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Unread 15-03-2006, 11:51
CraigHickman
 
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Interesting Drive Train Idea...

Hey all-
I had an interesting Idea, and I was wondering if it would be possible, or even plausible. I'm in the process of designing an off-season drive train, and I decided to give it a little more push.

So the drive train would have a 2 speed, 2 small CIM gearbox, outputting at slow speed of 6.9 fps (the bot's ground speed). Now is where my idea comes in. On the side, in a seperate mechanism from the normal gearbox, is a Large CIM on each side of the drive train. This large CIM has a sprocket reduction, that makes it's output speed equal to that of the shaft on the wheel (at slow speed). Now at the end of this sprocket reduction would be a dog-shifter type mechanism, which engages or dis-engages the large CIM.

So here's how it would be used during a match: You drive around normally for a while, using only the normal gearbox. then you get in a pushing match, and you hit a button on the OI. a pneumatic fires, and engages the large CIM to your drive train. Your previously 4 motor drive train now turns into a massively tourqued 6 motor drive train.

So am I just spewing a random idea that's not possible? Or am I actually on to something?

(and by the way, I have in no means copy protected this idea, so if it works, have at using it.)
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Unread 15-03-2006, 13:46
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Re: Interesting Drive Train Idea...

Why not have the large cims connected so that they drive all the time? Or am I missing something?
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Unread 15-03-2006, 15:27
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Re: Interesting Drive Train Idea...

^ Yeah, as I think sanddrag (I might have the wrong person) often says, even though that extra motor consumes more power, the load on each motor is also less than what it'd be without. So, the power consumption is not hugely better when only engaging two instead of three.

That said, I like this idea and have a similar design that invloves a torsion spring and a window (or globe) motor.
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Unread 15-03-2006, 16:05
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Re: Interesting Drive Train Idea...

It should work, as long as you build it right. The problems that you may run into here are just the situation that you are in.

Say you have the same motor set up next year as we do this year (4 cims, 2 mini-bike, 2 globe ect.), you have 6 motors now dedicated to your base, particularlaly the ones with the highest rpm/torque ratio. Do you really want to restrict your manipulator like that? Possibly an idea you may want to play around with is a step down from what you are thinking, have 1 Mini-Bike driving full time, and then 1 small cim that can engage/disengage with your boost. This will still keep windows open for your manipulator to use high speed/high torque motors.

Also as an extension, you can save your battery life and eliminate power spikes by never really turning you extra motor off, when its not in use it is spinning at only 10% of it's potential speed and engage it on the fly.

I like the idea though, it may open a few doors.
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Unread 15-03-2006, 16:18
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Re: Interesting Drive Train Idea...

I had a similar thought a couple months ago, and here's what I found out, as people have said above me: You really reap no power saving benefits by engaging and disengaging the extra motor. In a gasoline vehicle you would, because all the engines are running at generally full output all the time, but with an electric motor, the load is shared between the motors. So, if you have a single motor, you draw 40 amps, but with two motors, you still draw 40 amps, but each motor only draws 20. So now I thought, having learned the basics, why not just use one motor and save the weight? Well, by having two motors on thee, you really gain nothing except a cooler drivetrain until you start pushing. Then, when you could only draw, say, 40 amps through one motor, you can now draw 80 total, doubling your wattage to the wheels.
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Unread 15-03-2006, 16:23
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Re: Interesting Drive Train Idea...

Something to keep in mind is that an increase in torque is no good if you can't translate it into pushing force. You'll notice that with some of the most popular traction materials out there (wedgetop, roughtop) and the current total weight of approxametly 150 pounds, the wheels on most robots slip during a pushing match. If your wheels are slipping in this situation, it isn't going to be of much use to increase your drivetrain's torque (since the torque already exceeds the frictional force dictated by the normal force and coefficient of friction). So, in essence, if you aren't slipping in your lowest gear, it may be worth it to add in the additional CIM.
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Unread 15-03-2006, 16:36
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Re: Interesting Drive Train Idea...

Just a side note, if you aren't slipping when you are going full power against something not moving, you better start slipping. Although you won't have as much pushing power, if you don't slip and you aren't moving, you're stalling the motors and will very quickly trip your breakers.
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Unread 15-03-2006, 18:00
CraigHickman
 
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Re: Interesting Drive Train Idea...

thanks for the quick comments guys.

So a couple fo things: this is a side project bot, which will have the function of a corner goal scorer. We're trying to build it so it could compete, just for the sake of practice. My idea to use all of these motors comes from the fact that we would only need window motors for our ball gathering and expelling system, thus we would not be contstricting other areas of the bot.

