Jump to content
Science Forums

Recommended Posts

Welcome to hypography, Jon!

 

Air Gear/Air Treck fiction is way cool – but not as cool, IMHO, as the smart wheels in “Snow Crash”. In both cases, the smart suspensions are arguably more important than the propulsion.

 

I’ve seen (on TV, not hands-on) 2 basic kinds of powered rollerblades: ones that drive an existing wheel on the skates, and ones that drive an extra wheel, either directly behind, or to the side.

 

The simplest one I’ve seen is just a right-angle grinder with a wire brush, duct-taped to a skate, and wired to 60 volts of batteries carried in a shoulder bag. (see Go-llerblades: Motorized Skates - Part 1 - Instructables - DIY, How To, ride, offbeat)

 

I saw a neat one with a gear drive on a skate wheel, driven by a variable speed cordless drill – on Mythbusters, if I recall right.

 

There are commercial gas-powered rollerblades – see Tric Rides - MotoSK8 Motorized Skates.

 

I don’t think anyone has yet made a really good powered rollerblade, or even a powered razor scooter. The gas ones are heavy, noisy, and smokey. The electric ones are slow and limited range. All of them mess up the normal performance of the rollerblades.

 

What I’d like to see is an electric skate with regenerative braking allowing it to be charged gliding downhill or on the level, that could give a good, fast boost for about 1000 m up a steep hill. I’m personally interested in making a trike scooter - maybe built around an electric cooler chest, like this one or this one, but big enough to carry 2 adults for several round trips up and down a steep-ish (about 10% grade). I’ve got an event site where a volunteer gate crew has to sit at the bottom of a long paved road checking arriving cars, occasionally needing to get up and down the hill pretty quick. It’s not especially hard to hike or jog, but the coolness factor of a scooter is irresistible. :shrug:

Link to post
Share on other sites

could just strap a couple of K250-20s to your roller blades, light them off, and away you go :cool:

 

(don't attempt or even think of doing this, it will certainly kill anyone who shall attempt, or even think of attempting this)

 

Welcome to hypography, the only place you know where we try to strap a motor to anything, to make it move if it already does not :)

Link to post
Share on other sites

hey, what about using motors out of 1/10 model cars, either using electric motors (i say motors, because i think you should try for 2/blade) You can get pretty powerful motors, plus high gear ratio will ensure you will move, and i dont think its a daunting task of attaching them to the blades. then you need a couple of batteries, and you should be able to controll all of them with a single remote...

Link to post
Share on other sites

yeah i was thinking of using a 2:1 gear ratio so they could both move, also i was thinking that the front wheel should be able to spin backwards for a brake instead if using the traditional holding brake. as for the motor idea do you know where i could find one?

Link to post
Share on other sites

google is your best friend for finding anything :hihi:

 

here's an example rc car motors

 

first result A Main Hobbies - Radio Control ( R/C or RC ) Cars, Trucks, Airplanes and Helicopters, beautiful, both gas and electric motors ;)

 

As for front wheel backwards spin. I know a thing or two about braking, trust me, i use up brake pads on my bike faster then once a year, and i don't put over a 2k miles on it (well endo's, wheelies, all rely on braking). That is not the brightest idea i have heard of. First of all, if you use a gas motor, then you are all set, it does not have a clutch (as far as i know), so it will brake anyways. and you can leave the default brakes (the ones that you wear through). It may seem dumb but at the moment i think it is the only viable option for stopping without any serious injuries in the testing process.... lol, though i would buy a better compound "pads" then the stock ones on the cheesy roller blades (i used to own quite a few different kinds when i used to roller blade.... well owned over the years that is, personally i always took all brakes off, and used various other techniques for braking, anything from what you see on skis, to sliding both roller blades sideways, almost like you see in ice hockey :photos: )

Link to post
Share on other sites

yeah, i think using a denser variant of rubber might do, but also the brakes used in cars use steel instead of rubber. bikes are all mechanical energy (gears and pulleys) they're a reletevly simple machine. but once you put a motor of any sorts in a machine it requires a lot more braking power to stop. so even if the motor is small, i'd think that there should be two types of braking systems friction brakes(bikes and cars) and the frontwheel backspin.

