As we anxiously await the double D solution, we were running our base around yesterday and one of the gearboxes locked up. The other has intermittent high-friction spots. We are using the two CIM adapter and the 16:1 conversion. Upon disassembling the locked gearbox, we found that the last sun gear had seized on the output shaft. In the working gearbox, the last sun gear can spin, but not freely. The end of the output shaft was rough, and a groove was worn inside the sun gear. Is it necessary for the sun gear to ride on the output shaft? Can the end of the shaft, just above the double D, be cut off?
It sounds like maybe you are putting too much side load on the output shaft. Is the shaft solidly supported at the other side of the load (load = sprocket, wheel, etc)?
Yes, we’re useing the matching bearing block.
2xCIM at 16:1… Wow! That’s a LOT of torque. (And stress… both on the gearbox and the team until this double-d thing gets worked out.)
I can’t say for sure we experienced the same thing as we are just using 12:1 trannies with one CIM, but we had some similar “lock up” symptoms and shortened the spacer on the motor shaft and ground down the end of the motor shaft about .10" and everything started to move a lot more freely.
There are some great suggestions towards the end of the “Double-D Reloaded” thread, as well as a .pdf near the bottom of the 56mm tranny page on the Banebots site that can explain this more clearly.
However your symptoms sound slightly different from ours (we had a lot of wear on the end of the CIM where the gearbox pushed the spacer against the motor) so if you have already shortened the spacer and are still getting this lockup problem… my apologies for posting a non-solution.
Jason
Hrm. I was having a similar issue with one of my gearboxes this week while installing a new carrier. It was binding at a particular angle and it seemed like the shaft was forcing the sun gear to be off center in the planetaries. The solution (which I can only semi-jokingly recommend) was to find the position of most binding, lay the flat spot of the sun gear on a vice, and tap the bearing block gently with a hammer to try to force the end of the shaft to bend slightly in the opposite direction. It seemed to work, but it may have been all in my head.
Getting the alignment perfect on these gearboxes is a tough but worthwhile adventure. I reassembled two this week: one went together with no problems at all and drew less than 2.5 amps. The other had alignment issues, most caused by my new carrier plate, and originally drew over 4 amps. But after breaking it in, tearing it down, polishing the bearing block to make it a better fit into the ring gear housing, and reassembling, it is now also down to 2.5 amps and sounds a lot happier.
Can you post a photo of how the bearing block is mounted? If it is not fully supported then it isn’t going to do much good.
Another problem may be that the lubrication at the pinion/shaft area where you are having problems is probably not as good as it should be, maybe you need to take the gearboxes apart and lubricate them kind of often?
What purpose does it serve to have the sun ride on the output shaft? On the first stage, the sun is not supported, nor are any of the stages in the 42mm 64:1 gearbox.
In the first stage, the sun gear is supported by the motor. You’re right about the lack of sun gear support in the center stage of the 3 stage boxes. Although the sun gear in any of the stages after first is somewhat supported by the planet carrier that drives it.
You could probably get by without the support for the sun gear on the final stage, but you might want to take it apart and check the wear pretty often…then again, you might want to take it apart and check for wear (and add new grease) pretty often no matter what you do!
The upside is that they’re fun to take apart and play with.
We had a similar problem this weekend and after a complete teardown of the tranny, discovered WHAT the problem was.
What we discovered was that TILTING the tranny (or the robot for that matter) may cause one of the planetary gears to slide down the pin it is mounted on and get JAMMED between the ring that is used to mount the tranny to the adapter (the one with the 6 little allen key screws). This does NOT happen everytime you tilt the tranny, only if the planetary gear happens to stop in the right spot (not sure what the tolerance on getting “lucky” is).
I wish I had the pictures we took, am working on that now.
We have our lead mechanical working on creating a spacer to put between the planetary gears and the 2-stage gear to prevent any of the planetary gears from dropping down and jamming.
Other than a spacer of some type, not sure if there is any other solution. I am also not certain if BaneBots or FIRST is aware of this second issue (it ONLY affects the 2 CIM adapter). You can certainly NOT guarantee that your robot will not tip over 
As soon as I can get the pictures, will post them.
I don’t see any reason to have the output shaft go through the sun for stage 2. It may help allign things but I believe that every thing should work without it.
One thing that caught my eye in you post is that the shafts siezed and/or scored. I wonder if the chaft was not smooth to begin with? It is possible that is part of the problem. Also, it is possible that somehow the surface did not get greased properly.
On another note, WaterFreak brings up a very good point. Looking at the parts, I can definitely see that the tabs on the 2-CIM adaptor can cause a jam if one of the planets gets up in the space between the tabs.
