Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Just curious....what kind of attatchment was it that you had on that gearbox? assuming it was an arm or something, how much weight how far out with what kind of gear reduction?

inquring minds want to know :)


(also....how deep is the failed area into the carrier plate? looks like there was way too much end play in that trans!)

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

These plates look exactly like the torque to failure tests that I did on the bench set up.

There may have been some extra end play in the gearbox but it is hard to tell because the carrier plate sort of screws off if you know what I mean.

I am very interested to know what your setup was. Did you hit end stops? Was there other significant dynamic loading?

Please share more info.

Thanks,

Joe J.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Here's an interesting thought for everyone... ((please bear with me, I don't know many technical terms for this))

We are using a banebot transmition on our arm. the arm weighs about 7 lbs, 2 of which are used as a counterweight. After spending a day with the programmers, we noticed at least 25/30 degrees of backlash. When we took our transmition apart, BOTH of the plates were bowtie shaped.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Was this the 56mm kit transmission? What, if any, additional reduction?

And when you say both plates, do you mean the final stage plate on two separate gearboxes or both stages of a single gearbox. (The latter case would be very interesting and as of yet undocumented.)

In light of the last few posts, I'd have to agree with everyone who has said that direction change from the load side is what is killing these plates more than the actual amount of torque applied from the motor side. A 7 lb, well-counterweighted arm may sound like a less threatening load than a 120 lb robot, but it may all be in the dynamics.

Some other data to consider: I made 42mm plates out of tool steel, which I was going to harden. Dr. Brooks suggested that they would become too brittle, so for now I am using one as it comes (annealed), which is actually slightly softer than the stock 42mm plates, which have been shown to deform the same way as the 56mm in some conditions (the original post by Karthik). (Note that the 42mm plates and my plates are both harder than the 56mm plates.)

Our setup is a 256:1 gearbox (supposedly the worst case, although I don't think the actual reduction matters much if the loading is coming from the arm side) with a 72:10 sprocket reduction to a light-medium weight arm (1"x1"x1/16" Al box extrusion, 3.5' length, globe motor mounted about 1/3 the way out, 1.5 lb end effector, no counterweight yet). We've been running the arm for three days, with and without motor braking, and we've been using it to deploy a 26-lb ramp and platform. THERE IS NO NOTICEABLE BACKLASH at this point.

Besides being slightly softer, the only difference between the plate we are using and the stock 42mm plate is that the double-D flats are a closer fit to the shaft. (I cut them undersized and filed out until it slipped on...not a press fit though). This leads me to believe that if you can get full engagement of the shaft on the plate (42mm or 56mm), you will be a lot better off. Also, even when deploying the ramp and platform, our motor never draws more than 10-12A...much much less than its stall torque. The extra 72:10 reduction makes a huge difference and the arm is still plenty fast, ~30 deg/sec.

Sorry for the long post. I've been following this and the other threads from the beginning and I still can't wrap my head around the problem, so I occassionally need to just dump my random thoughts out so others can maybe see a pattern that will lead to a way to protect these plates.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

No end stops (well there are, but there are some magnetic limit switches set a little piece from both that would slow it down gradually to a stop). Smoothing in the programming for speed, bearing opposite to keep shaft straight. Everything as suggested in other forums. Our set-up had a spool which wound in cables to lift extrusion up along sliders. And as we let the cable out slowly, it would drop it with gravity.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Last night one of our Kit 56mm gearbox failed. Here are the answers to the questions that Dr. Joe asked for.

1. Approximate weight: 100-120 pounds. (we added weight to the front of the robot to make 100 -120 lbs.) See picture.
2. 7” Diameter Aluminum wheels 1" wide with urethane on the outside with needle bearings on steel hardened shafts. Six wheel drive with the middle wheels down approximately 1/8”. See picture.
3. 30 tooth sprocket on transmission shaft to 40 tooth sprocket on wheels with #25 chain.
4. 2 CIMS adapter.
5. 12:1
6. supporting outside shaft, gears are approx. ½” from gearbox. See picture.
7. Do not know.
8. One gearbox was not able to turn the wheels. We did not tear the 2nd transmission apart.
9. See pictures below. We removed the weight from the robot to take the transmission off the other side.
10. We were mainly driving forward and then slamming it in reverse. Doing some turning. We do not have an exact count of how many times we did this. We are guessing 75 – 100 times.

This was a practice frame that we put together to see how the transmissions would work. We ran the robot for a day about a week after after kick-off and then off and on since then.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Excellent data. Thanks especially for the pictures. Is there significant backlash on the other gearbox? Will you please check it and report back?

Joe J.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

I checked the backlash on the other transmission. It is approximately 25-30 degrees. I marked one of the teeth and rotated the gearbox until it stopped. It moved about 2-1/2 teeth of a 30 tooth sprocket. 2-1/2 teeth on a 30 tooth sprocket works out to about 30 degrees.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Alright, I got a chance to drive ours. Stock original plates. It has been driven maybe a total of 10-15 minutes. right now it weighs about 55-60 lbs including battery. 6wd, dual CIM adapter kit thing, another bearing supporting the shaft, blue roughtop tread ~0.75" wide. Drives great. about 10 degrees of backlash is apparent right now. I'd estimate perhaps 150-200 normal game play style direction reversals. Will update when more testing is done.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Ok heres some more info on our second gearbox failing (it is used for an arm!!!) don't have pics yet may post in a day or two.