With the wheels that we are going to have made, (they're the same as the ones on our bot now) we have never had our wheels spin in a match. Their traction is so high that the extra tourque qould go straight into pushing another bot.

Also, ignoring the power issues, would the extra tourque be worth the weight? Or would it be one of those really-cool-but-never-used mechanisms?

Last edited by CraigHickman : 15-03-2006 at 18:11.
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Unread 15-03-2006, 18:20
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Re: Interesting Drive Train Idea...

Well, don't make it a mechanism! Make a multi-motor, constant drive gearbox!

However, as evolution has said, most FIRST robots have FAR more torque than they can effectively use. I'll put it this way: using the kitbot gearboxes, geared to an 8ft/sec top speed, pretty moderate to good, we still slip our elevator wheels at like 75%. And we can push alot of people.

* The nice thing about multi-motor is, you can have a high speed robot without sacrificing good pushing force. But, with both worlds, comes a massive battery drain at stall!
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Unread 22-03-2006, 00:33
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Re: Interesting Drive Train Idea...

I'm thinking it might be useful to use 3 motors with something with very high traction such as tank treads. This will allow the robot to be an insanely effective defender.

With perhaps, 4 motors on each side(2 smalls, 1 large, 1 fisher-price) and heavy treads - i'd hate to get into a pushing match against it.
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Unread 22-03-2006, 08:11
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Re: Interesting Drive Train Idea...

Quote:
Originally Posted by 114Klutz
I'm thinking it might be useful to use 3 motors with something with very high traction such as tank treads. This will allow the robot to be an insanely effective defender.

With perhaps, 4 motors on each side(2 smalls, 1 large, 1 fisher-price) and heavy treads - i'd hate to get into a pushing match against it.
In a head on pushing match yes, but because of the amount of torque you have your robot would be able to get over the scrub that is associated with tank treads much faster causing your robot to bounce quite a lot. With a highly maneuverable robot, you could easily overcome this robot simply by going around it. Plus you are severely limited to what you can use for your manipulator which in my opinion is the most essential part of the robot.

Has anyone ever though of this, Omni tank Treads?
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Unread 22-03-2006, 08:23
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Re: Interesting Drive Train Idea...

If you wanted to get real crazy you could mount a setup similar to what starter motors use to the shaft of the big CIM.

If you design a pinion similar to what starter motors do as soon as they turn on to work in both forward and reverse you wouldn't have to worry about locking it or unlocking the motor from the wheels.

If your unfamiliar with starter motors what happens when you turn the motor is rather simple. The rotation or lack of rotation of the motor forces the pinion back and forth along the shaft to either engage or disengage a gear the pinion meshes with, usually the attached right to an engines flywheel.
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Unread 22-03-2006, 08:39
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Re: Interesting Drive Train Idea...

Quote:
Originally Posted by DjAlamose

Has anyone ever though of this, Omni tank Treads?

Yes. Us guys at 1002 have been batting around the idea for about 2 years now, but can't figure out a way to make the treads without them being either insanely heavy(full tread links for rigidity on roller mounts) or being too weak to take the side forces on each roller without torqueing the belt (continuous flexible belt).

Also, back to the 6 motor drive. It might be interesting to see the pushing power that you can get out of a system like that(and I do stress power, not just force) in the offseason. It would give you good experience with dog shifting and the tradeoffs involved in a multi-motor drive base. However, balance your motor use for actual competition bots as a fast, precise manipulator is sometimes a greater advantage.
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Unread 22-03-2006, 12:20
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Re: Interesting Drive Train Idea...

with a drive train with at least 3 motor on each side of the robot would be great for pushing power with the right set up.

Some of you said that you would like to use the power some where else.


What you should be working on is using the drive train to drive and then to power something else.

Back when you had to lift your robot up on the pole. if you could of used the power on your drive train to also do the lifting, this would of been great. same way like this year. Most people had to stop before they shoot. just think if the motor you used to drive with also ran the shooter.

We have been working on this for awhile to make a light gear box to do just that. take the power from your drive train and put it to something else
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Unread 22-03-2006, 12:50
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Re: Interesting Drive Train Idea...

That is called PTO or Power TakeOff. Team 60 did it in 2004 to lift themselves up to the bar. It looked really funny when they drove into the side of the platform, and then just hit full throttle right into it (spinning their wheels) for a couple seconds until the slack was taken out of the winch cable.
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