pic: Team 30 Dual-Motor Transmission

[Rob Colatutto]

Originally Posted by RobDeCotiis

sarahb,
dremeling off the gear only poses a threat to the motor of you're lazy. Make sure you don't get shavings inside the motor and i see no reason dremeling the gear off would cause harm. Cutting into the drill motor shaft slightly won't cause problems, unless you hack it to bits. Some people don't have presses, and honestly, you don't need one. The dremel works fine for removing the gear, and simple expansion/contraction properties of the metals will allow you to put the gear on. freeze the motor(or just the shaft, assuming you have liquid nitrogen in your chem lab ) and heat up the gear with a blowtorch and you'll be able to get it on, and when it cools down, good luck getting it off. Try to think a little more about reasoning before you post. You yourself have seen the motor ryan put the gear onto, you know it works fine, the motor isn't damaged, i don't really see what the problem is. anyway. beautiful looking gearbox, ryan. nice job

Team 30 forever
Rob DeCotiis

I'm no electrician here... but I would take a guess and say putting your motor in liquid nitrogen is probably not a very good practice if you want to have a working motor... Taking a blow torch to the gear could also severly weaken it. There is nothing wrong with having concern and giving advice against doing something that you know isn't the correct method doing the job. We are trying to learn about engineering and teaching others in FIRST, not about cobbing up a job that is easily done correctly.

Ryan, could you post up or pm me the gear ratios in there? It appears that you have the bosch motor pulling up atwood above its free speed. (also not a very good thing to do)

[RobDeCotiis]

Originally Posted by Rob Colatutto

I'm no electrician here... but I would take a guess and say putting your motor in liquid nitrogen is probably not a very good practice if you want to have a working motor... Taking a blow torch to the gear could also severly weaken it. There is nothing wrong with having concern and giving advice against doing something that you know isn't the correct method doing the job. We are trying to learn about engineering and teaching others in FIRST, not about cobbing up a job that is easily done correctly.

dipping the shaft in liquid nitrogen won't cause any problems to the motor. using a blowtorch on the gear won't either. both of these are common practices in the engineering world. When fittings are needed that are extremely tight, to the extent that the shaft diameter is greater than the hole diameter by very large amounts, these practices are used along with a press fitting. The end result is an EXTREMELY tight interference fitting. If a team doesn't have a press, these practices are accepted in the engineering field, and because, as you say, we should be teaching engineering, i figured i'd throw a little bit more engineering knowledge into the mix, being that nobody's posted that as a way to fit the gear on. again, please look into what you're talking about before making blind assumptions

[SarahB]

Originally Posted by RobDeCotiis

sarahb,
dremeling off the gear only poses a threat to the motor of you're lazy. Make sure you don't get shavings inside the motor and i see no reason dremeling the gear off would cause harm. Cutting into the drill motor shaft slightly won't cause problems, unless you hack it to bits. Some people don't have presses, and honestly, you don't need one. The dremel works fine for removing the gear, and simple expansion/contraction properties of the metals will allow you to put the gear on. freeze the motor(or just the shaft, assuming you have liquid nitrogen in your chem lab ) and heat up the gear with a blowtorch and you'll be able to get it on, and when it cools down, good luck getting it off. Try to think a little more about reasoning before you post. You yourself have seen the motor ryan put the gear onto, you know it works fine, the motor isn't damaged, i don't really see what the problem is. anyway. beautiful looking gearbox, ryan. nice job

As Rob said before, using liquid nitrogen on a motor is a really bad idea. It could damage many parts of the motor, including the cracking the cooling fans or the bush assembly. I would listen to him, considering he knows enough to be a technical moderator of these forums.

Yes, I have seen the motors that Ryan modified. All of them have damaged shafts(lots of little cuts), at least one has shavings in it, and two have damaged bush assemblies. All three were replaced, and I believe the gears from the new ones were pressed off the right way.

Once again I will ask all of you to please stop encouraging other teams to damage their motors. If you don't trust my assessment that Dremeling off pinions is bad, please refer to the numerous other posts that agree, especially the ones by Paul Copioli, a well respected professional engineer and Unsung FIRST Hero.

