Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

Okay thanks a lot. What are the advantages of that over 4 wheels? I guess you use lss motors, but isn't it more stable with 4 wheels?

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

I don't know if it is really an advantage or disadvantage but I will point out one difference between the two.

With 3 wheels at 120* intervals when going straight forward you have only 2 of the 3 motors driving. But each of the two motors is getting roughly 86% of it's speed being applied in the forward direction.

With 4 wheels at 90* intervals when going straight forward (or sideways or backward) all 4 motors are driving but you are getting roughly 70% of the speed of the motors being applied to the direction of travel.

So I suppose you could say 3 wheels is more efficient because there is less vector cancellation.

With 4 wheels it is naturally square while with 3 wheels it is naturally triangular

4 wheels/motors gives more traction

3 wheels/motors looks cooler?


When it comes down to it, I don't see any reasons for picking 3 over 4 other than less weight and less power consumption and possibly greater speed for the same gearing. If anyone has any other benefits of only 3 wheels I'd sure like to hear about them.

The main reason I'm building mine with 3 is so I can use one of these nifty little doo-dads http://www.robotlogic.com/product_omx3.html So I don't have to program a thing. :)

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

the drive 357 was cool but they were easy to push at philly they got pushed around, but it was an awsome drive to watch i still say 25 in 2003! lol sure it didnt move side to side but! it didnt need to

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

A clear advantage of Kiwi drive over Holonomic that Sanddrag didn't mention is that the traction on each wheel isn't thrown off by slightly varying terrain.

It was mentioned with the holonomic that when one wheel would get up on the loading zone triangles it would throw off their traction on the wheels and make control a little shaky. With the Kiwi its like the difference between a four legged object and a tripod - the four legged chair/table or whatever will teeter if not on a flat surface, whereas the tripod doesn't care.

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

Kiwi drive has me intrigued a bit. I'm probably going to design one this summer and see how far I can get. My team is pretty hesitant to use omnidirectional because of lack of pushing power and ease to build. I'm still going to do what I can though. How would you calculate gearing for a kiwi robot?

Interesting ideas:
Drop down tank drive like 111's
Shifting kiwi (AM shifter, anyone?)

Thanks,
Daniel

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

When you say ease of construction, I take it you include programming?

From a mechanical standpoint, it shouldn't be all that hard, so long as you aren't making your own omni wheels.

heck, just slap 3/4 NBD's on there and you're good to go :)

I imagine the programming is the much more complicated aspect.

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

This has intrigued me about the NBDs. How hard is it to get the servos to shift everything at the same time? I've not dealt with a multi-speed drivetrain (yet), but I can imagine that having one side in first gear and the other in second would be less than desirable.

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

actually when it came to making the drive train for our robot this year it gave us far fewer problems with basic drive than our previous drive trains had (we tried to add extra function that our gyro wasn't acurate enough for). The programing is relatively simple (just sine and cosine) and the mechanics was almost simpler to build than the drive train given in the kit, we had only one custom part per wheel which could be made in a half hour on a lathe which we used to adapt the wheel to the shaves of the kit transmit ions.

The other trouble that arises from three wheels is that to move forward (if there is a solid arm on the bot) you must drive one wheel across its face. This means that if it hits any bumps (especially if there is a large load on it) then it is far more likely to cause the robot to trip and fall. The other option is to have the wheels drive towards the center instead of perpendicular to it and while this type means that the robot is less likely to trip you can't actively turn the base and anything hitting the robot will turn is.

About four wheels yes they will never all touch the floor properly if they are simply shimmed it is just as easy to put a suspension on them than to try to solve the problems faced by a three wheeled design. This is why when we found that we couldn't control our chassis because one wheel would loose traction and it would steer off to the side instead of making a new chassis or modifying the one we had we put a suspension on the wheels. It is now extremely easy and fun to drive while it is still stable and it doesn't trip over its own wheels.

Alex

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

Programming was included as well. NBD would work, as long as I can see how to do it. I am not too good with drivetrain construction, since we have just used the kit stuff in the past few years. I feel that we should start stepping outside of this now, but I can't do it alone.

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

Thanks a lot for the explainations.

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

You don't need to shift them, I just figured it would be the easiest, and lightest way to get the reduction without making your own gearbox (unless the kit gearbox is lighter than a transmission, which I doubt).

Re: Most Impressive/Advanced/Unique/Cool drivetrain you've ever seen
 

This is true, nobody says you have to shift anywhere (just ask the folks that used the kitbot this year). However, I'm a sucker for taking things to The Next Level (tm) when I can. ;)