Step climbing?

Water could be a problem if it starts sloshing about, you'll end up with the thing oscillating like mad, or tipping slightly, then all the water moving in the direction of tilt and pushing it still further. However, if you can build tanks so as to avoid this problem and can pump the water fast enough to compensate for tilting, I'd say they could be better than shifting a huge weight - for one thing, the weight could only easily be shifted along one axis, whereas various tanks could be placed anywhere you liked and could probably shift the centre of mass anywhere you wanteed within the shell. Also, you'd probably have to sacrifice a HUGE amount of valuable chassis space inside the machine to make a cavity or tunnel for the weight to move through, and you'd also need the weight mounted on very strong inflexible mountings, because any acceleration of the chassis will cause the acceleration of the large weight to put enormous forces on its mountings, while water tanks and pipes can be squeezed in around any other internal systems and can be simply bolted directly to the chassis without messing about with heavy duty bearings and things.

As for stair climbing, this has always been a tough nut to crack in the hobbyist budget and skill range. I'm working on a modification to Gordon McComb's "walkerbot" to allow it to climb stairs (and maybe any other lumpy surface) easily and also keeping the chassis itself horizontal at all times. The basic principle is sound and easy to work out, but the implementation is a nightmare - I need to build a non-symmetrical pantograph mechanism for each leg in order to raise and lower the feet by about 8" whilst keeping the pattern they describe when driven by the main motors the same - unfortunately, I have to choose between two evils: The first is to use a straight four bar pantograph, with a minimum of awkward joints, but each leg will stick out by 9" on either side of the machine when fully retracted, making it far too wide to navigate the average staircase. The second is to double up the pantograph like lazy tongs, reducing the width of the machine while retracted, but increasing the number of joints that can work loose, wobble, or weaken the legs' lateral strength. I still haven't decided what to do about that one.

Tom

got this link a few weeks ago. complex but workable to climb stairs. Theres a pdf file with all dimensions.

"Kevin Boergens" a écrit dans le message de news:c1vusq$1mh8ij$ snipped-for-privacy@ID-213387.news.uni-berlin.de...

Hi!

Thanks a lot for your link!

After a bit of googling, I found out that there needs to be a point between als and epfl *g*

Search back on comp.robotics.misc a few weeks ago - to about 20 Jan

stair/step climbing capability?

Hi!

HAND, Kevin

Hi!

This isn't our largest problem at the moment and I fear a bit the combination of water and electronics, so I tend towards the solution using a block of metal.

This seems to be some kind of standard. Nonetheless I haven't heard anything about it yet. Any pictures/links?

HAND, Kevin

I would have gone with the water, but that's a matter of personal style, I suppose. Everyone tackles a problem in their own way.

It's probably become a standard because of the high popularity of the book. It's also relatively cheap and easy to build, compared to certain more conventional mechanisms like caterpillar tracks, which require lots of bearings, and perfect precision if you don't want the tracks popping off the rollers all the time. The walker only really needs a lot of angle girders and a few chains and sprockets (though I found a way to build mine with nothing but aluminium girders, strips and bolts, avoiding chains which are almost as tricky to work with as tracks).

Gordon himself frequents this group from time to time, and I don't mean to cause any offence, but the design, while an excellent starting point and quite easy to build, does have a couple of flaws, at least in my experience. Others may have been more succesful than I have. It requires careful synchronism of the two drive motors to prevent excessive jolting (and I only made the crank radius on my machine half an inch - I can only imagine how bad the jerkiness must have been on the original, which will have had even bigger strides). Built straight from the plans, it is also impossible to turn the machine around without disturbing this synchronisation, so it can only easily walk in a straight line without extra modifications.

I added two extra legs, in the centre of the front and back faces of the machine, moving perpendicularly to the six primary legs, each on an independent motor. By programming a combination of movements in a microcontroller to convert simple commands like "left wheel, right turn, forward, etc" into leg sequences, it can be arranged so that only the two auxiliary legs and the two central ones on the sides are in contact with the floor, all acting to produce a turning moment about an axis in the centre of the machine, allowing it to turn fairly gracefully on the spot. Well, that's the hypothesis - the mechanical hardware is ready, but I haven't started on the microcontroller yet. The problem with this system is it limits the machine to a series of motions not unlike an army drill squad - it can only turn on the spot through fairly large increments, or paces, in order to reallign the legs in the right position to then take a forward or reverse pace.

For perfectionists out there, another problem is a certain amount of energy will be wasted when the machine walks in the vertical motion of the machine as the legs push up and down - it will also put quite a bit of strain on the motors as the machine gets heavier when you start adding subsystems. Perhaps it could be fixed with an arrangement of a carefully machined cam on each leg adjusting the length so that the motion of the feet while in contact with the ground is purely horizontal. The vertical motion might also cause a few problems if you want the machine to serve drinks or anything like that...

Just a few suggestions, hope they help. As for pictures, I'm afraid I haven't got any of my machine yet, and probably wont until it's finished. If I do take any, I'll try to remember to post them here.

Tom

It's in both both editions of my book, Robot Builder's Bonanza (first edition printed 1986). I've seen some pics posted from time to time over the years by people who have built their own, but most are school-based, so the sites come and go. It's a VERY large robot -- almost three feet long. It wouldn't work for stair-stepping as-is, but there are some mods like using a "tri-star" wheel arrangement that might work, if the wheels are large enough for the stair risers. Apart from the mechanics of stair climbing is the horsepower requirements. Stairs are basically 45 degree inclines to a robot...lots of power needed to get up one of those.

-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza

Hi!

HAND, Kevin

Just a thought .... but maybe one might add a special "helper arm" to the front of a walker to help boost it up the steps. Basically, would be a bar held by 2 outriggers [that would rotate around in synch], and essentially "pull" the rest of the bot up the steps, kinda like a baby using its front hands/arms to pull its rear end along. Also, something like the front-end flippers used in Urbie. The bar would only engage for climbing over things, and might need to be retractable, but the mechanics would be simpler than jointed legs/etc. Still take some power, but it could be geared very low.

I whipped up a quick drawing to illustrate - [not a very good draw program for this] - shows 3 different positions for the helper arm:

- dan michaels ======================