What Motors Should I Use?
 

In the 2003 season I used drill motors with the gearbox provided in the kit. While they had sufficent power they werent good for direct drive. They broke mounts quite often, and stripped out couplers when put under too much stress. Doe anyone have any suggestions on which motors would be best for the same type of drivetran. I was think that the CIMS would be best. What do you think. Do you think that we should try a different type of set up for our drivetran?

We used the Chias geared down 3.5:1 to match the drill gearbox in high speed. We then had a 4.8:1 reduction to the 8.5 inch wheels. We used all sprockets and chains. This setup work astonishingly well and we never had problems with the drill motors, gearboxes, mounts, or couplers. The only thing we had a problem with was getting our shafts aligned correctly and keeping proper chain tension. These two things caused us a lot of binding and high current draw but we didn't trip the 40 amp breakers. Our battery just died fast.

Our drivetrain fabrication required the use of a mill and a lathe to make shafts and pillow blocks and to bore holes for bearings.

What would happen with our drivetran in order to make it break the couplers and the mounts was that when we would get into a power struggle with another robot our gears in our gear box would try to reverse when we were not winning and the anti-roll back pins would then not let the motors be reversed so the drive shaft that connect the motor to the gear boxes would move under the force of binding up, as a reasult it pushed back towards to the motors and broke the mounts. So to fix that problem we took out the anti-roll back pins from the trany, then when we would get into a power struggle we would be pushed backwards and the gears in the gearbox were moving in the opposite direction of the motor causeing the threading in the coupler to be stripped out. WE do not have any knowledge what so ever in the gearing of drivetrans because of our lack of engineers. WE have one engineer and he is an electrical engineer. So I having a little bit of knowledge due to the fact that I am an ASE certified auto-technition built the best drivetran I could. We had a lot of problums with it, but all-in-all it was alright. But I think that we had to be the only team with that problem.

When you put this drivetrain together, were you sure to insert the left-handed screw into the center of the drill output shaft?

That screw prevents the shaft from backing out.

Even the left-handed screw caused us a bunch of problems back at 2000. Not sure if the ones this year is much stronger or not, but don't take it for granted that it will hold together all the time.

We snappend 5 or 6 left handed-screw that year, and they are very hard to replace.

Try gearing your robot to be stronger and slower.


Also, about the thread in your coupler is stripping out... Did you put a pin in the coupler? By adding a small pin, part of the force will transfer onto that pin. But if you are still having trouble even with the pin, I suggest building a new shaft completely.

Ah, okay. I've never used the left-handed screw, instead deciding to make my own output shaft for the motors. My first run-in with the left-handed screw was at Nationals this year, when 713 experienced a similar problem with backing their motors out and having them disconnect from the drivetrain -- all because the left-handed screw had been bored out.

If anyone is interested, I have a pretty simple part made up in Inventor for the 2003 Drill Motors. We put flats on two sides of the drill output and then threaded my shaft extension on, using two set screws to keep it from unscrewing itself.

Just let me now and I'll toss the part and drawing up on the web.

What is a left-handed screw? I only have limited knowledge? Is it like the stops that they gave us in the kit? I put the drive tran together exactly like the plans on the FIRST website.(www.usfirst.org) THe plans for it are under team resources>documents>drivetran closeup. GIve or take a few change like I didn't put on the locking rings. The driveshaft is the 3/8 keyed axle that they gave us.

A left-handed screw is threaded such that it tightens and loosens by being turned in the direction opposite of regular screws.

Righty-tighty, lefty-loosey, y'know? Well, left-handed screws are just the opposite.

The outside of the drill output shaft is a normal thread, so spinning something to the right over that thread would tighten it.

Inside that output is a small center-bored hole. The inside of that hole has a left-handed thread.

If it takes less force for the motor to unscrew itself from the shaft coupling than it would for the motor to move the robot, it'd unscrew. Imagine the motion you'd make when you screwed it all together. Now, imagine that your hand is replaced by the motor. See how it's the same thing?

Well, by putting a left-handed thread and right-handed thread together, it makes that unscrewing impossible. For as long as they're spinning together, one screw is always trying to tighten itself while the other tries to unscrew. They keep each other in equilibrium, meaning that most of the energy output by your motor goes to the wheels -- not to taking apart your drivetrain.

If you didn't put the left-handed screw in, you'd find that the motor was unscrewing itself from the coupling, especially in pushing matches. Since everything is locked in place and the force isn't going toward making your wheels spin, something, somewhere, will break.

Similarly to the left-handed screw, and as Ken mentioned, a pin through the shafts ensures that they always rotate together and is another every effective method for keeping things from breaking. Just be sure to use the proper diameter pin to withstand the forces in the system.

(See what engineers can do for you?)

Thanx for the information. I have two questions for you know if you do not mind. Where can I get one of those parts? How would I attach that to the couplers provided by first this year(the alluminum ones that fit inside the large black plastic piece)?

Two of the appropriate left-handed screws were supplied in the kit this year, though, admittedly, they were easy to lose. If I recall correctly, they were packaged in a small, clear plastic bag. I don't remember if they were packaged individually or together.

There is a hole in the hex coupling where this screw fits, and then screws into the drill output.

If you do not have or cannot find those screws, and you are sure that was the problem you were having, you can just go buy some.

The specs for those screws can be found here .

Thanks for the help. I actualy have one of our striped out couplers beside me right now and I can see the hole that you are talking about. I can't open .pdf files on my PC, so what do they look like(besides the fact that they have reverse threads)? :D

M6x1.0-6g left-handed screw, with threads 20 mm long and overall length of 29.7 mm. They have a flat header point and they're also countersunk.

Thanx again

team 166 used a 2 speed shift on the fly x-mission low was 4ft/s and high was 9ft/s. we used the CIM motor's. the major reason we used these motor's are as follow's.

reliable
simple no gear box's
easy mounting
spur gear's require only minimal rework to mount to output shaft.

we found it would require alot more machined parts to mount the drill motors and gear box's then simply drilling two holes to support the CIM motor.

Thanx for the halp. Team 166