stabilisation of castor wheel
stabilisation of castor wheel
(OP)
Hello,
We have the following case. We have an electrical wheelchair with 2 driven wheels and 2 castor wheels. At the moment its maximum speed is 10 km/h. When we raise the speed, the castor wheels get out of balance and start to shake. We are looking for a solution to stabilize the castor wheels.
We are thinking about stabilizing it with a sort of rotational damping. We don't know if this already exists in simalar constructions. My question is if any one knows about this, if yes could you tell me where to find some more information about this.
The castor wheel is mounted in a bracket with a vertical shaft welded on. This shaft is mounted in 2 roller bearings.
Regards,
Sjoerd
We have the following case. We have an electrical wheelchair with 2 driven wheels and 2 castor wheels. At the moment its maximum speed is 10 km/h. When we raise the speed, the castor wheels get out of balance and start to shake. We are looking for a solution to stabilize the castor wheels.
We are thinking about stabilizing it with a sort of rotational damping. We don't know if this already exists in simalar constructions. My question is if any one knows about this, if yes could you tell me where to find some more information about this.
The castor wheel is mounted in a bracket with a vertical shaft welded on. This shaft is mounted in 2 roller bearings.
Regards,
Sjoerd
RE: stabilisation of castor wheel
Specifically you need to change the axis of rotation os that it is not vertical, and the intersection of the steering axis with the ground may need to be moved.
I think you will striggle to control it with a damper, although motorbikes sometimes do, using a little friction damper or a hydraulic unit. So check out motorcycle steering dampers.
Cheers
Greg Locock
RE: stabilisation of castor wheel
Am I right in thinking you control steering by changing the speeds of two separate drive motors (one for each driven wheel)?
I which case you need the other two wheels to caster fully through 360 degrees, which in turn requires the vertical steering axis.
Have you tried pneumatic tyres for the caster wheels? This might provide some damping on its own.
Most motorcycle friction dampers are linear units attached to brackets on the frame and front suspension legs, and are only suitable for a limited amount of steering.
It sounds like you want to try a fully rotary damper, with perhaps a rotating vane in a pot of grease or oil.
I have no idea if such a damper is commercially available, but it should be fairly easy to fabricate a prototype to see if it helps.
RE: stabilisation of castor wheel
Cheers
Greg Locock
RE: stabilisation of castor wheel
Norm
RE: stabilisation of castor wheel
Sjoerd
RE: stabilisation of castor wheel
How about changing those parameters?
Norm
RE: stabilisation of castor wheel
We may have found a supplier who could provide us with a rotary damper. We will also do some tests with changing trail.
Regards,
Sjoerd
RE: stabilisation of castor wheel
2: Castor assembly (front wheel) (see figure 2)
a. To minimise rolling resistance the castor stem should be perpendicular to the
ground. Also if the castor stem is not in an angle of 90 degrees with the ground
you will notice that the front part of the wheelchair will go up or down when
turning the wheelchair.
b. The castor fork is bent backwards. This bending provides how big the castor trail
will be (see figure 3). When castor shimmy appears the castor trail is not big
enough. The manoeuvrability of the wheelchair depends on the castor trail but it
is not possible to define an optimal position.
RE: stabilisation of castor wheel
In this case you don't, admittedly, but that statement is not true in the general case.
Cheers
Greg Locock