[RobDeCotiis]

How exactly will cooling the motor damage it?

[sanddrag]

OMG, don't you all understand that they will not be dipping the whole motor in the LN. All they need to put in is like 1/2" for the shaft, not the whole motor can too. The only part in the LN should be the shaft.

[Venkatesh]

Each one of these has a weight of approximately 9 pounds. Fine devices, really.

[JVN]

Originally Posted by RobDeCotiis

sarahb,
dremeling off the gear only poses a threat to the motor of you're lazy. Make sure you don't get shavings inside the motor and i see no reason dremeling the gear off would cause harm.

Actually,
One of the best motor guys on these forums, a professional who does this thing for a living came on here and said NOT to dremel the drill pinion off as you will likely destroy your motor.

RobDeCotiis, please refrain from talking about things which you "know" unless you really know them.

Simply be searching these forums, you can find someone who's opinion really matters.

Team 30--
The gearbox looks good.
Unlike my teammate I won't try to count teeth and check your ratios. I just assume you would have done it right the first time. Good luck, and we'll see you in Long Island.

JVN

[Chris Fultz]

Originally Posted by RobDeCotiis

dipping the shaft in liquid nitrogen won't cause any problems to the motor. using a blowtorch on the gear won't either. both of these are common practices in the engineering world.

Cooling the shaft is probably OK. Blowtorching the gear probably is not. You can create huge stresses in the part, and you are chaning the material properties. The sudden change in temperature can be damaging. Parts are usually heted in a controlled process, like an oven that gradually increases the temperature.

Originally Posted by RobDeCotiis

When fittings are needed that are extremely tight, to the extent that the shaft diameter is greater than the hole diameter by very large amounts, these practices are used along with a press fitting. The end result is an EXTREMELY tight interference fitting.

Yes, the practice of creating interference fits is common and used in many engineering applications.

It is a very controlled process. Part diameters are defined, analysis is completed. An interference might be thousandths or ten-thousandths. When you create this tight fit, you add new stresses in the mating parts and if the fit is too tight, one or both parts can fail.

Do you know what kind of interference you are making? Did you measure the parts first?

Originally Posted by RobDeCotiis

and because, as you say, we should be teaching engineering, i figured i'd throw a little bit more engineering knowledge into the mix, ... again, please look into what you're talking about before making blind assumptions

No further comments.

[Mike Martus]

Caution to all reading this thread. Some of the processes expressed by some of the teams are very risky. Please use well thought out processes based upon "best practice" and above all practice safety at all levels.

Also consider advice from the persons that have expertise in the field of question as more reliable but not faliable. All are entitled to their opinion on how to best do something but again excercise caution.

[sanddrag]

We are broaching and milling keyways in all our gears this year to lock them to the shafts. While we have not run it under significant load yet, so far it appears to be functioning extremely well.

[Al Fielder]

In another post, I described how to remove the pinion from the Bosch motor. It really wasn't difficult. Taking a Dremel to remove the pinion seems to be alot of work, with risk, when a puller will work just fine. The press fit for a new gear should be in the .0003-.0005 range, specially if you are installing a gear with a P.D. of around .7-.8 so that you don't yield the new gear.
If the new gear yields, you lose the press.

[Dorsk65]

Well, on a completely different note, well done. This gearbox is vastly smaller and lighter than ours, mainly because our sprockets are 1:1, so we needed extra gears. We used the 20 Pitch gears also, and I hope to post pictures soon. The only problem we are having seems to be heat, so you might want to mount some fans on it.

Once again, very well done, paticularly on the weight and stability.

Robert Bloom

[Ryan Curry]

Originally Posted by Dorsk65

Well, on a completely different note, well done. This gearbox is vastly smaller and lighter than ours, mainly because our sprockets are 1:1, so we needed extra gears. We used the 20 Pitch gears also, and I hope to post pictures soon. The only problem we are having seems to be heat, so you might want to mount some fans on it.

Once again, very well done, paticularly on the weight and stability.

Robert Bloom

Thanks for the vote of confidence Robert, I hope to see pictures of your gearbox up here soon. Wish we were having your nice Hawaii weather here in the Northeast.

-Rc