Rookie team drive tream idea

[Max Lobovsky]

Originally Posted by Solace

Ok, here goes

The two chips are not quite as powerful as the drills. I think that the drills give you a little under 350 watts and the chips give a bit over 250 watts. The next highest motor in power capabilities is I think the fischer price motors, with something like 200 watts. (don't quote me on the numbers).

That being said, the chips are more useable. The are more symmetrical than the drills, so they run at the same speed in both forward and reverse. Its a lot easier to make the robot run in a straight line that way. They are also a lot easier to mount, and are much harder to overheat. You can run them longer and harder without ever having to worry about hooking up cooling fans and heat sinks.

The good thing about worm gear transmissions is that you can't backdrive them. The bad thing is that you can't backdrive them. It's a mixed blessing. There isn't really any aspect of this years game that requires you to hold your ground in a pushing match, so it probably wouldn't be that useful. Also, you wouldn't believe how much harder it is to simply transport your robot when you can't just push it along the ground.

The skyway wheels will provide traction.....up to a point. They will be good enough for driving around, but they will not be able to stand up to a higher traction wheel, such as a pneumatic. However, unless you see yourself doing a whole lot of bashing against other robots, that won't pose a problem. On the plus side, having low traction wheels allows you to turn easier.

The best gearing to put into your transmission is, believe it or not, almost entire determined by the kind of wheels you are using, and the geometry in which you make your wheel base. Basically, you want to be able to drive as fast as possible while still retaining your ability to turn quickly.

Just for comparison, last year 571 used a four wheel tank drive drive train, powered by both the chips and the drills. We had 2 high traction 8" pneumatic tires and 2 low traction 8" skyway wheels. The bot topped out at about 12 ft/sec while retaining its ability to turn. This relatively high top speed let us outrace most other opponents, but came back to bite us in a way as well. though we could still turn at a reasonable speed, the process of turning drained an excessivly large amount of battery power (we couldn't turn at all until we replaced the back pneumatic wheels with the lower traction skyway ones). Learning from last year, this year we are going with the more versatile 6 wheel drive base in order to make turning easier in high gears.

In your case, running only on chips, I would not suggest running on any wheels that had a whole lot more traction than the skyways. 8ft/sec, while not blazingly fast, is fast enough to keep up with most of the competition. While i would not suggest using a worm-gear transmission, i don't really have any basis for making that suggestion other than personal preference.

I'm sorry, i confused the Skyway with the new 12" pneumatics they are giving us. I guess that means we need to trade out two of 'em for lower traction ones.

I don't understand how bots have such a huge range in power in their drive trains. I believe FIRST suggests a simple drive train with the Fischer-Price yet some teams, like you, will have nearly quadruple that power. What do we really need?

[Solace]

Originally Posted by maxlobovsky

I'm sorry, i confused the Skyway with the new 12" pneumatics they are giving us. I guess that means we need to trade out two of 'em for lower traction ones.

I don't understand how bots have such a huge range in power in their drive trains. I believe FIRST suggests a simple drive train with the Fischer-Price yet some teams, like you, will have nearly quadruple that power. What do we really need?

Yes, I would hesitate to use 4 pneumatic wheels with a two motor drive train. You will most likely have some difficulty in turning. 2 pneumatic and 2 normal skyway wheels will hopefully allow you to turn enough.

I think that FIRST suggests a simple drive train for the rookie teams, as they are often not very experienced in what they are doing (hence the name rookie). Veterans like us have had the opportunity to go around and see what works and what doesn't, so we are much more likely to pull off a more complicated drive train.

Having quadruple the power gives you lots more speed and power in tight situations. It's nice, but NOT completely necessary. Even at a slower speed, if you're robot is pulling 8 ft/sec, you will be able to compete competetively against the majority of other teams. As a rookie team, its nice to see you trying something a little more challenging. Just be careful not to set your sights too high.

Personally, I would stick with the drill motors. Though a little bit more difficult to work with, they do give you a bit more power then the chips would. You can usually take care of any possible overheating problems with one or two well placed muffin fans, something that is really not all that difficult. With 4 wheel drive, you will experiece enough side friction so that the asymetrical aspects of the drill motors will be all but imperceptible. I wouldn't use the exact transmission system that FIRST gives you with the kit (as its just a bit too slow for my tastes), but its a good place to start. Gearing the drills to 7 or 8 ft/sec will probably work out just fine.

If you still want an extra challenge, you can experiment with using a servo or a small pneumatic cylinder to switch between the built-in gears on the drill motor transmission itself. This gives you a whole range of extra options.

In the end, there is no right answer. While more power and speed is always better, I've seen too many rookie teams lose all hope of being competitive because they set their sights too high and attempted something that was beyond their ability. You have to determine what you're capable of before diving into the really tricky stuff.

[Cory]

Originally Posted by Solace

With 4 wheel drive, you will experiece enough side friction so that the asymetrical aspects of the drill motors will be all but imperceptible.

I beg to differ. I can tell you, as will many other teams, it is hardly imperceptible. In 2002, we had to angle our robot a good distance to the side of the goals, just so that when we got to them, we would have drifted enough to be kind of straight. Last year, the robot never went straight either. Im not talking about slow drifting, Im talking about pretty sharp movement. Sure, you can correct it in programming, but coming from a driver, if you dont, its extremely annoying.

Cory

[Eric Bareiss]

Wow, you guys are all over the place with your answers.

I would say Yes to all of the original questions except the gearbox question. I would reccomend that a newer team with little machining help or expertise not try to build a gearbox from scratch. If you are deadset on using the Chips, try to keep it as simple as possible.

As for traction I can't imagine having too much traction with these new wheels. You should be able to turn just fine and go up the step without too much trouble.

[Max Lobovsky]

Originally Posted by Eric Bareiss

Wow, you guys are all over the place with your answers.

I would say Yes to all of the original questions except the gearbox question. I would reccomend that a newer team with little machining help or expertise not try to build a gearbox from scratch. If you are deadset on using the Chips, try to keep it as simple as possible.

As for traction I can't imagine having too much traction with these new wheels. You should be able to turn just fine and go up the step without too much trouble.

It's very tempting to go with your suggestion; it was the only one that gave me a complete answer .

That still leaves me with a question, if we shouldn't build the gearbox, where should we get one?

[Max Lobovsky]

If there are any other Rookies out there following this, here is a very pertinent paper about being able to turn with tank style turning:

http://www.chiefdelphi.com/forums/pa...le&paperid=222

Based on this paper, I think maybe some friction tests (in both directions) of these 12 inch wheels are in order

[Eric Bareiss]

As for using a gearbox, my suggestion would be to use the one that comes in the kit. I haven't seen the one from this year, but I know the one from last year could be retrofitted for use with chips.

I'm not saying that making a gearbox is totally out of the question. You can surely do it with a drill press if you had to. I would get a good idea of what you think you are capable of and work from there.

My suggestion to you is to find a veteran team who would be willing sit down with you for a day and help you work out some plans for a gear box, maybe even help you machine it. It looks like team 25 is only about 15 miles away from you, I'm sure they would be willing to help.