MotoGP: WHAT DUCATI KEEPS IN ITS 'SALAD BOX'
With the terminology it might be joked it just contains some leaves of cavolo nero (foodie reference). But by shifting the exhaust tail pipe off-centre, it was clear that it wasn’t some simple add-on, but a key part of the bike’s design. I wrote about the Salad Box last year, speculating on what it might contain, and it transpired I might have I got some of the points right.
The unit had remained a secret through out the 2017 season, only a winter testing crash gave us insight to the contents (http://www.crash.net/feature/888062/1/picture-inside-ducati-salad-box). Although the appearance of some electronic TV boxes inside the case prompted some to speculate the box was only ballast. There was something else below the electronics and this I believe is the real secret of the Salad Box..
I speculated last year it might be amongst other things a Tuned Mass Damper (TMD) or an Inerter, my understanding now is that it’s a hybrid of both. Further talk with some suspension experts in the field of Inerters & TMDs, further reinforce that this is the case. Especially as one contact had already proposed such a solution some time ago to both Ducati and Luigi Dall'Igna (before he joined Ducati).
This hybrid Inerter/TMD makes use of both damping solutions, one enabling the other and allowing for its remote mounting in the tail, as opposed to being a direct node on the mechanical suspension set up. Inside the case from the Crash.net picture we can see a silver casing with a long slot and what appears to be a spindle running in the slot.
My view of the set up is that the hybrid device works as follows. It’s based around a rack and pinion set up, the TMD is formed of weights attached to the rack, this slides back and forth, by the undamped accelerations induced into the bike by the movement of the suspension. The rack movement being controlled and re-centered by springs. Alone this TMD would help damp the accelerations put into the bike's frame.
But the Ducati solution goes a step further, by the toothed rack of the TMD spinning a mass mounted centrally on bearings in the casing. This clearly mimics the inerter used in F1 and other categories to control accelerations in the suspension system. However, these racecar systems use an inerter directly coupled to the suspension. Ducati’s interpretation uses the TMD to spin the mass, hence the hybrid solution.
As the Ducati Salad Box is a Hybrid device, I suspect this is a direct solution to manage chatter. Chatter is a resonant effect passing through the tyre, suspension and into the sprung mass of the bike frame. It’s created as the sprung effect of the tyre is out of phase with the sprung effect of the forks. Springs and conventional damping can only control some of this effect, having an Inerter\TMD allows Ducati to tune out specific accelerations in the suspension movement. Its likely the hybrid device can be tuned with different sliding masses, spinning masses and helper springs, to obtain the best anti-chatter set up for a specific tyre and track.
It’s entirely possible that other teams could adopt a hybrid Inerter/TMD (or its individual elements) on their MotoGP bikes, it needn’t be of the same design as the Salad Box, it could be mounted elsewhere, it could be directly mounted to the suspension (as I speculated last year). As yet, I’ve not seen anything to suggest, but we can keep an eye on the development of bike’s chassis this years.