pic: DeWalt Gearbox with two CIMs
 

Re: pic: DeWalt Gearbox with two CIMs
 

Boy I wonder how far over the safety factor of design you will be pushing those dewalt gearboxes. If the design engineers could only see them now I bet they would be white as a ghost.


I like the concept I am just not sure that the dewalts can take the abuse of that over a long period of time. Make sure you have lots of spares.

Re: pic: DeWalt Gearbox with two CIMs
 

(this was made while checking to see if the thread was moderated.)

Re: pic: DeWalt Gearbox with two CIMs
 

OK, not to be too pedantic about this, but "direct drive" and "gearbox" are oxymoronic when used to describe the same system. A direct drive system is, by definition, one in which the load is coupled directly to the output shaft of the motor with no intermediate gear box or other torque/speed modification in the linkage.

Other than the terminology issue, this looks like a nice design. If you are going to go with the idea of a 0.5" drive shaft running the length of the robot, I would suggest that you consider using a torque tube rather than a solid shaft. A 0.1" wall torque tube 24" long with a 0.5" bore will save approximately 40% of the mass of a solid 0.5" shaft made of the same material (and even more if the torque tube is aluminum vs. a solid steel shaft).

-dave

Re: pic: DeWalt Gearbox with two CIMs
 

This is still a conceptual design at this point. We have not run the calculations yet to determine if the Dewalt transmission is going to hold up to this kind of abuse. The idea is to see if we can come up with a two-motor, shift-on-the-fly drivetrain this year. Matt decided to try this approach since we have some extra Dewalt parts left over from a couple of years ago, so the cost to experiment is low.

Dave- it absolutely will be a torque tube design for the power transfer to the wheels, with an aluminum tube. Once we have the torque calculations we will decide just how light the tube can be. (He's working with a bunch of mentors that design spaceflight hardware, the first question is always "so just how much does that weigh?" :) )

Re: pic: DeWalt Gearbox with two CIMs
 

Last year i made a concept using the opposite of what you have here...i never made it but this is what it looked like. Here.

Re: pic: DeWalt Gearbox with two CIMs
 

Team 40 beat the living snot out the Dewalts and they never even marked a gear.

They are hardened to very high rockwell, we lost one of the mentors to Dewalt and the engineers couldn't believe we even were able to bore out one of the gears from what she told us. From what I understand the rings or posts for the gears will break if anything does. In which case they should be easy to swap out.

Re: pic: DeWalt Gearbox with two CIMs
 

Are you trying to save weight, space, or are you just throwing around ideas?
Looks cool, though with the torque you have going into the DeWalt transmission I would definitely test it first.
If you are trying to save weight, how much do you expect the whole thing to weigh (minus the motors)?

Re: pic: DeWalt Gearbox with two CIMs
 

http://www.chiefdelphi.com/media/photos/26104
There is the updated version.
This gearbox is mostly me just throwing ideas around. I like the ease of a prepackaged 3 speed gearbox in the Dewalts, but I wanted to use two motors per gearbox for torque.
Without the motors the gearbox is just under 2.5 lbs. More weight can be removed though if necessary.

Re: pic: DeWalt Gearbox with two CIMs
 

(the delete button seems to have vanished from me.... it's not where it was)

Re: pic: DeWalt Gearbox with two CIMs
 

To specify my question, why not get the extra torque after running each CIM through their own DeWalt transmissions? Though I have to say, if it only weights 2.5 lbs without the motors, that would be a good reason. If you build it make sure to post pictures and results!

Re: pic: DeWalt Gearbox with two CIMs
 

Running each cim into it's own transmission would not give you extra torque. In most if not all cases the total torque is the same. Since each motor has a maximum amount of power it can generate at 12 volts within the given amperage requirements all you would be doing by making separate gearboxes is spreading out the load. In this situation the only reason I would consider doing that is if I was concerned with the torque of 2 cims breaking the deWalt transmission (yes I am thinking that).

From my experience in drive train design I will always advise that people go with a central gearbox and power transmitted through chain or another means. This is due to your overall friction force (another discussion) but basically if you spread out the load to all of your wheels each wheel can take the total torque produced in the situation where another set is off the ground (assuming the mass is over the wheels touching the ground) that is where the normal force/ weight of the robot plays in (yet another discussion) either way keeping your motors together will save you weight in the long run and give you the nice ability to put the torque everywhere you want it to be in the correct situations.

Re: pic: DeWalt Gearbox with two CIMs
 

I'm confused... I don't quite see where this paragraph fits in with proving that there will never be more torque if you put the motors through separate gearboxes. Maybe it's just me only having a highschool physics background, but are some of the words taken a bit out of context? maybe a diagram would help me? I understand the terminology, this paragraph just confuses me.


But then again, maybe it is because it is 2:30 in the morning.

Re: pic: DeWalt Gearbox with two CIMs
 

not a problem, I am only half awake myself. That paragraph is talking more about the design system then proving that there won't be more torque. But since you asked I will explain why you don't get more torque.

Torque from dc motors is theoretically limitless, the more voltage you put to the motor the higher the torque you can create. Now in a real world (FIRST included) motors can only take so much voltage before they burn up. So especially in FIRST where your voltage is limited so is your maximum torque. The best way that I can think of describing the scenario in question is by comparing it to water. If the gearbox is designed correctly to maximize torque without drawing more then 40 amps then you have 1 full water container. This container got it's water (torque) from both motors combined (the max before tripping breakers). Separating the motors is like pouring the water into 2 glasses, you still have the same amount of water it is just in a different place. Because torque is limited by voltage and amperage it doesn't matter how you split it, it will remain the same.

Assuming the same gear ratio in each gearbox consider the following

max torque out of 1 transmission with 4 motors
=
combined max torque of 2 transmissions with 2 motors each
=
combined max torque of 4 transmissions with 1 motor each.

Now there are other things to consider like gearbox inefficiencies and other losses but for all intensive purposes you can pass the water around all day but in the end you are still left with the same amount of water.

Re: pic: DeWalt Gearbox with two CIMs
 

Another thing that you hinted at was that if you have 4 transmissions, if some of your wheels lose grip or leave the ground then you suddenly have less torque available. (If your wheels are leaving the ground during a pushing match you have other problems.)