Hi everyone,
I'm asking you for a basic calculation but a little too old for me. I want to size a geared motor to make a turntable.
The data are:
HDPE table top 500 Ø1980mm ep 30mm (mass of 90Kg)
Maximum load 100 Kg distributed over the diameter
Rotational speed 7rpm
Stress recovery by rollers under the table (4 Ø100 polyurethane wheels on bearings)
Training at the centre
So I want to calculate the torque needed to drive all these people with my geared motorcycle.
Thanks in advance
In fact, the drive torque is "zero" at steady speed.
Torque is needed in the event of a change in speed, so this data is missing.
Hello
Yes, except that! there is a couple resistant to start-up ;-)
We cannot ignore the kinetic inertia to be overcome at the start and in addition the kinetic energy is proportional to the mass and it is proportional to the square of the speed, in other words if the speed is multiplied by two, the kinetic energy is multiplied by four.
The problem must be reduced to the calculation of the start of a flywheel (because the load is outside the circle). Otherwise we have to calculate the inertia of the different elements (one for the axis + one for the disk + one for the masses located on the periphery. But to put it simply, taking the one from the outside is enough for the problem mentioned.
If the applicant is not keen on calculations, Leroy Somer motors offers a configurator that should allow you to determine a motor (it seems to me that ABB also offers one but be careful to select the geared motor
http://www.leroy-somer.com/configura...urateur_F.html
Kind regards
Just to quibble and avoid missing something: is the start really a speed variation?
No! No! you don't quibble! I didn't understand your thought ;-)
A great classic "how long do you want to reach the speed of 7rpm?
Yes! we go from 0 to N rpm of course I was thinking about the torque needed during the whole acceleration curve. This will influence the choice of the geared motor motor and its possible electronic servo.
That said, with an angular velocity of 0.7330 Radian/second it's quite reasonable ;-) .
Kind regards
PS: we don't get paid a lot but we have a lot of fun ;-) ;-)
Sorry to break your gut guys, but my problem isn't solved yet:)
I'm just looking for the formula to calculate the starting torque (in N.m) needed to make all this little world leave. I could then choose the right geared motor to make this F*** turntable.
Thank you in advance
/HS on/ Hey, I've never tried to smoke guts to get a trip, to test... /HS off/
More seriously, @Zozo_mp in his first answer gives you the simplest solution: go through the manufacturers' websites that often have calculation modules. But I think that the data of the rotation time (time needed to go from 0 to n rpm) will be asked of you.
Another link that explains the approach completely: Rollix: torque determination
Hello
I looked at the link from Rollix and thank you, I made an EXCEL table with it, I won't put it tomorrow on my computer, but the approach is clear with the use of an abacus for one of the parameters.
You are right Stefbéno, there is some information missing to complete the study:
- the time available to spin your tray. ok seen.
- the diameter of your roller ring
For the initial velocity we can assume that it is zero, starting at 0 rpm.
Good luck.
Spectrum.
It's all pretty, I think you've summarised the approach well.
A few small remarks:
- it's kN and kNm instead of KN and KNm (to nitpick). This conversion (Nm to kNm is not necessarily essential, to do with your true values but it is more likely to mislead you for the future;
- the Crc torque is specific to the crown, you have to see with the system you will actually use.
Knowing the torque, the power is expressed with P=Cw, where P=power (in Watt), C=torque (Nm) and w is the rotation frequency in rad/s if I'm not writing nonsense (it's also a bit far for me). This will allow you to pre-size your geared motor, but be careful to take into account the number of gears per unit of time (a few times per hour/day...)
Hello @stefbeno
I have the impression that @spectrum is not the same person as @ronathan who is the first applicant ;-) but maybe it's the guts that smears me with error.
Kind regards
Erratum for the trip! ;)
Thanks for the spectrum form, if I follow you the starting torque needed is about 1000 Nm?
If so, I find it huge all the same, not easy to find a geared motor with this torque.
Or maybe I didn't get it...
Good evening
Careful:
1°) you have to use a geared motor
2°) the reduction ratio is 96.6 for a speed output engine of 1400 rpm
3°) do not forget that in a reduction motor the input torque is equal to the output torque (minus losses),
BUT what is important to remember is that the time is not the same for the motor and the output axis of the gearbox. The engine will deliver this power in 1400 rpm while this same power will be delivered in 17 rpm at the gearbox output.
I'm rambling but you still haven't answered our questions ;-) ;-)
a) how long it takes you to reach this speed of 7 rpm
b) the number of start-ups in 24/h
c) What happens to the masses once the platter is launched
However, these three pieces of information are necessary to calculate service factors K1, K2, K3
In your case you will need a double-stage geared motor and a reduction ratio of 193.6 for a motor at 1400rpm and for a motor power of 1.1KW the torque output will be 848.
But you don't give information about the mass, especially if something is holding them back.
(cf @Stefbeno's remark on the board once launched) what power is needed once the board is launched.
Indeed, if there is a contre_force or if it is a flywheel it is not the same problem, so it is not the same engine power
The excel file can be confusing from this point of view because there is no notion of time and it says nothing about the effect of the reduction described above.
Anyway, the supplier of the geared motor will ask you all these questions and even others ;-) and this no matter what we say ;-)
Kind regards
a) For me the speed should be reached in about 5 seconds
b) 20 to 30 start/stop per day
c) The masses are in fact crates of vegetables, so I would say that they are constantly moving and that they vary according to the intensity of production
Hello Ronathan,
Thank you for your initial conditions:
- speed to reach 7 rpm
- 5s time.
Could you tell me how many crates will be present during the production/work of the people, this will give a fairer calculation, for the moment only one box deposited?
Your occupied surface area for one of your boxes.
You can then choose a suitable geared motor, and choose its location.
Then you will have to estimate the friction torque.
You can do your calculation with Fundamental Principle of Dynamics:
Starting Torque (cm) - Resistant Torque CR (No-load without load, and after depending on the number of crates placed on the tray).
Your steady state is known to be 7 rpm.
Kind regards.