long run!

Words to live by Slickginger....

slickginger

Here she is so far... I've got some ideas for how to transfer the load better and a bunch of refinements after test-fitting a 3D printed prototype, but I'm interested to see how this holds up as is. Your thoughts are welcome!

wesgreen

Looks great. Is this pic upside down?

slickginger

Thanks. No it isn't, why do you think so? I was thinking of putting the Brompton block a bit higher than the Dahon/Tern bolts, but you could flip it pretty easily.

wesgreen

Just asking; wouldn't it be stronger if turned upside down, based on simple mechanics and gravity principles?

slickginger

Depends on the material, but either way it doesn't make a big difference in this case (not much length to have a column buckling issue). Nylon or other plastic materials actually get stiffer upon compression, so in this case it's actually good to load it up a bit. Just for funsies I ran it the inverted way to see. Less than 5 MPa difference, with the lower stress being in the designed orientation:

Upright Cantilevered


Inverted Cantilevered


Disclaimer: It's worth noting that the resulting stresses here are HUGELY conservative (probably too much, but I'm too lazy to make a really complex analysis and don't want it to break). This is being treated as a point load to the outer extreme of each of the holes, which is like taking the entire bag's weight and hanging it on a hook on the OUTSIDE of the block (where those blue arrows are). And also, this is with a 200% safety factor. So there's that.

Second prototype just finished printing, time to go test fit it!

badmother

This is interesting.



About time somebody did something to solve this problem.

When do you start selling them so we can get them too?

slickginger

Well now I need a REAL prototype made, which is probably going to take at least a week. After that it's test, break it, probably find something wrong with it and have to completely change the design, test again, find that the new design fails and give up on the idea entirely.

So, a couple weeks?

Here is the latest prototype all fitted to the bike. Going to try to make some changes to make it use the stock Brompton screws. Right now they don't reach.

badmother

Nice!!

Winfried

While travelling accross Europe, I notice very few Dahon/Tern riders actually carry a bag in the front making use of the lug soldered on the frame.
Maybe it's because LBS just don't sell the truss + bags so people aren't aware of that solution, or the luggage truss only takes 7kg/14lbs and the bag swings a bit too much while loaded. As a result, people just carry their stuff on a backpack.



Incidently, does someone know why Dahon/Tern (or Klickfix itself?) decided to go for that long truss instead of a block à la Brompton which would keep cargo closer to the frame? Because of the cables/housings?

I would suggest that you provide two different adapters and sell them through eBay:

• The one you're currently working on that makes it possible to use a Brompton bag on a Dahon/Tern
• A Brompton-like luggage block but compatible with Klickfix: As it'd be shorter than the Dahon/Tern luggage truss, it could take more weight and not swing sideways

As a reference, a small French company called Theravada tried to sell a luggage lock for Dahon/Tern bikes to carry Brompton bags, but it failed commercially:



Either way, those after-sale adapters are terrific add-ons to Dahon/Tern bikes.

slickginger

Yay! Just got my prototype in made of sintered nylon and the fit is PERFECT into the Brompton carrier block. It's a nice press-in fit, since the Brompton block has a draft angle on the interface. I accounted for that and it feels guten tight!



Two developments:

1) I was trying to use the stock Brompton bolts, but it looks like in order to do that I would have to compromise the structural integrity of the adapter. No way Jose. I would already have new bolts, however I live in New England and we just got a ton of snow so the hardware store is closed. Sigh.

2) I'm noticing in the above pictures (thank you for the reference by the way!) that their mount puts the bag in a vertical position, instead of parallel to the headtube as the Brompton block. So I'll have to find out whether that's a problem or not once I get a Brompton bag. Looking at the Carradice lineup, although they're hard to get over here.

Rick Imby

I find it amazingly stupid for bike manufacturers to come up with their own standard once one has been set. I am assuming the Brompton mount was available long before the Dahon or Tern mount. As I am a Dahon dealer they do not have anything in stock in the USA to fit their mount---really? You come up with a new type of mount and then you don't come out with a line of accessories to mount to it?

While Swift did just the opposite---He intentionally designed his stuff so as many industry standard parts as possible would work.

There should be one industry standard front of the frame accessory mount. The folding bike market is tiny enough that there should not be multiple standards on something so simple.

fietsbob

Ford water Pumps don't fit GM engines either .. get over it.

You can Order a Bike Friday Tickit*, with a mount that will take a Brompton block,
But They Build your Bike from a Menu as your order comes up in the Queue.

Brompton and Tern and Dahon fill Shipping containers full of boxed bikes .
whole different Manufacturing model.

* hurry that bike production time is being shelved to make way for their lighter Pack-It bike.

Winfried

"The nice thing about standards is that you have so many to choose from."

https://en.wikiquote.org/wiki/Andrew_S._Tanenbaum

desriantoandika

desriantoandika

https://goo.gl/photos/HB1T7iJPvuBPjxPx5

Dahon Front Carrier Block, S Bag Brompton

slickginger

Looks great man! Is that a custom solution or did you make/buy an adapter?

slickginger

Update!

So this is why testing is important. I underestimated the counter-torque requirements of the captive nut pockets, and as I was trying to take pictures Monday night I realized I couldn't get my Brompton bolts out... they just spun because the flats that the nuts rely on for counter-torque had just sheared away in the adapter. I tried like hell to break off the mount... literally jumping on it sideways with the bike on the ground. The good thing is that WOW this thing is strong! The bad part is that I need to dremel my adapter prototype apart to get it off

So I've got a couple plans for how to fix this, but either way it looks like I'm going to be delayed by at least a week. I've verified this thing's strength I think, but now I just need to sort this counter-torque problem so that you can actually take the thing off!

Winfried

Keep up the good work

badmother

I bet it is not easy to make one or it would be all over e-bay by now

If you are making only one you could try aluminium..

I just drilled a new hole lower down on the B block and used the holes of the Dahon and the Dahon screws.. after digging out plenty stuff to make space for the bigger Dahon mount.

The Brompton luggageblock when mounted on a Brompton the sides of it encloses the the mount on the frame. I bet this makes it stronger and helps stabilizing the whole thing (block with bag). Same with the older clickfix bag holders. I have not seen the new alu ones close up (are they Dahon or Tern) but my impression is there is nothing on the sides, just strapped to the front but then again it is aluminium.. Your adapter is just holding the parts against the front of the mount with with the bolts and nothing on the sides and top to stabilize the whole thing. Did you give this some thought?

slickginger

GUYS. I'M SO EXCITED. Just got my new designs in. Although I was prepared to go more drastic if necessary, the only tweak is that I snugged up the clearance around the captive nuts. Now it's a true slip fit, and it feels GREAT. Just to put this thing through the wringer I tightened it all the way on and then disassembled it several times. No gouging to speak of! As I suspected, it was acting just like someone who was using the wrong wrench for a bolt: rounded corners. That appears to be completely fixed now. Woohoo!



If you're interested in giving one of these a try, they are now for sale here. Let me know how they can improve!