A cardboard prototype sled with flexible frog feet!
Continuing on from last update, it took a while to brainstorm a new design for the feet. Eventually, we figured out that the outside toes have to be sturdy enough to push the leg, then the inside toes are the ones that can grip, then flex once the outside toes are no longer touching the ground.
This realization resulted in a few changes:
- The inside toes don’t need a bone in them, as it prohibits their flexibility
- The outside toes have to be angled properly so that the toes hit the ground at the same point as the end of the ankle
- The inside toes need a cut to increase their flexibility in the middle of the foot, exactly where we would want it in order to have more grip
With this in mind, it was time to design a new model for frog foot v4!
If you look closely enough to the above screenshots, you will notice that there are construction lines representing the important places mentioned in the list above. The cuts on the bottom foot were accomplished by revolving a rectangle (making it become a cylinder), cutting away from the existing shape, then adding a fillet to smooth it out.
Here is what the bone looked like:
The mould prints:
The 2nd piece of the mould didn’t print properly, however it was only missing the last couple layers so we used it anyway. It was trickier to get the cast out of the mould once it was set, because it was in all of the infill shapes.
After cleaning up the mould, here was the foot that emerged:
The cut on the back of the foot appears to be working as planned:
It was time to put the foot to the test, and it works!
With the addition of the ‘sled’ to the cardboard body, it was able to climb an obstacle that was greater than its body height!
See it in action: (also it survived the fall from the table)
We weren’t sure if there should be cuts on both sides of the foot. It wouldn’t hurt to try, and also make a few quick fixes. These fixes included: removing the fillet from the top of the foot bone, extending the length of the middle toes a little bit further (only a few mm).
After printing out the new mould, foot bone, and adding a new “special” ingredient, here is frog foot v4.5!
Apart from the green food colouring, another aspect that was different from v4 to v4.5, was that for v4, we placed the moulds in the freezer for 20 minutes before adding in the silicone. It helped extend the set time, thank you to Gav for suggesting it. For v4.5 we didn’t, and it was a little trickier to get all of the material in the mould before it became too sticky.
Already, there is something noticeable that has to be fixed:
This can either be fixed by making a better rig to hold the foot bone in place when adding it to the mould, or making those toes a bit larger in diameter, and adding a flap on the exterior of the toe side.
To attach the foot to the froggymobile, the same technique from last time was used: failed prints cut up + hot glue, to attach it to the motor.
It started to move around like this:
But, that is a little slow…
We mentioned last time that our multimeter was broken. It turned out that the ‘Hold’ button was on, so that is why nothing was working. Oops. Still not sure why the other L293D blew up, but oh well.
We added 11.1V to the froggymobile, and it started flopping around frantically!
Here is underneath the froggymobile. Also, you can see some dirt that the white foot has picked up… heh!
We were tweeting out photos and videos of the frog feet whenever an interesting development happened, and it was really great to see the replies, rt’s, favs. Thanks for coming along in the adventure with me, haha!
There are a few things to finish off with the frog feet: small improvements, as well as flipping the design so that there are right and left versions of the foot.
Still not sure if there should be four feet on the robot, or only two. Maybe there can be four, but only the front or back will be active at one time. If the back feet are backwards, then when they are activated, the robot could reverse its direction.
… Obviously we will need to fix the L293D for this task, though!
Our next big design task is for the chassis!
- Coupler from the motor to the leg
- The leg
- Motor mounts
- The chassis (this is a large, daunting step)
Although the chassis looks like a sled, what if it would be made out of a flexible back bone or something? Would that even work? Much more brainstorming to do…
After the chassis, would be the sensors and feedback for the feet- but that is a little further in the future from now.
We want to get this done by Dec. 15th. Think it’s possible? Eeek!