Gearbox issues

[JamesCH95]

Originally Posted by PortugazD.Ace

1. I was thinking that I would need a more powerful motor. My problem is that I can't find one. If you have any links or recomendations for this while still being a workable size for my concept, please post.
2. There is a black box where the CAD rendering should be. I'll have to figure that out and get back to you.

What are your power requirements? Do you have a top speed or acceleration in mind? If you can give us some parameter to work with we can help determine how much power you will need, which will determine what size of motor you should get.

Drill motors are a good way to go, they can pack a ton of power in a relatively small package. Gearing most motors down is going to require a bit of space, so using a flexi-shaft as PAR_WIG1350 suggests might be a good way to go.

I would immediately surrender the notion that you will find a motor that can fit inside of a roller blade wheel and supply any meaningful amount of power.

[PortugazD.Ace]

In terms of acceleration: the system accelerates in proportion to the users kick. the motors are just assist motors to make you kick last longer. I have already figured out where I'm going to put the gearbox to gear the system down. the gearbox is going to fit inside the wheel. I can manage 2" of space for the diameter of the motor, and 3" of space for the length. But I can't manage any more space because I also need to fit control electronics, brakes, suspension, air cusion systems, etc...
Any ideas?

[JamesCH95]

An average roller blade rider can get going a little over 20mph, with the roller blades going slightly faster than that, say 25mph, which is about 37 ft/s. Get your wheel circumference and calculate how fast you need the wheel to spin. at max speed. Go to robot market place and pick out a geared motor that will fit in your space requirements, then figure out if it can apply any appreciable amount of power. Your average human can do about 350watts sustained, and up to 1700watts at a full sprint.

[Chris is me]

Originally Posted by JamesCH95

An average roller blade rider can get going a little over 20mph

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

[PortugazD.Ace]

But don't forget, there are also people who can reach street speeds on rollerblades(beleive me, I've seen them). 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?

[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.