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Tech Tips

We create these tech tips based on common questions. If you have a question please email us at [email protected]


Create Longer Servo Extensions

Here is an easy way to put ends on your wire and create a longer servo extension to your specifications. When using our bulk servo wire, cut a short servo extension in half and splice the pieces onto the bulk wire.


Choosing gears based on two fixed axes

When selecting gears based on two fixed axes, pay close attention to the pitch diameter (PD). The distance between the axes will be equal to (PD1 + PD2)/2.
For example, if you want a set of gears to mount on the Actobotics channel at a distance of 1.5” you could use a 76T, 32P gear (PD=2.375”) with a 20T, 32P gear (PD=0.625).
(2.375” +0.625”)/2 = 1.5”


Integrate 1” PVC into your projects

Our new PVC Clamp Hubs allow you to integrate standard 1” PVC pipe into your large scale robotic project. The new clamps offer a quick and inexpensive way to increase the size of your project by using common building materials from nearly any hardware store. The PVC Clamp Hubs have the Actobotics hub pattern which means they’re compatible with the entire line of Actobotics components.


Functionality of the Dual Ball Bearing Hub

When designing a mechanism that involves a rotating shaft, our Dual Ball Bearing Hub (545444) can be a very useful part. Since the hub has two bearings (one pressed into each side of the aluminum housing) it eliminates the need to mount two bearings separately. By simply bolting this hub to your structure, the bearings are sure to be in-line with one-another and they can handle a cantilever load on the shaft. The Dual Ball Bearing Hub has both tapped and thru-holes to increase its mounting options. The thru-holes have counter-bored holes to allow socket head screws to set below the surface and out of the way of moving parts.


Add a pan system to the bottom of your Slider Kit A

ServoCity recently released the Slider Kit A, a compact and lightweight slider kit that is perfect for camera phones and GoPro cameras. To add yet another element to your video, you can install a pan system to the bottom of the Slider Kit A. The 170 degree viewing angle on a GoPro camera won’t allow you to install a pan system on top the slider rail as it would capture the rail throughout the majority of the video footage. By installing a pan system to the bottom side of the rail, you can capture footage without having to worry about the slider rail creeping into view.


Help Negate the Side Load Applied to a Servo or Motor

Motors and servos operate best when side-load is isolated from the shaft. Side loading can be created by an unbalanced load, a tensioned belt or a tight gear mesh. To negate the side load from being applied to the motor or servo, a bearing can be used for a support mechanism. You can extend the shaft of a motor or a servo using a ¼” coupler and a ¼” D-shaft. The ¼” diameter D-shaft will fit inside the coupler and be held in place with the set-screw. The shaft can then protrude through a supported bearing or bearing mount and will isolate the side load from being applied to the motor or servo. This setup will provide a more stable drive mechanism that operates smoother and quieter when compared to an unsupported drive mechanism.


Compatibility of Parts

Be sure to check the size of the inside diameter of your product, especially when working with shafting and tubing. For example, if you select a ¼” OD shaft from ServoCity, it is specifically designed to work with any ServoCity part that has a ¼” ID (bearings, bushings, collars, hubs etc.) The components will be able to go together with slight pressure.


Choosing a motor for a slider or conveyor system

In order to choose a motor for a slider or conveyor system, you will need to select a pulley or drive mechanism to mount onto the motor shaft. You must also determine the speed at which you would like to the slider or conveyor to travel. For this example, we’ll select a 1” diameter pulley (#615386 timing pulley or #615130 smooth pulley) and a linear speed of 48” in 1 minute.

First, we’ll figure the circumference of the pulley which is equal to n * diameter.
3.14 * 1” = 3.14”.
This means that each rotation of the motor will cause the slider to move 3.14”.

We can then calculate how many revolutions of the motor it will take in order to move the 48” that we selected.
48”/3.14” = 15.29 rotations. This is the number of revolutions it will take to move 48” and since we selected a speed of 1 minute, we can conclude that a 15RPM motor is needed to be very close to the desired speed. If we had selected 30 seconds for our time rather than 1 minute, we would need a motor that is twice the speed since 30 seconds is half of a minute.


