PDA

View Full Version : One-way Slider Design



dberndt
03-14-2011, 07:26 PM
Looking for some input here. I'm thinking of building a bike rack for the back of my car and would like to use an over the wheel type hold down system. An arm would wrap over/around the top of each tire to hold the bike securely down.

Here is a link to something similar to what I'm looking for to give you an idea of the geometry. http://www.flickr.com/photos/bikecentric/3752846123/

The arms would need some way to lock in place. Ideally they should slide freely in one direction but require some sort of a quick release to be pressed to allow them to return/release. I haven't worked out the requirements exactly, but if it could resist about 20-50lbs of force working against the lock I think that would be plenty.


I've browses MSC and McMcaster Carr and I haven't really found anything that really looks anything like I'd want. Maybe I am just not using the right phrases.

Some Ideas:

A smallish rack with some sort of spring loaded pawl to function sort of like a cable tie or tie wrap. I could fairly easily profile some bar stock with the "teeth", it would be a bit tedious and the solution offers only fixed locking points, not a friction based infinite adjustability.

A spring loaded pin sliding across a bar with holes ever .X". Same problem as the above, not infinitely adjustable.


If anyone can think of some sort of one way cam or ratchet that's commercially available or fairly trivial to make I'd love to have your input.

Dave

fredf
03-14-2011, 07:40 PM
Looking for some input here.

A spring loaded pin sliding across a bar with holes ever .X". Same problem as the above, not infinitely adjustable.


If anyone can think of some sort of one way cam or ratchet that's commercially available or fairly trivial to make I'd love to have your input.

Dave

this might work but would be difficult to release under tension . . .

http://www.adjustableclamp.com/3700-imgt.jpg

fredf
03-14-2011, 07:42 PM
drat -- the dreaded double post

darryl
03-14-2011, 09:24 PM
What's the beefiest zap strap you can get? Some are releasable- still incremental, but smaller steps. There is, or was, a similar type of thing in the hardware section of outdoor shops. I got a few parts that would ratchet together to tighten ski boots, then release by lifting a tab.

The most common fastener in this area is the strap hardware. Backpacks have these- you can adjust the strap length, then leave it there. Clip the parts together to hold, pinch one part to release.

adatesman
03-14-2011, 09:58 PM
Might be fairly easy if you modify the design in the pic a bit... If you make the short red ones go over center (doesn't look to be the case in the pic) it'll be self-locking to a reasonable extent, and if you make the long-ish silver ones they're attached to adjustable length in some manner it'll handle different size frames/wheels. From there a simple pin/detent to keep the small red ones from popping back over center when you hit a pothole and you're in business.

Black Forest
03-15-2011, 01:12 AM
Just replace the bars on the bottom with gas struts. The problem is how to hold them open when loading the bike. I would just use my foot but I am a farmer!

darryl
03-15-2011, 02:14 AM
Seems very simple in retrospect. Start with a round rod, stainless probably. Cut some pieces of flat bar and drill two holes- one for the strap or rope, the other a slightly loose fit over the rod. When there's tension on the strap, the bar piece is cocked sideways and jams on the rod. Finger pressure to straighten that piece makes it loose on the rod. The principle is the same as the bar clamp.

Turn it around and put the rod on the end of the strap. Fixed to the frame somewhere is a hole that you poke the rod into. At the top of the hole, the piece of flat bar sits above the hole, but is spring loaded so it automatically cocks sideways above the hole. Depress the bar and the rod can be inserted through the hole. Let it go and the rod is automatically locked. The tighter the pull on the rod, the tighter the bar will grip it.

dberndt
03-15-2011, 07:10 PM
Thanks everyone. I'll be trying to make a sample as per Darryl's specs shortly.

studentjim
03-21-2011, 08:13 PM
Use the setup in the link with a ratchet tie down strap between the top of the wheel bars to pull them together.

Paul Alciatore
03-21-2011, 08:54 PM
I am thinking a cable from each end clamp to the center. Bring it down to the bottom channel and put them on the back so they don't interfere with loading the bike.

Now, a rotary crank mounted below the channel with a handle on the outside and two arms on the inside, one for each cable. Some stiff springs on the cables to provide tension with a little bit of give - not so much give as to release the bike even with the spring fully extended. The outside handle has a spring loaded pin that engages the bottom channel at both sides, one for open and the other for locked. And a safety to keep that pin engaged while traveling.

Now a question from me.

I have been thinking of a similar bike rack for my GMC pickup. I am wondering if such a rack could be mounted in a trailer hitch socket with just the standard pin to hold it. I do have a heavy trailer hitch. I would want something that could be mounted or removed in a minute or two. Probably need extra supports at the two sides, perhaps cables with springs that hook on the bumper. I would probably use aluminum as I would want something very light. I would use bolted construction as I am not set up for welding at present. Any thoughts? Or is there a commercial one available that would mount like that?

Paul Alciatore
03-21-2011, 09:08 PM
I have to wonder what effect the vibration due to driving would have on the holding power of Darryl's suggeston. Maybe OK, maybe not. What's your bike cost?