A slipper clutch is a mechanical assembly that transfers excess energy in to heat. The heat created is from friction between clutch pads and a clutch hub. Slipper clutches are not found on all RC cars. In fact almost all RC on road cars will not have one. Common types of RC cars to find these on include Rock Crawlers, Off road buggies, monster trucks and a few more. Correctly tuning your clutch for the conditions that you run in is important for the longevity of the clutch.
How Does the Slipper Clutch Work
A slipper style clutch is typically placed on the spur gear that meshes with the pinion gear found on the motor. It utilizes what are known as slipper pads to act as braking material for the clutch. These pads are forced under pressure by an adjustable nut and spring to maintain pressure against the slipper hub. The slipper hub would serve the same purpose that a disc/rotor would on a brake assembly. The slipper hub is typically locked on to either the spur gear or the shaft on the input side of the transmission. In the image above, it is located on the far right hand side. The clutch pads on the clutch above, are mounted directly to the spur gear. It is these few parts that allow the slipper clutch to function.
The clutch is loaded with torque from the motors pinion gear. The spur gear is forced to rotate with the slipper hub. If the torque is too large for the setting of the slipper clutch, the clutch will begin to slip. The slippage occurs between the slipper hub and the slipper pads. Over time, the slipper pads eventually will wear out requiring replacement.
The Goal of the Slipper Clutch
The goal of the slipper is as mentioned above, to turn mechanical energy in to heat energy. It would not be beneficial to turn all energy in to heat energy, however only when there is a “shocking” amount. Yep, I just did that. Any type of driveline shock can be damaging to the weakest link within the driveline. The slipper clutch is put in place to help dampen these shocks. Imagine sending your RC off of a large jump. Then you need to hit the throttle to rotate the car around to land flat. But as you are on the throttle the wheels touch the ground and load the entire driveline. It is this exact scenario or similar that leads to a spike in driveline load. All the inertia built up in rotating the wheels now comes to a halt when the tires hook up on the ground. If the RC that was jumped used a slipper, the clutch could slip at this exact time and save the rest of the driveline from any spikes in torque.
How to Detect Slippage
When the slipper clutch is slipping, it makes a higher pitched whining noise. It is this noise that can help you to determine if your slipper clutch is set correctly.
A slipper clutch that is set too tight will never function as intended and allow all forms of energy to be absorbed by the driveline. Too much driveline shock can be damaging leading to failures.
If the slipper clutch is set too loose, excessive amounts of heat can damage the slipper quickly leading to burnout.
Tuning the Slipper Clutch
Tuning your slipper is actually quite easy. To get started review the manual for your specific RC car. In your manual the manufacture will provide the procedure to set your clutch to the factory recommended settings. If your clutch is too loose and causing excessive slippage, tighten the slipper in steps of 1/8 turn. If your slipper is not slipping at all, loosen your clutch in steps of 1/8th of a turn at a time.
Conditions that may require adjustment
Running your RC car in extremely loose surfaces will require a more loose slipper setting. Opposite to this, running your RC in extremely grippy surfaces will require a tighter slipper setting.
Using your RC in an environment that causes the drive train to load up will result in requiring a tighter slipper tune. The perfect example here is if you are trying to crawl up a rock fairly slowly. The driveline can spike load if a tire were to get wedged stuck on something.
Upgrading your power system to provide more output power will require a tighter clutch setting where the opposite is true for having less power.
Note that it can be more problematic for your clutch when it is excessively slipping. Excessive slippage can cause the clutch to overheat and fail prematurely.