We need a base for the wheels to mount. Then we can connect the drivers to the steppers and see something move. Still a ways off but we know where we are going.
Taking inspiration from the Makerbot Mini the stepper motor holds against the belt a tensioning bolt that you use be for tightening the bolts on the motor. I need the same thing in fact a spring with a self locking nut would be perfect. The motor mount will have a slot for it’s bolt whitch will allow it to slide as you tighten the belt then lock it down.
Without a 3D printer and Fusion360 I don’t know how you would do this. I have knocked parts together but never so professionally looking.
One thing I am thinking about is which way to slice it to make it resist the stress it will take. The layer lines can make a big difference. I think I over built it enough. Lol
Wow this is the best I have seen the Makerbot Mini perform!
The stepper motor bracket looks great too
Now that we know what the motor and wheel well size needs to be, let’s layout the base. The base design has changed ten times from plywood to aluminum frames and tin. Now I need to commit to something.
The base holds the heavy batteries and must not flex and of course holds the body. I think I am going to use plywood and after cutting all the wheel openings it should lighten it up a bit and be strong and easy to bolt the parts to.
What is the overall size of the base for K-9?
Well like most props he was made several time and measured and drawn more than that, apparently. I have a Dr who book that has a K-9 drawing that doesn’t match a drawing floating on the internet.
So you just have to make it your size and that is ok. This drawing is showing 18″ x 30″ to the edge of the leg reliefs. The odd thing is that the dimensions are in inches and we know it was built at the BBC which must have been in metric. Crazy!
One thought I had was not to make it full size but around 3/4 scale to make it more maneuverable but I have already committed to the head build and it is 100% size.
So full size it is.
Holes for the wheels will be layed out and cut then other areas that can be removed to reduce weight. The shaft bearings attach below and the stepper motor brackets attach from above.
Wheel are spaced as wide as possible without them hitting the side under panels. The battery will be placed as far back to offset the weight of the head. Trying to keep equal pressure on all four wheels so they will actually work properly. It only by working out the cross section of the angles can we make sure not to have interference.
The wheel size determines the hole as well as needing clearance for the belt pulley. Then we know where the holes for the bearing mounts will go.
Picked up screws ay Atwood’s. The pack of 6/32 x 2″ screws was $7 and the locking nut were as well. and put in all the spacers in the two wheels I have printed so far. Nice!
A list of more puzzle pieces.
As the Mecanum wheels work together to create the direction you want to go, all four wheels must be in contact with the floor. In a perfect world the solid mounted wheels work perfectly. Sadly a perfect floor is not going to exist. What can I do to improve odds of wheel contact? Building a fully independent suspension might be a bit complicated, but putting in a little flexibility might go a long way. One way it to mount the front two wheels solid but add a rocking carriage for the back two wheels.
A bar down the centerline holding the rear carriage on a bearing might be easily doable. Then mount a stop on each side to let it control the limit of movement. It doesn’t need springs, it will self adjust as it runs over uneven sections of the surface. I see it in my mind but it might need some drawing out.
I was playing with the grandson and his little wooden toy train. He likes me to push them around with him. The best cars had very defined, loose fitting axles that let the wheel have tolerance to adjust to the very uneven track sections. Some cheaper made car would just fall off the track and you could see the design differences. The engineers needed to play trains with their own toys and it would have shown the fault.
I’m sure my first attempt want be without errors but you have to build something to find out what works or doesn’t.
Still waiting on funds for filament. I got a lead on a brand that is better at unwinding off the spool called Elegoo. They make printers for the most part but also sell filament. Ebay has a PLA roll at 20 dollars and free shipping. Can’t wait to try it.
Dream it… Print it.
Thanks for stopping by
Ron
Seahorse 3D Printing 