Help me understand SEW-Eurodrive gearmotor calculation
Help me understand SEW-Eurodrive gearmotor calculation
(OP)
Dear Engineers,
I will be responsible for calculating the parameters and selecting the appropriate gearmotors in our company. However, I almost have no experience in doing that. We are buying SEW-Eurodrive gearmotors, but due to policy of our company (it is a long story under this situation which I shall not bother you with), we must buy gearmotors through another company in another country. The "seller" is only the reseller, having no qualification in calculations, therefore I must give them a complete order page (which is generated in SEW Drive configurator) with full information. So I have to learn how to select an appropriate gearmotor without a help from official representative of SEW. The only source I have is old calculations of previous engineers, and also - current working motors in our factory that I can inspect - see the working current, get information about their lifetime (some of them are working for years, some lasted for 1-2 weeks), and so on.
I started with studying the SEW manual “Project planning for drives”:
download.sew-eurodrive.com/download/pdf/10522913.pdf
When reading the document, I face some questions that I can not understand because of lack of experience or knowledge, and I can not find these answers in the internet. I will post short-accurate-exact questions in this thread, and I hope somebody shall find a few moments to explain them. I believe these will be easy for professionals of the field, but they are not even near to being easy for me as a beginner. I appreciate your help in advance.
I will be responsible for calculating the parameters and selecting the appropriate gearmotors in our company. However, I almost have no experience in doing that. We are buying SEW-Eurodrive gearmotors, but due to policy of our company (it is a long story under this situation which I shall not bother you with), we must buy gearmotors through another company in another country. The "seller" is only the reseller, having no qualification in calculations, therefore I must give them a complete order page (which is generated in SEW Drive configurator) with full information. So I have to learn how to select an appropriate gearmotor without a help from official representative of SEW. The only source I have is old calculations of previous engineers, and also - current working motors in our factory that I can inspect - see the working current, get information about their lifetime (some of them are working for years, some lasted for 1-2 weeks), and so on.
I started with studying the SEW manual “Project planning for drives”:
download.sew-eurodrive.com/download/pdf/10522913.pdf
When reading the document, I face some questions that I can not understand because of lack of experience or knowledge, and I can not find these answers in the internet. I will post short-accurate-exact questions in this thread, and I hope somebody shall find a few moments to explain them. I believe these will be easy for professionals of the field, but they are not even near to being easy for me as a beginner. I appreciate your help in advance.





RE: Help me understand SEW-Eurodrive gearmotor calculation
RE: Help me understand SEW-Eurodrive gearmotor calculation
RE: Help me understand SEW-Eurodrive gearmotor calculation
http://download.sew-eurodrive.com/download/pdf/168...
It's a guide to converting DT motors to DR motors. If either work, go with the newer.
RE: Help me understand SEW-Eurodrive gearmotor calculation
Would you have any comments between prices of IDENTICAL (same kW, same accessories, same RPM) motors DT versus DR?
RE: Help me understand SEW-Eurodrive gearmotor calculation
- used new technologies in manufacturing
- it has better efficiency, possible to order premium efficiency motor
- it has a modern design for integrated encoder - which saves some space
- may have 3 versions of brakes depending on needs
- DR is up to 200 kW, DT - only up to 120 kW
- possible to order compact size motor
- many possible flange options
- can have temperature measuring devices
...and many other optionsThere is a small site for DR motors: http://www.seweurodrive.com/dr-motor/
There is also a PDF, which shows how many new features can be ordered in DR motor, while not available in DT: sewmotortruth.com/SEW_DR_Motor_Series.pdf
So, this is enough for comparison i think, except it would be really interesting to compare the price range of DT and DR if somebody has an opinion on that. Thank you in advance
RE: Help me understand SEW-Eurodrive gearmotor calculation
RE: Help me understand SEW-Eurodrive gearmotor calculation
In the document I have mentioned previously - “Project planning for drives”:
download.sew-eurodrive.com/download/pdf/10522913.pdf
Page 71 - there is an explanation how to calculate the appropriate starting frequency of the motor in behalf of ratio loaded/unloaded cycles:
In this example, it is allowed to start the motor 112 cycles/hour in loaded condition, and 247 c/h in unloaded. In my opinion, if this motor would work in the mixed load (sometimes loaded, sometimes not) then the permitted starting frequency would be somewhere in between. But according to this calculation (and all the other examples in this manual from SEW) this formula is present, which represents a lower number of mixed condition starts than the fully loaded condition starts. How can this be explained from physical point of view? Because now it means that the motor can be started 112 times in fully loaded condition, but only 76 times fully loaded + 1 time unloaded. I don't understand this, how can it be?
RE: Help me understand SEW-Eurodrive gearmotor calculation
I worked on contract for a few months for SEW and got to know these calculations intimately. But it's been a long time. With the "planning" document, you're as good as you can get. The German approach is very rigorous. Admirable in some ways.
That calculation is about "starts per hour" and is all about heat dissipation. In order to ...ahem....optimally...size the motor for an energy-sensitive location such as Germany and NOT like the US (...yet, anyway), then these "starts per hour" must be analyzed. Take your best shot. If your best shot is no good, simply solve the problem by upsizing the physical size of the motor so that the bigger mass will handle the multiple starts per hour (which, essentially, is a short circuit and therefore creates a bit of heat that must be dissipated).
Some years after my stint at SEW I had the opportunity to do a gearmotor sizing exercise. I chose Dodge as the supplier. American. Murcan. Much more brute force unsophisticated get-it-done type of calculation. That's when I discerned the truth about an alternative path to going home on time. Upsize that b*tch and call it a day: it's just torque, and the bigger motor will last forever because it never overheats.
Aw heck...my whiskey glass it empty.
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: Help me understand SEW-Eurodrive gearmotor calculation
Anyhow, I completely understand the number of motor starts equals to short circuit in the winding, dissipating more heat. What I don't get is - how can it be that you can start a motor 112 times per hour fully loaded, but only 77 times in mixed mode (say 50 loaded ant 27 unloaded). How can these 27 no-load starts be equivalent to 112-50=62 loaded starts?
Again - 27 no-load starts will give the same amount of heat like 62 loaded starts IF motor is started in mixed mode
BUT - if there is only no-load starts, then it can be as much as 247
?
I say this might be a mistake, but the same formula is in so many examples ...
I really must know everything I can on this topic. I have seen too many broken gearmotors due to inappropriate calculation, and production lines staying off work waiting for gearmotor replacement ...
Thank you in advance