I read through the BiomechanicalStudy.pdf paper on your site and thought your comments about elliptical pedalling motion matched the conclusion I had come to when I was trying to figure out why that motion works. Basically they ellongate the ellipse so most of the leg movement is horizontal with relatively little vertical.
But now that several companies are making elliptical pedal scooters some of them seem to perform pretty well. In particular the elliptigo has very credible claims regarding its speed, distance, and hill climbing ability. So that's making me re-think the merits of that design.
The elliptigo also has an internal hub with 8 gears so that may be a big part of its performance. In the videos I've seen of the dreamslide it seems to have quite respectable looking quickness too, but have you had a chance to directly compare elliptical pedaling vs the APS?
Wow, that is an amazingly detailed and thoughtful response! It's so nice to get feedback like that straight from the developers.
I had no idea what the dimensions of the movements on the two vehicles (dreamslide and elliptigo) were, and the greater vertical movement while the feet trace a shorter total path length sounds like a real win for the dreamslide. I guess time will tell whether you guys get the award for most efficient drivetrain for a scooter, but you're certainly a contender.
And I do especially like how small and portable the dreamslide is. As an urban utility vehicle or "last few miles" range-extender for use with public transportation size matters and the dreamslide is more conveniently sized than just about any other scooter out there (don't let that stop you from making the microslide though, that would be pretty awesome too).
Back to the drivetrain conversation, the angle of the ellipse makes me think that one of the reasons people talk about the elliptigo climbing well is that the ellipse gets rotated to have higher and higher vertical travel as you angle the elliptigo up a hill. I think ergonomically there's going to be some limit where their bike gets very uncomfortable doing that, but at least they would get to generate some extra power on the hills as long as the rider can deal with the ergonomics.
I know I've seen a video of someone riding up Fargo street in LA (32% grade, or 17.7 degrees) on an elliptigo. I think that angle would increase the vertical travel on their ellipse all the way to 43 cm at that grade (although they still have a longer total foot movement to contend with).
So what happens to the APS when it's rotated? Clearly the path is still circular, but it seems the gear ratios around the pedal stroke could get skewed off their optimal values.
Not that extreme hill climbing is the most important measure of a scooter of course. Sometimes it's easy to hyper-focus on things that don't really matter that much, but I'm still curious how well the APS handles moderate rotation. Maybe this could be tested on one of those static machines you made? I don't really know to what extent scooter riders keep their bodies exactly vertical with the world while riding up steep hills vs leaning back so their bodies maintain the same relative-alignment with their scooter though. Any thoughts?