Using a power supply in place of a battery

When using a power supply in place of a battery, make sure that the amperage is equal to or greater than the amp draw of the item you intend to power. If the amp rating of the power supply is lower than the item it is powering the performance will be diminished. For example, if you power a 12V motor with 400oz-in of torque and an amp draw of 5A with a 12V, 2.5A power supply, the motor will not be able to exert the full 400 oz-in of torque since it requires more than 2.5A to do so. It is okay, however, to have a power supply that is rated for more amps than what the item you intend to power will draw. This will not harm it in any way since electronic devices only pull the necessary amps from the power source. Some power supplies will also vary between their rated voltage and true voltage output. Before plugging a power supply in, it is always a good idea to check the true voltage output so that you do not accidentally damage the components that you wish to power.


Differences between servos and DC motors

There are many differences between servos and DC motors but when deciding between the two, these characteristics should be considered first.
1. Servos require a PWM signal from a specialized controller. Motors just need the specified voltage to run.
2. Servos have feedback and can go to a commanded position (Closed Loop). Motors simply rotate with a given speed and direction (Open Loop).
3. A standard servo rotates 90 degrees maximum in stock form (180 degrees after being modified/programmed). Motors do not have limits and can rotate continuously in either direction.


Functionality of the Servo Mixer

A servo mixer can be useful when using servos that have been modified to continuous rotation as the drive mechanisms for a robot. Each drive wheel requires a separate channel to operate. When using a wireless radio system without a servo mixer to operate this type of robot it can be difficult to operate. One servo will be controlled by the up/down movement of the joystick while the other servo is controlled from the left/right movement of the joystick. This means that in order to drive straight, the operator must push the joystick diagonally. Using a servo mixer will combine these two channels and greatly simplify the way the servos operate together. The servo mixer will allow you to move the joystick straight up or down to go forward or backward and left and right to turn the vehicle accordingly.


Functionality of the Precision Digital Speed Controller

The Precision Digital Speed Controller (ESC-72-24) is used to control a DC motor by way of a servo controller. A DC motor is not directly compatible with a servo controller such as a wireless radio system. The electronic speed controller converts the servo (PWM) signal to a DC motor signal so that you can operate a motor via your servo controller. The PWM signal from the servo controller will determine the speed and direction of the motor. The ESC-72-24 does require a 12VDC input from a battery or power supply but there is an integrated circuit that will feed 5VDC back to the servo controller so that you can power your wireless RX (or servo controller) and the ESC from the same power source.


A clean and simple way to extend servo wires using CAT6 cable

If you’re running multiple servos several feet from your servo controller, the CAT6 extension boards not only clean up the wiring but also clean up the square wave signal sent to the servos for smoother operation. The CAT6 boards are capable of running up to 4 servos at one time and can carry the signal up to 100” without decreasing the overall performance of the servo. The chip on the receiving board boosts this square wave signal prior to sending it to the servos for jitter free operation.


Another use for flat snips

As hobbyists, we all have our favorite tools that tend to get used more than others in the toolbox. Some even get used for intentions other than what they were designed for. One of our common misused tools is the flat snips. These snips work just fine cutting wires, zip ties and other small items, however they also work well removing brass pinion gears from servos, and even tightening up ¼” diameter aluminum standoffs. Our brass servo pinion gears have a broached spline that is a very snug fit when going onto the servo. This does mean however that it’s a bit difficult to remove the servo pinion gear from the servo if needed. Using the flat snips, you can grab down in two valleys of the gear and wiggle the gear back and forth to remove it without damaging the gear or the servo. The tool can be used in a similar fashion to hold an aluminum standoff from spinning while tightening the screws. The jaws behind the cutting surface are smooth so that they will not mar the surface of the standoff.


