ETERNAL CYCLE WORKS
  • Blog
  • Projects
    • Electrified Velomobile
    • Torus Prototype
    • Catrike CoroVelo V2.1
    • Catrike CoroVelo V2
    • Catrike CoroVelo V1
    • Trike Trek '11 Velo
  • About
    • Velomobile FAQ
  • Contact
  • TT'11 Tour Journal
  • Blog
  • Projects
    • Electrified Velomobile
    • Torus Prototype
    • Catrike CoroVelo V2.1
    • Catrike CoroVelo V2
    • Catrike CoroVelo V1
    • Trike Trek '11 Velo
  • About
    • Velomobile FAQ
  • Contact
  • TT'11 Tour Journal
Search by typing & pressing enter

YOUR CART

6/18/2021 2 Comments

Raven issues - Redesign (Project on hold)

Since I last posted, I have gotten the seatbacks mounted, chains routed and brakes hooked up, and I have taken the Raven for a few test rides on pavement and dirt roads.

The test rides have taught me four things.
  1. The weight of this build is starting to become problematic. I have not yet weighed it, but I have calculated the frame weight alone (without seats, wheels/tires, motor, battery, brakes, chains, etc.) to be nearly 50 lbs (22 kg). Getting myself to stop takes longer than I find safe, and that's without e-bike components, a passenger, a body, and cargo.
  2. The chain routing is both overcomplicated and ineffective in providing stiff & reliable power transfer to the rear wheel. Pedaling feels rubbery due to idlers getting slightly deflected under load, this effect is multiplied by the number of power-side idlers in use (currently 4). On top of this, the chain can still sometimes hop off track on rough dirt roads, so additional chain tubing is necessary.
  3. The front steering knuckles lack the required rigidity for the lateral forces placed on a 26 x 3.0" wheel, and because of this, the disc brakes rub in turns - unless they are adjusted such that their pad clearance is too great to provide a good feel at the brake lever.
  4. The turning circle is not great because the wheelbase is over 8 feet (2.44 m). 
  5. The distance to the rear wheel is problematic when there is only one rider. On steep dirt roads, I simply do not get enough traction to keep my momentum up and I stall out.
Much of this weight and complication in the steering, chain and cable routing is due to my desire for the seats to be low to the ground. The low center of gravity does make the trike feel planted, even with a narrow-ish track (38"), but the complication it has caused is too much of a compromise for a real-world, everyday application.
Picture
So, I have redesigned the main frame. The design is much, much simpler. It uses two main tubes, a straight crossmember, simple underseat (or overseat) steering design with two tie rods instead of three, utilizes aluminum seatback support tubes, single upright seat supports and now all power is routed to the rear wheel through the mid drive, which reduces the number of chains required, eliminates the need for a special tandem shift cable and should also allow chain routing to only require one power-side idler as opposed to 4. Also, the wheelbase has been reduced by over 2 FEET (609mm), which will greatly improve the turning radius.

The compromise here is that the seats are about 6" higher off the ground than the previous design. To counteract this higher center of gravity, I will likely increase the track width by as little as 5" and possibly as much as 10", for an overall width around 48". The seats are also 10° steeper, putting them at 55° rather than 45°. This puts the occupants in a position more similar to driving than before. I am also going to have the bottom bracket a bit lower to the ground so that visibility and chain line are optimized when it comes time to build the shell.


​If it's not already clear to my readers, all of these changes basically mean starting over. The seats and tie rods will be re-used, but the rest will be cut apart and the usable pieces will be saved to be used as scrap parts for the next build and future projects. This is, unfortunately, one of the realities of prototyping experimental vehicles. This is not the end, but unfortunately it is enough of a setback that the project needs to be put on hold. Partially because of financial reasons, but also because by September 1st, my Fiancé and I will have moved to Boston for her postdoc position she was offered at MIT. Should we find suitable arrangements including a garage for me to work from, this build will resume part-time with the new, simpler redesign around then. Until then, I need to begin working again, packing up my tools and parts, and preparing to move our lives a 29-hour drive away.

If you know of any bicycle shops in Cambridge looking for an experienced mechanic to wrench in and/or manage a service department, I would greatly appreciate the introduction! Until then, I will post any updates here that I think you all will find entertaining, and I'll get back to work on this project as soon as I can.

- Chase
2 Comments
John Westlund
7/29/2021 11:55:01 am

Hopefully you can find a place to continue progress. I like your work. You did choose to forego suspension though. In many parts of the U.S., the roads are so terrible that it is not optional and your trike will tear itself apart without it and you could easily lose control of the vehicle. I speak from experience on this, unfortunately. Having 350-400 lbs of load on an unsuspended frame greatly increases the amount of mass of frame/components needed to handle the load, possibly moreso than the weight a simple suspension would add. Ever been sent airborne from hitting a pothole at 20+ mph? I have, had no control of the trike for the duration, and could have easily lost control and flipped once re-establishing traction with the ground if I changed my steering trajectory before hitting the ground. Adding a front suspension fixed that and made the trike a lot more controllable.

In any event, a tandem trike is a market niche that is very useful, and commonly ignored. I suspect the completed velomobile with no electric assist will weigh around 100 lbs. Anything over that makes it very difficult to pedal up steep grades without e-assist. You really want the e-assist use to be optional if at all possible, so as to eliminate range anxiety.

Reply
Chase
10/26/2021 08:44:22 am

Thanks for the comment John!

I could not find any suitable "simple suspension" designs for tadpole trikes. Ideally it would be a double A-arm suspension like F1 in the front, and a swingarm design in the rear. It's something I'm sure I'll venture into in the future, and I agree that it is important, but having ridden 1200 miles across the U.S. on a rear-suspension-only tadpole trike with 1.5" tires, I would say that it's not critical to the operation of a low-speed vehicle. The early ELF and PEBL velomobiles, for example, had no suspension, and some still do not. For this particular vehicle though, I decided the added complication (rather than the added weight) wasn't worth the time investment.

Anyways, I have a space to build from again, but my environment here just outside Boston is not conducive to a streamlined two-seater that can use bike lanes... The roads are much too hostile towards cyclists. I'm working on a bicycle car instead!

Reply



Leave a Reply.

    Archives

    March 2023
    June 2021
    May 2021
    April 2021
    April 2020

    Categories

    All

Powered by Create your own unique website with customizable templates.