Too much traction can be a bad thing. It leads to motors burning and smoking. Not to mention as the person above me said too much traction actually leads to increased current draw as the robot turns. Plus tank treads if not built properly will pop off when you turn.
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If you use chain, be ready to use tensioners. A slack chain is one that’s just begging to fail.
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Lube! Getting your bot slick and oiled can be like adding RAM to a computer, it’s cheap and gives you a huge boost in performance. If it takes 1/4 throttle just to overcome the static friction in your drive and get moving, something is in need of lubing or redesign.
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Keep it clean. Dust, carpet, rubber, blood etc. will all get picked up and find it’s way into your drive. Compressed air and a tooth brush every few matches will keep it from building up.
-Andy A.
Consider using worm gears because the worm gear can turn the gear but the gear cannot turn the worm gear, this allows from some serious “stayin put” power.
Planetary gear systems are great if u have a limited amount of space and need some serious reduction or serious durability.
I would also suggest that everyone on the team read this:
This will give everyone a nice understanding of the basics of gears and allow them to talk inteligently to the judges on the subject.
Excessive use of pneumatics is a NO NO!, if you are going to employ pneumatics into a drive train, be sure to keep the range of movement to a minimun (for instance short strokes). Example… a gearbox, though a very risky undertaking in itself for a rookie, or even some veteren teams… use short stroke cylenders to and little room for error.
Also, don’t forget wear and tear, especially treds. Though a tred system may be perfect on AUTOCAD, after a few uses, stretching of the material could jepardise the whole design!
Aside from all that, the key to a long lasting prescision drive train might not be in the calculations and the tolerances… But a rugged chassis. If u have a sturdy chassis, it greatly improves the performance of the robot… and affects of age.
If your using chain between your drive motor/transmission and a sprocket on the drive shaft, consider using 3/8" (#35) pitch chain. Too many teams (especially rookie teams) wind up running around in circles due to broken 1/4" (#25) drive chains. Try to minimize the lengths between components to keep the weight down.
Consider using worm gears because the worm gear can turn the gear but the gear cannot turn the worm gear, this allows from some serious “stayin put” power.
Note: the “anti-back-drive” property of worms depends on a bunch of factors (number of threads on the worm, friction in the system, lead angle on the worm). It is not a guarantee if you just put a worm/worm gear in your drive system that you will be impervious to back drive.
Worms also have an added inefficiency due to sliding contact between the worm and worm gear. This is a function of the contact friction between the two. Use lubrication. And be prepared to lose a little of your “available work” to friction (which is not as big a problem with spur gears).
Worms and worm gears experience significant thrust loads! The thrust load in our drive system was sufficient to push the snap rings holding the gears into the proper position out of the groove. The worm would also grab the key in the shaft and shove the shaft around. We ended up putting in spacers to keep everything in place.
Make sure you properly support all shafts. You might want to use angular contact bearings on each end of both your worm shaft and your worm gear shaft in order to accommodate both radial loads and thrust loads.
We designed our first worm and gear system last year and are still crawling up the learning curve. I think it is probably worth the effort. But, there are a few more quirks than we expected.
Excessive use of pneumatics is a NO NO!, if you are going to employ pneumatics into a drive train, be sure to keep the range of movement to a minimun (for instance short strokes). Example… a gearbox, though a very risky undertaking in itself for a rookie, or even some veteren teams… use short stroke cylenders to and little room for error.
Maybe they’ll give us air motors some year.
For those of you who have used pneumatics, how many things can you drive at once? Do you experience “sag” in your devices as the match proceeds?
Can you charge your air tanks to 200 psi before a match? Or just to 60 psi? This seems to be an extra source of potential energy and therefore a good thing.
Andrew, Team 356
i designed a pneumatic drive but never actually built it… i started to but then my injuries got in the way(not injuries from the pneumatics)… from my calculations the engine i designed would have 1 horsepower and be able to run constantly at around 10 feet per second… not bad, eh? too bad i dont have a machine shop to use. its too time consuming to precisely cut steel with a hacksaw 
or aluminum for that matter.
Can you charge your air tanks to 200 psi before a match? Or just to 60 psi?
If I remember correctly, the rules stated that you may pre-charge your system but only with the existing pump. The pumps have a pop-off valve that release at around 100 psi.
There hasn’t been any rule that excludes using other pneumatic cylinders as additional storage tanks however. The tradeoff is the additional weight.
*Originally posted by RobDeCotiis *
**i designed a pneumatic drive but never actually built it… i started to but then my injuries got in the way(not injuries from the pneumatics)… from my calculations the engine i designed would have 1 horsepower and be able to run constantly at around 10 feet per second… not bad, eh? too bad i dont have a machine shop to use. its too time consuming to precisely cut steel with a hacksaw
The only components that you are allowed to hook up in the pneumatics system are the components they give you. You cannot put anything custom-built in the line under current rules.
*Originally posted by Andrew *
** Can you charge your air tanks to 200 psi before a match? Or just to 60 psi? This seems to be an extra source of potential energy and therefore a good thing.Andrew, Team 356 **
I believe that FIRST allows a stored pressure of 120 psi and a working pressure of 60 psi. The pressure switch stops at 120, and the regulator restricts the flow to 60.
