Drill Motor + Gearbox + Breaker Problems

[ttedrow]

What are you using for the non drive wheels?

[sear_yoda]

I won't go so far as to say what our problem was, but I'll warn other teams to CHECK THE BATTERY POWER before you take out the gearbox!

(We'll check around for an ampmeter, but a fresh battery seems to have fixed the problem for now!)

Thanks for all of your help.

[Greg Needel]

just looking at your pictures i think i can tell why you are having your problems. with the direct output of your gearbox going all the way to the wheel your axle is acting like a huge lever and missaligning your gear box. while it may seem like your wheels might have a flex of only a milimeter it will affect your gearbox. what i might sugest is to separate that axle and conect it with a flex coupler to account for any mis-alignment that may occur. if you have a second set of the black plastic couplers that first gives you, you could cut your shaft attach the hex gear to either side and use the black coupler as your flex coupler...hope this helps feel free to PM me if you have any questions



btw have you made sure that the clutch is in the drill setting aswell...try this first

[Al Skierkiewicz]

Originally Posted by sear_yoda

no, we're outside of detroit

Ok,
I can't run over there this afternoon, but you have a lot of teams close by that could give you some help if they were to see this in action. You have removed the locking pawl from the drill transmission, haven't you?
My advice again is remove the drill motor and transmission and the driving shaft. The remaining shaft with wheel on should turn freely. If that is OK then, put the robot on the floor and try to push it. It should just keep going by itself, in a straight line. If it doesn't keep going but goes straight then the bearing on the wheel shafts are not in alignment. If it rolls, but not straight then you do not have the wheels parallel.
If all of that works OK then put the driving shaft back in and check everything again. Remember that the driving shaft and driven shaft must be perpindicular else there is side friction on the gear faces. Check that the gears are in correct mesh alignment. This is a hard one. Visualize a line perpindicular to each shaft (as if drawn on the face of the gear.) Those lines should meet perfectly. If the tangent of the driven gear is not aligned with the center line of the driving gear, additional friction is built up. If all of that is OK, you should be able to set the wheel in motion by turning the hex coupler on the driving shaft and the wheel should continue to turn by itself for a few seconds. It make take a little trial and error to get everything to the point where it can make this test. When it is all moving freely, put it back on the floor and test again. There should be a significant improvement. Once that is OK, put the drill and transmission back in and try powering the motors again off the floor. Again the drive should free wheel after you remove the driving power if you have the speed controller set to "coast". If all of this is OK then put the robot back on the floor and try to drive. If everything was OK up until now and the breakers still trip, you may have to add a bearing to the wheel shaft. The weight of the robot may be putting too great a load on the bearing you are using. Let me know what you find. I will check in again in an hour.

[Joe Johnson]

If the problems start up again and you can't get through them, PM me with your contact info, I may be able to either talk you through the process or stop by (though our machine is not running yet, so you know where my mind will likely be).


Joe J.

[Dale(294engr]]

Assumptions:
Battery is fully charged
(high current testing requires constant attention to charging)
(battery depletes fast with two 40A breakers cycling;
good 40A breakers open @ ~50A ea x 2 = 100A,
and open at lower currents as cycled more frequently)

BTW: 18AH SLA battery is discharged in 3 minutes at 54A to 8V !!!
see the mfr discharge curves to verify, docs: 18ahExide.pdf

so at 100A continuous expect only a couple minutes at full energy.....

DO measure the current where the breakers open, (on full batt charge)
last year we found many 40A rated opened at 30A (~26A rating)

How ??
Use a DVM, 200mV scale connected across the 120A main breaker.

when ckt bkr closed the current is ~1A for each mV on the DMM !!!

A 3 digit DMM will thus read +- 199.9A

(The open ckt bkr reads ~12.6v, which will not harm a DMM)

First impression from photo's:

with 12" wheels you are geared too high

(are other wheels unrestricted castors ?
if so it should do circles rather well,
but may be hard to drive straight line)

use smaller wheels 3" would move well
or Gear Down 3:1, 4:1
I know neither is attractive at this point, sorry....

[IMG]F:/Robotics/2004/MANUAL/18ahExideDischgCurves.jpg[/IMG]

[ZZII 527]

For two years our team has had problems with the helical gears...but we didn't know it. We always had a problem turning with 4 wheels due to the lateral friction involved in tank steering. This year, we though we solved that problem by increasing the wheelbase and moving the front and back wheels closer together. But, the clutch still slipped. In direct drive, the 40A breakers popped, just like you are saying.

If the clutch slips, it probably isn't a problem with the actual motor (which must be providing enough torque to make the clutch slip). It is much more likely that there is just too much resistance somewhere...especially if turning is even harder than driving straight.

So after two years of bad luck with 4WD and the drill motors, we tried something today that we never did before: lubricating the helical gears. The difference was AMAZING. How stupid could we have been! Anyway, if you haven't already tried this, it might help.

[Vince]

There may not be a single solution here, but rather a combination of factors. Many of these have been mentioned and I'll add a few ideas.

1. The drill motors (even in low) with the supplied gears and the 12 inch wheels are not a combination suited for motor effeciency and non-tripping action. Having said that, you can still use them, but you must be very careful (as you are seeing).

