pic: 254/968 Gearbox - Destructive Testing Results
 

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Good job! I think this is one of the first times strength testing has been performed on a FIRST robot powertrain?

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Wow. I knew that it was strong when I played with it... But not THAT strong. Props on a seriously sweet design!

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Not all teams have a gearbox that is also a senior project though. Its cool to see this information. I seem to remember travis saying that it wouldnt be to practical to manufacture at the same level/cost as an AM shifter. Thats too bad. I'd love to throw a couple of those on my robot.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Kind of...except that transmission output shafts are subject to the torque from the engine, times the gear reduction in low gear. Which is why automotive transmissions have larger output shafts than input shafts.

Interesting tests, thanks for sharing! It's a nice transmission, but not nearly as cost effective as the AM shifters as noted. Unfortunately real life generally means economic considerations are top priority for a design.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Yes, automotive torques are measured at the wheels in a ~1:1 gear or at the crank... However, I will stand by my original point that 170 foot pounds of torque at the wheels is still more than a honda civics engine can output. Correction: (without a transmission)


I am not saying this will withstand that torque, as there is no factor of safety present, I am simply giving a basis for comparison for those who see these results as just numbers.

Also, with regards to cost effectiveness, that's not always true. This project was based around a model of weight being the utmost concern, and cost being forth of fifth down the line. Also, weight can become a cost savings itself. When it costs ~$3,000 to $5,000 per pound (estimate) to send a sattelite into space, that weight savings sometimes can create an economic savings greater than the added cost of manufacturing.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Wow! That is one strong tranny.
Were these results close to what you were able to calculate?

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

More or less. We didn't concentrate too much on these forces, as the gear teeth would strip long before any of the shafts or webs would fail. We spent considerable time calculating bending strengths on the gear teeth to make sure they would be okay.

As such, yes, these were very similar to what we calculated and predicted. Some components had an initial 10X factor of safety in them, but due to the design, the shape and size couldn't be changed much and further weight wouldn’t have been easily removed. Since the components didn't weight much at this point anyway, we didn't feel that a design change was worth while or necessary.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

How were you able to calculate the strength of the components?

Thanks, Travis

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

For gear tooth strength, we used the Barth revision of the Lewis bending forumula. For other strengths, we used other bending eqns, torque eqns, and shear strength eqns depending on the part we were analyzing.

We also did finite element analysis on all of the components to verify that our initial calcs were correct.

Here is an example of the FEA for the 80 tooth gear. These parts were subjected to two 20 KSI loads on the gear teeth, ~ 90 degrees apart.

Stress Distribution





Displacement

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

So, how much are you guys selling it for next season? :)

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

I think the real question is, where can we find the plans/instructions so we can make it better? (Is that even possible??)

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Always! "Continuous Improvement" is the future! ;)

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

(first part removed, I think we cleared that up)

In the real world, cost is a major factor affecting design. The 254/968 robot, and space missions, are notable exceptions. AndyMark sells a lot of transmissions, because they have a very cost effective design.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Yes, torque is increased as the gear reduction increases... of course. I think I added a little too much there at the end with "transmission or otherwise" My ASSumptions were based on engine output torque, neglecting that fact that you have the ability to increase that torque in lower gears. Sorry.

I think the confusion here stems from my failing to explain that this rating I quoted is the "specification" value. Usually these horsepower and torque ratings are measured on an engine or vehicle dyno in a gear close to 1:1, or simply at the flywheel if on an engine dyno.

So no, this shaft wouldnt handle the torque at the wheels in 1st or 2nd gear on a honda civic. However, most people wont say their honda has a torque of 400 ft lbs because that is entirely dependent on the transmission and gear reduction, as you mentioned. And it would in fact be strong enough to handle the torque coming out of the engine.

I should read more carefully next time. ;)


Also, I should add as I was somewhat upset by the other comment... we did do a cost analysis and mass production process and material selection. As the quantities get higher (very high), these gearboxes actually do have the ability to be cheaper than a steel alternative. Material costs become negligible, and the decreased machine run time and tool wear begin to make up for the costs added by anodizing and additional lightening. As manufacturing engineering students, we were far more concerned with these issues than we were the mechanical engineering based calculations.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Interesing points about the reduced costs with very large production runs.

