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# Mechanical Engineer Matt I need to get a motor and maybe a…

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Mechanical Engineer MattI need to...
Mechanical Engineer MattI need to get a motor and maybe a gear reducer. I'm burnt out tried the formulas and my answer is igly.The weight is 14 pounds.
The length is 11 inches. .
It will take 1 seconds to reach maximum acceleration.
The desired speed will be 12 degrees in 1 second.I used
Torque = w x Inertia / acceleration timeInertia = 1/12 Mass Lengthsquared
Inertia = 1/12 14pounds x 121inchessq
Inertia = 1/12 x 1694
Inertia = 141.16 poundinchesRotational acceleration desired is 12 degrees/ 1 secsquared maximum velocity.converting degrees to to radians pi radions / 180degrees.
To move 12 degrees x 3.14 /180 = 37.6/180 = 0.209 secsquared radiansTorque = w I
Torque = ( .2099) (141.16) / 1 secondsquared
Torque = 29.629 newton meters.I'm ready to shoot myself. Can you do the correct formula or math for the torque please? I'm guessing I will need a gear reducer also?
Can you recommend a motor that will work? I'm thinking DC as it must be slow and steady. I've looked at automationdirect.c and I'm guessing the motor/gear reducer might weigh about 5 pounds ?
Submitted: 8 months ago.Category: Car
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Customer reply replied 8 months ago
Thank you. I've looked at automationdirect and found a dc motor with gear MTGP-P06-1J008 but it seems too big...am I on the right track?
My motor will be used sporadically for about 30 minutes 5 times a day, every day. On off switch only needed right now. Will I be able to reverse the rotational accel?Could you say how long you need for a response?
Customer reply replied 8 months ago
I believe I'll need a dc gear motor that can reverse direction and that is low noise. Any suggestions?
Customer reply replied 8 months ago
Thinking of info you may want to know beofre considerations,, the motor does not work against gravity.
8/1/2017
Auto Mechanic: Matt, Engineer replied 8 months ago
Matt, Engineer
Category: Car
Satisfied Customers: 22,933
Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
Verified

Hello

can you elaborate a little on the mechanism you want to automate ?

as you have a rotating motor that your're trying to slow down to lift an arm?

Customer reply replied 8 months ago
Thanks Mat. Imagine a Chinese fan inlaid in a table. I want my jagged metal teeth art tools to drag across and into the fans and back again much like windshield wipers. I looked at motion control sure steppers on autodirect but need to know the max torque I think tp choose which size motor or a. Different system that accomplishes the same. It's a huge art underta king.
Customer reply replied 8 months ago
My WiFi is sporadic here so speech is unreliable.thx .what else is needed to go to my next step . These numbers are the max load. I'm not lifting..no gravity.
.
Auto Mechanic: Matt, Engineer replied 8 months ago

Ok

I've got a better idea of what you're trying to do

I've attached an image of a typical wiper mechanisim

is this what you are planning?

if you use the paperclip icon you can post up an image of your mechanisim

this would really help

Customer reply replied 8 months ago
The wiper is an analogy only as far as the arc that the wiper blade cuts out. on the window. the 11" inches length of my teeth blade is just what i need to pivot, one way and then back over the other, like wiper blades on a window. . I dont know what the radius of the motor crank is. I'm guessing the motor itself has maybe 2 inches radius or 3.5- 4.5 inch diameter. maybe weighs up to 10 lbs. , maybe 1/2 2 hp . I am a potter, and know not motors, nor posting photos. I'm getting there, but not there yet. Thanks for your clarifications.
Customer reply replied 8 months ago
Looking at your image, 2 inch crank would probably work but I'm guessing a stronger motor than what the wipers require.
Auto Mechanic: Matt, Engineer replied 8 months ago

Hello

OK there's 2 things to work out here

1 your mechanisms leverage ratio which then gives the required torque on the motor shaft

and 2

controlling the amount of electric power

when you're selecting a motor you'll need an working rpm and a shaft torque rating

if you give a DC motor voltage it will just run as fast as it can until the resistance matches the effort so to control the speed you'll need a 'speed controller' circuit that will throttle the current to allow you to control the speed

or you could use a DC power supply thats adjustable for voltage

Auto Mechanic: Matt, Engineer replied 8 months ago

So you need 12 degrees/ second for the mechanisim

therefore 12/360 = 0.0333 revs / second = 2 rpm

if your mech has a leverage ratio of 10:1 then then motor will need to run at 20 rpm

which won't work as 90% of electric motors run at least 200 rpm

so you'll need a geared motor with a reduction stage of 10:1 say

this will boost your torque at the cost of speed so your 200 rpm = 20 rpm output on the motor shaft

to work out your required torque its then a case of knowing the mass you have to move and how much leverage you have

so if its 14 lbs with a leverage of 10:1 then the motor needs to move 1.4lbs

Auto Mechanic: Matt, Engineer replied 8 months ago

I'd really need to see a rough diagram of your mechanism to work it all out exactly

Customer reply replied 8 months ago
Ok. Yes, I understand the math there. So needs to move 1.4 lbs means, (only 14 pounds all the time? ) at the rpm at 200 and gear box at 10:1 a so the torque is the 1.4 pounds and not Nm??I've guessed a dc motor but is it better/wiser, to have an ac motor? my mechanism has no other numbers that i know., except that the weight of the metal teeth blade may change.
If i went to the store and asked for a 200 rpm motor and 10;1 ratio gearbox, would they know what i need? Will they ask for the torque in Nm?
Auto Mechanic: Matt, Engineer replied 8 months ago

Motors are usually rated in torque as Nm or ft/lb so your store will need that last piece as well as 200 rpm and the gearbox ratio, bear in mind unless you buy a speed controller you won't be able to control the motor speed accurately / safely

so you'll need a motor that can move your mass

for example if your mass is 14lbs = 6.35kg = 62Newtons

your mech has a leverage ratio of 10:1 so every degree of movement at the mech end needs 10 degrees of movement from the motor so this will amplifier the motor torque 10X

so to just move your mass you'd need a motor torque of 6.2Nm

ideally I'd multiply this by at least 2 so you have a safety factor to overcome friction , inertia etc

so you need a motor with a 12.4Nm

and if the motor has a reduction box on it ( I think its the best solution) of 10:1 then the motor torque is only 1.2Nm

Auto Mechanic: Matt, Engineer replied 8 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

Matt, Engineer
Category: Car
Satisfied Customers: 22,933
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Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.

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