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pic: 2 Speed Transmission
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Looks good! You should include some sort of description or explaination though!
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Re: pic: 2 Speed Transmission
I'd try to eliminate the third shaft by going with bigger gears on the second shaft, a bigger gear on the primary reduction (the middle one), and smaller gears on the first shaft. What is your target speed?
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Re: pic: 2 Speed Transmission
I am shooting for 15 ft/sec and 5 ft/sec. I chose 3 stages because I could then use the free 14 tooth and 50 tooth gears from the KOP transmission and machine them how I want.
The gear ratio is as follows. 14 tooth gear on the motor geared to a 50 tooth gear. Then, the two gear ratios to the dog shaft are 25 tooth to a 50 tooth, and a 40 tooth to a 35 tooth gear. The final reduction is a 14 tooth gear and a 50 tooth gear. As you can see, there are a lot of 14 and 50 tooth gears in the gear ratios that I chose. I only have to buy 25 tooth gears, 40 tooth gears, and 35 tooth gears. |
Re: pic: 2 Speed Transmission
15 fps is probably too fast for FIRST purposes. Most teams and drivers agree you lose the ability to easily control your robot after about 11-12 fps. Additionally, you can easily outrun most other teams at around the same speed.
If you wanted to keep the 3:1 ratio, I'd aim 12 fps and 4 fps (with inefficiencies slowing it slightly from those values). |
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I think the ideal low gear is in the 5-6 fps range, and the ideal high gear is in the 11-12fps range, after inefficiencies, but those numbers (especially low gear) may not be very feasible, depending on the weight of the robot, and the tread being used (that is, how strong the robot needsto/will be able to push). I have always thought that robots moving in the 3-4fps range were too slow. Basically, I agree with the OP's speeds.. I would even say to make the low gear a bit faster, but blah.. I understand the current draw issues that may arise as soon as some good tread gets put on the wheels. |
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As for outrunning most other teams...if most teams shoot for 12 fps you won't ;) The general rule of drive trains is you can always go slower, and you can always have use less torque; it is when you try to do things the other way that you run into problems. |
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What part of the transmission is most likely to break? I am mostly worried that the first time that we get into a pushing match, the transmission will fail.
I am having trouble putting this next sentence in plain english, so bare with me. When the dog's teeth just leave the face of one of the two gears with holes cut in them to accept the dog's teeth, how much clearance should I have between the dog's other set of teeth and the other gear? Thanks for all of the feedback so far. |
Re: pic: 2 Speed Transmission
<These are my thoughts, some suggestions from my experience, if some of my hypotheses are no good, please correct me>
If you want to shoot for 15 fps and your team has a good driver, I'd say go for it. Last year, we put our bot up on blocks to find its freewheeling speed, and high gear was around 14 fps. Once we got the bot on the ground, we never actually clocked it very accurately, but our rough figures said that it was running about 12 fps. You may not lose as much speed as we did, depending on the efficiency of your drivetrain and the type of wheels you use. (We ran a six wheel #35 chain drive with 4 go-cart tires and two pneumatic Skyway look-alikes. If you use smaller wheels I wouldn't think your bot would slow down as much as ours did) Ours seemed blistering fast, it was fine for '06 (the field was open and our driver was great), but I wouldn't recommend it for a playing field that has a lot of obstacles like it was in '05. Also- two things we learned the hard way- -make certain that the key for your output sproket/pulley is TIGHT. We had problems with shearing, yes shearing, keys off on our output because they were too lose and were getting slammed back and forth a lot due to our defensive strategy (ram, back off, repeat, etc.) -try not to shift when your motors are under power, it tends to be hard on the dog. when we took our gearboxes apart this summer, the dogs' corners were worn worse than they should've been. Just try to shift only when the motors aren't running at full power, and I think you'll be alright. As for the clearance, I know exactly what you are talking about, but I can't remember what ours was. I'll check the bot tomorrow and get back to you. I would reckon that 1/8 would be plenty, but I honestly can't remember. Good luck! |
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Acceleration is a factor, as well. I agree with Jeremiah that last year (2006) was a good year to have a "zippy" speed to fly across the field, but in 2005 (and, arguably 2004) a superfast robot could have proven to be a hinderance. In 2004/5, all the stop and go and fine adjustments left the fastest of robots not usually going above 9-10 fps, even though they were capable of more speed.
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A majority of the "racing" in FIRST actually happens when a bot breaks free of a defense in one "axis" and then moves along the other to create space from the defender. For example, Team A is trying to score in goal A, which is down the length of the field. Team B is blocking them by moving back and forth along the width of the field, preventing Team A from getting by. Team A eventually slips by Team B, and moves down the length of the field towards the goals as fast as possible, as to score as many points as they can before Team B and orient themselves along the length of the field to resume defending against the Team A. In this situation, the maximum speed of the bot is only reached for a couple seconds, and the speed in which Team B can turn is usually far more important than either of the robot's top speed. Additionally, in this situation, both teams pushing power and speed come into play when Team B is blocking Team A in the beginning, as the having both pushing matches, and the speed the correct their positioning is critical. The ability to shift-on-the-fly is typically fairly helpful for both teams in this situation as well. Quote:
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