Brush - Brushless Motors

What are the advantages of a brushless motor over a brush motor? 
Brushless motors are commutated electronically as opposed to the mechanical commutation (brush/commutator) of the brush motor. With the absence of brushes, the brushless motor can obtain higher speeds and longer life.

Brushless motors also have higher continuous torque ratings. This is the result of The stator winding being on the ‘outside’, allowing a higher thermal conductive path.

What is a Slotless Brushless DC Motor?
A slotless motor uses a cylindrical lamination as opposed to the traditional slotted lamination which use teeth to contain the winding. The magnetic poles of the rotor interacts with the teeth causing a detent (cogging) torque, an undesirable component. Since the lamination used in a slotless motor does not have teeth, the detent or cogging torque is eliminated.

When would I select a slotless brushless motor over a traditional slotted motor?
Slotless Brushless Motors suit applications that require precise positioning and smooth operation without cogging, which is more apparent at lower speeds. They are also more efficient at higher speeds due to the lower frictional lose in the lamination.

What is the difference between your High Performance Slotless Motors and your Standard Slotless Motors?
Our High Performance Slotless Motors are designed to handle high speed (up to 100 KRPM) low torque applications such as that used in medical hand tools. These motors are also available with high performance planetary gearheads for higher torque applications. Our Standard Slotless Motors are more of an instrument grade motor with speeds typically under 10 KRPM.

What is the difference between 60 electrical degree hall spacing and 120 electrical degree hall spacing?
These are two methods for hall phasing with equivalent results. Both methods will provide six step commutation for brushless motors. Most motor drives can accommodate both types of hall spacing, but there are drives that are configured for only one type of hall spacing.

Do your brushless motors have an international protection (IP) rating?
Pittman EA057A, EA090A, and EA121A series Automation Grade Motors are IP65 rated. All other motors have various ratings – please consult the factory for details.

Do your brushless motors have any agency approvals?
Pittman EC057B, EC083A, and EC121A series motors are UL rated.  Due to the low voltage at which many smaller Pittman motors operate, UL, CSA, or CE are not required

Are any of your motors autoclavable?
Yes, our ET010A and ET013A High Performance Slotless motors are autoclavable.

What autoclave cycle are the ET010A and ET013A motors capable of?
ET010A and ET013A series motors are capable of 138 degree C, 2 ATM., 100% R. H., 10 minutes for 1,000 cycles.

What is the life expectancy of your brushless motors?One of the main advantages of a brushless motor is longer life over many other motor technologies. Many factors are involved in determining the life of a motor. These include, but are not limited to operating environment, duty cycle, mechanical load, etc.. Under nominal conditions, the life is determined with the ball bearing. Since motor life is application specific, it is suggested to contact an Applications Engineer with your requirements.                                

Can you apply a voltage to a motor which is higher than the "Rated Voltage"
Yes - Rated voltage is just a reference point which indicates the associated rated current, rated torque and rated speed. When applying a voltage above the rated level you must be carefull not to exceed other motor specifications (Tp, Max speed, Max Terminal voltage, Ip, etc.) or damage could occur. If you are not sure how to consider these variables, we recomend you discuss the details of your project with one of our application engineers.     

What are Pittman's Standard Outgoing Performance Inspection Tests ?
100% of all outgoing units receive a minimum number of tests depending on the complexity of the unit. Motors are tested for back EMF, no load current and terminal resistance. Units also receive either a DC hi-pot [ units with internal capacitors ] or the traditional AC high-pot to check for possible shorts. Motor- gearboxes also add a gearbox integrity test which checks for torque capability and speed. Tachometers are tested for generated voltage in both directions and terminal resistance. Brakes are checked for their ability to provide their rated holding torque when mounted. Encoders are screened for number of channels, counts per revolution and channel symmetry. Additional tests can be added to the above to meet special customer requirements at additional cost.   

Do you Have Standard Gears, Pulleys, Connectors, Etc. for Your Units ?   
As a rule, no. But, we do offer a limited number of cable assemblies with connectors for some of our encoders and brushless motor types.  However, in most cases, we are willing to provide customer parts as specified or by Pittman approved methods especially in the attachment of gears and pulleys.                      

What is the Backlash of the Gearboxes ?
The present spur gearboxes have a 3 degree maximum backlash when new. The planetary units that Pittman offers come from various sources including our own designs. Since these vary by source and ratio, it is recommended that the factory be consulted for the specific gearbox in question.      

Do the Gearboxes Come in Other Ratios Not Shown in the Catalog ?
Yes, with some being more extensive than others, Please check with our Application Engineers for specific models and the ratios offered because these are subject to change with new periodic updates.                                                                                                                                                                                                  

What information do I need to provide in order for you to help me select an appropriate motor solution for my application?
The absolute minimum information required to properly select a motor solution is the supply voltage, available continuous and peak current, load torque, speed at load, and desired motor technology (brush or brushless).  It is also helpful to have a description of the application, duty cycle (time on, time off), ambient temperature, and motor size requirements (maximum diameter, length, and weight).  Other application details that can be important include radial or axial loads, environmental conditions (exposure to water, dust, humidity extremes, special atmospheres), feedback requirements (encoder resolution), EMI/RFI suppression requirements, and brake requirements.  For positioning applications, load inertia, angular displacement, move time, and friction torque can be provided instead of load torque and speed at load.  Finally, providing quantity requirements will help us to determine whether your needs are best served with our Pittman Express offering or with a custom solution.

