Calculating Rim Speeds

You may know that our stock metal is all statically balanced to 6500 ft/min, but some of you may not know how to find out what rpm and diameter combination that equates to.  I’ll show you how.  This can be useful for not only maximum rim speeds, but also when you need to find out what rpm at which to run a head roll of a conveyor.

You need the sheave/sprocket outer diameter and RPM.  For this example, let’s use a 10” diameter and 200rpm.

Step 1, Find Perimeter.

Perimeter = 2*pi*r          or            Perimeter = pi*d

Where r = radius and d = diameter

Example: pi*10” = 31.415”

Step 2, Calculate Rim Speed

Rim Speed = Perimeter*RPM

Example: 31.415” * 200rpm = 6283 in/min

Step 3, Convert to proper units

12” = 1ft

Example 6283 in/min * (1ft/12in) = 523.59 ft/min

As always, feel free to call us if you have any questions.

If It Leaves the Ground, a Gates Belt Can't be Found

The purpose of this blog post is to expand on a previous blog regarding Aircraft Applications.

The Gates Corporation has had a long standing policy of not recommending the use of our power transmission products on aircraft, including kit, home-built or ultra light aircraft.  Whether the aircraft is FAA certified does not change this policy. This policy applies to any application where the equipment leaves the ground. A recent request serves as a great example. A customer called to receive assistance for designing a belt drive on a pump. The pump itself didn't leave the ground, but it supplied water at a high pressure to a water powered jet pack. Clearly, we could not support this customer because the application goes against our safety policy.

Only automotive and industrial belts and belt drives are sold through Gates distributors or the open market. Those belts and drives are NOT designed or made for aircraft.  DO NOT purchase Gates belts or belt drives for use on aircraft. This is a safety issue. Airplanes and cars are quite different as far as belts and belt drives are concerned. 

To emphasize this important point, do not use any Gates belt, pulley, or sprocket on a propeller-driven or rotor drive aircraft, and not with any in-flight accessory drive application or other drive in an aircraft.  For all types of applications, belt drives must be properly designed, installed, tested, and maintained.  It is impossible to inspect a belt and predict the remaining belt life. A broken belt means immediate loss of power and ability to fly! 

Feel free to contact us at ptpasupport@gates.com or 303-744-5800 if you have any questions or comments.

HP and Torque

People use the words hp and torque quite a bit, however, they don’t always understand the relationship between the two units.  I’m going to attempt to clear that up a little bit, and maybe make designing a little easier in the process.

Torque (Q) is basically a force at a distance.  If you think of a ratchet that is one foot long, and you apply 2lbs of force at the end of the ratchet, you are applying 2ft*lbs of torque (1ft x 2lbs).

Horsepower (hp) is a unit of measure of the rate at which work is done.  Let’s take the example above.  We are going to assume that applying the 2lbs of force will allow the ratchet to turn the bolt.  We count every time we make a complete circle (revolution) over a specific amount of time.  If we use minutes, we have RPM (revolutions per minute).  To calculate hp from torque and rpm you can use the following equations:

hp = (Q * RPM)/5252      This equation is when Q is given as ft*lbs

hp = (Q * RPM)/63025   This equation is when Q is given as in*lbs

You can see that hp is always a function of torque and rpm.  In the case above, if we can turn the ratchet 300 time per minute, with 2lbs of force, we are creating a huge 0.114hp.  These equations really start to become useful when you need to calculate the amount of torque that can be produced at a driven sprocket after a gearbox.  This will allow you to determine if your motor is big enough, and your reduction ratios are correct.

Diameter Differences

When asking questions about a drive, a lot of the time people take a diameter measurement to give to us.  On a synchronous sprocket, this can be a little deceptive.  There are three main diameters that are important, and this may not be obvious to the person taking the measurement.

First, if at all possible, always get a tooth count (or the part number).  Tooth count is exact, and is the best way to get you the correct answer.  If a diameter measurement is the only option, there are a few things that you need to know to get the best result.

