The SmartDrive MX2+ power assist unit is designed to help people who use manual wheelchairs. The Smart Drive is a portable, battery powered accessory that attaches to manual chairs. Permobil - the manufacturer of this product - specifies this power assist device as follows.
The MX2+ Smart Drive is made for people who weigh no more than 250 pounds, and who use a manually propelled wheelchair. The drive's performance is automatically adjusted by control circuitry which infers the desired movement (similar; in principle, to some high-end vacuum cleaners). The drive motor power rating is 250 Watts (746 Watts is equivalent to one horsepower). The recipient wheelchair's rear wheel diameter must be one of the diameters listed among the order options (above). Additionally, the Smart Drive is compatible only with wheelchairs exhibiting:
Control options include both wired and wireless types. Among the wired options are what the manufacturer calls the "SwitchControl" (formerly called the thumb throttle) and the "Speed Control Dial" (available beginning Jun 15, 2022). One of these wired control options - whichever you choose - comes with the SmartDrive. Among the wireless, wristband control options are the "PushTracker E3" and the Apple Watch via a free app that controls the SmartDrive MX2+. The wireless options are sold separately. Regardless of which control option you select, using the SmartDrive requires manually using the wheelchair wheels/handrims to steer.
The new MX2+ model's performance is substantially more user-selectable than the older MX2 model which was introduced with only an "outdoor" mode, and the earlier MX1+ Smart Drive model which exhibited discreet "indoor" and "outdoor" modes. The PushTracker wristband controller has a 64 x 32 pixel OLED display which can show the number of thrusts (i.e., pushes) on the handrim and other data. There are three PushTracker strap sizes - the wrist circumference ranges being: small (4.5" - 6"), medium (6" - 7.25"), and large (7.25" - 9") or small (114mm - 152mm), medium (152mm - 184mm), and large (184mm - 229mm).
The MX2+ can be used with an optional free smart-phone app. Neither a smart-phone nor the associated app is required to operate the MX2+. At the time of this writing, the PushTracker app does; however, offer at least two features not inherent in the wristband-only (i.e., no app) scenario. The two app-specific features are the ability to view push, coast, and other usage history beyond the present day, and the ability to update the PushTracker wristband software via the app when Permobil provides software updates. The smart-phone app communicates with the wristband controller via the bluetooth radio frequency protocol.
To tell the MX2+ to "go" - press the button on - or tap - the wristband. To tell it to "stop" - tap the wristband against the wheelchair hand rim or other object. The Smart Drive MX2+'s drive battery is incorporated into the wheeled drive unit - it's like the former MX2 drive unit. The overall weight of the MX2+ is identical to the former MX2 model, being several pounds lighter than the no-longer-made MX1+ model.
When used with a folding wheelchair, the SmartDrive's optional adapter bar allows the MX2+ to be quickly disengaged from the chair by pulling back on the adapter bar's spring-loaded flanges.
Rigid and folding wheelchair frames can be used with the Smart Drive. Folding frames require the installation of an adapter bar to which the Smart Drive connects. The adapter bar is sized to match the clearance between the innermmost points of the wheelchair's rear wheel axles (note the "between rear axles" order option). The adapter bar can be shipped with the Smart Drive.
The manufacturer's warranty is two  years and does not cover the rollers. The older MX2 SmartDrive model can be upgraded to an MX2+ model as seen in the price options (above). Some options (e.g., the Speed Control Dial, PushTracker E3, etc.) will not work with SmartDrive models prior to the MX2+.