Choosing the screw head type that best suits your project

Choosing a screw head type comes down to two key factors; space limitations, and driver type. Servo City screws either use a Philips or a hex driver. The hex system allows more torque to be applied to the screw without inward force. The risk of stripping the head is minimal when using the correct size driver. Philips heads on the other hand require inward force when applying and have some risk of stripping. When considering space requirements, the socket head screw has the smallest diameter followed by the pan head. If head clearance is limited, the flat head will create a flush surface, but the hole will need to be countersunk. If countersinking isn’t an option or isn’t required, the truss head has the lowest head height followed by the pan head.


Differences in servo gears

Servo gears come in various materials such as nylon, Karbonite, metal and titanium. Nylon gears are typically found in servos with relatively low torque output. Nylon wears well but cannot handle the abuse that other make-ups can. Karbonite gears wear even better than nylon and can withstand abuse better. Metal gears do not wear as well as the nylon or Karbonite gears but are less prone to stripping out when used in demanding applications. Titanium gears are found in the high end servos and have the best wear characteristics and are nearly indestructible.


Pre-tinning wires when soldering

When soldering on small components it is a good idea to pre-tin wires and connectors. Pre-tinning will reduce the amount of heat applied to the electrical component when making the connection, thus protecting the component from becoming too hot and becoming damaged. It also reduces the amount of solder required which makes for a cleaner and less bulky solder connection.


Igus Slider Kit

The Igus 1080-B 1 meter rail has been a very popular choice for photographers looking for a manual slider. Many of these users reached out to us in order to assist in motorizing their manual slider. Our recently released Igus Slider Kit makes attaching a motor to the Igus slider very simple. Having a motorized slider allows for smoother motion and is excellent for long exposure shots such as timelapse. The kit is compatible with any of our 3-12VDC or 6-12VDC precision gearmotors so that the user can select just the right motor speed for his or her application. Â Additional accessories for the slider kit include a limit switch kit in order to kill power at the end of the travel and a foot kit to stabilize the rail on uneven surfaces.


Attaching two or more components with a screw

When attaching two or more components together with a screw, make sure that only the last component is threaded. Threaded holes between multiple components are not indexed to one-another and therefore will not allow the parts to be tightened down against each other. If only the last component is threaded, the parts become sandwiched between the head of the screw and the last part (with the threads) for a proper fit. This practice can also be applied to our clamping hubs; we sometimes receive returns from customers claiming that the clamping hub is defective. In actuality, these customers had accidentally installed the pinch bolt through the tapped hole side first. No matter how tight the bolt is, the clamping hub won’t tighten down on the shaft/tube since the pinch bolt is just bottoming out and not pulling on the opposing side of the hub.


Choosing a battery connector style

As the R/C market has grown so has the selection of battery connectors. Tamiya connectors used to be the norm for R/C batteries and ESCs however as the market has progressed, higher amperage connectors became a necessity to handle the current demanding brushless motors. When choosing a connector style, be sure that the connector is capable of handling the amperage that your motor or electronic device can pull. Tamiya connectors are still a very common power connector and they work great for applications requiring less than 10A. For larger and more demanding applications a Deans (Ultra) connector would be a better fit. Deans connectors make a solid connection that is less restrictive and more tolerable to heavy amp loads.


Linear Actuators vs. Linear Servos

Although linear actuators and linear servos look similar from the outside, they operate much differently.
Linear Actuator: this linear drive mechanism has 5 wires coming out of the casing. The + and - from the motor, and the 3 potentiometer wires for potentiometer feedback. Most users simply tie into the motor wires and never use the potentiometer wires. By supply power to the motor wires, you can run the actuator out till it hits the limit switch. In order to reverse the direction, simply reverse polarity by swapping the red and the black wires which will allow the actuator to run back in till it hits the inboard limit switch. Whenever power is removed, the actuator will stop. The speed can be controlled by changing the voltage supplied to the actuator.
Linear Servo: this linear drive mechanism also has 5 wires. Three wires are intended for a servo controller that is able to transmit a PWM signal. The power wires require a constant 12VDC. The position, speed and direction can all be controlled by changing the PWM signal sent from the servo controller. The potentiometer is being utilized in order to read the position and allow the linear servo to correlate with the PWM signal. The internal BEC will automatically supply 5VDC to the servo controller so that everything can be powered from a single power source.


