Re: Banebots 42mm gearbox: Recommendations for use
 

I am not sure that some of your dimensions make sense, I think you meant:
Outside Diameter: 25mm

I measured the Double-D Diameter to be .493" or 12.49mm

Re: Banebots 42mm gearbox: Recommendations for use
 

Woops. :eek: It's been a long week. Yes, outside diameter is 25mm and double-D diameter is 10mm. (I'm pretty sure it's 10mm or perhaps slightly larger. The 56mm plates have 12mm diameter double-Ds.)

Re: Banebots 42mm gearbox: Recommendations for use
 

:cool: Paper weight? :yikes:

From the title of the post "Banebots 42mm gearbox: Recommendations for use"

I could think of some others:
Weapon
Spacer
Barbell

Sorry couldn't resist. In all fairness I have designed many things that haven't worked as planned. This is a learning experience for us all.

Great job JOE and everyone else for pulling together.

Re: Banebots 42mm gearbox: Recommendations for use
 

Last night we experienced a weird failure on our arm while we were tuning a PID loop.

We have two 42mm 256:1s on our shoulder joint with further reduction after that. One Fischer price and one banebots.

We were tuning, and therefore some oscillation of the arm was unavoidable.

After some test, we found the arm couldn't move. At all. We removed the chain and found the BB gearbox could spin, the FP one was jammed. We disassembled both and looked inside. The BB was fine, the FP however had sheared about 1/3- 1/2 of the teeth off each of the brass planetary gears in the final stage and had jammed shut. We replaced the damaged gears (The sun and carrier were fine), closed it up and it worked.

What was interesting about all this is that the Double-D joint was fine in both boxes, and had no more backlash than our untouched gearbox.

We found that the BB motor PWM had become loose, so we never gave current to the motor, and therefore were putting to much strain on the FP gearbox. This is just a guess, any insight would be appreciated as we hope this does not ruin this season if it has the potential to reoccur.

Re: Banebots 42mm gearbox: Recommendations for use
 

The only thing I can think of (other than what you said about backdriving the BB with the FP) is something that happened to our 42mm gearbox: The four long screws that hold it together came loose little by little until eventually the entire housing would twist under the torque from the motor. This would not occur if you are using the holes on the sides of both bearing plates to mount the motor, but we are only using the front face of one bearing plate. Luckily, we spotted this before it became a problem, but I imagine it would really mess with the alignment of the gears and could cause them to bind. The simple solution is to Loctite them and tighten a lot.

Glad to hear that your carriers are holding up, though. Team that are using the 42mm with FP as speed sources with a lot of extra reduction should be okay.

Re: Banebots 42mm gearbox: Recommendations for use
 

I can't believe I forgot that.

We noticed the gearbox (from front to back) twisted about 15 degrees when we tried to move the arm. That makes sense.

We are face mounting as well, but I think I have a simple solution; We will make a plate out of 1/4" (maybe a little thick, but we have the weight) that just bolts to the bottom holes and helps prevent that twist in case the bolts do loosen again.

Thanks

Re: Banebots 42mm gearbox: Recommendations for use
 

We finally got a full, uninterrupted day of practice time to really put everything to the test. With four BaneBots gearboxes (2x56, 1x42, 1x36) on our robot, this was the true shakedown for the carrier plates.

My hardened carrier plates for the 56mm gearboxes held up fine, no noticeable backlash whatsoever. I believe they are of similar hardness to the BaneBots replacements, so I suspect that these will also be sufficient for the case of 1 CIM and hopefully also for the 2 CIM adaptor.

The soft 42mm replacement plate I made is just now starting to show backlash, to the tune of about 10-15 degrees more than usual. I took it apart and there is definitely a bit of a bowtie (sorry, no picture), although it is not in any danger of failing soon. Still, I will be more comfortable changing it out to one of similar hardness to my 56mm plates.

Which brings me to my next point. I have an entire strip (18"x4") of O1 tool steel 5/32" stock just waiting to be cut. I have been cutting small quantities on the waterjet, but I could potentially produce as many as will fit on that stock in one cut. A few issues:

As Dr. Brooks has noted, tool steel is not ideal for this application because it can become too brittle. Tempering back to RC40 can help this problem and the ones I've made have held up without fracturing, but this can't be gauranteed.

They would not be finish-machined (reaming pin holes and filing double-D). I would only have time for a rough cut on the waterjet.

They would not be hardened. (The steel comes annealed, actually slightly softer than the stock plates, and is supposed to be hardened after all machining is done.) That being said, they may be still useful as spares (I've had one in our gearbox for a week of driving practice and it is just now starting to show deformation) or perhaps others could do the hardening + tempering. (The materials lab I used originally cannot do large quantities and is now in use for classes anyway.)

