by slomobile » 19 Jul 2022, 17:52
This is a common problem across all wheelchair brands when stopping on a ramp, and is unavoidable to some extent.
Rolling backwards happens when the chair transitions from being held in position by motors to being held by brakes.
If you just keep moving the joystick near the center position rather than letting go, it will keep the motors on and prevent the parking brake from engaging. If you have typical programming settings(not aggressive acceleration), It doesn't matter much which direction you move the stick as long as it is constantly changing and near the center it wont move the chair much and just hold it in place.
Of course there are some times when you just have to let go of the stick. So just be prepared for that rollback followed by a sudden stop. And when starting again on the ramp, its common to roll backwards before the controller ramps up enough to start moving forward. Especially with typical low acceleration programming.
You can eliminate rolling back when starting on a hill by just pushing the joystick farther forward initially to ramp up current faster, then quickly lower the joystick to a more reasonable level to prevent popping a wheelie and going over backwards. Its a tricky, risky move, but possible with good hand control.
I can't really speak knowledgeably about how Burgerman's programming would change the way you need to handle the stick. I still haven't got my hands on an Rnet programmer. But I did just get a van w/ ramp, so I'm getting lots of practice trying not to tip over.
In a system like Lenny's where we have fine control over all aspects of programming, this rolling backwards could be tuned out if we provide a means for the controller to know when it is on a ramp. An accelerometer, or wheel encoders, along with a bit of code could keep the motor current flowing until just after the brakes engage, rather than before.