挑选舵机¶
鉴于需要考虑的选项众多，挑选 舵机 起初可能会令人望而生畏。本指南旨在为比较不同的舵机选项提供一个起点，并在最后提供一些精选建议。
重要
在选择舵机时，牢记特定供应商的可靠性非常重要。亚马逊和其他类似网站上的制造商和经销商通常会明显夸大其舵机规格，或选择不切实际的最佳情况来衡量规格。我们的推荐仅限于那些在发布准确伺服规格方面历来可靠的供应商。
根据经验，知名制造商（Hitec、Savox、ServoCity、goBILDA、AndyMark 等）通常会公布准确的数字，而对于来自市场（亚马逊、AliExpress、业余爱好商店等）的舵机则应持怀疑态度。
舵机类型：常规或连续旋转式¶
舵机 舵机可以根据 PWM 输入信号旋转到给定位置的舵机称为 常规舵机 。此外，还有 连续旋转舵机 ，它们实际上只是 舵机 舵机外形尺寸的小型电机。它们没有位置控制，而是使用 PWM 信号来控制转速。
小技巧
连续旋转舵机甚至并不总是采用传统的舵机外形。从规则和控制系统的角度来看， Melonbotics Super Servo Plus 虽然被视为连续旋转伺服器，但其本质上是一个小型电机 + 正齿轮箱。 1000rpm 的额定输出速度使其成为大型、重型标准电机的绝佳替代品，适用于小型、高速机构，例如 active intakes 。
FTC® 供应商的许多舵机都是双模式的，这意味着它们可以在连续模式和常规模式之间切换（通常需要使用单独出售的舵机编程器）。这些舵机既可用作连续旋转舵机，也可用作常规舵机。
舵机扭矩和速度¶
舵机 输出功率以速度和扭矩来衡量。速度（通常以秒/60度为单位）是指在标准旋转模式下， 舵机 转动 60° 的速度。
为什么是每 60 度几秒钟？
从历史上看，FTC 中常用的舵机是为 RC（无线电遥控）汽车设置的。这些汽车的转向连杆的最大侧向行程通常为 60 度，因此制造商通常会用 60 度的秒数来宣传他们的舵机。
扭矩（通常以 oz-in 或 kg-cm 为单位）是指 舵机 可以施加到杠杆上的力的大小。作为参考，如果在舵机上安装一根 1 英寸的杆，然后在杆端安装测力计，就能测出舵机的额定扭矩（单位为 oz-in）。
您可能知道，速度和扭矩通常呈反比关系。你可以找到一些动力强大的舵机，但速度却很慢（慢于 0.20 s/60°) ，或者一些动力较弱的舵机，但有较快的转速（快于 0.12 s/60° 的都被认为是快）。
为您的应用找到合适的 舵机 可能很难，但一个好方法是尝试决定您是否需要更高的速度或扭矩，以及您的 舵机 是否会承受冲击负荷。
耐用性和舵机齿轮材料¶
威胁 舵机 寿命的两件事是内部电机烧毁和更常见的 齿轮 在 舵机 内部剥离。电机烧毁的情况并不常见，但在长时间大负载的情况下也会发生。
小心
永远不要将舵机安装在不动的模块上。
当驱动部件所需的扭矩超过 term:舵机 <Servo> 最大扭矩时，就会出现齿轮剥离问题。这种情况主要有两种。
外力产生的冲击载荷会剥离 齿轮 。例如，部件撞上场地墙壁或其他机器人。
太重的物体在反转时产生的冲击负荷会使 齿轮 脱落。扭矩随质量和与旋转中心的距离而增加。如果被驱动的部件远离 舵机 ，则杠杆臂长意味着扭矩大。此外，如果部件在移动，反转方向也需要更大的扭矩。因此，原则是部件要轻，不要突然反向，以延长 舵机 的使用寿命。
抗冲击负荷能力直接受到 齿轮 所用材料的影响。材料范围从塑料到钛，让我们从最弱的开始往下看。
**塑料**（通常为尼龙）：对于低功率 舵机 ，如果确保它们不会受到冲击负荷，则可以使用。一般用于模型飞机，如副翼。FTC 应用包括不会直接接触任何游戏元素或场地的轻负载机构。例如，用于打开活板门或移动机器人内游戏元素的舵机。
碳钢 ：Hitec 的 gear 塑料比尼龙更耐用，随着时间的推移磨损更少，但在 FTC 中的冲击负荷下仍很容易剥落。
Brass: Brass gears are stronger than plastic, but also suffer greatly when faced with shock loads in FTC such as intake wrists and deposit buckets. Brass gears are found on slightly higher end servos such as the original REV Smart Robot Servo.
Steel: This is where we start getting big. Steel gears are very durable and you’ll have a tough time stripping these. The goBILDA Proton servos, goBILDA Dual Mode servos, REV V2 Smart Robot Servos, and Axon servos are all examples of steel gear servo.
Titanium: Titanium is where you get into really high end servos. Starting from $75, they can reach over $150. A common misconception is that titanium is stronger than steel, however its advantage is in strength to weight ratio (as in, titanium gearboxes will often be lighter than steel gearboxes).
Servos with weaker materials (e.g. plastic and brass) used for their gears will often strip quite easily. Servos with steel gears are significantly harder to strip; some teams have even reported stripping the aluminum hubs attached to their servos while the servos themselves survived with no damage.
舵机尺寸¶
Servos come in different sizes. Fortunately, almost all manufacturers use the same standard set of servo sizes, ranging from sub-micro to large. The size most commonly used in FTC is the standard size (which includes REV Smart Robot Servos and goBILDA Dual Mode Servos) servos. Micro size (which includes the Axon Micro) servos can be useful when a particularly small mechanism is needed, though they usually are significantly less durable than standard size servos. Large size (also known as quarter-scale) servos are quite uncommon in FTC.
