Monday, December 19, 2016

Greetings, Updates and Plans from Dan the Blogger

As some long time readers or diggers into old posts may know, I have, for quite a while now, been dealing with some issues that have been competing for the attention previously devoted to this blog. In particular, I wrote several years ago that I was caring for four elderly family members. That number is down to two, and I have finally simplified their living arrangements (sold two houses) to where they can still manage to live semi-independently. This has given me a large part of this last summer and fall to catch up on pursuing my long-term goal of developing my humble homestead on some land I own in New Hampshire. This is a monumental and urgent task for a man of my age, (62) especially since some amount of sweat equity therein has always been an important (and long postponed) component of my retirement planning.  At 85 and 87, my remaining relatives will surely and increasingly pull me away from these goals again in the near future, and so I must work around the clock while I can. My current lodging is completely off-the-grid, in a remote streamside cabin (not pictured) which I have managed to make quite comfortable except for the winter months, when provisions would have to be brought in by snowmobile. I love this Thoreau-style life, but there is no internet and even phone signals are very spotty. My projects there are varied and challenging, both mentally and physically, and I have found it difficult to switch my focus away from matters at hand even when I get to more connected places, such as the town library. (the nearest McDonalds is 25 miles away!) I do fly back to Houston frequently to help out and try to get caught up when in the city, although I am busy here as well. So I guess what I am saying is please bear with me, and don’t hesitate to comment, even if I take a very long time to reply! BTW, this problem is years old. Way back in post 106  you can see the experimental bent-roof structure pictured above when it was just a skeleton of 1x3 boards, and note that even back then I was making excuses for being out so of touch!

Recent long, cold nights, however, have afforded some time to sit by my wood stove and do some design work on the “Mama Bear” bogie design. What I am working on, specifically, is a design that is fully buildable for prototype and testing purposes. To this end I am refining the design from a standpoint of what is most practical in terms of milling, welding and assembly procedures. 

Pictured above is an exploded view of a SMART (Suspended Multi-axis Automated Rail Transport) PRT bogie of the mid-size variety. (Mama Bear) If you are completely new to the site and the concept, this is the motorized part of a hanging Personal Rapid Transit vehicle that rides within the track, so that the carriage may hang from it. This design features an unmatched combination of tighter turning, steeper climbing, faster speeds, and other many other attributes that long-time readers will recognize from earlier iterations. If it seems like there are an awful lot of parts, I would point out that many are identical, may be machined with the same set-up, can be ordered pre-cut to a shape from a steel or aluminum supplier, and so forth. A mass produced equivalent would be quite different, ideally with self-turning wheels (axial flux, hub motor driven) mounted on a stamped metal frame. This design relies on a lot of supplier-cut sheet and plate shapes, with lathe-cut “stand-offs” and lots of threaded rod, nuts and bolts to hold it all together. Below are the assembly stages. Note: I did not include every single nut and bolt, nor is this CAD file scaled to the precision customary for shop drawings. Some plate thicknesses might vary, depending on choosing aluminum or steel. If plates appear thick, they are probably aluminum.

The design starts with 1.25” square and rectangular tubing, flame-cut 1/8sheet steel and some round tube and bar, all welded.

The stand-offs are pipe which is filled with foam that is drilled to help center the pieces during assembly. 
The track switching components are assembled separately. These utilize pre-milled (for exact thickness) aluminum plate material, which is an off-the-shelf item. Aluminum can “smear” into ripples instead of wearing smoothly, so for more than a few thousand switching cycles nylon or bronze bearing surfaces should be inset for those dark blue (steel) switcher arms.
This assembled unit shows how both sets of switcher arms are sandwiched between milled aluminum plates, and how this assembly must be stout enough to never become bent to where the arms might become bound. Note that each arm’s pivot point is across the unit while it is raised and lowered by a cam near its midpoint. This geometry transfers load directly to the frame without stressing or inducing rotation to the camshaft once set into the up or down position.  

Above we see how the nearly completed switcher assembly is inserted and bolted into the frame, and additional motor mounting parts (plates and stand-offs) are added.
Finally, standard trailer wheel spindles are added as are the guide wheels and axles.

There. Now you just need 4 of Golden Motor’s 5 kw BLDC motors, ($376. Each) for a total of 26 HP, some timing belts and pulleys, 4 heavy-duty trailer tires and hubs and you are practically “good to go.” 

Lastly, sprockets are attached to the belt pulleys, (so they rotate as one) and a free spinning wheel tops off each wheel axle assembly. The sprockets act as cogs for climbing a “ladder” of dowl pins or even a mounted chain. The free-spinning wheels are used to press the sprocket into engagement, so it cannot skip. When the sprockets are engaged the tires free-spin. In this mode the bogie is extremely manuverable and can even climb straight up. That is it; except, perhaps, for adding some safety sensors to keep an eye on things out in the field, wire harnesses and other small stuff.

And one last thing – ideally the bogie should have a controller package that can make the motors behave like servos – that is to be able to numerically select (via a real-time program) the speed and number of revolutions of each motor so that, for example, the outside wheels can rotate proportionally faster than the inside ones while turning, or the front and rear wheels can rotate at different speeds when switching from cruising to climbing mode.  Post 131 explains climbing and 162 discusses using digital rotational control in general. It is, however, possible to use 4 of Golden Motor’s ($585.00 - Ouch!) controllers, unmodified, in a pinch. This is an inelegant control solution because it is inaccurate and overly complex, but it would do for now… I will discuss this option in a future post.

So, do we have any volunteers to go out and build this puppy? Oh yeah… Track will be (I would guess) about $200.00 per ft. erected… What’s that, you say? Too expensive?...  Baby bear?... Well, that is still on the drawing board.

Anyway, have a great time these holidays! Best Wishes from DTB! (Dan the Blogger)