Using the correct screwdriver for the job

It’s common knowledge that each size of Allen head screw takes a different and very specific size of Allen driver. The wrong size driver will leave you with a stripped out screw and a major headache extracting it from an assembly. Phillips head screws also, believe it or not, call for a specific size of screwdriver. Screwdrivers are typically labeled on the handle and the size is determined by a pound sign followed by a number (#0, #1, #2, etc.). For most R/C and robotics projects, having a #1 and a #2 Phillips driver will suffice. For most head styles, the #1 driver will cover from 2-56 to 4-40 (M2 - M3 Metric) while the #2 will cover from 5-40 up to 10-32 (M3.5 - M5 Metric).


Using Actobotics Standoffs as Bearing Mounts

The Actobotics line has numerous parts that contain ball bearings which are essential to a rotating assembly. In many cases, the bearings are fixed to the main structure and support a shaft or a tube that is able to spin independently. In some builds, however, it is desirable to have the shaft fixed to the main structure and attach the bearings to the rotating assembly. The aluminum Actobotics standoffs can be used to create a fixed, non-rotating shaft that will support the bearings. These standoffs are unique in that the OD is just under ¼” so that a ¼” ID bearing can easily slide on. Each end of the standoff is tapped to 6-32 for ease of mounting.


Spur gears vs. Planetary Gears

ServoCity recently started carrying gearmotors with planetary gears which has generated some questions about the differences. The answer to most of these questions is strength. Planetary gear trains utilize multiple planet gears which rotate around a central sun gear so the torque is shared between these gears. Spur gears each have to bear the entire load individually. For real world applications this means there is less chance of breaking a gear, especially in cases when the motor may be pushed to stall or have unexpected forces applied.


Understanding Torque

Understanding torque is crucial when choosing a motor or a servo. Torque is calculated by multiplying Force x Distance. As you can see in the diagram, Force is a linear pull or push that is applied at a Distance from the center of rotation. For example, a motor that has 100 ounce inches (oz-in) of torque could apply a 100 oz linear force using a pulley with a radius of 1”. That same motor could apply a 50oz linear force using a pulley with a radius of 2”. This means that when selecting a motor for an application you must also consider how far from the center of the shaft the force is going to be applied.


Beef up your channel using Aluminum Standoffs

The Actobotics channel is very strong but there are times when the two sides need to be tied together in order to better support heavy loads. In the case of joining two channel pieces together perpendicularly, the channel that has an end cap becomes extremely strong since the two sides are connected. The channel that it is connected to is left without support between the two sides. There are several components that we offer that will make this connection (bearing mounts, hub mounts, end caps, etc.) but the most cost effective and easiest way to connect the sides is to use 1.32” aluminum standoffs. The 1.32” length is the exact inner dimension of the channel (1.5” outer dimension - .09” wall thickness on each side of the channel) and they are threaded to allow a 6-32 screw to pass through any .140” hole on the channel and into each end of the standoff. By tying the two sides of the channel together, the structure will be significantly stronger.


Gear Ratios

A gear ratio, in its simplest form, can be calculated by dividing the number of teeth on the large gear by the number of teeth on the small gear. For example if the large gear has 72 teeth and the small gear has 24 teeth, the gear ratio would be 3 to 1 or 3:1. This means that the small gear will have to rotate 3 times in order for the large gear to rotate once. In an under drive application, the small gear would be attached to the motor shaft (or driving shaft) and would cause the large gear on the driven shaft to rotate at exactly 1/3 of the speed of the motor. While this setup would cause the large gear to move 3 times slower, it would increase the torque at the large gear on the driven shaft by 3 times when compared to the motor shaft. If the 3:1 ratio was reversed so that the large gear is placed on the motor and the small gear on the driven shaft, this would be considered an overdrive setup. The driven shaft and small gear would then have 1/3 of the original torque but would move at 3 times the rate of the motor shaft.