Link to post
Share on other sites

by bikes i mean motorcycles :hihi:

 

and, no, if you really want, institute a bicycle-like brake on all the wheels at the same time.... backspin sounds dangerous, it will wear out that motor, and gears that go with that, stick with tested stuff :(

 

Cars and motorcycles use other compounds, yes, but they also use high pressure systems to power those slipperier things. You are trying to stop over a thousand pounds of mass, at rather high rates of speed, that is a lot of kinetic energy to dissipate in heat, rubber would simply melt from that much braking, that is why they use special metals, and sometimes even ceramic materials (not simple steel) that have the ability to quickly dissipate heat, and not be easily tempered by it, and minerals and other materials (used in pads) that will be heat resistant (this way your rotors heat up, and pads stay relatively cooler, but are not as hard as the metal, but provide a fair amount of grip, and just wont melt... I mean the new super cars are migrating to silicon-infiltrated carbon-carbon composite brakes (aka silicone carbide). Ceramic material it's used in brakes for high class super cars. They are fade resistant to 1200C, and they are able to dissipate SO much heat, SO quickly; that is why they are used for rotors.

Pads used to be, and still, some are, asbestos, though more and more they are being changed to aramid fibers based materials, that are very heat resistant and strong, you may know this family of fibers, one of the more well-known of which is kevlar...

 

but for someone going under 25-30, with virtually no weight, you sould be able to institute a system similar to bycicles (modern ones, that use car-like brakes)

 

Biggest problem with your design is the fact that in order to brake, the front wheel needs to track, well somewhat, you say you want it to spin backwards, which means you have to lift it off, spin it up, then moderate tracking, it's like putting brakes in in the car, only on rear wheels, and powering the pump by another motor, so you have to pull it to start and then attempt to slow down (which will be a thing on itself, from 65 mph i estimate it to take an average car, with this system anywhere from 600 feet on to just brake that is not taking in the consideration the time it will take you to pull the engine started (which will be multiple hundred feet of travel prior to braking) (mind you high way regulations say that travelling at 70 mph the car should come to a complete halt in under 140 feet). One, this is too complex, two, it is not instant and three, requires you to shift your ballance... a more readily deployble system must be a must....

 

oh here is an idea, you will have a big gear for the group of 2 rollers, why not make it into an inegrated brake disk?

Link to post
Share on other sites

nice, didn't think of that. um...so far i've been getting my ideas from Air Gear.(they have a step by step construction animation of the roller blades. so, besides that all i've thought up for using a motorized roller skate is making a mini turbine and small turbine tunnels throughout the base of the roller blade. then, when you get up to speed you hit the turbine switch with your toe or something and the turbine pulls the air through the tunnels and pushes the accelerated air out the back torwards the ground, pushing the rider faster than before. it's a bit more complicated than that but thats the gist of it.

Link to post
Share on other sites
...so far i've been getting my ideas from Air Gear.(they have a step by step construction animation of the roller blades…
Cool. Where can I find this animation? (I’ve got netflix access to the anime, so can check it out pretty fast if I know where to look)

 

Just so anybody reading is clear on this, Air Gear is fictional. Though mechanically-focused manga/anime can be pretty realistic speculation, it’s not bound by the real laws of nature, so as a technical guide, has to be approached skeptically.

 

From the looks of it, with this fictional tech, the power system is less important than the suspension. It’s not all that difficult to supply a lot of power to the wheels of a skate, but making doing it in a way where you have a hope of actually staying up takes some smart, exotic engineering. I suspect Stephenson is right in “Snow Crash”, where nothing like this actually uses smooth, circular wheels, but instead has “smartwheels” consisting of lots of rubber feet on the end of individually controlled telescoping spokes.

Link to post
Share on other sites
...so far i've been getting my ideas from Air Gear.(they have a step by step construction animation of the roller blades…
Where can I find this animation?

I watched the first 2 episodes of Air Gear. The animation I was asking about is in the first minute after the titles of the first episode, part of a TV commercial being watched by the main character, Ikki.

