Vacuum Rated Motors Have Been Successfully Installed At:
Vacuum Rated Motors
Frequently Asked Questions (FAQ)
Click the questions below to receive information on any of these questions.
Commercial motors are designed for lowest cost, without consideration of possible use in a vacuum. Glues, insulation’s, varnishes, greases and other materials selected for lowest cost, typically evaporate or outgas very quickly in a vacuum. In addition special attention needs to be given to open connections to prevent arcing when the insulation effects of air are removed. Finally, without the cooling medium of air, the motors run hotter than normal, the higher temperatures lead to rapid failure.
Typically a standard motor will operate for a short time and then fail. In general, standard motors will not survive in a vacuum of 10-4 Torr or lower for very long. The primary reason is that the lubricants and the insulation materials will evaporate, a phenomenon known as outgassing. In addition to destroying the motor, outgassed materials can contaminate optical components, delicate mechanical devices and other sensitive equipment inside the vacuum environment.
Careful attention to details which are not normally considered by a designer of commercial motors. It has taken Empire Magnetics, Inc. many years to assemble all of the details which allow us to build premium motors for vacuum applications. Experience and hard work allow us to offer a quality product with the assurance of a warranty.
Empire Magnetics, Inc. considers its materials lists and processing specifications to be proprietary information. In those situations where an economic basis and specific customer needs can be demonstrated, material lists will be provided after. appropriate non-disclosure agreements are executed.
Some sources of useful hardware are: MDC @ 510-887-6100 or ISI @ 510-887-8664. The Northern California American Vacuum Society may be reached at 408-737-0767.
Yes, we do offer cables as an option. The vacuum grade motors are normally made with 12 inch lead wires. It is possible to splice a cable to the lead wires or we can build a cable into a custom built motor at the time the windings are installed. When a cable is added it is necessary for the customer to specify the final winding configuration, (series or parallel) Addition of cable options may significantly impact delivery schedules.
n vacuum rated products Empire Magnetics, Inc. can offer: stepper motors, resolvers for feedback, brushless servo motors, brakes, gearheads and assorted support materials.
It is quite common for customers to ask us if a less expensive "standard" motor will work in their vacuum application. In this situation the word standard has no useful definition since there are thousands of possible variations of commercial motors. Since there is a cost associated with testing and publication of the test data with no apparent reward to our company for these efforts, our stockholders feel we have better uses of our resources. Therefore we don’t have data on products we do not sell.
No. The technical problems associated with brushed DC motors in a vacuum have been left to others. We wish them luck.
The products detailed in our price list are the least expensive versions we know how to produce in the quantities justified by the marketplace. Custom designed versions incur additional engineering and tooling costs so they will normally cost more than products we have already developed. There is an exceptional case, when a product will be used in high volumes for a carefully defined application, it may be possible to design a product which has a lower production cost in volume. However unless a commitment to production can be made, the costs of the design and tooling can not be absorbed.
No, the motor will have the same torque/speed characteristics in a vacuum, as they do in air. However they motors will typically be hotter for lack of cooling.
Yes, with some material and process improvements. The key to being able to reach a hard vacuum is to select materials that have a very low vapor pressures. These materials will also maximize the motor life inside the vacuum. However these materials may not be easily used in the making of rotary components, so the expense increases.
No, the laboratory grade motors often satisfy many but not all of the space application requirements. Typically space applications include shock, vibration, thermal cycling, and reliability issues not addressed in off-the-shelf vacuum rated motors. Including such items in the general product offering would make them too expensive for commercial users.
Empire Magnetics has supplied numerous motors for space applications on a custom basis. The laboratory grade motor is a good starting point, but in each program a detailed specification was eventually developed which was beyond the scope of a standard product. (refer to Space Rated notes in the FAQ section)
There are two bearing lubricants used for the laboratory grade motors: a PTFE based grease and a dry film lubricant. The PTFE based grease has a vapor pressure of 10-12 Torr at 20°C and the dry film lubricant has a vapor pressure of 10-14 Torr at 20°C. In terms of wear life the PTFE based grease can be expected to last four times long.
No, our cryogenic motors can be used for vacuum applications, refer to CYVX grade products.
Vacuum rated electrical feed through are available from MDC (510- 265-3500). |
This is a complicated question to answer. The variables that contribute are: drive voltage, current in the windings, drive type, winding configurations, motor speed, switching speed of the drive, duty cycle and the amount of work being done.
Having said this, a rough estimate is that 20% of the input power to the motor may be converted into heat. This figure is typical of a positional type application. The actual figure will vary depending on the application.
How do I get rid of the motor heat in a vacuum chamber?
Motors that do work generate heat. It is not possible for the motor supplier to eliminate the heat source. Therefore it is up to the user to provide a method of removing the heat.
In a vacuum the primary means of heat transfer is conduction from the motor into the mounting structure or into active cooling coils. Generally speaking, the addition of cooling fins is not very effective. However, a few turns of copper or stainless steel tubing with cooling gas or fluid running through them is usually sufficient. Assistance from a mechanical engineer with experience in thermal calculations is recommended.
Without the fluid medium of air to provide convection cooling, the heat transfer is limited to the less effective mechanisms of conduction through the mounting surface and thermal radiation. Since outgassing rates increase with temperature, high temperatures lead to shortened motor life.
How much heat must be dissipated to avoid overheating in a vacuum?
This varies depending on the motor and the drive (among other factors) but as a first order estimate, 20%-30% of the electrical energy going into the motor may be assumed to convert into heat. To obtain more accurate data testing will be required.
Yes, Empire Magnetics offers a resistive temperature device (RTD) to monitor the motor temperature.