2. Even when EVRYTHING is corrected, you probably do not want to drive this combination more than 1/2 power. The good news is that even at 1/2 power (easy software fix, with a button to over ride in an emergency) you will move around the field quite fast.

3. From your photos, it appears there is lots of metal / plastic "dust" on the gearbox housings - something is wearing that shouldn't be. You need to find that and fix it (especially on the right side).

4. It is hard to tell from the photos, but are you using 6 Bearings on each side? The resolution gives when zooming, but it looks like some bearings might not be used in your gearbox.

5. Be careful that you do not contort the plastic gearbox mounts when tightening things down. These plastic mounts are designed to fit over the 2x4 AL beam in the kit - they have small cut outs to fit. If you tighten up on the mounts too much, you can distort the mount (i.e. cause misalignment) AND press the bearings against the frame. Also I'd use Nylock nuts to avoid having things work free (and leading to more alignment issues).

6. Again, it is hard to tell from the photo, but it looks like the left outside gear box is bowed out. If so, a likely cause is a spacer that is a bit too large (and associated misalignment).

7. You have to be VERY careful with the key on the gears. If it is a bit too long, it will work its way under the spacer, leading to additional unwanted wear. You have to be very careful that thess keys are EXACTLY the correct length.

8. The 3 spacers used to center the large gear can lead to unwanted problems. Better to use a single spacer of the correct length.

9. Your motors are having a difficult time dumping the heat they build up. Can you provide some air route from above the motors? As mentioned earlier, fans would help as well. You also might want to add some cooling fins to the motor case (be careful not to cover any existing air holes on the case). Finally, the plastic mounting frames act as a good electrical and thermal insulator. If there is a way you could use your robot frame as a heat sink (i.e. some good hunks of metal between your motors and the extruded AL) you can pull off some of the built up heat. Again - this is patch to a more fundamental problem (i.e. this combination not being efficient).

10. When your system is running, be very cautious of the motor temperatures. With this combination of systems you cannot run the design for long periods without giving the motors a chance to cool down. Stop every 2 minutes of use (the time of a match) and check the motors - if you can't hold a finger to the case for x seconds - stop ( the larger the x you set the better off you will be). You must pay attention to this, or even worse things start to happen (things that don't reset with time).

11. Your design has the motors / gearbox mounted such that they are "out of sight - out of mind" - no problem with their location, but don't adopt that thought process. The drive motors / gears are the most important part of your robot. Even though they are hard to see in your design, spend time (regularly and often) inspecting them to detect problems that might be starting but are not yet critical.

Again, there are many layers to the situation at hand. If you are still having problem, take up some of the other local teams for help as soon as you can.

For the problems you are experiencing, you might say "am there - am doing that" with regards to some of my comments (see the link....)

Feel free to email me if you are still running into problems - Vince"am there... am doing that....."

[Al Skierkiewicz]

Originally Posted by sear_yoda

I won't go so far as to say what our problem was, but I'll warn other teams to CHECK THE BATTERY POWER before you take out the gearbox!

(We'll check around for an ampmeter, but a fresh battery seems to have fixed the problem for now!)

Thanks for all of your help.

Did you guys get a fix on the problem yet? Was Joe able to help out or did you find it yourself? We are waiting on pins and needles. Are you going to Greatlakes? Then see you there. Come and get me if you still need help.

[Joe Johnson]

Originally Posted by Al Skierkiewicz

Did you guys get a fix on the problem yet? Was Joe able to help out or did you find it yourself? We are waiting on pins and needles. Are you going to Greatlakes? Then see you there. Come and get me if you still need help.

Must be okay because I have not heard anything...

Joe J.

[sear_yoda]

As far as I can tell, slightly adjusting all of the areas of alignment and replacing the battery has solved our problem. The drivetrain folks are coming back tomorrow evening, so I'm going to show them all of your replies and let them decide if it's fixed or not.

Our team will be at the Great Lakes regional, so I'll be sure and say thanks to you in person, Al.

[Al Skierkiewicz]

Originally Posted by sear_yoda

As far as I can tell, slightly adjusting all of the areas of alignment and replacing the battery has solved our problem. The drivetrain folks are coming back tomorrow evening, so I'm going to show them all of your replies and let them decide if it's fixed or not.

Our team will be at the Great Lakes regional, so I'll be sure and say thanks to you in person, Al.

Anytime, that's what I'm here for. Joe, Too!

[caffel]

One suggestion that's simpler than the great current sensors.
Go to JC Whitney and look for their $10 ammeter that straps onto the outside of a wire (used for testing starters & alternators).
Attach this to the battery cable and watch it as uyou run the robot through some of the moves that load the motors the most.
Last year we had no luck until we did this test and realized that the many theoretical calculations were misleading us. We were simly drawing too much current. At the end (November) we had a slower, more powerful and completely reliable drive train.

[andy]

I think I see a potiential problem

We suffered a similar problem last year, we had our drill motors mounted on a piece of 12 awg steel plate in the supplied holders. The plate flexed on us and the drill gearboxes (fragile) would taco and bind up. This would happen whenever there was torque on the motors (always). Something you might want to look into is replacing the plate that the motors are mounted on with a thicker plate.

Just a thought
Comments Welcome!

Good luck ya'll
-Andy