Paola

I'm new to the forum and learning a huge amount about clipless pedals due to an engineering project we've been working on all year. We've designed and built a man-powered vehicle that employs a stepping motion for propulsion. Currently, we have installed SPD (PD-M520) pedals. These were at hand (stripped off of the pilot's bicycle). However, in this new application, when the pilot pulls his foot up, it frequently unclips. We took some footage of his stroke and don't think he's exceeding the 5 degrees of float on these pedals. Is there another reason his foot is unclipping? If so, is there another style pedal that will allow a powerful upward pull without unclipping?

BTW, our vehicle is a submarine. The pilot compartment is fully flooded, so he's operating in water. If you'd like to see our project, you can visit this website: [URL="https://calamaro.weebly.com/"]

Thanks for your help! Our sub reports in for competition next week, so time is short. One bicycle mechanic we consulted suggested switching to Speedplay pedals which offer up to 28 degrees of float. I don't fully understand the mechanics of clipless pedals, so don't know how they behave under significant upward pull.

davidad

You either have the wrong cleat or do not have the adjustment tight enough. https://techdocs.shimano.com/media/te...9830672281.pdf

jowilson

+1 one on the wrong cleat. Either that or the cleat is so worn down that it can't hold in anymore. If you got a new one, that would confirm this theory, but the pedal may also be worn as well. Check the tension on the pedal too, as it can be too loose and slip off easily, but I have never slipped off even at the lowest tension.

dabac

Keep in mind that human anatomy didn't evolve with powerful upwards pulls in mind. While riders certainly may pull upwards a fair bit when starting from stationary, or other time-limited situations, the majority of riding is done with about as much upward pull needed as to make the upward-bound leg look "weightless" from the perspective of the downward bound leg.

If your contraption hinges on significant, extended-duration power coming from the upward pull your pilot may well be putting his knees at serious risk.

If you insist, try SPD-SL AKA road pedals and cleats instead, which are supposed to offer better retention.

FBinNY 

+1 on both the limited benefits of any design counting on upward pull generating power except for short burst intervals analogous to hill climbing or sprinting.

In any case most road pedal/cleat interfaces offer better retention against upward pull, with Look's system possibly being the best. You want a rear engagement with a shallow ramp angle at the cleat/clip interface so vertical force doesn't wedge the latch backward and allow disengagement.

If you want absolutely positive zero disengage on vertical lift, file both the cleat and latch to 0° engagement angle, or to a slightly negative angle so vertical load tightens the latch rather than pushing it back or out.

CACycling

Clips and straps may be a better option for this application.

HillRider

I also expect you have the wrong cleats as Shimano makes two versions of their SPD cleats. The SH-51 "Single Release" model will only release by rotating your heel outward or inward. The SH-56 "Multiple Release" model will release by "twisting in any direction" according to the Shimano tech document. I expect you have the SH-56. I have the SH-51 cleats on my shoes and they NEVER release on a direct upward pull.

zebede

I have used the SH-56 for years....they do indeed release far easier than the more common standard SH-51. 56 is for more casual riding, commuting etc.. 51 is for roadies.

Pars 

Time ATACs are pretty hard to pull out of unintentionally, and since they are also a MTB-style pedal with a 2-bolt cleat, would allow retention of the shoes your pilot is using...

sreten

Hi,

FWIW stepping type drivetrains have long been touted as the future
for recumbants and other HPV's and have never taken off. Why ?
They are simply worse than pedals at doing the job.

Pedals hit around the optimum 6:1 rest to work ratio for muscle power output. So
far, no better arrangement has been found, and loads of a lot worse suggested.

rgds, sreten.


The muscles that flip your leg forward when running are relatively
tiny, and at best, as someone else has stated, unweight the none
drive leg rather than provide any additional real power on the upstroke.

caloso

It's not the range of float so much as it's exceeding the break force at the end of the range. Try new cleats first, then try increasing the tension on the pedal release (it should take a small (3mm?) hex wrench. If the pilot is still pulling out, try road pedals like Shimano SPD-SL or Look Keo.

jim p

If you don't have time to check out your system, then get out the ole duct tape and tape the shoes to the pedals. Make sure that the operator can get his feet into and out of the shoes.

gsa103

SL-56 are silver and have an "M" stamped on the bottom. SL-51 are generally black.

The tab at the front of an SL-51 is flat on top (the side towards the shoe). The tab on an SL-56 is ramped, and much easier to pull out of on an up-stroke.

TheReal Houdini

Not sure I'd want to be more firmly attached to a heavier than water object under water. Duct tape? Oh hells no.

jim p

Duct tape should be no problem for TheReal Houdini. I was also thinking that if the pilot ran out of air and forgot to unclip it might be his last tombay.

RubeRad

+1. If you had a pair of "Multiple Release" and "Single Release" cleats in your hand, you'd be able to see how the MR have the edge that holds onto the pedal chamfered (cut at an angle? is that the right word?) so you can release by pulling the heel sharply upwards. The SR cleats are square there so lifting the heel remains secure, and only sideways motion will release.

ThermionicScott 

+1. No offense to the OP, but engineering students come up with some of the most interesting "bad" ideas.

davidad

In my years in the field as a fitter I have found that graduate engineers can come up with some horrible ideas.