The provisions for overcoming the heating problem in a vacuum are as follows:
- Permit the motor to withstand higher temperatures— Empire Magnetics laboratory, standard and commercial grade vacuum rated motors are made to withstand internal temperatures of 180° C, 155° C, and 130° C, respectively.
- Select the appropriate drive electronics— a low voltage drive and a series connection will reduce motor heating. The reduced standby current option offered by many drives may also be employed to reduce motor heating.
- Limit the duty cycle— when possible, reduce or turn off the current to the motor when it is not being used. this is a simple and effective way to reduce motor heating.
- Improve the heat transfer mechanisms— conduction through the mounting surface can be improved by creating a simple heatsink consisting of metal tubing with cool fluid running through it.
Outgassing is the evaporation of oil, dirt, or any other substance from a surface after it is placed in a low pressure or vacuum environment.
The amount of outgassing depends on the vacuum grade. If the amount of outgassing is a concern, Empire Magnetics recommends its laboratory grade motors and related products. Some years ago a prominent aerospace company performed outgassing tests on two of our laboratory grade motors. After being baked at 125°C for 24 hours at less than 5 x 10-5 Torr, the two motors had a total mass loss of 0.00107 grams and 0.00088 grams. This far exceeds NASA specification SP-R-0022A "General Specification Vacuum Stability Requirements of Polymeric Material for Spacecraft Application."
We also sent some laboratory grade motors to a National Lab for testing. They were able to provide some qualitative data via spectral analysis (i.e., identify what substances were present) but to date they have not been able to quantify the amount of material loss as it was so minimal.
For some sizes of VX grade motors, tests of condensable outgas products (COP) have been conducted. For a VX-U21 that had been baked at 125 degrees C. in a vacuum of 10-5 torr for 24 hours, the amount of material that collected on a cold plate in the vacuum chamber was 0.00088 grams.
We hasten to add that 125 degrees Centigrade is significantly higher than normal operating temperatures of the motors. Since vapor pressure and outgassing rates increase rapidly with temperature, this test result is much worse than a typical application. From experience we have found that optics designers want to have zero outgassing. While our testing shows the amount of material is not zero, we are not aware of any motor technology that provides lower material losses.
Many sources of vacuum equipment reference NASA Specification SP-R-0022a. This specification requires that condensable outgas product, (COP) shall be 0.1% or less. In our test the COP was less than 0.0004%
The amount of material collected is so small that quantification has proved to be very difficult. Efforts by one of the National Labs to quantify the materials have not yet been fruitful.
Yes, Empire Magnetics, Inc. has supplied motors, gearboxes, resolvers, brakes, rotor nut motors and other motors and assemblies for satellite applications.
Some examples:
Wake Shield Satellite: Empire Magnetics, Inc. supplied a stepper motor, gearbox and resolver assembly. This assembly was used to position the solar arrays in orbit. The satellite has made two trips into orbit aboard the space shuttle. The project engineer is pleased with the results.
Long Wave X-ray Telescope: This space based telescope is being assembled by the Smithsonian Observatory. Several motors, gearboxes and brakes have been supplied by Empire Magnetics, Inc. to support this project.
Space station air locks: Boeing at Marshal Space Flight Center is using several Empire Magnetics, Inc. brushless servos to control the air locks on the new space station.
European Space Agency: Empire Magnetics, Inc. motors are being used to scan a calibration source over the face of a scintillator in a satellite. The satellite was built by Alania of Italy, the scintillators by Bicron Technologies in Pennsylvania, USA.
CTA Space Systems: has used several Empire Magnetics, Inc. motors in various satellites including a rotor nut assembly to compensate an inertial guidance system.
Ground support of satellite development programs is a very common use of Empire Magnetics, Inc. products. Customers include: Hughes, Boeing, Lockheed, UC Berkeley Space Sciences Lab, Space Industries, ITT Aerospace, Ford Aerospace, Grumman and most of the National Labs.
George Cinti, Vice President of Engineering at Empire Magnetics Inc. has many years experience in the Saturn Apollo programs. He designed and built electric motors that were included in the Lunar Lander. However, due to his unique experience, his time is in great demand, as such we must be selective about the projects that are accepted.
Each project has been a custom engineering task, Non Recurring Engineering charges have ranged from $20,000 to $150,000 depending on the project. Hardware items are in addition to NRE.
Typical Applications:
Laboratory
- Space based optical systems
- Semiconductor manufacturing chambers
- Electron beam equipment
Standard
- Experimental chambers subject to frequent openings
- Sputtering and diffusion equipment
- Clean room equipment
Commercial
- Vacuum forming
- Vacuum casting
- Vacuum welding
Frequently Asked Questions (FAQ)
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Learn About Vacuum Rated Motor Selection & Installation
Operating a motor in a vacuum is often perceived as a design challenge. Among engineers, the problems -- outgassing, contamination and temperature -- are well known. What is less well known is that there are now well-developed solutions to each of these problems.
Why Choose Empire Magnetics
Government Projects & Defense Applications
Empire Magnetics has been awarded and completed US Navy contracts in excess of $100,000 as a prime contractor. The Cage code number assigned was OYMU1, CEC code 19665900H. As a subcontractor to RSI/Comsat, SAIC, Lockheed Martin, Westinghouse, General Electric and other prime contractors for the US Government, contracts in excess of $200,000 have been awarded and completed.
Nationwide & International Distributors for Specialty Motors & Complete Motor System Solutions
Empire Magnetics products are distributed by a nationwide and international network of motion control sales professionals. Your local distributor carries the drives and controls, and the accessories needed to build a complete motion control system.