Many teams rely on others to shoulder the "up front" cost of buying/leasing CNC equipment, and end up buying parts that available off the shelf ....it's neat that you had the opportunity to design and make these transmissions!

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Any chance you'll do endurance (constant fluctuations in fatigue) testing with this transmission? Granted these things are built for (at most) 3 competitions and a bit of practice (about 120 minutes of run time if you make the finals at competitions) but what would happen if you tried to put the robot under its stresses for say, twice that amount of time in a competition-style environment?

My Material's Science intro class went over a bit of sheer stress analysis but the details escape me at the moment. Is there a way to get a product lifetime estimate from the tests done already?

Excellent opportunity you have to be able to do such a disciplined and detailed analysis.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Funny you ask. We did do long term accelerated wear and fatigue testing.

We built a total of 16 gearboxes. 4 of them went on competition robots. 254's comp bot saw ~8 hours total run time including practice at 4 events. 968's comp bot saw only ~4 hours run time including practice at 2 events.

However, there were another 4 gearboxes built and used on two practice robots which each saw ~100 hours of driving. After these 100 hours of aggressive use, we saw little to no difference between the practice robot gearboxes and the competition gearboxes with less than 10% of the runtime the practice ones saw. It was determined that the anodize wears initially after 2 or so hours of use and remains at that worn, broken in point for the remaining time.

In addition to those 8, we used 2 more gearboxes on an accelerated wear test platform. We mounted the gearboxes onto a mock side rail and programmed a continuous loop program to cycle the motors and actuate the shifting cylinder: full forward, shift, full reverse, shift, for another 100 hours under load.

Here is a picture of that test platform after the 100 hours of testing. You can see the anodize wear, but after measurement, the involute tooth profile is intact. We also disassembled the gearboxes and checked for any fatigue issues and further damage or wear... while we didn’t have the ability to do a thorough lab test, our brief visual inspection showed no damage or signs for concern.





Also, here is a video showing the test platform with a wheel mounted for later use as a demonstration unit. As shown in the video and pictures, there is no load on the output shaft. This video is strictly to show the cycling procedure used. We may bring this to IRI if people want to see it?

http://sivart.org/misc/Demo%20Gearbox.avi

Lastly, here are the components removed from the test platform after ~100 hours of continuous use. Some wear is noticible, other portions are just dirty from the anodize wear.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

These are amazing results. Even better, Travis has done a great job explaining this testing and failure modes.

It is one thing to be a great designer, it is another thing to be able to explain what you did, how things work, and why things happen.

Personally, I appreicate this work. Needless to say, FIRST will see better designs from many people because of this effort. This design has indeed "raised the bar" in FIRST.

Most respectfully,
Andy Baker

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Very nice, very strong, looks like a great piece of equipment.

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Travis,
Great work guys. I have been fascinated by these transmissions ever since the first pic shown and have spent a good amount of time at LA, SD and champs admiring them. The amount of work put in is really shown in every part and detail. Also, the fact that you are going to such great lengths to publish your results (I know you did the test anyway for the senior project) is much appreciated. I am already inspired and thinking of what I can do for my Senior Project at San Luis Obispo and I haven't even finished my senior year of high school yet.


Sorry, couldn't resist, but does AndyMark have any improvements planned to the your shifters?

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Yes, there will be a new version of our shifter available this fall, but I don't want to take the focus off of what 968 and 254 have done here. There will be enough information about that later.

I am looking forward to IRI for many reasons, and one of them is to talk with Travis and get a tour of this gearbox.

Andy

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

Wow! A very impressive effort both in the design and the quality of testing. Really nice work, guys!

Re: pic: 254/968 Gearbox - Destructive Testing Results
 

I checked these out in Atlanta and they're the real deal. Quite possibly the most amazing transmissions I've seen to date in terms of simplicity, quality, and resilience. The coolest part is just picking it up, like a mechanical feather or something...

I'm anxious to see what other ideas come as a result from these gearboxes. Great job guys.