DC Motor Torque

Why not just use the DC motor out of a standard battery powered circular saw? (I hope that wasn't the invention!). There is a formula that will take into account the the reduction in torque caused by the gearbox and blade diameter, but you still need to know how much you will require so you can size the motor accordingly. Simply put, the bigger the motor, the bigger the torque (how much torque do you actually require). What is the intended use (or target material, material cutting speed (mm/second,) etc). Does it have to be DC, as an ac motor may be a better and cheaper option (especially if speed control is not required).

You know, this sounds exactly like a standard battery powered circular saw to me. What sets your design apart from it?

And of course the obvious statement "EXERCISE EXTREME CAUTION if planning to build a prototype!".

(Oh, and I cannot remember the formula of the top of my head, but I am sure someone else can help you).

A mechanist handbook will have the data you requested. You will also need the set/cut angle of the blade tooth, and the type of material you wish to cut. Look under the "Speeds and Feeds" tables as a starter and work back through the gearing to the motor.

HP=T*N/(5250)

T in ft lb

N in RPM

allow 95% efficiency for any gears

Run motor at about 90% load to allow a little overhead.

Doesn't matter if it is AC or DC, equation still holds.

Now, how about that commercial saw motor?

I have an old 8" Beaver table saw (cast iron table and heavy saw mounts) that used a .5HP induction motor. It burnt out. I bought a cheap portable table saw (basically a mounted skill saw), took out that motor and used it on the old table saw. Far superior results!

One of the most important aspects of "INVENTING" is to understand what you're doing. As someone else pointed out, power is torque times speed. You've started out with an 18 volt battery and want to know how to calculate torque! Simple! As armature resistance approaches zero, armature current approaches infinity, and one can get as much torque out of a DC motor and an 18 volt battery as one wants. Invent a motor with conductors supercooled with liquid helium, and I think you'll get somewhere . . .

Start over! How much torque do you need?

Pulse width modulation can give you a lot of torque through out the RPM range

in this mode of supplying power to the motor, the motor always sees the maxim voltage of the power source and the variable speed is attained by changing the frequency of that voltage

I used it in the fastest electric skate board for eglide company

www.http://www.e-glide.com/

it can climp or move you even at low speed

That sounds real cool, I have read a lot of praises for 'pulse width modulation' over the past few years. My dream machine is an electric bicycle, with a powerful motor secreted in the hub gearbox, Electric model helicopters have tiny motors that develop nearly a full horsepower. This bike would have no chain or drive whatsoever, peddle power would simply charge the battery, as would braking. We have some very steep hills here in Lancashire UK, the motor would have to cope, perhaps two motors, one up front for steep climbs. The bike would have to fold away, so one could catch a bus if needs be.(no chain to bother with).....I have even wondered if gears could be excluded altogether. The only bits that needs to revolve are the tyres (closed cell foam filled, so no punctures to spoil the trip). So those could be mounted on a magnetically suspended disc affair. There are loads of scrap neodymium magnets from old hard drives to make a ring of rotor magnets. The hub need only be about a foot or 30 cms in diameter, add the tyres and the overall diameter would be about 14 inches. Pulse width modulation on the stator coils attached to the 'stationary' hub. Electronics could sort out the rest.

We could carry six light weight attachable turbine blades (perhaps doubling as comfy back rests to the seat?), so that both front and rear wheels could be mounted on a pole (tent poles) to become wind generators. Those Lancashire hills are always windy. A 500 watt electric fan cooled Seebeck Effect electric generator might also be handy,P.& N doped Peltier units from ice boxes might do? Stop for a brew over a small camp fire. be on ones way again in half an hour or so. Electric Sleeping bag when camping, run off the turbine wind generator wheels?.....The stuff of dreams. Project 2007 perhaps? Happy new year CR4 Readers.

Hello Alastair Carnegie,

Actually for a bicycle I would use a 3 phase DC brushless which I deal with in different potential applications.

reasons:

1- no brushes to deal with

2-the same motor can develop 1 or 2 or 3 or more horse power in a very small form factor (4 inches diameter by 3 inches deep container 2 rows of super magnets Neodynum),

3-it does not care too much about the source voltage resonably,

19 20 36 48 any thing in between it is all about control once you have the right design

actually this motor is basically a servo motor with the feed back loops to the controller other than telling it that it is ready to receive a power pulse at the right time. the feed back in servo is used to recover from mishaps of the machine it is driving so not to loose the whole sequence.

the magnets/rotor arrangement is such that you get a pulse in betwen coils tripling the number of power stroke within a shaft revolution

this makes it very torquy at any rpm and all in a small package for a fraction of the cost, size and weight of a servo motor

We are talking about changing from servo motors to this type for the very deep ocean submarines for research and echo tourism and Mel Fisher (the man who discovere the Galeon Etosha) purchased one for his central America Operation last year check it out at : www.SeaMagine.com

I will be posting some interesting link on my website about this kind of developments some time in the near future after I clean up busines side of it (too busy responding to inquiries about my NanoLube applications)

www.NanoLube.com

www.Nano-Bearings.com

back to the bicycle only one of those motors need exist for hill climbing as long as you implement correctly.

I have a very interesting idea generating power for an electric bicycle chain need not exist any longer and again thanks to advanced electronic controls.

Talking about bicycles I drive a Segway for the last 4 years and take it any where I go, I fly with it go to trade shows people laugh when I call it a bicycle but eh it has 2 wheel what else could it be, a picture below the day I trained the astronaut Buzz Aldrin on my Segway

http://www.sitekreator.com/SegwayPetaluma/index.html

PS. Andy Germany is right about the corroletion between diameter and torque and speed we had problems with magnets flying out with centrifugal force problem was resolved brilliantly (not by me) and yet it looks so simple after the fact like many brilliant simplistic elegant designs

in General the bigger the diameter the more torque at lower speed

another by product would also be gyroscopic effects to consider sometimes beneficial sometimes not desireable

I love this CR4 forum it is the most elegant interface I have seen in a long time.

Have all a wonderfull end of the Year and Bright New 2007

All your points noted with many thanks. I have a good neighbour who makes pin money scrapping old computers...... They pay you to take them away!....I have seen for myself the phenomenal gauss of those hard drive magnets. a matching pair in each hard drive. The bicycle tyre permanent magnet 'rotor ring' would become effectively a brushless motor. I am glad you reckon only one back wheel needs to drive the bike, I note from GobalSpec, that Panasonic have just brought out some advanced Nickel Metal Hydride Batteries. They are great for erratic charge/discharge cycles. Lithium and NiCds are rather fussy. The tree phase setup looks like the perfect solution.

By the way Neodymium magnetic flexible strip has been available for some time now. the price is constantly dropping. So I am in favour of the tyre/ring being magnetically suspended. Even high grade ferrite flexible strip might do. but there would be a weight penalty. Glad you enjoy the forum, in my view about the best on the net.

I agree with a lot that has already been written but nobody has mentioned that the design of the motor can increase torque without increasing current. It is to do with the diameter of the rotor.....generally speaking (its a bit more complicated than I mention here!)the larger the diameter, the greater the torque......you may need a specialist motor....theoretically a flat rotor with a large diameter might be what you are looking for....you also need to be able to get rid of any heat produced easily.....certain servo motors used in large printers (in byegone years!)are fantastic in this area.....they use what is called a PC Motor (as in printed circuit!).