Bevel Gears

Bevel gears are an efficient way to transmit power from one shaft to another shaft that is oriented off axis (typically 90 degrees) from the first shaft. The Actobotics line now offers 1:1 ratio straight cut bevel gears, commonly referred to as miter gears since they are the same tooth count that create a 1:1 ratio at a perfect 90 degree angle when paired together. A bevel gear setup is not only very efficient, but also extremely robust. These gears can be run inside the Actobotics channel to create a very clean and compact gearbox.


Understanding the Actobotics hole patterns

Actobotics Pattern1.50" pattern0.77 Pattern

The Actobotics line of components utilizes two different hub patterns. The smaller of the two hub patterns measures .770” center to center across the middle of the pattern. The .770” dimension has been chosen so that when a component is attached to the pattern with pan head or socket head screws, the ½” center bore is left unobstructed. This pattern is repeated down the entire length of the channel with a .750” spacing from one center hole to the next. While most screw holes in the channel measure .140” in diameter, the shared hole in-between the ½” center holes must be slightly oversized (.160”) to allow them to properly align. Both the .140” and the .160” holes work well with the common 6-32 fastener sized used throughout the Actobotics line. 

While the .770” pattern is excellent for the majority of construction projects, there are times when a larger pattern is advantageous. The 1.5” hub pattern is measured diagonally across the middle of the pattern. Just as the .770” pattern is repeated along the channel around each ½” center hole, so is the 1.5” hub pattern. One common application where the 1.5” pattern is used would be the Actobotics motor mounts. Many of the mounts utilize the 1.5” hub pattern to attach the motor to channel in order to increase side stability and spread the load out on the channel.

Since the 1.5” distance is the diagonal dimension (considered the hypotenuse if you create a triangle that passes diagonally through the center to opposite corners), each side dimension of this pattern is slightly shorter. The sides measure 1.0607”. Many of our mounts utilize this
1.0607” dimension derived from the 1.5” hub pattern. Components with the 1.0607” pattern can be mounted upright inside the channel or flat across the top of the channel.

The 1.5” pattern also leaves room for a large center bore through components such as clamping hubs, bearing mounts and adaptors. Our 1” clamping hubs utilize this pattern so that the 1” OD tubing can slide through the hub without obstructing the center bore for routing cables and wires.


Determining the proper spacing between two mating gears

We field a high number of tech questions that deal with how to determine the proper spacing between the teeth of two mating gears. This spacing is a preset distance on the Actobotics Channel at 1.5” to allow 2 gears with the sum of 96 teeth to mesh properly; but what if you’re working on a project that the spacing is not determined by a piece of channel or a frame with predetermined holes? The formula is:

(Spur + Pinion) / Pitch = N where 0.5N = the center to center distance

So let’s say we want to use a 108 tooth spur gear with a 48 tooth pinion gear to create a ratio of 2.25:1 (figured by dividing the big gear by the small gear). Both gears need to be the same pitch; for this example we’ll use 32 pitch gears.

(108+48)/32 =4.875 which is equal to N so half of that number (2.4375”) would be the ideal center to center distance between the 108 tooth spur gear and the 48 tooth pinion gear.

The same formula can be used if you have a preset center to center distance and wish to find the number of teeth that would properly fit in the space provided. Using the number we found above:

2.4375*2 = N, therefore N = 4.875”
4.875 x 32 = 156

This means that the sum of the 2 (32 pitch) gears must equal 156 to fit within the preset center to center distance of 2.4375”. You can then adjust the ratio as needed by adding teeth to one gear and subtracting from the other.

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