Here are a few tips that has worked for me since I developed Ataxia and which might work for other people.
1) Mobility scooters take less co-ordination to control than powered chairs cos its simple lever that controls forwards or reverse. Most scooters have a speed control so you can set it at slow maximum speed and keep the lever held at full speed position without needing tiny movements of lever to go from slow to fast. .. you need more gross motor strength of arms though to turn tiller (as if steering a bike) especially on the larger heavy duty scooters.
2) Most powerchairs do have a speed control so you can also set it to a max slower speed and just hold the joystick in full position, You need less gross motor control to turn them but more fine motor control in general as joystick controls 8 directions rather than just 2.
3) You can also buy computer joysticks that work the same way and have speed control so you can control how fast the cursor moves across the screen. They also often have functions such as Drag lock which makes scrolling easier and reduces the need to both hold down a button and move joystick. trackball at same time.
4) Technology such as Headmouse and Eye Gaze maybe more difficult if you have head tremor or more involuntary movements in general. This is because the technology is continuously tracking your movements. You may find it difficult to keep the cursor steady enough for it to activate a link once you reached it.
5) Joysticks or trackballs that allow you to remove hand (or foot) off it once you have reached the point you want the cursor at may work better, some software can be set to dwellclick after a given time that is adjustable. You may prefer to have a separate switch to activate a click if you find the dwellclicker is activating too many things for you, as then have to be very careful where you 'rest' the cursor (it's not over a link or other clickable item)
6) sometimes placing a switch alongside a larger muscle such as thigh (works well for wheelchair users) maybe easier than using a switch that requires fingertips to activate it. You may find you can respond quicker and software that scans your screen item by item may be an option.
7) Positioning can really make a difference! Having items like mice (and mice alternatives) on a table infront where arms are outstretched can increase tremor. Instead try using bluetooth keyboard with keyguard on your lap or a mouse alternative with on screen keyboard, keeping arms tucked in and trunk supported by cushions (if in regular chair) or lateral supports (trunk pads) for wheelchair users can really make a difference for some people, to the amount of control you have over your arm movements. If you prefer arms on table (if can get chair right under) infront try placing a V support cushion under them so the V's run the length of your arms with joystick etc in the middle.
8) If you need to use a communciation aid (and are wheelchair user) it is easier to type with something on your lap and arms supported than having a device mounted vertically so you have to reach out with nothing under arm when you're trying to line hand up to hit the right key. I use the Trabasack tray, you can get them with hard top or soft velcro top. If you prefer to have device mounted, try angling it so its positioned over your knees as if on a tray, placing cushions under elbows may help you keep optimum position for accessing your device with hands. A stylus maybe helpful for those who find it easier to keep hand in a fist and hold something (or attach stylus via a splint)
Often the tremor or involuntary movements in Ataxia come from the fact your brain is trying to establish where your limbs are in space in relation to the rest of your body (proprioception) it creates them as a form of feedback for the brain. Making sure arms (and trunk) are supported will make it easier to sit still, reducing the amount of shake or jerky movements you will get trying to use your arms.
Hope you find these tips useful
Kati