Big wheels on a heavyweight

[tom_kane]

Its genius, doesn€™t include gaffer tape though

[craig_colliass]

Shane I dont know about the springs, but the rest seems quite brilliant!!!!!!!!!!!!

I was thinking about using the ctr of a car wheel say 200mm dia then bolting the plastic to each side of that (with spacers to get the 80mm) then fitting some type of tyre perhaps a Motorcycle tyre what do you think?

I have bought some trailer hubs for the stub axels they are quite light but very strong the stud pattern is 100mm 4 stud.

[maddox]

HDPE has several advantages in this application.
Easely worked, very light, flexible but springy, even limited self repair capacity, and contradictionary to the easy worked and softness, very tough. Easely damaged, almost impossible to destroy. What is demonstraded in the TAN wheels, in use since 2002, and its not that TAN was left in the shed for all those years.

These wheels are made from a 12mm HDPE plate, turned to fit in the thin walled 16 drainage pipe, with a bit of messuring and tapping with a hammer the plate was at the right depth straight and then welded in.
Then we put the wheel in a large chuck on the lathe and finished it so it was straight in all dimensions, a nice centring hole to fit the custom Hubs Kos turned and milled to perfection.
The first set of wheels used the surface of a rather soft and worn cartyre fixed with short wide head woodscrews. But the thickness of rubber and steel braid in it makes this a very heavy option. Also, car tyre is made for cars, not 100 kg robots,the grip is less than optimal.
Other option we tried.
Running surface from a wheelbarrow wheel. Not grippy enough, but very light.
And since then we have a formula One style mounted set of wheels.

But the best result on wheel surface coating was my first experiment in that respect, the billet HDPE backwheel from Project Two: Hexem, what was fitted with the softest compound dirtbike mud tyre we could lay hands on. Kevlar reinforced, thin rubber, high studs and so grippy it glued itself to the floor.
But the main disadvantage, and the reason we didnt do that on TAN, was the pricetag, and TAN would have needed 2 of these tyres.

[swanaldo]

the idea of the springs between the poly would let it flex but tie the 2 bits together. if you did it with quite strong springs it would allow flex. would absorbe energy when another robot impacted with them too. if i were to redesign the wheels for that version of hells teeth knowing what went wrong i would do them like that. but then experimenting with other ideas is a good thing too.

[craig_colliass]

now i get it thanks Shane.

[craig_colliass]

Things seem to be moving on ok with The Saint Mk2 Ive sorted out the hubs modified from car trailer units, and the drive will be my Bosch750 motors with a 19:1 ratio. It looks like the wheels will be about 550 - 600 mm Dia made from HDPE about 15mm thick would that sound about right?

Also if the robot flipped it may get stuck on the face of the wheel, how do I stop this, I know some robots have domes spun from steel like Stinger, is this the best solution? Where would I get them from or made? Thanks guys.

[maddox]

Other option, think War Chariot style blades on the wheels.

One source of steel domes are LPG tanks. The ends are dome shaped.
Pulveriser used these.

[swanaldo]

craig i have some 20 to 1 gearboxs if your interested. used with bosch750 in hells teeth3. i will bring them to swindon you can have a look. might be of some use.

[craig_colliass]

Mario thanks for the idea for the dome, I will look out for some tanks, also old air compressor tanks as they have two domed ends!

Shane please do bring the gear boxes They sound very interesting if not for saint 2 then saint 3! If you know of any Bosch 750 motors anyone has. I need those too, but I know they are like hens teeth at the moment Jonno wanted some a few weeks ago but I think he had to buy new.

[craig_colliass]

I did some measurements on the Saint regarding the drive

I have 2 Bosch750 motors with a sidewinder speed controller and standard Hawker bateries16Ah I think.

The battery voltage measured at 24.7 volts with no load
The volts going to the motor on full speed measured 22.7 volts
The voltage at the battery terminals under full speed was 23.8volts
I think I am loosing about 1to 1.2 volts through the speed controller is this ok?