Jan 16
I have added in some of the final key details now so that you can go ahead and start the build. I have included the chain lines including the mounting points for the chain guides. I have also modified the rack so that it can be adjusted to fit on any bike with 700c road wheels.
Here are some images of the CAD files as the design stands now:
This shows the chain path. There will need to be 3 pulleys that will be mounted to the frame to guide the chain under the seat, and back to the rear wheel. This is necessary to avoid the chain rubbing against any of the frame members. The low tension side of the chain, will be guided through a plastic tube, as in many recumbent bikes.
I changed the design of the rack to be more adjustable, so that we can accommodate different road frames.
I think that we are now being pretty close to being able to begin to hand this off and start to actually build it. Lets plan to talk some time in the next couple of days, to discuss any final changes, and to get ready to start building this bike!
Tagged with: adjustability • chain spacing • chainline • cranks • design details • spacing • sprockets
Jan 07
Here goes. I have spent more time today ironing out details of the running cart. I will post a series of images taken from the CAD and describe each:
This is a side view….. you can see that the handles for for the runners are connected to the frame via an S and S coupling. The handlebars have bar ends on them where a brake lever could be mounted (to avoid the runaway situation).
The front end of the frame is also connected via an S and S coupling. This way You detach the two halfs of the TriBike, and join on the front end of the running cart.
This is the isometric view. The casters are 16 inch bicycle wheels. This is a standard size used on kids bikes and recumbents. Tires should be relatively easy to find. The forks that make up the casters are custom, but they attach to the frame using a standard 1-1/8 threadless headset. The casters are also fairly widely spaced to try and lend as much stability as possible.
This is a rear view of the same.
Close up showing the S and S coupling in the frame.
Front view
Now that all the fundamental geometry is worked out, I changed gears to start addressing some of the other issues that we had discussed.
Jay commented that Caroline had handles on her stationary bike and that they were quite useful for her stability. So handles mounted to the seat rails seemed to make quite a bit of sense.
Also we had talked before about having a safety net in case Carolines feet were to fall from the pedals. This has taken the form of a fabric net attached to a tubular subframe, that is welded to the bottom of the member to which her cranks will be attached.
Side view with handles and foot restraints
Another isometric.
There are still some things that need work:
- Shoulder harness/ chest strap for the seatback.
- We should discuss this, because there are several things that come into play including cost. We could do a totally custom seatback with lots of support and shoulder straps, but we run the risk of this getting rather expensive if we need to cut a special mould and need to make custom cushions for the seat. I will defer to you guys for this, lets talk it over tomorrow.
- Chain lines…… we will need chain guides to take the chain under the seat, to the rear drive wheels.
- Cable routing…… we need to figure out which way the cable is going to go, so that we can plan to have Reid having control of Carolines shifters, and brake in cycling mode, and then transfering the control of the brake to the handlebars in running mode. This is where the cable splitter will come in.
- Checking the geometry of Jay’s bike with respect to the hitch rack. I think that I will need to go back into that section of the design and make the rack a little more adjustable. It will definitely need to fit Jay’s specialized, but it should also be capable of fitting other frames of the same size.
If there is anything that I am forgetting then please let me know! We didn’t manage to connect today, but lets try to talk tomorrow.
Jan 06
Just a quick update to show you the progress on the running cart:
I have got the couplers in. There are still a few geometry issues that need to be figured out. Will post more detail tomorrow as I work on it.
Tagged with: casters • Geometry • running cart
Jan 03
Happy New Year!
I think that I have nailed down a good ball hitch for the TriBike. It is an off the shelf tie rod end. It will allow up to 60 degrees of angular motion to account for undulations in the road (dips, uneven paving etc). It will allow the bike to articulate in the middle.
The part is a McMaster Carr component Part number 6960T11
Cost of the part: $20.36
See www.mcmaster.com
It has 1/2 inch shanks and is rated to accept a load of upto 16240 lbs static radial. Our load is thrust, but despite this we should be WAY under the rated load for the ball.
Next I am going to work on the rack for the back of the lead bike.
Tagged with: ball hitch • hitch • tie-rod end
Dec 07
Following the same procedure for Reid’s measurements. The only difference here is that I added 0.75inches to the lower leg measurement to allow for shoes. Resulting position is 0.75 less Throw for Reid than Caroline.
Tagged with: BB • BB Position • BB rise • Bottom Bracket • bottom bracket position • Reid
Dec 07
I have a few questions about bottom bracket rise/drop. I have set the rise to 7.5 inches, but I need your input to figure out whether Caroline will be comfortable with that much rise. (see below for the definition of BB rise)
With the current seating position (as in the sketches from the last review on Friday). We need to have rise, otherwise Carolines heels will get too close to the ground. If you think that this is too much rise then we can raise the seating position and lower the cranks. That way her heels will not protrude downwards so steeply.
For most riders 7.5 of rise should be an ergonomic and aerodynamic seating position, and if Caroline will be comfortable in this configuration, then it will give you the highest performance.
You guys are going to be the best judge of this. Let me know your thoughts, so that I can make changes. Bear in mind that the throw will be adjustable but the rise may not be.
For our purposes BB rise is defined as the perpendicular distance of the bottom bracket above the seat line.
Here is a geometry drawing for your reference:
In this study, I have set the comfortable cranking position to be at the point where the leg is bent 10 degrees at the most extended position while pedaling. The throw will be adjustable, so at this stage I am just trying to pin down the neutral location of the pedals.
The other measurement that I am going to need is the distance from the seat corner to hip joint. I have assumed it to be 5 inches (as you can see in the geometry study above. If you could get this measurement also that would be great.
Tagged with: BB • BB Position • Bottom Bracket • Caroline
Assuming that we can extend the hub axle by 3/4 inches on both sides, I think that this rack should work to join the 2 bikes together, without interfering with foot clearance for the rider of the lead bike.
This study tracks the path of Carolines foot to make sure that it has clearance throughout its range of motion. In particular I wanted to make sure that there was plenty of clearance with the ground. I was concerned that there might not be enough space to include a safety strap under her pedals.
Next steps are to work on the hitch mechanism with the lead bike. As well as the coupling system to turn Caroline’s half into the running cart.