 

Though you can’t actually read the labels of all the parts flying together in it, along with the voice track, it make the basics of these fictional skates are pretty clear:

  • A conventional-looking 4,000 W motor, roughly the size of a roll of quarters, mounted long-wise on the middle of the skate (for non-metric folk, 4000 W = 5.33 HP).
  • … with small gear (I’d guess about 3 mm) on the end of the motor shaft
  • … that meshes with a large gear (nearly the diameter of a wheel, I’d guess about 100 mm) on the rear wheel
  • No sort of suspension, other than perhaps some energy-absorbing material between the skate trucks and the boots, or the boots and your feet. The wheels appear to be mounted rigidly.
  • Some sort of stuff that may be batteries – I couldn’t really tell.

This doesn’t agree very well with the wikipedia article, which I assume was written by folk who know the anime well, which talks about an “air cushion system”, but given the physical impossibility of a lot of the stuff that happens in it, just shows that you shouldn’t take animation art as actual engineering or physics.

 

A really powerful 1/2" cordless drill, like a Panasonic EY6450GQKW, can be had these days with around 1800-2600 W power (390 to 550 in-lb = 44 to N-m, at 400 RPM = 6.67 revolutions/sec = [math]44 \,\mbox{to}\, 62 \cdot 2\pi \cdot 6.67[/math]) . With its handle, gearbox, and other drill-ish parts stripped, while not as small as the motor in the anime, these look small enough to me to fit between a pair of big wheel (I’ve never heard of skate wheels bigger than 100 mm diameter, though the ones in Air Gear look bigger).

 

It takes about 1600 W to go up a steep (10% grade) hill at 20 m/s (45 MPH), while a good cyclist can overcome manage to overcome rolling and air resistance at this speed with 1000-2000 W. So a pair of 2000 W motors should give you more power than you’re likely to want.

 

The gears in an old, junked 700 RPM cordless drill of mine have 2 reduction gears of 11:55 and 8:48 teeth for a combined ratio of 40:1, so I’d guess most drill motors turn at a max of about 28,000 RPM or 470 rev/s. For a 110 mm wheel to go 20 m/s, it has to spin [math]\frac{20}{0.11 \pi}[/math] = about 58 rev/s or 3500 RPM, so for a motor like mine with an 11-tooth motor like mine, the gear attached to the skate wheel should be a crown gear with about 90 ([math]\frac{470}{58} \cdot 11) teeth. For a smaller wheel, just reduce the number of teeth – 80 mm wheels would need 76 teeth, etc.

 

If you can find or make such a gear, attaching it to a skate wheel shouldn’t be a major drill-and-bolt challenge. Widening or scratchbuilding a skate frame to have enough clearance shouldn’t be too hard, either.

 

Though in the anime, the skates are self-contained and controlled by foot angle, that’d be a lot of work, and a lot of battery weight on your feet. For a prototype, the easiest thing to do would be to just hand hold the drill bodies you took the motors from, and run a cord from it to the motor in the skate, and control it with the triggers. It’d be nice to hang the batteries on your belt, but you could just leave them attached to the drill bodies.

Link to post
Share on other sites
perhapse if you incorporated something like this into the bearings of your wheels.

 

Slim spindle motor and micro-drive ... - Google Patents

The problem with a spindle motor, either this new design or any of the current ones used in CD/DVD drives and harddrives, is that they have very low torque. The one in the patent application, were it scaled up to a 5 cm radius, would have about 0.01 N-m, or about .2 N at the wheels if the motor is nearly as large as the wheel, about 1/4000th that of a strong cordless drill. On a perfectly smooth surface, 8 or them would accelerate 75 kg of skates and skater at about .02 m/s/s. It would take about 5 minutes to get up to 5 m/s, about running speed – not exactly extreme sport performance :wink:

 

To get an intuitive sense of the problem, try starting a fliptop CD/DVD player (like a later model PS2) with your finger on the CD. You can barely feel anything, and the disk won’t spin ‘til you let go. Now imagine trying to get up to speed on skates driven by motors with similar torque.

 

Wheel motors” – what GAHD’s describing - have proven workable, and even a record-setting, since before 1900 – check out the cool picture of a 1901 Lohner-Porsche with 4 wheel motors peaking at about 5000 W each. Problem is, I don’t they don’t scale down well – to get the same sort of performance from those big 19th century wheel in a skate, you’d have to somehow cram an equivalent amount of magnet wire and permanent magnet into something less than 1000th the volume.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...