Pitch Diameter (PD):  This is a theoretical diameter, and cannot easily be measured by hand.  However, this can be calculated.  The formula is:

(#teeth*pitch)/pi.  Pitch diameter is slightly larger than outer diameter (OD).  The diameter listed in the catalog is the PD, so if you are measuring the sprocket trying to identify the tooth count, the PD number should be slightly bigger than your OD.

OD:  Outer diameter is measured on the tooth surface.  This is the measurement we need if you can’t provide a tooth count.  Be careful when measuring this, as there is not always the tip of a tooth 180 degrees apart from one another, and you could get a measurement that is a little smaller than your actual sprocket.

Flange Diameter:  This is the one that gets people into trouble.  The flange is the largest diameter of the sprocket; it’s the part that keeps the belt from running off of the edge of the sprocket.  Not all sprockets have flanges, and sometimes the same flange is used for a couple of different sprocket sizes.  This means that if you provide us a flange diameter, we have to guess as to what sprocket you may actually be using.  Avoid measuring the flange if at all possible, but if you must, make sure that you tell us that it is a flange that you are measuring, and not the OD.

Sheave Gauges

Sheave gauges are a great tool that surprisingly people don’t always know about. They have been around for quite a few years, and are just as useful as ever. They are small plastic cutouts that you place inside a sheave groove to see if there is enough wear that the sheave should be replaced. If more than 1/32” of wear can be seen between the gauge and the sidewall of the groove, the sheave should be replaced. Worn sheaves are a big contributor to premature belt failure.

With the set, you get a gauge for multiple sections, and each gauge has 3 different angles for measuring a wide range of diameters within that belt section. These can also be used to help identify what type of belt a particular sheave is designed for if it is not significantly worn down. There is also a belt gauge in the set that can be used to help identify the particular belt section as well.

Stainless Steel Poly Chain® Flange Color

Customers sometimes ask about the pinkish color of Gates stainless steel Poly Chain sprocket flanges. The discoloration is a result of the high temperature shrink process used to mount the flanges.

Flange discoloration is seen in both the stainless steel and the standard Poly Chain sprocket lines. During the shrink fit process, the standard sprocket flanges (low carbon steel) usually turn black or brown.  Conversely, the stainless steel flanges typically take on more of a pink hue.

Flange discoloration is normal and will not impact the performance of the product.



Standard Sprocket

Stainless Steel Sprocket

FIRST Come, FIRST Served

It's getting close to the end of the year, and you know what that means. The kickoff of the 2013 FIRST Robotics Competition (FRC) is around the corner! Starting the week after the kickoff, Gates will allow teams to order belts and sprockets online at www.Gates.com/FIRST. All of the available components will be 5mm pitch, 15mm wide, PowerGrip HTD belts and sprockets. There will be several predetermined sizes available to teams and they are provided in a first come, first served basis. There will also be a limit on the parts so we recommend designing the belt drive first then ordering the parts you'll need.
As always, go to www.Gates.com/FIRST for belt drive assistance.

Internal Combustion Horsepower Ratings

When designing a belt drive with an internal combustion (I.C.) engine it’s important to understand that an IC engine is not like an electric motor. The horsepower rating for a NEMA motor is not the same as a horsepower rating for an IC engine. There is no conversion factor. HP is a HP is a HP. Engines just have different characteristics. Electric motors may have a hard start whereas IC engine may not. IC engines can’t run at their peak torque for a long time. An IC Engine with a HP rating higher than the power needed should be selected. Altitude and other factors can affect an IC engine’s performance.

Internal combustion engines are typically rated based on brake horsepower (BHP), or maximum BHP.

This BHP rating of an engine usually means the horsepower produced by a test engine in a laboratory.  During the test an engine is ran without a fan, generator and other accessories.  The ambient temperature is corrected to some standard, such as 60°F., and the atmospheric pressure is corrected to some given altitude, such as sea level.  The BHP rating should not be used for design, since the standard production engine, with accessories, cannot reach this output in actual usage.  Gross BHP is the term used for test data without any accessories and net BHP is with all of the standard accessories.  This is the horsepower measured at the crankshaft flywheel.  An I.C. engine spec will not contain any other mention of horsepower.

