For everyone that has attempted, or wants to attempt, to design their own gearbox/transmission design for the FIRST competitions, sit up and take notice - there is a new sheriff in town!
I had a chance to see the drive system designed and built by Team 33 this past weekend at the Richmond regional competition. It is, without a doubt, one of the most elegant designs I have seen in the nine years I have been working with the FIRST program. They have built a dual-motor, four-speed, shift-on-the-fly, AUTOMATIC transmission that is amazing.
It is the ultimate in simplicity - you can build it with a lathe and a drill press with an X-Y table. The gearbox itself is very small and compact - under two pounds. The gearbox and combination of the motors are separate subsystems, so the gearbox can be used with a single-motor (or triple-motor) design without any redesign. The shifting gears are all cut from 12, 14 and 20-tooth, 16-pitch pinion wire - the large tooth profile, small DP-to-diameter ratio, plus 15 mils of designed-in backlash makes on-the-fly shifting trivial.
But the best part is the automatic shifting function. The system detects wheel speed to determine the output of the gearbox. They have calculated the power curves for transmission in each of the four gears, and determined the optimal crossover points for the curves. The control system has been programmed to sense when the system reaches one of the crossover points, and automatically fires one or both of the shifting pistons to bump up or down one gear. All the robot driver has to do is push the throttle, and the system just goes. It auto-shifts all the way up to fourth gear for high-speed runs. Bump into something and need to start pushing harder? No problem - it just senses the drop in speed and auto-shifts back into first gear.
The Killer Bees have set up a great demo board with a prototype of the design all laid out, along with their design specs and performance analysis. They are very open with the design, and indicated that they will be writing up a white paper on it later in the year. If you are going to be at the Detroit or Canadian regionals, make sure you find a way to see this drive transmission in action (and if you end up against them in competition, you will definitely see how effective it is). My only regret is that I didn’t get a chance to get any photos of their gearbox - if anyone has any, please post them!
I spent a good amount of time just staring at that thing, it was absolutely fantastic. If anyone has a chance to, I highly reccommended checking it out. I’m new to FIRST, so I don’t know how common this kind of thing is, but I was blown away.
My team took some video of it, along with their coach explaining it and it will be up on our website soon.
I loved the CVT designs that have popped up a few times in recent years. But with ones like the ThunderChickens design, we could only look on with envy and the realization that it was a design we could not build without a much better fabrication capability. That is why the Killer Bees design is so brilliant - they get a similar level of performance (particularly with the automatic shifting function), but you don’t need any high-end tooling to put it together. Just about anyone with access to a moderate high school shop can build it. In that respect, it is a truly elegant design.
Thanks for mentioning this. I can’t wait to see a whitepaper. I’ve started to look for a new drive system for next year and something like this sounds great. We don’t have the best machining ability so something that can’t be done in a high school shop would be great for every team. Since next year will be our third year it would be nice to make a transition from a single speed chain drive system to a multi-speed transmission. I will have to look into this.
actually our team(701) built a CVT transmission much like thunderchickens without that much machining capabilities UC davis did housing plates BUT it wouldn’t have been hard to do it w/ out mill but when the mill came we didn’t know how to use it …lol (it came like 1 week into the competition)
If I remember correctly, your system only gave you a constant torque at all speeds, rather than the Thunderchickens, which gives them variable torque at different speeds. (It’s still a very cool pseudo-CVT, and does work well for it’s intended purpose, congrats for pulling it off!)
To get back on topic, 33’s drive system sure sounds amazing, and I can’t wait to see pictures of it.
Thank you very much for the kind words. Working with the team to design that transmission was a lot of fun, and we learned a lot! But after looking at Team 33’s design, all pride of ownership in ours went right out the window! Our immediate reaction was “we GOTTA build one of those next year!”
Thanks, I’m glad everyone likes our design.
We have made two speed transmissions for the past several years. Each year we try to make them simpler and smaller. I found that with the kind of high/low shift range that I like to have (3:1 or more) that the robot would tend to lurch severely if you downshifted at high speeds. I really want to make a 3 speed with an intermediate gear to help this. It turned out it was easier to build a 4 speed than a 3 speed ( its really two small two-speeds in series). We focused the design around reliablity and ease of construction, the demo unit on display was made entirely by high school students in a few evenings using no special tooling.
Once I had a design with 4 gears I was pretty much forced to automate the shifting in order to keep from overloading the driver. I talked with a few Automatic Transmission experts at DaimlerChrysler on how to do a shift scheduler and viola…a fully automatic electronic robot transmission.
It really is pretty neat, providing a nearly flat power output across a very wide RPM band with a 5:1 total shift span.
I plan on posting the design and engineering here as soon as I get a good set of drawings made up (I’m not a CAD guy, I made the ones in the robot from a napkin sketch).
This may sound wierd…but we still haven’t tested our low speed yet…haha…we will hook up the current sensors etc…AT COMPETITION!!! (funny i know) …but they actually said their transmission doesn’t give a different torque…torque remains constant…as for ours we still think it might give dif torque outputs but they say it won’t…we probably have to test it… lol…
btw AWESOME transmission…just saw the pic
I saw the robot in competition, and it was great. I was really impressed with how you were able to speed accross the field at high speed, then push the mobile goal with little effort. I am guessing that this is a shift on-the-fly transmission. Could someone tell me how some teams have transmissions that cannot be shifted while driving, and others can? How are they diffrent? Sorry if these sound like stupid questions to you but, I do not know that much about drive systems.
They are all different…most of the shifting ones i’ve seen have 2 sets of gears and a pneumatic slides an input gear into one gear and out of the other, one that we built a while ago based on Technokats had dogs which catch on to the gears and engage them…the gears are on bearings so they don’t do anything without a dog…
its kinda hard 2 explain…check out some pics and you will understand
Very Nice, Very simple. The best part is definaly making it automatic. It is something new and refreshing so to speak. Very cool that you guys actually took time to calculate the power curves and shift at the right points, props to you guys!
I really must say that this is an awesome system. Congrats to team 33.
I’ve thought of automatic transmissions for a couple seasons now, and I never thought of monitoring output RPM. In my theoretical designs for an automatic transmission, I would have monitored current to the motor, and shift based on that information. At different gear ratios, the stall current of the motor is constant, and if you set upper and lower thresholds, you can shift up or down, depending completely on whether you need less or more pushing power, respectively. I’m sure it’s more complicated than I’m making it sound, but as I said, I’m stuck in the realm of theory, here.
Just my take on the theory of an automatic transmission. With all of the talk of constructive vs. destructive criticism that went on recently, I want to say that I’m very impressed by this system. Again, many congratulations to 33.
Our immediate reaction was “we GOTTA build one of those next year!”