The electric cruiser

[SimpleSimon]

My neighbor (to whom I sold a motorized bike a couple of months ago), has run into some difficulties recently. He's a mechanic, auto air-conditioning specialist, and does computer repair and custom systems fabrication as a side-line. Last week he had a hoist in the shop fail, dropping a 60 passenger school bus on his right leg. Amazingly, no bones were broken, but all of the ligaments in his knee were ripped loose.

So, he can't ride the bike I sold him for a while, but he has become addicted to getting out into the wind. He has asked me to design for him a tadpole recumbent he can build in his shop (VERY well equipped), and after discussion of the legal issues here, we have decided to go electric for the power system, but a tad different than most to keep johnny law happy. He has just gotten a temporary handicapped placard for his pickup, and the accompanying ID card, so he can qualify for use of a "mobility impaired" scooter. He goes to the same doctor I do, who is perfectly willing to write a prescription letter for the trike.

It will be powered by two 350 watt hub motors in 20 inch front wheels to begin with, and with the intention to add a rack-mounted GEBE drive at the rear later. This way, he can stealth around in electric mode, and eventually add gas power for longer distance runs out to the lake, which he does regularly to go fishing.

As drawn, the picture shows the bare bones of the frame. He wants rear suspension, so I crunched some numbers, and it appears to me that for simplicities sake the best option is the horizontal rear mono-shock approach. Keep in mind, this is intended for a vehicle with a maximum speed of 30 mph. He has tried and does not like side grip tadpole steering, so it will utilize more conventional steering geometry.

Specs are:

Wheelbase length: 48.5 inches
Wheelbase width: 26 inches
Overall length: 88 inches
Overall width: 30 inches
Steering geometry: Full Ackerman, zero point steering at 15 degrees.

The picture is just the bare bones at this point. I have wire-framed the seat position, which will be adjustable for angle of inclination. The forward pedal boom is adjustable, with an X seam range of 35 to 44 inches.

He tells me that he'll have the main boom bent, suspension pin for the rear triangle in place, and the cross boom for the front suspension done next week. After that it is a matter of waiting for his parts orders to come in, and getting it all assembled.

Comments, suggestions, critiques are solicited.

 

[PatrickW]

Hi there, S.S. Looks good coming off the drawing board, but there is something I need some help with understanding about this 'single, horizontal shock' suspension." I can see how, when the rear wheel hits something thrusting it either up or down, the shock will dampen the impact as the rear arm pivots. But, I am not familliar enough with these things to know just what it is, without some sort of return spring mechanism, that the shock will be brought back to it's neutral, center positin ie, from being expanded or contracted. Does my question make any sense?

 

[SimpleSimon]

Valid question. As drawn, the pictured shock is mostly a placeholder in the diagram. Drawing a spring in SketchUp is possible, but it is an exercise in extreme tedium. What is intended is a shock which is designed to primarily function in extension, as compared to the more usual compression. Those can be had from commercial sources.

 

[PatrickW]

Do you mean a gizmo that would be somewhat like a sort of 'horizontal strut'...as ised vertical in the front suspension of most automobiles now...a (shock surrounded by the sping) only on a smaller scale?

Also, the nose of the main fraim member would nave to be bent upward, it seems, for him to get a clear shot at the front crank...or am I missing somethng there, too...<shrug>

 

[Turtle Tedd]

Can those 20 inch hub motor wheels , with dics , be ordered complete or do they basicaly have to be built from scratch to the hub motor after you get it??

 

[SimpleSimon]

Can those 20 inch hub motor wheels , with dics , be ordered complete or do they basicaly have to be built from scratch to the hub motor after you get it??

They can be ordered complete, but he has stated that he intends to do his own alloy inserts that will go into standard 2.125 rim sets. He has a design for a hexagonal cellular array he plans to mill out on his CNC mill from some titanium stock he has in hand. He says he is going to set marine bronze rivets in the spoke flange holes to lock it to the rim - I've asked him to get me pictures once he has one completed. I think the combination of the aluminum hub motor housing, the aluminum rim, and the titanium flanges held in place with bronze rivets ought to be quite striking.

He is waitiong on arrival of the hub motors to check carefully the dimensions, as he tends not to trust published schematics much. Wise precaution, I think.

I've given further thought to the basic design issues, and while the horizontal mono-shock is workable, I got to thinking about road grine and possible shock wear issues, and have done a different mount for a leveraged vertical shock similar to that seen in many mountain bike rear end mounts.

He is out of it this evening - came home from physical therapy and took some pain mes, so I'll get together with him tomorrow about the possible design changes.

PatrickW raised a good point - on recumbents maximum thrust is at full leg extension, and as drawn that is not possible, so I am modifying the pedal boom as well in the design, and plan to lower seat bottom recline angle from 5 degrees to 2 degrees. With the web sling type seat envisaged, that works fine. He ist talking about an armchair style seat, however, so that may change as well.

This is, right now, in design stages, so it is subject to change.

 

[PatrickW]

Suspension for The Meteor...

Hi, again, SS...While you have been working on the suspension for this tadpole project, it has given me thought to the 'non-suspension' on my Meteor. I'd like an opinion and comments on what you might think of my latest Wile E. Coyote idea. If you check the Trailmate.com site, and go to the specs on the Meteor, there is an "Owner's Manual" w/blown-up parts list. There is an inset of the monster seat. It is thick, rather hard, molded foam attached to a metal plate. The plate is attached in the front via a hinged pivot point, and the back is bolted directly to the 'slide' on top of the frame.

What might happen if I mounted a solid aluminum bar to the bottom of the seat plate (about 2.50" wide X 0.25" thick and just a little longer than the metal seat plate is wide) to the bottom of the plate, and a corresponding one to the bottom of the lower frame rail. Then connected the two bars with a pair of those "shocks with springs"?

Think that is at all practical, possible, or am I chasing my tail?

I don't do any fancy CAD work, or even use Sketch-up...when I need to visualize something, I break out a piece of paper, scale, straight edge, compasses, and pencil. I did this, and in about 10 minutes came up with the attached drawing...It will take some imagination, but I think you should see my weird idea. Let me know what you think. If it's too embarrassing, do it by PM. <roflmao> Thanks.

Patrick

 

[SimpleSimon]

That looks very doable to me, but I'd suggest two modifications. Use a piece of fairly heavy "T rail", which is just an aluminum extrusion in the sahape of a capital T in cross-section. Something like this stuff T - Rail.

Put the vertical of the T downward, and instead of the type of shock I was suggesting use a beehive" type seat spring pair - one at each end, or a pair of pretty stiff compression springs - valve springs out of a diesel engine head might work.

 

[PatrickW]

Excellent idea...as soon as I can get out of the house (due to the restrictions of these broken ribs and other problems) I'm gonna check into it. Aluminum "everything" is quite available due to all of the screen cages and things fabricated here. I am just not too sure about the "springs", "shocks", or "sping/shocks"...Remember, I am at the end of the earth, here...<g> You are going to go into more detail about that 'Beehive' Springs, I have already considered valve-return springs, but have not been able to get over to the local auto/truck parts store...I have a good one near me.

 

[SimpleSimon]

Round 3

I didn't post round two of the design process because my neighbor didn't like part of the design.

This is round 3 - the trike specs remain essentially the same, but as you can see, the shock mount has been repositioned to a more conventional arrangement. I still need to sketch in the drivetrain elements, but I'm in no real hurry to do so. He went out on the powerboat with his daughter and son in law, and fell getting out of it - he's in yet more pain and pretty much a zombie on pain pills right now.

So he isn't getting any shop time at all right now.