I’ve selected a motor configuration from your catalog.  How do I compose a part number?
Given the wide selection of features and options for our motors, the number of valid combinations is enormous.  It would be very difficult to institute a part numbering system that accommodated all of these possibilities.  For this reason, our part numbering system is not fully configurable.  Typically, the first half of the number represents the motor family and some basic options.  The second half is sequentially assigned and represents the remaining unique features of a particular unit.

Initially, you can simply provide us with the base motor number followed by a description of the remaining features.  For example, you could specify the following:

DC040B-5 with 24V winding, G51A 19.7:1 gearbox with wide-face gears, an E30B 500 cpr 3-channel encoder, ball bearings in the motor, and an output ball bearing in the gearbox

Our sales department will advise you of the unique part number for that configuration once it has been determined.

The exception is our Pittman Express program, which offers a selection of stock items listed in the catalog by a complete part number.  These products should be specified by these part numbers.

Do I have to run a motor at the rated voltage?
No.  The voltage shown for the available motor windings is listed as a reference voltage, and it is just that.  Certain motor parameters, including no-load speed, peak torque, and peak current are voltage dependent.  Therefore, a voltage must be chosen in order to show these values.  The choice is subjective to a degree, but provides a convenient way of comparing different motor windings.

Motors can typically be operated safely from zero to about 125% of their reference voltage.  However, speed is dependent on voltage and is also a consideration.  There are optimal operating speed ranges for motors as well as maximum recommended input speeds for gearboxes.  A general rule of thumb is to maintain motor speeds above 1,000 rpm for brush-commutated motors, and motor speeds below approximately 6,000 rpm for gear motors.  It is not uncommon to exceed these recommendations for supply voltage or motor speed, but there are tradeoffs involved.  It is recommended that you discuss your application with us prior to exceeding these limits.

Are your motors and gear motors reversible?
Yes.  All of our brush-commutated and most of our brushless units are reversible.  The only exception would be a brushless unit with built-in control without the direction input function.  Simply reversing the polarity to the motor terminals or leads will reverse the output direction of our brush-commutated units.

How do I determine my load torque?
The torque requirement for an application can be calculated, measured directly using a torque measuring device (torque watch), or measured indirectly using a DC motor.  When using a motor, measure the current draw of the motor under load, and calculate the torque using the equation below:

T = (I – INL) x (KT x N x h)

Where

I = Current

T = Torque

KT = Torque Constant

N = Gear Ratio (Equals 1 if there is no gearbox)

h = Gearbox Efficiency (Equals 1 if there is no gearbox)

INL = No-Load Current

Please be aware that this equation approximates the true load torque and does not take thermal conditions into consideration.  The results are reasonably close and suitable for most purposes.

How do I determine the rated current for a motor, or the required current draw of the motor for sizing a power supply or fuse?
The current draw of a motor is given by the equation below:

I = T / (KT x N x h) + INL

Where

I = Current

T = Torque

KT = Torque Constant

N = Gear Ratio (Equals 1 if there is no gearbox)

h = Gearbox Efficiency (Equals 1 if there is no gearbox)

INL = No-Load Current

Maximum continuous torque can be obtained from the catalog specifications and used as the torque value to obtain maximum continuous (rated) current.

Please be aware that this equation approximates the true current draw and does not take thermal conditions into consideration.  The results are reasonably close and suitable for most purposes.

How do I determine the rated speed or the speed at a specific torque for a motor or gear motor?
The output speed for a motor or gear motor is given by the equation below:

w = [VS – (I x Rmt)] / (KE x N)

where   w = Speed

                VS = Supply Voltage

                I = Current (Obtained from previous equation)

                Rmt = Motor Terminal Resistance

                KE = Back-EMF Constant

                N = Gear Ratio (Equals 1 if there is no gearbox)

Maximum continuous (rated) current can be obtained from the previous equation and used as the current value to obtain the speed at the maximum continuous (rated) torque.

Please be aware that this equation approximates the motor speed and does not take thermal conditions into consideration.  The results are reasonably close and suitable for most purposes.

How do I determine the maximum continuous output power (wattage) of a particular motor?
Output power is a product of the torque of a motor and the speed of the motor at that torque.  For a motor speed in rpm and a torque in oz-in, the power in watts is given by the equation below:

Speed [rpm] x Torque [oz-in] x 0.00074 = Output Power [W]

Maximum continuous torque can be obtained from the catalog specifications, and the motor speed at that torque can be obtained from the previous equation to determine the maximum continuous output power.

When do I need to specify ball bearings instead of sleeve bearings?
Ball bearings are generally recommended over sleeve bearings for applications requiring high speeds, extreme temperatures, excessive radial shaft loads and any axial shaft loads, as well as for use with certain encoders.