1. 15 lbs it was lifting
2. N/A
3. 24 sprocket to a 24 sprocket (I think, either way its 1:1 and in the 20's) bike chain
4. 1 CIM
5. 12:1
6. yes and 1/4 inch away
7. first gearbox (DEAD see pics) second gearbox, little over 15 degrees
8. Will post soon.
9. N/A
10. smoothing function on the arm, and never over half speed

and at the moment we are making our own 12:1 gearbox...

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Our team had done some basic testing for about 10 minutes with a low load (50lbs max) and we took apart the gearboxes to take a look at the plates, when we noticed some slight bowtieing on the DD holes. We've decided to not risk further damaging the plates, and have replaced the parts with significantly harder metal that we've heat treated as well (having a machine shop next door is so helpful) which hopefully should eliminate the bowtieing effect.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Yes, it is the standard kit transmition.

No additional reduction. Drivin from the keyed shaft.

One transmition with both of the stages bowtied!!! :ahh:

Edit: We also tried making our own hardened stages... those rounded out too, but maybe they just weren't hard enough. I'm not sure.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Okay, I think we have confirmation that the plan we have in place to address this issue is sufficient.

Special thanks to Alan Fallone & the great folks from Team 1279. These guys took time away from their own robot to work this out for the rest of us. AND they are not even using the KOP transmissions. This is really what Woodie means by GP. Three Cheers and a mighty Hazzah.

Recall that the test buck was a 115lbs 6WD chassis with wheels covered with roughtop conveyor belt. The test set up was a 12:1 gearbox with 2-CIMs. After 500 hard cycles (each cycle was command full forward, get to up to full speed forward, command full reverse, get up to full speed reverse, command full foward again and repeat):

• With the shipped carriers, the DD in the carrier was noticeably bowtied (but still far from a total failure).
• With the new carriers, this is not an issue.

See the attached great pictures from Alan Fallone.

Like all solutions done in hurry, we had to take some risks. In general this solution has turned out well.

One fly in the ointment is that the carrier pins had loosened a bit by the end of the test. This is not a tragedy. The gearboxes still functioned just fine with the pins less than tight at the end of the test.

Alan reports "...the transmissions ran fine. The pins are a tight fit now that they have cooled off, I probably got the transmissions hotter this time, running the tests in one night with less time to cool off."


If we had more time to develop the press fit tolerances we could have addressed this but we did not so we are limited in our response. One thing Banebots is doing is pressing in the pins a bit deeper than we did on the first samples we tested. This should help keep the pins in place, but even if it doesn't the gearboxes still work fine.

I really want to emphasize to teams that this is not a sky-is-falling-in moment. Two important points:

1. Loose pins do not have a dire outcome with respect to the performance of the gearbox.
2. This may not even be an issue because this is a very abusive test (more abusive than most teams see in a season) AND Banebots has taken steps to improve the preformance over the tested carriers.

Bottom line: This solution seems to successfully address the DD joint issue. The pins loosening in the carrier is a condition that may occur after a lot of hard driving that doesn't have any serious consequenses other than that teams have more parts to loose while working in the pits.

Thanks to all who worked so hard on this issue. There are too many thank everyone by name but I have to give props to Ed & Rick at Banebots. These two have gone above and beyond the call of duty in my opinion.

Joe J.

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Wow, looks like the bowtie problem is fixed with the new plates. The pins look a bit shorter?

anyways, here's a slightly smaller pic to save others the hassle of dealing with the 2.5mb zip download

Re: Banebot 56mm gearbox - double D - V3 - It's Show Time.
 

Thanks for the smaller pictures. I get in a hurry and forget about the dialup folks.

As to the pins, yes, they are shorter. This too is a consequence of moving faster than we'd like. Many sources can provide a handful of 4mm pins. It is quite another thing to get 25,000 in a few days. Banebots wisely chose to go with a DIN standard 4mm pin even though it was slightly shorter so that they could buy from a dozen or so sources.

While I am taking about sources, many of who read the Nothing But Dewalt White paper have heard of Lou Oudin and Capital Tool. Capital has gone under but Lou keeps on keepin' on. He has started a new company, Sonic EDM. Lou was another hero that came to FIRST's rescue on this carrier issue. I highly highly recommend Lou and his company to anyone who needs work done (especially Wire EDM work -- Lou can get almost anything done but his speciality is Wire EDM).

Joe J.

P.S. Again I am forced to say that a have no financial ties to Lou and/or Sonic EDM other than I use his shop from time to time when I need good work done (both for Delphi and for my company Robotic Amusements). Over the years, he has become a friend, but the main reason I recommend him is that his prices are good and his service is off the charts great.