Red version: new lunging and biting crank drive: ‘topside’*
(Previous post, red version: “modifying the legs and claws”)
The new ‘topside’ crank drive looks like this:
(*But see the next post -this topside drive is later slung underneath).
The following notes describe how this was made and there is a video at the end.
One of the overriding principles of this project has been that it should be possible to build a fighting robot dinosaur at minimum cost. So a key feature has been the use of parts from economy cordless drills. A cordless drill has a powerful motor, a gearbox, a clutch, quite often has dual speed control and the casing can be used as the control consol (e.g., making use of the trigger). And all this for £10 to £15! (for example: B & Q).
The red version looked like this with the drill motor-gearbox-clutch crank system…
There are a couple of drawbacks however to using the components of a cordless drill. One is that the gears do wear out -or more often than not the smaller red gears eventually split.
The other and main problem is that it’s hard to remove the chuck from the drill. This is usually held in place with a left-hand M5 machine screw and the easiest method to remove it is using an impact tool as shown below. But the bits that come with impact tools aren’t long enough. I had to make a special-purpose attachment.
So the plan is to come up with an easier alternative. One possible solution is to use the same low-cost 200:1 motor/gearboxes that are used to rotate the claws. I have used these before, coupled to a crank wheel with a simple slip clutch (i.e., similar to the claws design).
A single crank/motor arrangement worked well with the ‘baby’ version.
I tried two together on a full size version (one above, one below) but it felt a bit underpowered. I think there needs to be four working together to have the same kind of power as the cordless drill motor.
The plan therefore was to combine them in pairs, each with a crankwheel and con-rod and to have one pair above the ‘main body base’ (‘i.e., topside’) and one slung beneath.
The first step was to make the crank wheel (with slip-clutch) and mount on the motor-gearbox shaft.
Two were then combined and a piece of flat acrylic used as the beginnings of the con-rod. This is then the basic drive unit. I have used sections of 5mm thick acrylic sheet and blocks of LDPE. the con-rod is made of acrylic.
The cordless drill motor and crank etc was then removed from the red version.
The new crank drive was attached along with a shaped con-rod.
The crank drive housing was then shaped to look a little less square.
The finished drive unit.
The drive was attached.
And wired up.
The red version now looks like this:
Video below: it’s a bit underpowered but I expected that, it will be quite good when all four motors are working (it falls over at the end!).
(Next post: the new drive slung beneath).