Will the light or heavy weight of an electric wheelchair increase the risk of backing up when going up or down slopes?
Recently, a customer asked: If the electric wheelchair is light, will it tip over when going up and down slopes ? If someone answers, we can teach him. The answer is: no . If it can tip over due to its light weight, then the bus will definitely not tip over, and the bicycle should not be able to go up the incline, right? In fact, the reason for the overturn is actually the focus, user attitude and knowledge!
In terms of physics:
When going up and down an incline, the force applied to the wheelchair can be divided into two forces, one is the force of gravity (F weight), and the other is the force exerted by the user's control (F applied). The force of gravity can be divided into the force acting on the plane (F ground) and the force acting on the inclined plane (F downhill) . Ignore the friction force for the time being, because when the wheelchair reverses, the front wheel will be the turning point, the friction force is on the same line as the wheel, and there will be no force distance to prevent the vehicle from overturning .
Take the falling slope as the verification situation, because the user's acceleration force and the falling slope force are in the same direction. When going up an incline, the user's upward acceleration force offsets the falling force, which explains why there is less chance of the vehicle overturning when going up an incline.
Mechanical diagram when falling:
We mentioned force moment (Moment / or Torque) above. To make things rotate, what we need is force moment . For a wheelchair to roll over, we need a positive force distance.
Moment is: the force is applied at a point, multiplied by the distance between the force point and the turning point. For example: when we open and close the door, the force is on the handle, and the turning point is the door hinge. This force distance helps to open and close the door; on the contrary, if the force we apply is near the door hinge, it will be difficult to open and close the door, because the points and points The distance is small and the force distance is small.
By the way, the closer the center of gravity of the wheelchair is to the ground, the less force it will have to overturn toward the ground.
Okay, let’s draw pictures, count, and analyze:
The wheelbase length of the wheelchair is L and the height is H. The center of gravity is generally located in the middle, about H/2, L/2.
If you want to roll over, the force distance M1 must be larger than M2
M1 = ( ma + mg sin( θ ) ) * H / 2
M2 = ( mg cos( θ ) ) * L / 2
M1 > M2 is ( ma + mg sin( θ ) ) * H / 2 > ( mg cos( θ ) ) * L / 2
That is, the system a * H + g sin(θ) * H > (g cos(θ) ) * L
That is, the system a > g (cos(θ) ) * L / H - sin(θ) )
Conclusion: The electric wheelchair overturning on a slope is not directly related to the weight (because the weight m has been offset)
And also get the following results
- The greater the speed applied by the user, the easier it is to roll over (the larger a, the larger the rollover force distance)
- The higher the angle, the less force the user exerts to overturn the vehicle (the larger θ and the smaller a are, the force distance for anti-overturning can be exceeded)
- The shorter the length of the wheelchair or the higher the body, the easier it is to roll over (the smaller the L/H coefficient, the easier it is to roll over)
To prevent rollovers, we can:
- Learn to use your electric wheelchair correctly
- Know how to choose a safe path to walk on
- Choose a safe and truly internationally recognized electric wheelchair. The center of gravity of the wheelchair should be in the middle or rear to reduce the chance of rollover.
Now that you understand the causes of rollover, you also need to know how to prevent it and use it correctly:
First of all, according to the Hong Kong government's barrier-free facilities (BFA) requirements, the general ramp ratio is 1:12, that is, 1cm high requires 12cm long, which is about 5°. A certified electric wheelchair or wheelchair can climb over. When we need to go up or down an incline, we should try to choose a path that is wide enough, straight, and has no hidden inclines or turns.
When going uphill:
- When going up an incline, first check whether there are any obstacles on the road. It is best to choose a straight path.
- You will feel the wheelchair tilt backwards, and you can balance it by leaning forward. Try to avoid having a backpack or other load on the back of your wheelchair as this will make you more prone to leaning backwards.
- Drive the wheelchair slowly to maintain control.
When going uphill, keep your body forward
- First check whether there are any obstacles on the road. It is best to choose a straight path and check whether there are obstacles on the slope.
- Drive slowly to maintain control.
- Inclines can be very steep and this can be compensated for by changing the body's center of gravity and leaning forward.
When going downhill, lean forward, wrap one arm around the handlebars, and lean back against the back of your wheelchair to help you maintain balance while going downhill.
Try to avoid the following paths
V-shaped upward oblique position:
There is a V-shaped edge at the bottom of the ramp. The ramp and groove will form a rapidly changing slope. The anti-reverse wheel will get stuck and it will be difficult to go up the slope.
V-shaped inclined exit position:
There is a V-shaped edge at the bottom of the ramp. If the pedal is adjusted to a lower position, it will be hit. It will also easily concentrate the force of the fall on one of the wheels, causing the user to feel a shock. When the descent is about to be completed, slow down the vehicle and ensure that both wheels in front leave the slope at the same time.
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