Several decades ago it was more common to refer to a maximum intermittent HP.  For short durations this was generally 85% of BHP.  Continuous duty or rated BHP was 75%-80% of maximum BHP for long duration service.  These terms are not referred to today in engine specifications.

It is still important to verify the horsepower versus engine rpm curves for those applications where the engine and drive are not intended to run at one speed continuously.  A percent time duty cycle is also helpful in selecting a belt drive.

Actual HP

Do you know that people are constantly using bigger motors than necessary? It can be a big problem, and doing so can lead to using bigger belt drives than necessary too. There is a common belief that bigger is always better. This is not always the case when it comes to power transmission components. Designing around actual loads not only saves on initial purchase price, but can also save money on replacement parts caused by excessive tensions, such as those placed on bearings when too big of a drive is used.

If you think your motor is too big for the load you are using, here is an easy way to calculate actual HP draw.

Actual HP = (Nameplate HP)x(Measured Amps) / (Nameplate Amps)

This means that if you measure the amperage draw of your motor, you can use the nameplate to find out what your actual HP draw is. Now sometimes it’s worth it to design around the rated load instead of the actual load. In situations such as hard starts, or unknown shock loads, having additional service factor is good, but when max loads are known, or size/cost is a priority, we can use the above info to get just the right size drive.

Tension Gauges: Pencil vs. Krikit

We all know that tension is important, and measuring tension with a gauge is a great way to prevent belt drive problems. However, there are a few options out there, and sometimes people are confused as to what they need.

Two of the lower cost options that Gates offers for tension testers are the Pencil Type Gauge, and the Krikit Gauge. Both of these are easy to use tools that allow the user to measure tension in the belt, and compare it to recommended tensions, but they function a little differently.

The Krikit gauge is generally seen as an automotive gauge used on front end accessory drives for cars and trucks. The way this gauge works is by depressing the finger pad on the gauge with the bottom of the gauge against the belt. The belt will deflect downward and push the arm of the Krikit up across a scale on the top of the gauge. At a certain amount of force applied to the finger pad, the Krikit will ‘click’. When the user hears the click, pressure should be released, and you can read the amount of tension in the belt by looking at where the front of the arm crosses the scale.

The Pencil gauge is generally seen as an industrial gauge, and uses two o-rings and a spring. You place the big end of the gauge on the belt, and set the bottom o-ring to the recommended deflection distance. You will need a straight edge, piece of string, or a mark on the wall next to the belt to determine starting height of the back of the belt. Set the plunger o-ring to zero, and push down on the plunger until the bottom o-ring meets the reference point you set for the starting height of the back of the belt. At this point, release the pressure on the plunger, and read the force recorded by the movement of the plunger o-ring. This is the value that you will want to compare to the recommended tension values for your drive.

As described above, there are obvious differences in how the gauges function, but the one thing that may not be obvious is the tensions that they are reading. The Krikit measures tension ‘in’ the belt, while the pencil gauge measures deflection force at a certain distance. This is important to note because different sources will recommend tension differently, either direct tension that the belt is seeing (the tension in the belt), or as a matter of deflection force and deflection distance.

Both of these tools are offered in several capacities for measuring tension, and both work very well, but they work in two different ways. It’s important to know which way your tension measurement is being given so that you can select the proper tool.

V80 and Belt Matching

A lot of people call us asking about a matched set of V-belts. This is an important design aspect, as drives that use multiple V-belts have to have belt lengths that are close to work properly. Back in 1980 Gates made a change to their manufacturing process that allowed us to meet RMA V-belt matching standards with our standard line product in the Super HC, Hi-Power II, and Tri-Power belt lines. Using any of these belts made to our V80 standard means that you can use off the shelf belts of the same size and not worry about matching them. This can save considerable time trying to find a set of belts.

We do have product lines that are not V80 approved, and do require belts to be matched. Our Predator line of V-belts are a good example. Because of the Kevlar tensile cords used in Predator, matching the belts to the same punch number is required.