Motor Sizing for Rack and Pinion

F = ma. Determine how fast you need to accelerate the total mass of motor, gearbox if any, load, and misc hardware. Then torque = F x pitch radius of pinion. Select motor to satisfy this torque as well the desired final speed.

Thank you very much. I think I am on the stage where I can progress. I will come back to you incase I encounter a problem.

The motor that turns the restaurant section at the top of the British Telecom Tower in London is of the order of 0.75kW. That's because this large mass turns slowly and is supported on low-friction bearings.

Motor power is torque multiplied by angular velocity divided by efficiency.

When was the last time you were up there ?

It been some years for me, think I was 9 or 10 years old.

It was actually on pneumatic tyres.

Try browsing through the catalogues of companies that sell motors, gear reducers, etc. Some of them have a section set aside for engineering calculations.

How fast do you want that mass to accelerate and decelarate?

What is the desired speed?

Is the motor AC or DC?

What is the motor RPM?

What is the pitch diameter of the pinion?

Try this site

http://www.engineersedge.com/motors/gear_drive_system.htm

I think I will just go for rail and wheel. I am worried about rack and pinion calculations. I just want the motor that will turn to both clockwise and unticlockwise. Which is better between AC and DC in terms of perfomance and cost for this case?

Not sure. It's been several years (10+) since I've worked on anything similar.

AC power is generally available. That would be my first choice.

Another thing you must consider is the load friction - can you make any estimate? What kind of bearings will you be using? What are the rolling surfaces (I-beam "track" and the wheels) like?

JohnDG, I am designing exactly what your talking about (electric beam trolley). If you copy and paste the website in bracket (http://www.google.co.za/imgres?imgurl=http://www.steelerectortools.com/i//Beam_Trolley_Dimensions.jpg&imgrefurl=http://www.steelerectortools.com/catalog/item/3974986/3727370.htm&usg=__MK2TWrZFoYSXUbJj_a-GCfD3uTI=&h=438&w=599&sz=32&hl=en&start=206&zoom=1&tbnid=HfzuO15CfWXR4M:&tbnh=151&tbnw=253&ei=T8SVTZLkC4_g4AaSntWmDA&prev=/images%3Fq%3Delectric%2Bbeam%2Btrolley%26hl%3Den%26sa%3DX%26biw%3D1007%26bih%3D678%26tbs%3Disch:1&itbs=1&iact=rc&dur=78&oei=HMSVTb3CIcqAOv-V7J0H&page=17&ndsp=13&ved=1t:429,r:0,s:206&tx=150&ty=119) you will see a simple drawing. Imagine just attaching rack under the I-beam and then attatch the motor to the moving trolley with a pinion from that motor running on the rack together with the load that can be attached to the trolley.

Are the "tracks" just rough metal (as supplied) or have they been finished at all?

You need a special support for the motor since the distance between its shaft and the rack can be variable. You risk an edge effect and correlated problems if the gear comes too deep into the rack. In such situations the motor is mounted on a compliant element so that if radial load becomes too important the motor can move outwards.

hi prohubble,

i seen your drawing and its correct, however installing a geared motor directly on one of the rollers is quite more simple than the installation of rack gear

mike

Hi,

I think the best way to drive your mass will be by wheel and rail, it is much easier to design and not so complicated.

Ok thanks, after trying to make calculations I also realised that I have to change my design a bit. I am going to try wheel and rail as you suggest.

hi,

Yes because here in our plant we do not use rack and pinion due to its complex design however if you use wheel and rail as the calculation will be as easy as 1,2,3..

Mike.

So you mean I can just install the motor in such a way that the motor shaft turns with the same speed as the wheel that will be attached to it?

hi,

strictly speaking if you say motor, it cant be done due to the speed but if you use geared motor, let see for example with an output speed of 60 rpm, then you can mount it directly...

mike

So you mean I can just install a motor in such a way that the motor shaft turns with the same speed with wheels? meaning the motor shaft is going straight to the wheel and turns together with that wheel?

Refer to the attached picture for your reference

Ok thanks. Is it not critical that I balance the extra weight of the motor? For instance by using another motor on the right side so that they can balance each other.

Just use a dead weight to balance it - don't need another motor.

hi,

Sorry for the late reply, yes johnDG is correct just use a dead weight.

Mike

Please consider the drawing you have sent to me and check my calculations for the selection of the motor to drive the trolley

Power calculation

V = 0.6 m/s (constant horizontal speed of the trolley on the beam)

M = 400kg (total mass to be driven by the motor at speed v = 0.6 m/s)

a = 1.5 m/s^2 (acceleration for the trolley to reach the speed v = 0.6 m/s)

0.03 (coefficient of rolling friction for the surfaces of the wheel and I-beam that are in contact)

g = 9.81 m/s^2 (acceleration due to gravity)

F = (ma + 0.03mg) = (400*1.5 +0.03 * 400 *9.81) = 717.72 N (force required)

P = F * V = (ma + 0.3mg) * V = 717.72 * 0.6 = 430.6 watts = 0.43kW

Torque calculations

N = 75 rpm (shaft output rotational speed of the geared motor attached to the wheel)

r = 0.075 m (radius of the wheel to be driven by 75rpm geared motor)

T = p / (rotational speed in rad per second) = 430.6 / (75 * 2 * pi /60) = 7.85 Nm

From (http://www.insanehydraulics.com/letstalk/powerfactor_ficheiros/motor_current.pdf) the standard motor of power just above 0.43kW is 0.56 kW AC 3-phase motor or 0.56kW AC single-

hi,

your computations are correct however you missed two factors, the Electrical Eff. of the motor and the Mechanical Efficiency of your Gear box.... hence your final equation should be:

Power (geared Motor) = 0.43 KW/ (0.85 x .85)

Geared Motor Power Will Be= 0.59 KW but based on your attached data the next higher kw rating is 0.746 Kw so its up to you to decide..

by the way, if you service crane is not 24 hours operational then you can use the 0.56 KW motor but if it is operating continuously then I suggest that you will use the 0.746 KW(0.75 KW).

for the phase, of course you should 3 phase for forward and reverse operation...

good luck,

Mike

Thank you very much.

Kind regards

Prohubble

Hi,

May I ask for the websites or catalogues that can help me with design calculations for the whole jib crane please. My I-beam trolley has to move on this jib crane. Anything that can help me to see if I am on the right track.

Does anyone know whether to consider the coefficient of rolling friction for rack and pinion drive or not??? im also designing a same kind of trolley which is driven by rack and pinion...pls help me

hello,

try this site, maybe it will help for your calculation....

http://www.atlantadrives.com/pdf/ads_racksel.pdf