Yet another crawler

[Hopey]

So, for this week's installment of "what can I do with lots of M motors", I decided to build a crawler. Inspired by z3_2drive and others, I wanted to make a lightweight, minimalistic one, but wanted to do it a bit differently, to make it stand out from the crowd...

(Apologies for the quality of the photos, they're taken indoors at night with a flash)

So probably the most obvious and fundamental thing to notice is that each wheel is driven independently by its own M motor, which attaches directly to the portal hub input, with 1:3 gearing down in the hubs. Why? Well, why not.

From there, I really just winged it, doing each element as simply as possibly.

Rather than a simple-yet-elegant system of links (which I don't have the pieces for), I separated the different rotation axes of each axle. For roll (one wheel higher than the other), each entire assembly is attached to a turntable. A rubber band (non-genuine, sorry) onto a beam attached to the centre part returns it to the upright.

For up-down movement of the axles, they simply pivot at the point where they attach to the turntable structure, with a pair of shocks at each side. These are actually probably too stiff, I might replace them with some softer ones.

I'm not really that well-versed in different suspension geometries, so I don't know what disadvantages might exist here, but it seems to do the job. It inherently eliminates any unwanted side-to-side movement, and prevents the need for complex articulation of the shock absorbers.

As for steering, initially I planned to control each wheel individually, and skid steer to turn. This didn't work out; besides the fact that I was too uncoordinated to control it, the skid steering just didn't work. It just tried to destroy itself without turning at all.

I didn't want to complicate the drivetrain at all, and giving it enough room to rotate the portal hub _and_ the motor seemed rather complicated as well, so I kept the wheels fixed to the axles and used a linear actuator driven by a 5th M motor to implement centre-pivot steering. This works quite well, albeit slowly. My experience with the Pseudo9398 taught me that having one M-motor stalled (i.e. steering at full lock) would significantly reduce the output of the other 4. This doesn't happen with this setup, as you only power the motor to change the steering, not to maintain it. The rigidity of the LA also prevents bumps from altering the steering angle. I haven't quite reinforced the structure enough for the LA though, it bends the whole thing a bit if you try to drive it to full extension.

I had also planned to do something a bit fancier with the motors, having them offset so that I could have the wheels a bit closer together, but having them that far apart (there's a 15L beam between the tops of the portal axles) doesn't seem to be a problem, and is simpler, so I went with it.

As for performance, I'm very happy with it. Power-wise, it had no trouble with the climbing and will flip itself over if you try and crawl up a 90degree wall (it only weighs 880g). It took me quite a few attempts to get it to climb up there, but I think that says more about the driver than the vehicle.

[rm8]

Crazy fasy crawler. Moves like little dog Jack Russel.

Jack, get out of sofa! Bad boy wow wow

Edited August 4, 2012 by rm8

[z3_2drive]

Your welcome for inspiration very 'interesting' design I like realistic suspensions, but I'll let that slide because WOW! That's fast! steering is slow but understandable-it could beat mine in a drag race by a mile Also it has nice torque, but not as destructively powerful as mine-It was climbing wall and rear link popped off under stress. This could look good and hide those odd mechanics with a simple body...Great job overall

880g...I need to weigh mine in comparison...

Edited August 4, 2012 by z3_2drive

[Saberwing40k]

It's cool, and fast, and uses a completely different system in relation to everything else I've seen. Great job!

[timslegos]

Nice steering system, although it does seem a little slow.

tim

[cottonwood]

Very interesting build there. This crawler is definitely 'original' in design. I'd love to see this fully realized with a body and everything!

[Zerobricks]

Really original and fast. Can you make the steering as fast too?

[Hopey]

Glad you guys like it.

So the typical English weather cleared up for long enough today for me to have a go of it outdoors.

I'm rather pleased with the results, although clearly grip is an issue. Would have to get some 3rd-party tyres to improve this.

The steering is very slow, but in order to make it faster I'd have to gear it up, and I'm not sure it'd be strong enough, and besides, I don't really have enough room (without completely redesigning the middle). It might work better with a small linear actuator, but I don't have any of those.

I don't think I can be bothered putting a body on it. For one, putting a body on a crawler like this always looks kind of silly in my opinion, and I'm more interested in modelling mechanical stuff than bodywork anyway.

[z3_2drive]

lol, I just weighed my crawler...what are the odds... 875 grams just a few pieces lighter!

[Meatman]

Really Cool model you got there.