Rookie team drive tream idea
 

Team 1257 (Parallel Universe or something like that.... don't ask me, I just build the thing :D ) is a rookie team this year without too much mentor support. We have started to settle on drive train idea but i have a few questions that no calculation or estimate could answer us well. We plan to use one Chiaphua per side (in a tank type steering system) in a four wheel drive with identical wheels front and back. We want to use a worm gear to gear it down about 15 times then a sprocket system for an additional 1.8 or so for a total of about 27. Assuming the the Chiaphua can give us 4000 rpm while driving the robot, that should give us a max speed of something like 8 ft/s.

1. Are two Chiaphua's sufficient to drive it and reach this speed?are the drills better for this situation?

2. Is it worth it to try to assemble the worm-gear-to-spur-gear gearbox ourselves (keep in mind it will be mainly students with access solely to drill presses and other basic power equipment), or should we buy it? If we should buy one, where do we get a gearbox like this for a reasonable price (I was thinking the seat motor, thats a reasonable price :D )?

3. Will the 12" pneumatic wheels provide sufficient traction?

4. Will tank type steering with wheels be possible when our robot has a relatively large aspect ratio (something like 1.5:1, assuming wheels are about at the corners of it)?

5. Any other suggestions?

Re: Rookie team drive tream idea
 

I would recomend buying planetary gearsets and then sprockets to gear the chip's down. We reconfigured our drive train post season and this worked well. Planetary gearsets can be purchased for a relatively small amount and they are very lite. we ran this with a 3:2 4 wheel drive chain/sprocket setup. works great

Re: Rookie team drive tream idea
 

is there some reason why you dont want to use one of the two drivetrains that FIRST supplied? we built a baseline/pratice robot from the ones they gave us last year (the 90° ones) and it works very well.

at least consider doing that as your plan B.

Re: Rookie team drive tream idea
 

^ See Reference Image (my avatar)

27:1 seems like a little too much of a reduction. Especially if you're running at 40 amps. You can get a good reduction simply with sprockets and chain.
We typically run a drive similar to what you've specified.
We run 1 chip per side, each at a 18:1 sprocket reduction, 40 amps/motor. We use 8" wheels; remember your wheel size will make your speed vary.
If you're gearing down the Chip's 27:1, you will not hit 8 fps, unless you have a large enough wheel. Having a wheel that size will compromise your gearing thus making it pointless.
Also, remember when your worm gear stops motion, your drive wheels won't want to move. In pushing matches or in conflicting forces in your drive, depending upon your worm gear configuration, you may be risking breaking your worm gear assembly. Trust me, I've seen it done. If you want to brake your drive instead of coasting, there are better options than a worm gear.
I'm glad to hear of some rookies trying something other than the drive supplied in the kit.
I would suggest that you shoot for 20:1 at most if you're running at 40 amps. The 12" wheels in the kit should get ok traction, but the 12" size can be a bit of an overkill, unless you're planning on driving up the side of the platform.
Either way, it sound like you guys are off to a good start!

Re: Rookie team drive tream idea
 

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.

Re: Rookie team drive tream idea
 

We are right on with our ratios, you forgot to take into account the difference in wheel size, ours 12 and yours 8:
12/8=1.5
1.5*18=27

Why is a 12" "overkill"? We thought it would make the steps significantly easier and, in addition, we already have two to play with.

The reason i wanted to do a worm gear is because i didn't want to deal with building a complex multiple axle gearbox. I understand the problem with the worm gear, but i still really don't want to try a gearbox like this. If anyone knows a way to simplify this 27:1 gearing (buy if possible), that would be great.

Re: Rookie team drive tream idea
 

There is absolutely no need to climb the stairs in this game.

Re: Rookie team drive tream idea
 

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?

Re: Rookie team drive tream idea
 

Think twice about the steps. You could get up them with far smaller wheels. Also, make sure you make your robot narrower than 30", or that your driver is darn good. It's going to be real tough for anyone to manuever around the fixed goal in such a tight space at such an angle.

Just some things to think about :)

Cory

Re: Rookie team drive tream idea
 

There is no need to do just about anything in this game.

Re: Rookie team drive tream idea
 

Hence the high aspect ratio of the bot's profile. And from everyone's suggestions, sounds like 8 inch wheels may be a better choice

Re: Rookie team drive tream idea
 

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.

Re: Rookie team drive tream idea
 

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

Re: Rookie team drive tream idea
 

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.

Re: Rookie team drive tream idea
 

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

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