Learnings

Outcomes

Frame Testing Results and Observations

The frame was able to be assembled in ~10 mins and took a further ~15 mins to set up on the hole and situate the mole (these times are adjusted for the time taken to explain the function of the mole). The end users quickly understood the functions of the controls on the frame and we able to operate the frame without direction for the majority of the trail.

The sighting pole was straight forward to place on the mole and use, however, as the frame was not initially level (near horizontal) the central body of the frame stopped the sighting pole from being able to be positioned vertical. This was resolved by levelling the frame with the adjustable height legs. It should be noted that the site chosen was fairly steeply banking and the launch direction was across and up the slope.

The weight of the frame was noted by the operators to feel lighter than the existing launch frame and easy to handle.

Once the frame was in the hole, the intended yaw (side to side) adjustment of moving the frame was hard to achieve due to the amount the uprights needed to be pushed into the soft dirt at the bottom of the hole. Despite this the mole was able to be aligned by manipulating the frame on the surface and repositioning the frame legs.

The friction when sliding the mole holders due to offset attachment on the uprights was prevalent and both pulling and pushing of the lifting arms was required to get the mole to the right attitude. One action pushing very hard on one of the arms caused it to buckle and it became bent.

When the mole was activated, the oscillation of the mole caused the spikes at the bottom of the vertical legs to elongate the holes they made in the soft earth at the bottom of the hole. This absorbed the force and motion from the mole which meant the mole did not move forwards.

After the initial launch attempt, the vertical supports and spikes were hammered further into the soil by ~100mm to offer added resistance to oscillation. The frame was also lowered on its legs and a number of the excavation brace pins were engaged at the edges of the hole. This further restricted the ability to adjust the side to side alignment of the mole but was done to test the frame with higher traction at the base of the hole. The additional resistance did allow the mole to move forwards as intended, however, the mole progressed passed the rear mount before it had fully embedded itself into the front wall and at this point the mole did not continue to progress forwards.

In a further launch attempt, the frame was moved forwards in the hole such that the mole would be embedded in the front wall when the rear clamp was passed. In this case, despite embedding the vertical posts in the earth at base of the hole once more, the action of the mole again overcame the resistance offered. A launch forward into the earth was again not achieved. 

In a final set of launch attempts the cross brace was added to stiffen the frame, this was successful in stiffening the uprights but also allowed the force from the mole to propagate through the frame and cause it to move above the ground. The mole did not launch successfully.

This testing showed that the design which suspends the mole from above the ground would require significantly more bracing at the base of the hole than was anticipated with the shallow ‘spike’ design that was incorporated in the prototype.  It was noted that the particularly soft ground conditions and the upwards slope launch attitude were challenging but not atypical of where a mole may be deployed.

Possible Frame Modifications 

Built in spirit level
While initially setting up the frame it only became apparent about the importance of the frame being level or near level for the sighting tool to be used correctly. The frame had to be re-levelled before sighting.

A spirit level on top of the frame would allow the frame to be levelled more accurately on the first installation.

Lower level bracing which does not rely on particular ground conditions
During the attempted launch of the mole during the field test it was apparent that the contact points between the uprights and the ground were not sufficient in soft ground to resist the oscillation of the mole. This led to the fixing points at the top of the uprights acting like a pivot. 

A second clamping point below the main frame or bushing would help stiffen up this joint between the upright and the frame. 

Although we believe a stiffer connection would be an improvement, we believe that if the mole support arms would also require to be more substantially braced at the bottom of the excavation. In not we think the mole motion will simply propagate through the frame, and back to the frame legs to the ground. 

Alternatively, some expanding sideways clamping arrangement could be used introduced in the plane of the mole. This would remove the need for an additional fixing point above ground so would be better to incorporate this into a revised approach. This approach would need a further mole alignment arrangement after clamping to ensure correct launch direction. 

The bracing arrangement would need to work for a range of excavation widths and ground types and conditions.

Lower bracing with spikes
The current prototype utilised shallow spikes to contact the ground.  Removing the need for large spikes and anchors was a conscious design decision in discussion with WWU to minimise the risk of hitting pipes/cables below the hole.

Spikes could be used at the bottom of the hole to offer the required resistance to motion from the mole. As these are predicated to be ~300mm. This would incur the above risks.

Stiffen up the lifting arms

Improve the lifting arm arrangement to work for both pulling and pushing and remove the offset load. This would for allow easier attitude adjustment.

Removal of separate Attitude Controls
If the design is progressed the suspended solution, then the attitude adjustment could be removed from the current design. This would simplify the design of the frame allowing attitude control to be carried out directly from mounting the mole into the uprights.

Alignment adjustment in the rear mole mount
During the alignment of the mole, it was commented on by an operator that a system which could change the direction of the mole independently of the frame would be valuable. e.g. have a fixed but pivoting front mole support, and then be able to move the rear to get the alignment (up, down and side to side) and then be able to lock this off prior to a mole launch.

An alignment and locking mechanism would need to be incorporated between the bracing.

Change to fixing of the frame to the inside of the hole
The current round bracing pins on the frame used to constrain the top of the frame into the excavation hole could be changed to textured plates to grip onto both soft dirt and hard surfaces.

Improve available configurations 
The field trial highlighted the utility of an intermediate configuration where the uprights are installed, and the legs are folded saving deployment time. It was noted that compact storage in the van is less important than overall weight.

Project Conclusions

Over the duration of the project the importance of convenience for the end user has been a key factor in the design of the frame. The trial day highlighted the importance of the ease and speed of use along with the ability to carry the equipment on the ‘payload weight constrained’ vehicles is absolutely crucial for the operators.

The outcome of the testing highlighted success in moving the user interface above the hole and showed the potential for a folded frame design to cover a range of hole sizes while packing down for storage. 

The testing also captured areas of the frame which would need further development. The trial, using the largest and most powerful 55mm diameter mole, highlighted the importance of being able to react the mole as close to it as possible i.e. ‘in-plane’. The load path and contact points of the prototype frame were not sufficient to brace the mole action and facilitate a mole launch, in what is noted to be typical ground conditions.

The potential modifications listed above may address the current design solution and how to further the effectiveness of a frame which sits out of the excavation and ‘out of plane’ to the mole. 

A key area to address is a much stronger connection of the frame near the mole and at the base of the hole.

It is suggested that the concepts generated early in the project are revisited using the knowledge gained from the prototype test day, to decide which course of action to take next in developing an improved mole launch frame.

The TRL of the project moved from 4 - 7

Lessons Learnt

The proposed ‘in person’ demonstration of the moling operation at the outset of the project, which was not able to happen due to COVID restrictions, may have proved valuable in setting the direction of the design work.  If it was able to be carried out early in the project (as originally conceived) better understanding of the moling action may have been identified and some issues could have been addressed better in the design process and direction of the final chosen concept to the eventual solution for which a prototype was produced.

A number of the modifications i.e. better bracing close to the mole, would require additional features or mechanisms to align the mole after bracing at the bottom of the excavation. It is noted that a stronger connection at the base of the hole may negate a number of the features that were included in the prototype design intent. The additional complexity and redundancy of other features on the prototype should be carefully considered in future work.

It is suggested that the concepts generated early in the project are revisited using the knowledge gained from the prototype test day, to decide which course of action to take next in developing an improved mole launch frame.