Gearbox issues

[PortugazD.Ace]

I have discovered a motor that could lift an average 7-year-old off of the ground. It has been proven that a window motor can move at least 60lbs. use four of them, and you get up to 240lbs that are able to be moved. and they are quite small two. They will even fit inside my space requirements.

[EricH]

Window motors, at least of the type used in FRC, are not renowned for their speed. Just ask Billfred.

Admittedly, FRC window motors include wormdrive gearboxes, which are really not fast.

I was thinking that based on your size constraints and power needs, you might want to look into something along the lines of the FP or the RS-550 that we get in the KOP. Drill motors are about the same size (don't believe the size of the drill). If two drill motors can move 130 lbs at a decent speed by themselves, after being run through a standard planetary drill transmission, and not smoke themselves very often, I'd say they can probably assist a rollerblading human pretty well. (Pre-2005, one of the most common drivetrains in FRC was a pair of drill motors.)

[JamesCH95]

Originally Posted by Chris is me

I would say 20mph is much higher than an "average" roller blade rider. 15 mph is a lot more accurate.

I based that number off of 3 years of experience riding on roller blades in NYC. I would routinely go 1 mile in 4-6 minutes (my commute to college) averaged between going as fast as I could, going slowly to navigate around pedestrians, and waiting at crosswalks.

Originally Posted by PortugazD.Ace

The assist motors are meant to take your kick, multiply the would-be resulting speed by 1.5-2, then use that result as the output speed of the wheel. So, in short, your speed gets increased by 50%-100%. Get where I am going so far?

I think we do.

Originally Posted by PortugazD.Ace

I have discovered a motor that could lift an average 7-year-old off of the ground. It has been proven that a window motor can move at least 60lbs. use four of them, and you get up to 240lbs that are able to be moved. and they are quite small two. They will even fit inside my space requirements.

Force or torque should not be confused with power. Sure the window motor can move that much mass, but very VERY slowly. Being powerful means that the motor can move the weight QUICKLY, not just simply move it. I also don't think that they are designed for continuous duty, I wouldn't choose to use them.

15-20mph is about 22ft/s-29ft/s, or roughly 2-3 times as fast as the fastest FIRST robots, and they are typically using 2-4 CIM motors which are good for ~340watts of power (as mentioned before). Two CIM motors, gear properly, would probably get the job done for what you want to do, so I would aim for 600-700watts of motor power. Combined with the power a person can output, you'll be at about 1000watts total.

I will point out that having 1lb on your feet is worth carrying 6-7lbs on your back (a rule of thumb for hikers and runners) so if you have 8lbs of motor and gears on your feet it'll feel like carrying about 50lbs on your back. Maybe the flexi-shaft drive isn't such a bad idea...

[PortugazD.Ace]

A little reply to that last pargraph, I walk around with two 2.5lb ankle weights straped to my legs. but I get where you are going with the power needed to do what I want it to do.