The original purpose of YardBot, beyond career education, was to have something that will either plow the driveway for me or allow me to do it with a simple remote control. With much of the robot chassis in a stable design state, I thought I’d turn my attention to the snowplow attached to the front and describe the process I took, along with the current revision.
Engineering is basically imagination with constraints and this element is no different. Whatever final design is made, it has to fit within these properties:
- Raise and lower in 2″ travel with this 150lb force 12V linear actuator
- Plow with this 36″ wide plastic snow shovel
- Fit to the front of YardBot in a semi-standard configuration
- Move from below the wheel plane up to some maximum height
- Yaw side to side in order to push snow like a conventional plow
In the top photo you can see where my design started from. The wheels have gotten larger (I’m planning on using snowblower wheels that are approximately 16″ in diameter) and the chassis itself has a better proportion. The plow has a horizontal arm that attaches to the chassis with a clevis pin and is allowed to rotate up and down. I’ve continued to use this design in subsequent versions but the main difference is that the tab on the top surface is no longer used. This panel is thinner 1/8″ aluminum sheet and it doesn’t have the strength of the 3/8″ plate used elsewhere.
A problem in these designs is the mechanism that translates 2″ of travel in the actuator into a larger change of the plow. Here I’m using a vertical tab on the shovel arm to make the actuator have a clear motion. It’s not a clean stroke and is very restrictive.
The result of the extra complexity is that the 2″ of actuator travel is converted to 5.5″ of shovel lift. The shovel arm was made wider, to 2.5″, in order to accommodate the actuator vertically. Each pin is a custom shaft with a hole for a removable cotter pin. Both actuator pins use shaft spacers to keep the actuator centred between the vertical links. In terms of manufacturing, the most difficult piece would be the shovel arm but even that can largely be done on a 3 axis machine. The rest are reasonably simple and can be routed from a single plate.
The second actuator is used to yaw the shovel left and right. It’s the same 2″ stroke unit as the lifter and can move the shovel up to 11° in either direction. Should more articulation be required, the actuator can be switched to one with a 4″ stroke and moved back along the shovel arm.
It’s been cool to see an actual practical tool get added to YardBot and it looks like it would work nicely. I don’t anticipate any material issues, as the actuator power isn’t all that high but I’ll still be going through some finite element analysis testing to validate my design.