Little Mister Anywhere (The 4WD Unstoppable Bot)

I look and laugh at all these shop bought "4WD off road RC car" or even other makers "off road robot"
All these years and I see these things climb pitiful little rocks, or travel across sand. I was sure I could do better.

And what was the result?

After much thought, and some more thinking, I had my own, unstoppable chassis. Currently it is driven by RC, and has no intelligence of it's own, but it can relay images back to your TV, so I can drive it from afar.
Unstoppable it is, for a thing only 16.5cm long, and 21cm wide, with a climbing gradient on most surfaces of 1:2, (on some surfaces >1:1), a vertical scaling height of 7cm, and the ability to transverse almost any terrain.

Cost:
I had most of the parts, so for me it was <$100 USD (only the video transmitter)
If I were to buy everything it would be ~$300 USD (servo's wheels, etc. Not including radio gear.)

Mechanics:
Mechanical Information

Max Length------------------- 22cm
Max Width--------------------- 16.5cm
Max Height------------------- 32cm
Minimum height------------- 11cm
Suspension Travel--------- 9cm
Wheel Diameter------------- 7cm
Main Material ---------------- Meccano with custom parts
Weight------------------------- 804grams
Ground clearance---------- 3cm
Waterproofing--------------- Splash proof bottom, none on the top. (can drive in wet grass etc. Has also been used in very light drizzle)


Electrics:
Onboard Gear

Motive Power------------------ 4x futaba s3003 servos modified for continuous rotation
Battery (drive)----------------- 4xAA Nicad pack (comes to 4.8V, 600mah)
Battery (Video)---------------- 2xAA lipo's (coming to 7.4V, 800mah)
Radio Gear-------------------- Futaba 2 channel AM radio (as ancient as they come too)
Radio Range------------------200m with obstacles, 500m line of sight
Mixing--------------------------- Picaxe 20X2 converts 2channels into 4 channels with skid-steer
Video Transmitter ----------- 2.4ghz 500mw, 300mah current draw
Video Range------------------ Not yet exceeded (ie more than the controller)
Camera ------------------------ 640x480@30fps PAL



Performance:
Overall results (when driven)

Vertical Scaling-------------- 7cm (overall)
Front wheels over----------- 12cm       (Can get it's wheels onto a flat this height, but not able to climb onto, after this then it flips over)
Rear wheels over----------- 15cm
One side over---------------- 10cm
Max Drop height------------ 75cm (it *could* survive bigger, but I don't want to try)
Max Descent height-------- 15cm (without the risk of tipping)
Roll Proof?------------------- Yes, rolling does no damage, and often it ends up the right way up again
Speed------------------------- ~20cm/s
Max Climb gradient ------- 1:2 some surfaces, 1:1 most, and 1.5:1 on very very few
Max usable gradient------ 1:2 (can still turn etc)


Terrain Results:
Performance on different surfaces

Smooth Dirt ------------------ Excellent, most testing was done on this.
Rough/loose Dirt------------ Excellent. Fine most of the time, but can slow down if it starts to dig itself in. Will always get itself out again though.
Small Pebbles -------------- Excellent.
Large Pebbles -------------- Average, can get caught on larger rocks
Bark (chips)------------------ Poor. Digs itself in on anything but the flat
Bark (live)-------------------- Excellent. This is the 1.25:1 stuff.
Grass-------------------------- Average. Plenty of grip, but if the grass is >10cm tall, then it can get stuck
Twigs ------------------------- Poor. Drags them behind it until they snag, and then it stops.
Vegetation ------------------ Average. Bulls it's way through leaves etc, but thicker stems (more than 0.5cm) will stop it. Can drive through flower beds and such though....
Mud--------------------------- Not Tested (will be soon)
Sand ------------------------- Not Tested (will be soon)

Carpet------------------------Excellent
Concrete-------------------- Excellent
Cock/vinyl------------------- Excellent
Paper/card------------------Average. Bit slippery on slopes, but then you never find cardboard slopes do you...
Wood-------------------------Average, same as card
Metals ----------------------- Average, bit worse than card
Skin/leather---------------- Excellent. Can drive over shoes, hands, feet etc


Plans:
Bigger, Better Faster Stronger.
I am planning to build a new version, using what I have learned from this.
The results were good, better than I hoped actually! But there are some things to improve. Things like the performance on grass, or in twigs and the vertical obstacle height can only be solved by using bigger wheels. Torque is no issue here, and it will flip on it's back if it encounters something too high.

So the next vehicle will have 120mm off road wheels, actually designed for it, not just re-purposed.
It will also use new servos, metal geared. They have a slightly higher rotation speed, bringing it's max speed to ~40cm/s.
The suspension system is OK, but on steep (1:2) slopes at an angle the uphil rear wheel tends to lift off the ground. I may or may not change this.
The electronics is fine currently. I may add tilt sensors to stop you being able to flip it on it's back, or something like that.

For the moment though I am happy, driving the car down the road from in front of the TV, climbing over tree roots and pushing everything to it's limits.

Enough talk, have a look at the images.
I will also be getting a video up soon.
(The first image is old, but points out where all the electronics is, also look at the later ones)