Re: Slickest drive transmission yet...
 

Jim,

Thanks for the additional information. That's what I was assuming on 1, 2, & 3 but just wanted to make sure. I don't know anything about hardening/heat treating either but if you can relay the info from your folks I'll pass it on to our folks.

Thanks,
Chuck

Re: Slickest drive transmission yet...
 

Jim,
Funny you mention this.
Heat treating came up the other day in a 229 design discussion.

If you (or anyone else) knows more about this process.
Please share!

I have the vaguest understanding.
I'm especially interested in "home" heat treating. I think it is possible to temper a shaft using only a torch and a coffee can of oil. Is this true?

John

Re: Slickest drive transmission yet...
 

Not sure if you already seen it, but Dave wrote one of his memorable posts about it a while ago. Here it is.

Re: Slickest drive transmission yet...
 

Manoel,
I had seen that before, but obviously forgot COMPLETELY about it.
Thank you for bringing it to my attention.

Remember folks, don't be like JVN -- search before you post.

John

Re: Slickest drive transmission yet...
 

Thanks for remembering the post, hopefully you will find it useful. Here is a little additional information -

If you do a water (instead of oil) quench for the hardening/tempering steps, you can improve the results and consistency of the hardening by using an appropriate surfactant in the water. As you quench the part, bubbles form in the liquid at the interface between the hot part and the quenching fluid. You want to move the bubbles away from the hot metal as quickly as possible, and and keep a solid surface of quenching fluid against the metal. The surfactant will break the surface tension around the bubbles, and allow them to quickly seperate from the metal and float free in the fluid. This will allow the fluid to restore contact with the metal, and lets it do its work cooling off the part. The "magic mix" that I use is 1/4 cup of Cascade dishwasher powder per gallon of water. DO NOT use a liquid dish soap or laundry detergent! You want something with a low "suds content" that will not foam up when you stir it around (remember, we are trying to avoid bubbles here!).

If you are using a low-carbon or mild steel, you will want an alternative to the quench-and-temper process (which is really only effective on high-carbon steels like tool steel). For low-carbon steel you can do small-job case hardening (which will basically add carbon to the surface of the metal and increase its ability to be temperature hardened). Heat up the part until it is cherry red, bury it in a surface hardening compound, reheat it and cool by quenching. The compound (I use Kasenit, available from MSC, and there are others) will provide a surface case hardening a few tens of mils deep, which should be good for most applications that we will run across. The case hardening will give you a harder surface, but the effect will not penetrate as deeply into the metal as the quenching/tempering process. You will have to figure out where you want to be in the hardness/depth trade space based on your application.

(note: there has been a lot of discussion recently in the hobby machinist community on this topic recently - if you can grab a few of the recent issues of the Home Shop Machinist, there are some good articles that will provide additional information)

-dave

Re: Slickest drive transmission yet...
 

i am sorta new to all of this. would it be possible for someone to e-mail me an inventor file for a 2 speed transmission. that would help us out alot!! also if its possible please send the specs of the transmision (i.e. gear ratios)

thank you!!!

Re: Slickest drive transmission yet...
 

Have you looked in the whitepapers? There is a lot of info there.

Re: Slickest drive transmission yet...
 

Is there any timeframe on when the companion automation software paper will be available? Our team would really like to see how you automated the shifting. Will it be available soon so that we may decide if it is something we can tackle this year or not? Even just some pieces of code would be helpful at this point.

Thanks!
Chuck D.

Re: Slickest drive transmission yet...
 

I too would love to see the code for the automatic transmission. Would any team be willing to post the automatic transmission portion of their code on this site? Even pseudocode would be helpful with our designs since we have never attempted this before. Thanks! :D

Re: Slickest drive transmission yet...
 

Having a shifting transmission is deffinatly a helpfull and worthwile modification; especially when you don't even have to worry about shifting. The only problem that i can see that might go wrong is that if you hit something at full speed and the wheel speed sensor gets knocked off or is rendered unable to sense wheel speed, you would be stuck in the gear that the robot was in before the sensor was disabled. Especially if you were in 4th gear. That battery might not last much longer! :eek:

Re: Slickest drive transmission yet...
 

What do u mean by wheel speed sensor
which sensor is that?
Isn't it built into the motor?

off topic:
has anyone built that spacer for the single sprocket
if so where did u find a diagram and what matters to use

Re: Slickest drive transmission yet...
 

In response to the above posts:

artic_raven: Cut one of these in half and you have a VERY easy to machine 2 speed transmission, not to mention tiny and light.

DeepWater and cabbagekid2: I have no idea if Jim intends on posting a software whitepaper, and if so, when.

1028_Machinist: There is no wheel speed sensor. If you look at the whitepaper, the output speed is measured by a shaft encoder. That is what the automation uses. If you knock that loose, I don't think you'd have to worry about driving around in any gear....I don't think you'd be driving around at all. You can put a manual override if you want, though.

Nitroxextreme: Wheel speed sensor would be a banner sensor (light sensor) aimed at a tone wheel. A tone wheel is basically just white and black stripes, and the banner sensor reads how fast the wheel is going by "seeing" the change between white and black as the wheel rotates. In our design, there is no wheel speed sensor, just a shaft encoder which reads how fast the output shaft of the transmission is spinning. There is no sensor built into the motor.

Re: Slickest drive transmission yet...
 

This is a nice easy to manufacture transmission design but the problem is that there is very little->no reduction. In high gear it is 1:1 which means you have to use some external reduction like a Dewalt drill gearbox and on the input end then maybe some sprockets and chains on the output end. Don't forget about all this stuff when looking at how light and small it is. What you see in the picture is not the only part.

Re: Slickest drive transmission yet...
 

I'll repeat my question from the other thread here since I haven't seen the software paper yet. Now that the season has kicked-off, I expect the last thing on your mind is documenting last year's work.

Jim, could you answer some general questions about how your software works?
1. Is shifting based on RPM alone? What other factors are used to determine when to shift? Current? Voltage? The commanded PWM value? To put it another way, are the shift points fixed, or are they different when you are accelerating at 50% throttle?

2. I assume there is some kind of hysteresis. Is it a simple pair of shift-up/shift-down values? Or do you add something like a "dwell time"?

3. Do the left and right transmissions shift at the same time? I'd imagine that keeping both sides in the same gear would make it easier to match speeds and keep the 'bot going in a straight line.

Of course I don't expect you to give away all your secrets, Gracious Professionalism or no. But some general guidance about the operation of the shifting software would be helpful.

Once again, great job 33! It's a sweet design.