If teams can live with this, I can start making the rough cut carriers this week and would just ask a PayPal payment or something to cover my costs. Since BaneBots won't have individual spares or hardened replacements for the 42mm, this might be a good option for the 42mm users. But I don't want to mislead people into thinking that these will be simple plug-and-play replacements. I can provide detailed instructions for all the finishing and heat treating I have done, which has held up well in the case of our gearboxes, but I would not have time to actually do it all.

Any suggestions/opinions/comments?

Re: Banebots 42mm gearbox: Recommendations for use
 

I'll take 2 !!

Along with any advice that you may have.

Re: Banebots 42mm gearbox: Recommendations for use
 

Since the failure mentioned above, and since we installed plates that eliminate twist, one of our gearboxes has seized up twice (well, two different ones once each but in the same arm location). The brass gears just shed teeth for some reason....

What confuses me is the Double -D joint is PERFECT?!?!?!

At a sunday scrimmage we noticed that the center gear on the early stages is the same as the brass gears and is pressed into that plate. We popped them out from 4 plates (we bought lots of spares) and machined them down (took about an hour) with the help of team 207 (their shop) and a local professor. We have ran these in the final stage of the problem gearbox through rigorous PID loop testing (I cringe every time our programmers test that thing.... shock load after shock load...).

We also noticed a FP motor in a stock 256:1 draws ~1.3 amps of current. The one with the new steel gears draws 1.0!

EDIT: looking at the motor stats, 1.0 seems unrealistic for a FP. but the fact that both gearboxes were tested on the same setup shows the steal gears run better, even though the actual draw may be inaccurate.

So far we have shown no signs of wear on any part on the inside, nor the double-d joint.

Re: Banebots 42mm gearbox: Recommendations for use
 

Our 256:1 drew 1.0A under no load at the most new and lubricated time of its life. 1.0-1.3A is definitely a good number. I'm not sure why the 2005 motor spec sheet has such high no-load current draw numbers.

Whoever on your team decided to buy so many spares should get MVP this year. We have just one. Luckily, it has survived okay so far. I thought all I had to worry about was the carrier plates. Now I have to think about gear teeth being stripped too? :(

Re: Banebots 42mm gearbox: Recommendations for use
 

This thread has provided a lot of good information, with all kinds of technical tidbits. I'll try to make my comments brief regarding our experience.

We bought two 256:1 to use with F/P motors for arm rotation. We used one gearbox with 1:4 reduction from the Banebots to the tower. The second was a spare. The first one failed almost immediately. We installed the second one, and it also failed almost immediately.

We, obviously, were asking way too much of the gearbox and ended up making our own gearing to rotate our tower with a big CIM. The bottom line is that anyone using a 256:1 Banebots with an F/P motor needs to isolate the output from all shocks, and probably avoid ever loading the motor to much below 80% of no-load rpm.

We are reliably using two 64:1 Banebots gearboxes for less demanding applications, but the 256:1 Banebots, F/P combination is a failure waiting to happen, and a very short wait.

Re: Banebots 42mm gearbox: Recommendations for use
 

Well, we thought we had the problem fixed (read above) by the steel gears, anti twist plates and reducing the input sprocket size to reduce the stress on the gearboxes.


They totally, totally failed today. We had some other minor issues, but none like that.


Luckily, during the fix-it window we machined new motor mounts that will use the A-M planetarys with small CIMs.

The only three matches we were working in were against 330, then 254 and then 968. After that we were working awesomely on the practice field. Then... total failure.

Our drivetrain is still working great luckily and we play great defense, since we are currently ranked 52nd, we're hoping some of the top alliances realise our defensive abilities.

slightly off topic, but it's been a long day.

Do not use the high reduction BB gearboxes, especially if there is any significant shock load.

Re: Banebots 42mm gearbox: Recommendations for use
 

That really, really stinks. I have been pulling for these little gearboxes, but I haven't heard any good stories recently. Could you elaborate on the nature of the failure? (Was it the double-D, the twising, the shearing of gear teeth, or all of the above?) My current thinking is that we will continue to use the softer-than-usual plates and just monitor the backlash carefully. At least it is a slow failure mode and I have an idea of how much the plates can handle. If I put in harder ones, it may just doom the next weakest link, whatever that is. Sigh...

Sorry to hear about it and I hope your AM solution works out.

Re: Banebots 42mm gearbox: Recommendations for use
 

1726 made it thru the whole weekend (AZ regional) with no problems with the 36mm 125:1 gearbox running our arm...hung 6 of the 7 tubes on the highest scored qualifying match...and made it to the finals....

Is that good enough?

Re: Banebots 42mm gearbox: Recommendations for use
 

Our initial problem with the 256:1 BB was with the double D. We then made an output shaft out of one piece of steel and pressed in the original pins. The pins broke. I think we also lost a gear tooth or two. The bottom line is that the F/P is a powerful little motor, and when you multiply its torque by 256, it is way too much for that little planetary.

We are using the 64:1, 36mm BB's for our roller gripper with no problem, and I suspect the single- or two-stage 42mm would be ok with the Fisher Price, at least if you limit shock load.