One hobby deserves another ... a TIG welder and necessary accoutrements are on the way to me from somewhere in China (surely!) and from New Jersey (seriously). It'll be a few weeks for all the stuff to arrive. And I'll likely have to figure out a 220VAC plug in the garage. And burn some metal practicing. Lots of practicing. But then, I'll be able to start the trailer welding. Don't take the sarcasm wrong! This is exactly what the hobby is all about for me: doing something independently because I can, not because it's the quickest (or least expensive).
In the meantime, I started up a small project that will leverage the welder, and clear a nagging infrastructure equipment issue. For the auto-launching, I really want a release mechanism for the tow vehicle. The same Prius that tows the trailer can double as the launch vehicle. The trailer's tow hitch will be pulled out and a new one inserted, which has the release mechanism already attached.
The main two requirements for the release mechanism are:
- Allow the line to be pulled in various directions and still transfer the towing force safely.
- Allow the driver to pull a release handle that opens the line.
Personally, I've made a few release mechanisms for RC applications that
all worked mostly fine. The ones that didn't work usually jammed
because the pull-pin was side-loaded. This leads me to reconsider those exact mechanisms.
After some looking around online, the Tost release mechanism is standard in nearly every sailplane. RC hobby aero-tow folks and hang-glider winch-tow folks have different typical release mechanisms, likely owing to their lower load cases. In-between is something akin to the Schweizer release, with a simple hook on a rotation pin, and a small lever-arm to release the hook end. I found the Schweizer release is sometimes used on the back of the towplane to release the sailplane or a banner. Time to copy the good idea...
I started with CAD to draw up my impression of a Schweizer release and printed a few 3D plastic parts.
An assembly with the 3D printed parts is a wonderful way to understand the mechanism and check its functionality. This always feels like a wasted day as I impatiently watch the printer print, but ideas and tweaks always come from spending the time staring at a single part as it prints.
With a total assembly, I went to the back of the car to see how it all fits. And yes there is snow on the ground right now. I'm not 100% sure how the rope will route to the driver quite yet, but I can confidently say this mechanism will release cleanly once the line is pulled. The large 3/4" bolt will also let the release mechanism rotate if Goat gets off of the runway centerline. Seems plausible so far.
With all the fit-checking done, I printed 1:1 scale drawings, pasted on 6061-T6 aluminum with 3M Super 77, and started cutting, drilling, and filing. Two hours later, it's starting to come together.
It's working great so far. Once it's all assembled from metal, I'll weld both the left line-guide tab and weld the release housing sides to the bottom plate.
Hopefully my next post will be of burning metal.
1 comment:
Hi Dan, good to see some progress happening.
A couple of observations with the car release that we use here in Oz.
1. I think the type of release you have designed works best when it is kept in line with the tow line. It needs to be able to rotate sideways as well as up to keep the force on the correct part of the release lever. Our releases are shackled to the car hitch to allow this freedom of movement.
2. Our releases also incorporate a tension gauge that measures the tow line tension at the car end. Monitoring the gauge allows the driver to keep a constant force in the line and more importantly limit the force. Earlier versions were based on hydraulic rams with a hydraulic hose routed to the cabin with a suitable gauge. Later versions use an electronic strain gauge and display. Line tension readings are typically between 50-100kg.
cheers Alan (Yando Goat)
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