Our team wants to use tank type treads this year. Can the motor be connected directly to the timing belt drive pulley? If not, what’s the best method to transfer power from the motor to the drive pulley? Chain and sprocket? Gears?
*Originally posted by Carl Owenby *
**Our team wants to use tank type treads this year. Can the motor be connected directly to the timing belt drive pulley? If not, what’s the best method to transfer power from the motor to the drive pulley? Chain and sprocket? Gears? **
In most cases, you will want more torque to propel your robot than the output shaft of a motor can provide. There are some motors, however, that can be used for direct drive.
I’d recommend using sprockets or spur gears to transmit power, as well as establish a favorable gear ratio. Each have their pros and cons.
In short, spur gears seem more reliable because they don’t rely on chain. However, changing the ratio between them is more difficult, as you’d be faced with the challenge of finding a new, acceptable ratio and maintaining the same center-to-center distance.
Sprockets allow more flexibility where changing ratios is concerned as all that is required is to change the sprockets and adjust the chain length. Chain, however, has the potential to skip teeth or fall off altogether. A tensioning system is a must.
I think the main advantage to sprokets is the ability to drive front and rear wheels off the same motor. Chains transfer power. I agree they can be difficult to setup (though so is a gearbox) and if not properly designed will skip and come off, if your worried about it I suggest using the drive train provded be FIRST.
Greg
*Originally posted by M. Krass *
**Sprockets allow more flexibility where changing ratios is concerned as all that is required is to change the sprockets and adjust the chain length. Chain, however, has the potential to skip teeth or fall off altogether. A tensioning system is a must. **
I agree with most of what you said, except for what you say about chain.
Chain doesn’t fall off (unless it isn’t tight enough), and unless you are using TINY chain, it doesn’t skip teeth either.
Our drive is going to be wheels this year, but a tank tread could be done in the same manner:
We’ve got the Chips and the Drills combined in a gear box (1 gearbox per side). We have 2 speeds - Obviously this would work without the 2 speeds as well. In your gearbox you would use gears to slow the motors down and get more torque from them. If you are only going to have 1 final speed coming from your gearbox, you probably want to look in the area of 5fps or so.
Now, on the output shaft of the gearbox, we have 2 sprockets. One of them has chain connecting it to the rear wheel, the other has chain going to the rear. On the wheels themselves we have another sprocket, chain goes there.
We did something very similar to this last year, but our gearbox only had 1 speed. Not once did anything skip or fall off.
So I guess basically what I just said was that for your tank tread: treat it as if you’re powering wheels, but obviously the wheels will be connected with the tread. And, it is probably a good idea to have both ends of the tread powered (the wheels at the front and back), because if you get in a pushing match, you dont want the tread to start skipping over the wheel that is powering it - by having 2, it is less likely to skip in both places at once.
Also, one thing that always seems to happen with tank tread people: They are not able to turn. Really the only thing people can do about this, is to make sure that their tank treads are able to slip sideways, so when they try to turn, the tread won’t be able to hold them in place…
So, make sure your tread looks more like
Rather than
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||
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or
x
x
x
Hope this all helps!
*Originally posted by Harrison *
**
Chain doesn’t fall off (unless it isn’t tight enough), and unless you are using TINY chain, it doesn’t skip teeth either.
**
Well, that’s exactly it. With time, chain stretches, it gets loose, and it falls off 
We’ve had some larger chain skip teeth, too. #35.
I don’t think the metal stretching is a HUGE problem for the 3 day competitions.
We’ve still got the same original chain on our bot from last year, and it is pushing walls and everything as well as it did last year - no skipping or falling off.
http://www.valleytech.k12.ma.us/Robotics/images/2002%20Gears1.jpg
take a look at this picture. it will show you how to hook your drive train up.
this is using the drill motor and the Chip motor.
we always use square shafts to put our sprockets on. so there are no need for pins or locking nuts.
Whats your final speed coming off of that?
Doesn’t look like you’ve geared it down much…
try brecoflex if you decide to go with a tread drive train they have some custom pulleys made for their timing belt. Basically you’d want to run your axle(s) to one of these cutoms pulleys and wrap the tread to the other points where pulleys would free wheel and just keep the tread in place. http://www.brecoflex.com It seems pretty simple if you look through their catalog. Good Luck!
we went from 300 rpm motor and put a 24 to 36 sprocket
we’ve had bad problems with treads, even though the traction is amazing, turning creates a whole new set of trouble. the amount of torque required to turn is immense, so don’t have too much traction otherwise the motors will draw too much power and reset. also you will get heat problems, so don’t completely encase them, leave an airflow channel and add fans! before you chose your timing belt, experiment as to which one gives the best traction without being to hard to turn, and keep in mind that each tread could have as much as 65 LB pushing down, so weigh them down when testing.