Hey guys this is our teams off season drive train prototype.
This drive train prototype was made to ensure that we could both design and manufacture a custom drive train. To accomplish this the whole drive train was designed, machined, and assembled in one week in our schools machine shop by a small group of students.
The drive train has a total reduction of 5.31 to 1 with an adjusted speed of 14.2 feet per second. It is a single speed setup with vexpro gears.
So far it has been a great success and we are excited to make a custom drive train in our second year of competition!
This looks very well done for a (first, even fifth or sixth) custom drivetrain. The only thing I would do differently is to use only 2 bearings on the gearbox wheel. Putting 3 bearings on one shaft that close together can sometimes over constrain the shaft and cause problems down the line. Additionally, it looks like you have 4 bolts mounting each gearbox to the frame. Two bolts mounting it to the frame might be enough but it is good you put 4 in there.
Great job on the design, and good luck next season.
I would definitely consider going to only two bearing on the gearbox shaft. I haven’t experienced any binding issues yet, but will keep this in mind for the future.
Makes me wish we had a shop where we could drill holes consistently enough for gearbox plates!
Just looking at the photo, not the CAD:
Do you plan to use a flat head screw in the motor mount hole near the cluster axle? It looks like the typical cap head screw would interfere with the large cluster gear. In any case, this would make it an involved process to replace that motor.
Edit: Saw the next two photos. That cluster gear seems to be inboard in some shots, outboard in others. The farther the cluster gear is from the motor, the greater the lateral force is going to be on the motor shaft, adding bushing/bearing friction and possibly more problems down the line.
I think this will be a great practice chassis. Your ratio is bold. Drivers who develop cycle-running skills at this ratio will be ready to adapt for many possible 2018 games.
As Gus pointed out, you should tweak the design to make it more friendly to the pit crew. If the hard-to-reach screw works loose it could cost you a match.
Also, consider an alternate inner plate that will accept a third motor. 3 MiniCIMs will be better for some games than 2 CIMs, especially if you need to move up to full weight by adding a scoring mechanism. 2 CIMs will be fine if you stay light and focus on cycle quickness.
Make sure y’all think about bumpers too. There are lots of ways to solve this, so it’s not a hard problem - but it is something that you should include in your offseason process if you’re wanting to ‘prove out’ the design for build season.
It appears as though your flanged bearing will interfere with your CIM faceplates. This will prevent the CIMs from sitting flat and the CIM pinions won’t mesh properly with the main gear. To fix this, just add a pocket to recess the bearing into the rear plate. Also, speaking of the CIM’s, remember to add the CIM retaining clips. Other than those few small things, it looks great! Keep us updated when you get it driving. Although it probably wasn’t the purpose of this project, make sure to have plenty of mounting points in your frame for mechanisms etc. Maybe consider using VersaFrame instead since it comes with pre-fabbed holes for mounting.
Also, loving the F360! A F360 archive file or STEP would be much appreciated.
Looks good! One thing that I might suggest is to switch the chain routing on the double sprocket such that the innermost sprocket is chained to the gearbox sprocket and the outermost sprocket is chained to the further wheel, just so that the furthest shaft from the gearbox isn’t cantilevered quite as much.
Also, how are you planning to tension the chain? I don’t see tensioning cams on the CAD, are you planning on having some sort of Delrin chain riding tensioner?
It’s become increasing popular in recent years to run drive chain without tensioning. The norm is typically to make it CTC + .018 or .02, but it varies across chain lengths and suppliers. Looks like they put the bearing holes straight into the tube, probably with some CTC add number, and called it a day.
I couldn’t agree more with moving the obscured flat head screw! It’s something that wasn’t apparent at first but quickly became one of the biggest desired changes moving forward to a competition gearbox!
We are very fortunate to have full support from our schools shop teacher, and an excellent shop due to the livermore national laboratory donating old equipment. This frame was made primarily using a 1984 Haas vf-1!
I intentionally designed with a very bold ratio to give drivers a taste of the speed that is possible in frc, last year we used a very conservative kit bot gear ratio (around 1/2 of this one), and thus i wanted to experiment with what we believe is the upper limit of speed for our drivers!
Again i couldn’t agree more with the obscured mounting position, we will definitely keep this in mind for our next iteration!
Fusion 360 has been so great! While my first love will always be inventor fusion has been great not only for sharing design with multiple people but also for moving straight to manufacturing with ease.
I will post some videos and a few more pictures while flogging it over our schools winter break trying to find a way to break it!
Yes you did spy the interference issue! I didn’t catch it until the other day, i may just make a small spacer to offset the cim that 1/16th of an inch to test it.
In season i am planning on adding strategic keen-serted holes, the stake in threaded steal inserts, into different spots on the chassis to facilitate mounting mechanisms etc.
like this: McMaster-Carr
strong threads, easy installation, and easy to mount super structure and other mechanisms.
You called this! we used a center to center distance add of +.01, i would definitely bump up to at least +.015 or +.02 to get the chain a little more taught. This being said with just +.01 i don’t believe we will be getting any chain skip.
Routing as you suggest makes more sense from a gearbox integration standpoint - the CIM pinions and large cluster gear in the inboard plane, the small cluster gear and drive gear outboard, and the master sprocket inboard. However, if you assume that the two chain-driven wheels on a side are each driven with about the same net torque/force, the lateral torque on the middle shaft is worse this way than on the end shaft the way it is pictured as the chain force is doubled. If you have a long-cantilevered double drive chain, this may well be good reason to put a well-secured inboard plate on that middle axle. This might be built like a single axis version of the gearbox. You would not use a bearing on the inboard side of the tube, similar to Cash4587’s concern.
