Tow with Confidence: The Roadmaster InvisiBrake Supplemental Braking System

In the world of automotive engineering, elegance is often found in solutions that are unseen. The challenge of safely decelerating a motorhome and its towed vehicle—a combined mass propelled by significant kinetic energy—is a formidable problem in physics. While the market offers various solutions, the Roadmaster 8700 InvisiBrake system warrants a deeper look, not as a product to be reviewed, but as a compelling case study in integrated, automated, and fail-safe system design. This analysis will deconstruct the InvisiBrake from a systems engineering perspective, examining the principles, trade-offs, and elegant logic embedded within its compact form.

The Foundational Problem: Overcoming Inertia and Thermal Load

Before dissecting the solution, we must precisely define the problem. Towing fundamentally alters a vehicle’s dynamics. A 4,000-pound towed vehicle adds its entire mass ($m$) to the system, drastically increasing the total kinetic energy ($E_k = \frac{1}{2}mv^2$) that the brakes must convert into heat to achieve a stop. Relying solely on the motorhome’s brakes is not only unsafe, leading to dramatically extended stopping distances as dictated by Newton’s Second Law ($F=ma$), but it also invites catastrophic failure through brake fade. This phenomenon occurs when brake components, saturated with heat from prolonged application, exceed their optimal operating temperature, causing a severe drop in the coefficient of friction. It is this unforgiving reality of physics and thermodynamics that makes supplemental braking systems a legal and practical necessity across North America.

System Architecture: A Four-Part Control Loop

The InvisiBrake is best understood not as a single component, but as a complete control system with four distinct stages: input, processing, output, and feedback. Its effectiveness lies in the robust simplicity of this architecture.

Input (Sensing): A Simple, Unambiguous Trigger
The system’s entire operation initiates from a single, reliable input: the 12-volt electrical signal sent to the motorhome’s brake lights. This design choice bypasses the complexities and potential inaccuracies of inertia-based sensors, which can trigger braking during bumps or dips in the road. By keying off the brake light circuit, the InvisiBrake ensures it acts only when the driver has intentionally applied the brakes, creating a direct and unambiguous command chain.

Processing (The Controller): An Embedded Logic Core
The signal is received by the controller, the brain of the operation. This unit is more than a simple switch; it’s an embedded system with state-monitoring capabilities and pre-programmed logic. It interprets the incoming signal, manages power distribution, and, most critically, executes the safety protocols that define the system’s character. Its logic dictates not only when to brake but also how long braking can be sustained, a crucial element we will explore later.

Output (Actuation): The Application of Pneumatic Force
Upon receiving the command, the controller activates an internal air compressor, generating approximately 80 psi of pneumatic pressure. This compressed air is directed to an air cylinder, a simple but powerful actuator. In accordance with Pascal’s Law, which states that pressure exerted on a confined fluid is transmitted undiminished, this air pressure is converted into a linear mechanical force. This force pulls a cable attached to the towed vehicle’s brake pedal, applying the brakes with a consistent and repeatable pressure. The choice of pneumatics over an electric motor-driven actuator is a key design decision, likely based on the high force, rapid response, and durability inherent in pneumatic systems.

Feedback (Monitoring): The Human-Machine Interface
Because the entire system is hidden from view, a reliable feedback loop to the driver is non-negotiable. The InvisiBrake employs a two-stage Human-Machine Interface (HMI). Stage one is a simple LED on the motorhome’s dashboard that illuminates with every brake application, providing quiet, constant confirmation of system operation. Stage two is an escalation: an audible alarm. This alarm is not a simple status indicator but a critical alert, triggered by specific logical conditions within the controller, designed to demand the driver’s immediate attention and intervention.

Core Logic and Embedded Safeguards: Engineering for Failure

A truly robust system is defined by how it behaves under adverse conditions. The InvisiBrake’s control logic incorporates several layers of protection that demonstrate a deep understanding of real-world towing challenges.

Thermal Overload Protection: The 15-Second Rule
The most sophisticated feature embedded in the controller’s logic is a defense against brake fade. On a long, steep downgrade, a driver might keep the brakes applied continuously. The InvisiBrake’s controller monitors the duration of brake application. If it detects an uninterrupted signal for approximately 15 seconds, it will override the input and momentarily release the brake actuator. This brief pause is engineered to interrupt the continuous heat build-up, allowing the brake components a critical moment to dissipate thermal energy, thereby preserving their effectiveness for the remainder of the descent. It is a proactive, intelligent safeguard against one of the greatest risks in towing.

Energy Management: A Net-Positive Power Architecture
A common ancillary problem in towing is parasitic battery drain in the towed vehicle. The InvisiBrake addresses this head-on. While the system itself has a minimal idle current draw of just 6 mA, its controller is designed to act as a battery maintainer. It draws power from the motorhome’s charging system and delivers up to 2 amps of trickle charge to the towed vehicle’s battery. This creates a net-positive power balance, ensuring that the braking system not only powers itself but also counteracts the battery drain from the vehicle’s own onboard electronics, effectively solving a critical user pain point through thoughtful system integration.

Catastrophic Failure Mitigation: The Breakaway Fail-Safe
In the unlikely but critical event of a physical separation of the tow vehicle, the system defaults to its most primitive and robust safety layer. A physical cable connects the motorhome to a pin in a breakaway switch on the towed vehicle. If the vehicles separate, this pin is pulled, closing a circuit that bypasses the controller’s logic entirely. It directly powers the air compressor, driving it to full pressure and locking the towed vehicle’s brakes. This purely mechanical trigger ensures that even in a total control system failure, the brakes will be applied as a last resort.

The Engineer’s Compromise: Integration at the Cost of Complexity

No engineering solution is without its trade-offs. The primary virtue of the InvisiBrake—its complete integration and invisibility—is inextricably linked to its greatest drawback: installation complexity. Unlike portable units, which can be placed and removed in minutes, the InvisiBrake requires invasive and time-consuming installation. This involves mounting the controller, routing air lines and electrical harnesses through the vehicle’s firewall, and precisely calibrating the actuator cable. This complexity is not a design flaw; it is the calculated price for achieving a “set-it-and-forget-it” system that becomes a permanent, seamless part of the vehicle. The decision to use this system is therefore a decision to prioritize long-term, automated convenience over short-term, flexible installation.

From a reliability standpoint, the system introduces potential failure points common to any complex assembly—the risk of pneumatic leaks, electrical connection corrosion, or component failure. The user reports of electrical faults or missing parts, while not universally representative, highlight the importance of manufacturing quality control and professional installation in mitigating these risks.

Conclusion: An Elegant, Albeit Demanding, Solution

The Roadmaster InvisiBrake stands as a powerful example of a well-conceived engineering system. It solves the fundamental physics problem of supplemental braking through a robust architecture of sensing, processing, and pneumatic actuation. More impressively, it demonstrates a holistic design philosophy by incorporating intelligent safeguards against thermal overload, managing the vehicle’s energy ecosystem, and providing clear, escalated feedback to the driver.

While its demanding installation process makes it a significant commitment, the system delivers on its promise of an automated, unseen guardian. It embodies a core principle of advanced engineering: the most complex systems are often those that create the simplest, most reliable user experience. For those willing to invest in its integration, the InvisiBrake offers not just a braking solution, but a thoughtfully engineered piece of mind for the open road.