How can we do reduce audible noise?
Audible noise can be generated by bearings, brushes, and gears.  What constitutes unacceptable audible noise is a highly subjective matter.  The sound generated by a motor has different characteristics once it is mounted in an assembly.  Minimizing motor speed tends to help reduce unwanted noise.  Pittman can provide special gear materials and types, which can also be beneficial.  Additional solutions can be provided upon request if the application is noise sensitive.

How can we reduce electrical noise (EMI/RFI)?
Pittman offers a number of solutions for applications that are sensitive to EMI/RFI emissions.  Ferrite beads, chokes, capacitors, and varistors are commonly used for such applications.  Ferrite beads simply slip over the wires’ insulation, whereas chokes must be soldered in series with the wires’ conductors.  Capacitors may be installed from the terminal to ground and/or terminal to terminal.  Depending on the unit, they can be mounted internally or externally.  Capacitors are generally effective for low-frequency noise (typically below 30 MHz), and ferrite beads for high-frequency noise (generally above 30 MHz).

How do I mount a Pittman motor?
Our standard motors and gearboxes are designed to be mounted by their front face.  The front mounting face contains a pilot for centering and a bolt hole pattern for fastening.  We can also provide special mounting features on custom units to meet your individual needs.

How do I mount an item (pulley, gear, coupling, etc) on the output shaft?
There are many techniques that can be utilized to mount components on a shaft.  For motors with access to the rear end of the shaft, items can be pressed directly onto the shaft.  Access to the rear end is important so that it can be properly supported to prevent damage to the rotor or bearings.  Another method is to secure items to the shaft with a setscrew.  The presence of a flat on the shaft helps prevent slipping, although it may not be necessary for low-torque requirements.  Items can also be secured to the shaft with adhesive.  It is advised that the adhesive is applied to the component as opposed to being applied directly to the shaft, and that care is taken to prevent adhesive flowing into the motor and contaminating bearings.  Another method consists of drilling a cross-hole through the shaft and securing an item with a pin.  Again, care must be taken to support the shaft to avoid damaging the motor.  These are just a few examples of the many methods that can be accommodated by Pittman.  Each of these methods has advantages and disadvantages, and the decision depends on such factors as the type of component being used, the torque requirement, and the associated cost.  We can also provide special shaft features on custom units to meet your individual needs.

What are your standard performance tolerances?
A table of our standard manufacturing tolerances for basic motor parameters is shown below.

Parameter

Tolerance

Torque Constant

±12%

Back-emf constant

±12%

Terminal Resistance

±15%

Inductance

±10%

Inertia

±10%

Motor Torque Losses

+30%

Motor Friction

+50%

No-Load Current

+30%

How can we keep the motor temperature to a minimum?
Temperature rise can be minimized by keeping the ambient temperature as low as possible, circulating air around the motor, making sure the motor is not insulated, and mounting the motor to a good heat sink.  Additionally, selecting a more powerful motor should decrease the temperature rise if it is an important consideration.

Can I get a replacement for a motor that is utilized in a piece of equipment?
If you have a motor that needs replacing in a piece of equipment, it is recommended that you first contact the OEM for information on spare motors and parts.  The OEM should be the most knowledgeable source of information regarding your needs.  Additionally, specific motor configurations are often proprietary to a particular company.

If you are unsuccessful with the OEM, check to see if the motor is part of our Pittman Express offering.  If it is, you may order it from us or from a distributor that carries it.  Keep in mind that OEM’s frequently modify the motor in some way, so check the specifications carefully to make sure it matches what you need.

If you are unsuccessful with the OEM and the motor is not part of our Pittman Express program, your options are severely limited.  The best solution becomes the closest available substitution from our Pittman Express offering.  Please be aware that the form, fit, and function of the closest available unit may differ significantly from the original.  There is no way to guarantee that the new unit would be a suitable replacement.

How do I size a DC power supply for use with one of your linear actuators when using a Constant Current Drive.
For example if you have one of our size 17 single stack linear actuators with 2.33 volt coils which is rated at 7 watts, out catalog shows the current per phase at 1.5 Amps/phase RMS. Since we recommend an 8:1 ratio between the supply voltage to the drive vs. the motor voltage, this value should be 18.64 volts for best results to help overcome the inductance of the motor coils. 18.64 volts is not a common value on most systems but 24 VDC is so we can use this value. The easiest way to calculate this is to double the wattage of the motor which in this example is 7, so our value will now be 14 watts. We would like for the rating of our power supply to be 24 volts at a minimum of .75 amps continuous. Therefore 24 volts x .75 amps = 18 watts which would be sufficient rating to drive the motor. A 24 volt supply rated at 1 amp continuous may be more common and provide 24 watts which is more than enough to handle the motor and drive. Sometimes users of our actuators will combine the current of both phases and assume they need 3 amps at 24 volts to run the motor but it is more about wattage and not a direct current relationship. If you plan to power other devices form this 24 volt supply, this will need to be factored in to calculate the wattage rating of the 24 volt DC supply.