Note that while it is easy to assume the larger the size, the more powerful the servo, it is often not the case. You can buy very powerful standard size servos - just expect to pay more for them.
舵机花键轴¶
The output shaft of the servo is commonly called the spline. Most servos have industry standard 25 tooth spline (also known as F3); in particular, this is the spline used by REV Smart Servo and goBILDA Dual Mode servos. Hitec servos using 24 tooth spline were historically also very popular, but are much less common today.
AndyMark servos are an exception to this, as they use a 5mm hex shaft as their output instead of a 24 or 25 tooth servo spline.
有关舵机花键的更多信息，请访问 https://www.servocity.com/servo-spline-info/ 。
舵机范围¶
非连续式 舵机 在保持位置反馈的同时可以旋转的角度称为量程。在选择舵机时，必须确保有足够的量程来满足运动需求。
By default, the FTC control system outputs 600-2400 microsecond signals. However, this range can be expanded to 500-2500 microseconds. When choosing a servo, it is important to make sure that its range will be usable for your application inside of 500-2500 microseconds.
备注
The default 600-2400 range of the FTC control system when selecting the “Servo” configuration limits the range of many servos to less than the advertised range. Make sure you select the “Full Range Servo” configuration instead to get the full 500-2500 range.
费用¶
舵机 范围从廉价的 7 美元 舵机 轻型应用，一直到一些近 200 美元的 Hitec 或 Savox 舵机 。
By far the best bang for your buck servos out there are going to be the goBILDA Dual Mode Servos and REV V2 Smart Robot Servos. In addition, the goBILDA Proton servos are an excellent value for low-load mechanisms when you do not need more than 180 degrees of rotation or continuous rotation.
Axon Robotics offers brushless, highly-programmable, steel-geared servos in the $90 price range. These servos are designed specifically for FTC, and are extremely popular among teams wishing to maximize their robot’s capabilities and performance.
推荐的舵机¶
备注
We do not recommend very low-priced servos. Due to their low strength, they end up requiring multiple replacements over time, negating any cost benefits.
goBILDA Servos: goBILDA offers a wide variety of servos suited excellently for FTC.
goBILDA Dual Mode Servos are very good price to performance/capability servos. They are dual mode, meaning you can program them to either standard or continuous rotation using a goBILDA servo programmer or REV servo programmer. In standard mode, they are rated for up to 300 degrees of range. They come in three gear ratio options: Torque, Speed, and Super Speed. They are rated for a reasonably high total mechanical output power (around 2.7W for the Torque and Speed, and around 3.2W for the Super Speed), and have steel gearboxes.
goBILDA 5 Turn Servos are 5 turn variants of their standard Dual Mode servos, which can rotate 5 turns while still tracking position. These servos have high range, making them ideal for use with external gearboxes, but are more expensive and have a lower precision than the normal variants.
goBILDA Proton Servos are goBILDA’s budget servos, coming it at approximately half the price of the standard Dual Mode servos. They come in two gear ratio options, Torque and Speed. Unlike the Dual Mode servos, these are not programmable, and therefore can not be used as continuous rotation servos. While their total mechanical power output of approximately 0.7W is a fair bit less than the Dual Mode servos, and they only have a 180 degree rotation range, their low price makes them a decent option for low-load mechanisms, and their steel gearboxes greatly reduce the chances of breaking the servos from accidental shock loads compared to other brands’ budget servos.
REV Robotics V2 Smart Robot Servos: These are similar to the goBILDA Dual Mode servos in price, performance, and capability. They are also dual mode, meaning you can program them to either standard or continuous rotation using a goBILDA servo programmer or REV servo programmer. In standard mode, they are rated for up to 270 degrees of range. They come in two gear ratio options, Balanced and UltraSpeed. The UltraSpeed is rated for a relatively high total mechanical output power of approximately 3.5W, and the Balanced is rated for a somewhat lower output of approximately 2.5W. They have steel gearboxes.
Melonbotics Super Servo Plus: This servo is different from the other servos listed here. While considered a continuous rotation servos from a rules and control system perspective, it is essentially a small motor + spur gearbox. The 1000rpm rated output speed makes it an excellent alternative to large, heavy standard motors for small, high-speed mechanisms such as active intakes.
Axon MAX MK2: This is widely considered to be the best high performance servo for FTC. It has uses heat-treated stainless steel gears for top-notch reliability, and has a very high rated total mechanical power output of 7.5W (only 0.5W below the 8W limit defined in the Competition Manual). The servo features an analog output wire, allowing you to read the absolute position of the servo. The Axon MK2 servos are also highly programmable with the Programmer MK2, featuring a wide range of adjustable parameters and modes (including standard and continuous rotation modes).
小技巧
Being able to read the absolute position of the servo can have significant benefits when programming your robot. For example, you can tell the servo to go to a position, wait for it to reach that position, then do the next action; as opposed to telling the servo to go to a position, waiting a set amount of time (which may be longer or shorter than the time actually needed), then doing the next action.
重要
The Axon MINI MK2 is very similar to the MAX in terms of total output power (though geared at a slightly faster speed/lower torque), and has the same features (including the heat treated stainless steel gears, programmability, and analog output wire). However, this servo is a slightly different form factor to the standard form factor used by the other servos on this list. While the height is shorter than the MAX, it is slightly wider, and the servo horn is in a different position compared to the standard servo size. Due to this, we don’t recommend the MINI for anything other than fully custom-designed mechanisms not relying on standard mounts and horn position.