3D Printed Pedal Project: Prototype

Left: Prototype pedal made with copolymer plastic with metal studs.
Right: Proof of concept pedal made with PLA plastic.

The proof of concept platform pedals I made a few weeks ago have been holding up great. (https://trail70engineer.blogspot.de/2017/09/3d-printed-pedal-project-proof-of.html)They do have a few issues. The grip isn't great. My foot slips off even during normal riding. The second issue is the PLA plastic I used. PLA plastic is very brittle. This means the pedal could crack and fail during normal use. This actually happened with one of my proof of concept pedals. PLA also has inherent low temperature resistance. This means the pedal could nearly melt if left in a hot car. I made a prototype to address these issues.

Extra Grip With Stainless Steel Bolts:

To help with grip I added some metal studs. This is a typical feature on most quality mountain bike pedals. I went with standard M3x22mm stainless steel allen head cap bolts and stainless steel hex nut. Both are completely standard and can be purchased from any hardware store. 

The bolt heads and nuts are a nice tight fit and sit right under the surface. No special tools, glue or metal inserts were used to achieve this fit. As for grip, the bolt ends protrude about 2-3mm above the pedal surface. With 8 bolts total, 4 protrusions per side, it provides enough grip for most riding styles.

For this design I had to use 8 22mm long bolts. In future designs I would like to use 12 or more shorter bolts to get more grip for the same amount of weight. Other than this, I was very happy with how it turned out.

Closeup of metal studs.

2mm to 3mm stud height 

Switching to ColorFabb XT Filiment:

Like I mentioned above, the proof of concept pedals were made with PLA plastic and PLA has some mechanical issues. Its brittle and warps/melts at relatively low temperatures. It's a great plastic for lots of mechanical parts but I really don't thing it would work great for pedals for a few reasons. Bikes are stored in cars and garages where temperatures can get hot enough to completely soften PLA. Pedals also need to to be extremely tough to withstand strikes with rocks, curbs and any other immovable object.

I did some research and eventually chose ColorFabb XT for the ideal material. Its extremely tough, has a high melting temperature, comes in a variety of colors and is quite affordable. There is even a version of ColorFabb XT with chopped up carbon fiber that should strengthen it even more. On top of all of that it is relatively easy to 3D print when compared to other high performance filaments like nylon or polycarbonate.

Print Settings and Other Info:

Layer Height: .17mm
Line Width: 0.35mm
Wall Thickness: 2.5mm
Horizontal Expansion: -.15mm
Infill: 35% Cubic
Print Temp: 240C
Plate Temp: 70C
Filament Diameter: 2.85mm
Flow: 100%
Print Speed: 70mm/s
Cura Generated Break Away support
Build Plate Adhesion: Brim 12mm
Print Time: 14hours 27minutes
Filament Used: 11.77m
Material Used: 95grams (Calculated by Cura)
Material Cost: €4.83 (Estimated by Cura)

Titanium Pedal Spindles:

I mentioned in the Proof of concept post (https://trail70engineer.blogspot.com/2017/09/3d-printed-pedal-project-proof-of.html) that I wanted to make a prototype with titanium spindles. I did a lot of research and eventually purchased a pair of titanium spindles direct from a manufacturer through Alibaba.com. This was a fairly disappointing experience. The spindles arrived after a week and while they looked good a first glance they were completely unusable. The manufacturer threaded the end of each spindle with a M6x.75 thread. An extremely uncommon thread size. They even went a bit further and threaded the end of one spindle with left hand threads. This makes it nearly impossible to buy a locknut to hold the bearing on the spindle.

I will continue to pursue titanium spindles but will probably have some made from scratch from a reputable manufacturer instead of purchasing pre-made ones. In the meantime its interesting to see the possible benefits of using titanium pedal spindles. The short steel spindles weigh 62 grams each. The longer titanium spindles weigh 34 grams each. This means I can make stronger pedals with a full length titanium core that will weigh about 56 grams less per pair.

Shows slight defects including the M6x.75 threads that make them unusable.

Steel Pedal Spindle Weight: 62g

Titanium Pedal Spindle Weight: 34g

Initial Comparisons:

Something I didn't do in the initial proof of concept writeup was compare it to a commercially available pedal. For this comparison I'm going to use the Race Face Chester as the benchmark because they are popular and great pedals with similar construction.

Picture and Specs courtesy of Bike-Components.de

Race Face Chester Specs:

Weight: 340g per pair
Spindle: Steel (CrMo)
Pins: 16
Height: 15-18.4mm
Area: 109x100mm = 109cm^2
Weight per area: 340g / {(109cm^2) x 2} = 1.56g/cm^2 (Lower is better)

Printed Pedal Prototype:

Weight: 162g each (324g per pair)
Spindle: Steel (CrMo)
Pins: 8
Height: 20-24mm
Area: 88x78mm = 69cm^2
Weight per area: 324g / {(69cm^2) x 2} = 3.35g/cm^2 (Lower is better)

Prototype Weight: 162g

Prototype Length: 88mm

Prototype Width: 78mm

Comparison Conclusion:

For very obvious reasons the Race Face Chester has outclassed my printed prototypes in almost every way. The Chesters are bigger and have more pins. The Chesters are heavier but only because my pedals have a small contact area. I do see potential however. The prototypes I made used very long bolts. If shorter bolts are used then I should have more pins for the same weight. The pedal I made is also a lot thicker than the Chester. (18.4mm compared to 24mm) If I make my prototype about the same thickness as the Chester than its g/cm^2 ratio should be more favorable. I don't think I will be able to beat the Chester in every categories but it would be great to make a DIY pedal that performs similarly. (Within 10%)

What's Next:

Design a thinner pedal using more studs and greater surface area for more grip.
Follow up with having titanium spindles produced.
Print a second prototype pedal and do some test rides with a  matching set.