When working with gears always use an odd gear ratio. ie. 40:11 instead of 40:10 This always promotes even wear and tear on the gears.
When working with any kind of motor it’s always good to keep the magic smoke inside the case. We have always used the Drill Motor for drive and think it is a quite reliable unit when geared properly.
After last year’s competition we spent part of the summer developing a new drive transmission design for our robot ED. The drive features a 1:4 ratio between low and high gears, 250rpm and 1000rpm peak power output speeds, up to 65 ft-lbs of torqe, uses the Bosch and Chiaphua motors found in the 2002 kit of parts, and an 8-millisecond response time to shift gears. The prinicpal feature is that the design can be constructed with hand tools, a lathe, and a mill. No CNC, wire EDM, castings, or carbon-carbon componsite construction capabilities are required (hopefully putting it within the reach of most teams)! We play-tested Version 1.0 of the drive system at the Maryland State Fair competition at the end of the summer, and refined Version 2.0 during the fall.
Rather than keep it as a secret, we are making the design available to any teams that want it. It is posted in the White Papers Section. Download it, build it, improve on it, or just look at the pretty pictures - it’s all up to you. All we ask is that you let us know about any feedback, and if you do improve on the design, please post your improvements so the entire FIRST community may benefit and improve their capabilities. In the mean time, we are off thinking about Version 3.0 for the 2003 season…
-dave
Besides agreeing with all of your other comments I would just like to add one thing if your going to have a Good Drive train its not just the Quality of the drive train. Its the quality and know how of who works on it. We all had some part in working on the drive train on fluffy but their were a few special people on our team who know those gear boxes like the back of their hand every, screw, every gear, every sound that those drive trains make they knew them. And in our case Fluffy our robot well it was very strong and robust but at both regional and nationals we had a few problems with the drive train. Those few select people I was referring to well they put their blood sweat and tears into to those drive trains. They rebuilt our drive train in under 3 hours changed treads in 5 min, and as a freshman last year I worked with many of these people and though they don’t brag and probably don’t even think about it but I hope that they realize they are really what brings our team and Robot together under pressure. That in my view is the most important part of any good drive train. And that is the only other thing besides design that really makes a drive train come together.
*Originally posted by wysiswyg *
**When working with gears always use an odd gear ratio. ie. 40:11 instead of 40:10 This always promotes even wear and tear on the gears. **
I was confused by this so I asked an expert…
"If the large tooth number is evenly divisible by the small tooth number, then the same teeth will always contact each other. So if one tooth gets
slightly damaged, it will continuously wear on the same mating teeth and wear out sooner. If the numbers are not evenly divisible, then the damaged tooth will mate with every other tooth after a certain number of revolutions. Thus the wear will be spread out across the entire gear. So, it does not really have to be odd and even - just not evenly divisible. However, in our applications, this is irrelevant because we do not expect the gear mates to last for many years of constant use. A much bigger consideration is to properly design the gears for size and materials based on the loads required to be carried.
Raul"
Is this what the criteria for the odd ratio is meant to achive?
Is this what the criteria for the odd ratio is meant to achive?
Yeah. I guess I should have explained this better. But thats the whole gist it.
The only components that you are allowed to hook up in the pneumatics system are the components they give you. You cannot put anything custom-built in the line under current rules.
ya i know… custom stuff were: crank shaft, connecting rods, cams. actuators would be controlled by the cams hitting into some limit switches… not a bad design… the cam shaft would be rotated by one of those little motors we got last year and depending on how fast u rotate the cam shaft, the bot goes forward or reverse, fast or slow… wouldnt have been IMPOSSIBLE like it was, had i had a machine shop to use
*Originally posted by Andrew *
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- List all possible types of drive systems (rear differential-caster front, rear differential-Ackerman front, tank drive (treads or chain driven tandem wheels), swerve drive, etc.
Andrew, Team 356 **
Can you define “rear differential”, “Ackerman front” and “swerve drive” for us?
Here is all of the info on Ackerman Steering (That you could ever want)
http://www.pbracing.com/handling/ackerman_steering_principle.html
Swerve - Is pretty much the same as 4 wheel steering which could be independent, front & back, or all 4 linked to steer together. The main benefit is incredible maneuverability. Think of driving straight toward something then ‘swerving’ to the side to avoid it, in this case think up to straight sideways
Rear-Differential (in my mind at least) allows each rear wheel to spin at a different rate opposite of a locked rear axle, by changing the speed of the rear wheels the bot can steer
*Originally posted by Matt Reiland *
**Here is all of the info on Ackerman Steering (That you could ever want)http://www.pbracing.com/handling/Ackerman_steering_principle.html
Swerve - Is pretty much the same as 4 wheel steering which could be independent, front & back, or all 4 linked to steer together. The main benefit is incredible maneuverability. Think of driving straight toward something then ‘swerving’ to the side to avoid it, in this case think up to straight sideways
Rear-Differential (in my mind at least) allows each rear wheel to spin at a different rate opposite of a locked rear axle, by changing the speed of the rear wheels the bot can steer **
Link not working.