In a previous post (‘Baby’ one: new drive system) a new head/neck drive mechanism was introduced based on a crank wheel design along with a slip-clutch.
This can be seen in action below…..
This was a lot slower than the original worm-and-wheel drive (which had to be abandoned as it chewed up the gears).
The crank wheel and associated parts were removed.
The 200:1 motor and gearbox was removed and replaced with a 120:1 version.
The following video shows the result.
As you can see this is slightly better than the video at the start.
There were a number of things that needed to be done: the whole head/neck assembly tended to point too steeply downwards, the jaws were originally cut out very quickly and were thus a bit rough and the ‘kinked’ neck strut had snapped….The following is a report on how these have been remedied.
The broken kinked strut is shown below.
A new strut was made using welding rod and electical eyelets.
I then made a longer aluminium bar to link the head to the red horizontal neck section with a bend which would make the head agle less steep. I also smothed the rough edges of the black jaws.
Modified head and neck section shown below.
Next task is to replace the 200:1 motor/gearbox that drives the head & neck with a 120:1 version to speed it up.
Modifying the smallest prototype Techno-saurus (the ‘baby’): removing the worm and wheel drive and replacing it with a simple crank with a slip-clutch.
The head and neck lunges backwards and forwards and this causes the mouth to bite as can be seen below.
This is achieved using a worm-and-wheel drive mechanism.
It’s fast and effective but the worm and wheel gears tend to chew themselves up very quickly.
It was decided to use a crank mechanism instead and with a built-in slip clutch similar to that used for the rotating claws.
The first step was to dismantle the above drive system:
Next a motor mounting plate was made:
The 200:1 motor/gearbox was attached beneath this:
The crank spindle was then attached to the motor spindle:
A crank wheel was made with a slot and slip-adjustment clamp that would provide the slip clutch function (and thus protecting the gearbox under excessive loading).
This was then attached to the crank spindle and secured with a split pin. A a crank pin was attached to drive the con-rod (M4 machine screw -actually attached before assembling as shown below).
A connecting rod was made and attached.
The finished crank design…
This can be seen in action below…..
It works but compared to the video at the top of this post it is too slow. This is due to the gearbox ratio being 200:1 which is perfect for the rotating claws but a bit slow for the lunging and biting mechanism. Because it’s slow, there is not the same kind of dynamic effect on the whole device which made it more life-like. I’ll change the motor/gearbox asap.
The ‘baby’ one was originally made with quite wide legs/claws made using ‘Polymorph’ (nylon-like material that can be shaped by hand when heated) …
These looked quite effective but it was found that a cam type shape is better and puts less strain on the motor and gearbox as the loading is more gradual.
The above Polymorph claws were quite wide, hence the wide red spindles shown below.
I decided to replace these with simple flat plastic cam-type claws as shown above (in line with the other versions) and incorporating a simple slip-clutch mechanism so as to avoid damaging the motor gearboxes.
The image above shows the claw which as it is allowed to slip, needs to be retained on the spindle. This has been done with a split-pin (cotter pin).
The image below shows the simple clip-clutch, achieved by cutting a slot and adding a screw to pinch the claw on the red shaft.
The modified prototype is shown below.
The next task is to rework the drive mechanism, that is, to change the worm and wheel for a crank mechanism (again, with a slip-clutch).
This prototype was made a few years ago out of odds and ends. It is the last of the initial versions that employed a worm and wheel mechanism to drive the head, neck and jaws.
The worm and wheel gears are plastic and subject to a lot of wear, the jaws are a bit rough, the teeth are rudimentary (pieces of clear tubing cut at an angle to make them ‘sharp’). Also the angle of the head is pointing downwards a bit too steeply. The red leg spindles are too long and need shortening and the green claws need to be modified to enable them to slip under excessive loads.
The plan is to:
-Trim the red spindles
-Modify the green claws to feature a simple adjustable slip clutch
-Use a crank-type mechanism (again with a slip clutch) to drive the lunging and biting mechanism