One easy fix may be to put a spacer on the cluster gear (over the sun but below the big gear). Here are some washers from McMaster that may work well for this purpose: 98038A268 The ID just fit over the sun and its OD is 1.3" will hold the planets out of the space. I would recommend using another washer below it to keep it spaced out right. If 2 washers work fine, but it looks like the spec as 2 washers being just a bit too thick (we need to space it out by .220" or so and each washer is 0.122-177" too think for 2). I think this wave washer may be just the ticket: 92161A035
I have to call Ed from Banebots on another matter. I will make sure that Banebots is aware of this issue.
UPDATE:
I was just talking to Ed, explaining the problem when I thought, “Hey, wait, isn’t there a washer or wearplate already IN that gearbox that would prevent the planets from dropping?” I had done my initial evaluation using a naked carrier, not a whole gearbox assembly. Investigations showed that, yes, there is a washer/wear plate in the gearbox. It may have been stuck up to the aluminum motor mounting plate, but it is there.
You can even see it in Banebot’s excellent instructions
“…Once removed, the back plate wil slide off. Make sure that the thin metal separation plate stays with the planetary gearbox as shown”
FYI
Joe J.
Just looked at the assembly instructions, I can say for certain that neither of our assembled transmissions has that spacer plate in it.
I will have to check when I get to our meeting tonight if they are with the “extra” parts from when the transmissions were taken apart to assemble into the 2-1 kit. Am wonder if that spacer plate is getting stuck to the block you remove and we just did not notice it.
Just a suggestion to pass along…In the assembly instructions, it might be a good idea to make a bigger thing of making sure that spacer is present. The wording is at the end of a small paragraph and might get easily overlooked. :eek: :eek: :eek: Seperating it out into its own bullet would make it harder to miss.
On the transmission I took apart, the black wear plate was well stuck (with grease) to the motor end aluminum block, and it would be very easy to overlook the fact that it’s a separate part, and needed with the new block.
That was what I was thinking was likely the case, that the grease might cause it to stick to the other plate (that you are removing), thus causing it to get overlooked.
Good thing for all the team using the 2-motor adapter to make sure of, otherwise any tippage of the transmission/motor abbembly OR of the robot (say when you might fall off a ramp???) might then lead to a seized motor :eek: :eek: :eek:
There have been a few creditable reports of this S4 problem (S4 = Second Stage Sun Seizing).
Here is another one:
I don’t yet know how much of a problem this is going to be but this is what I recommend to teams:
Take apart your Banebot 56mm gearbox and inspect it.
- I would look for contaminated grease (shavings, brass powder, whatever). If you find contaminated grease, I would clean out the entire
gearbox and carefully re-grease everything with an automotive or lithium grease from your local hardware store (you don’t really need any super duper grease for this application). Make SURE you lube the output shaft/second stage sun surface. 1. I would make sure that the output shaft/second stage sun interface has been greased well – check both the sun’s internal surface and the shaft’s external surface. - While I am looking for grease, I would make sure that both surfaces are smooth. Look for pitting, gouging and/or scoring. If I found any thing that bothered me at all, I would used some fine emery cloth to clean the two surfaces up and then I would clean out the entire transmission and re-grease it.
- If this S4 failure happened after I knew that the interface was smooth and well greased, I would consider cutting off the output shaft so that the second stage sun just floated in the gearbox. There are many proven transmissions that work this way. I would use it as a last resort, but it is an option to consider.
If any more teams see this S4 failure, please post a note in this thread.
More to come. Stay tuned.
Joe J.
how would we get the siezed sun gear off?
On our’s, there was about a 1/16" gap between the the sun and the the last stage planet carrier plate. There was not enough room to get any gear puller we had on it, but the one BaneBots sells might have fit. We clamped the output shaft in a vise, put a cressent wrench on the “D” of the sun gear, and worked it back and forth to loosen it a little. Then a second person pried up between the carrier plate and the sun gear with two screw drivers (but not so hard so as to bend the carrier plate) while the first continued to work the sun gear back and forth.
We had issues with the end of the output shaft grinding. Not thinking, I didnt get any pictures. After we opened it, cleaned the grease and shavings out, put new grease in we checked to make sure that the output shafts were perfectly level. They work fine now. Our guess is that originally we didnt have the output shaft level.
thanks
my father and i got impatient and within a half an hour of my posting we had a pen torch and a screwdriver. we heated up the gear and pryed with a screwdriver and it came off in about a minutes worth of work. Besides the sun gear being really freaking hot for 10 minutes there was no damage. we then deburred the shaft and inside of the gear and put it back on. the sun spins freely now and after putting everything back together it works fine and in general sounds smoother and less strained.
We had the same sieving problem with ours. I spoke to Banebots on the phone, and was told to cut the post off the shaft, it really wasn’t necessary. We did that, and everything seems fine now. It originally siezed while running it on the bench, no load, after about 10 minutes. We ran it after modification for about 20 minutes without issues.