pic: Shaft Drive Bearing Blocks

[Stuart]

the only thing that scares me about this is those little bitty gears direct driving those moderately sized wheels., but what do I know Im not a meche. good luck on that drive system though

[Ben Piecuch]

It looks like you are machining your own wheels. If that's the case, why don't you just make a center wheel that is slightly bigger that the two outer ones. The speed of that wheel will be negligibly higher than the outer two, but it will allow you to have a standard pillow block in there, as opposed to the IGUS ones. This could make for a possibly more robust drive setup, as some teams had problems with those plastic IGUS bearings last year.

BEN

[MAteo9944]

Originally Posted by Ben Piecuch

It looks like you are machining your own wheels. If that's the case, why don't you just make a center wheel that is slightly bigger that the two outer ones. The speed of that wheel will be negligibly higher than the outer two, but it will allow you to have a standard pillow block in there, as opposed to the IGUS ones. This could make for a possibly more robust drive setup, as some teams had problems with those plastic IGUS bearings last year.

BEN

This is actually something that I considered for a while, but one of my team's ME mentors talked me out of it. I can't figure out if it would be a problem or not. I probably need to test it out and see. If anyone has experience with this could you please help me out?

As for the IGUS bearings, they should be fine. They are not under too much load from the miter gears. We are using conventional ball bearings where there are higher loads.

[TubaMorg]

I always like the idea of a shaft drive. It can be quieter and requires less space and can be more reliable when put together well. I like the bearing support at the drive wheels. Some additional considerations: The drive pinion is ok, but should probably go to a larger gear, use the final gearing as a factor for the transmission. Also, you should consider incorporating a thrust bearing to absorb axial thrust. One other consideration. long shafts need more bearings for support. Have you looked into using a hollow shaft? There is always a certain amount of torque involved which a hollow shaft can absorb better without breaking. Or if you want to get really fancy you can use a quill shaft (you'll have to look it up). A quill shaft is essentially a shaft within a shaft that extends the effective length of a shaft. Length is good because that, too, increases torque flexion which reduces breakage.

[MAteo9944]

Originally Posted by TubaMorg

I always like the idea of a shaft drive. It can be quieter and requires less space and can be more reliable when put together well. I like the bearing support at the drive wheels. Some additional considerations: The drive pinion is ok, but should probably go to a larger gear, use the final gearing as a factor for the transmission. Also, you should consider incorporating a thrust bearing to absorb axial thrust. One other consideration. long shafts need more bearings for support. Have you looked into using a hollow shaft? There is always a certain amount of torque involved which a hollow shaft can absorb better without breaking. Or if you want to get really fancy you can use a quill shaft (you'll have to look it up). A quill shaft is essentially a shaft within a shaft that extends the effective length of a shaft. Length is good because that, too, increases torque flexion which reduces breakage.

I went with the solid shafts so that I could use shaft keys instead of set screws. I do like the idea of quill shafts. I will have to look into them.
Hopefully one day soon I can get hold of an ME for long enough to go over all of the calculations for the strength of the system. As of now the design is still without the support of the calculations, so the sizes and types of components are subject to change.

[Greg Needel]

Efficiency might be your worst nightmare with this system.

Chain & Belt Efficiency ~ 95% - 98%
Spur Gears Efficiency ~ 95% - 98%
Bevel Gears Efficiency ~ 90% - 95%
Planetary Gears Efficiency ~ 80% - 90%


Efficiencies multiply for every stage in your gearbox, so for your drive you have spur>planetary>bevel(x2) assuming that your gearboxes are that the top of efficiency you would be getting .98*.95*.90*.90= ~75.4% efficient at transferring torque. This also does not take into account the effects of torsion of your drive shaft on the efficiency. I like the idea and how different it is in application, but sometimes being innovative for no reasons can have adverse effects. That being said I would love to see this drive work, but I would be hesitant to build this for the competition season without building a prototype drive in the off season.

[John C]

My team has also designed a similar system. There is one thing you may want to take into consideration. In our design we use spider couplings in the driveshaft to allow for slight misalignments in the bearing position. This was important for us because if the robot frame becomes bent slightly in any way it will bind the shaft. Ill post the drawings after our next meeting on Tuesday so you can see where they are located.

[amos229]

Great design. but if the frame flexes chances are something is gonna skip or break. plus under the tremendous forces on that shaft i doubt the bearing blocks will stay in place. If its a flat game this year then it might work but even then the robots still take alot of beating.

[Jeremiah H]

Originally Posted by MAteo9944

I went with the solid shafts so that I could use shaft keys instead of set screws. I do like the idea of quill shafts. I will have to look into them.
Hopefully one day soon I can get hold of an ME for long enough to go over all of the calculations for the strength of the system. As of now the design is still without the support of the calculations, so the sizes and types of components are subject to change.

Cool idea. I like it.
On the keys/set screw thing, I suggest looking into using hex stock rather than round. I know that it will make the build phase harder, but I believe that the advantages gained will be well worth it. The hex gives you six corners to bear the load, and I would think that you could drill quite a bit out of the center without losing much strength. I know hex is used in John Deere hay balers for the main driving shaft, and I have never heard of there being problems with them (not there, at least). JH

[Dan Richardson]

Originally Posted by MAteo9944

I went with the solid shafts so that I could use shaft keys instead of set screws. I do like the idea of quill shafts. I will have to look into them.
Hopefully one day soon I can get hold of an ME for long enough to go over all of the calculations for the strength of the system. As of now the design is still without the support of the calculations, so the sizes and types of components are subject to change.

Yeah this is a neat design something you don't see very often, and there may be some good reasons, the efficieny is one thing, another is what you've addressed above.

It will be significantly important for you to go over the stress strain differentials with an ME. There will be many things you'll have to worry about, one is axial and torsional stresses, make sure the shaft is strong enough so that it can handled the axial stresses over the distance and that your degree of rotation is not very significant, as to where it could cause failure.

Make sure the shock, or impulse, of the robot flying full speed into a wall, or another robot is not transfered through the shaft. And if it is at all transfered make sure that the shaft is robust enough so that absorb the impact plastically without significant deflection and no deformation.

Also important, and quite possibly the easiest thing to overlook. is the frame. Frames over the course of competition have a tendancy to get all bent out of shape, it is often minute, but It does happen. In a system where allignment is paramount for optimum effciency its important that frame flexure is limited. A rigid frame will be important make sure that frame is designed in such a way that deflection is minimum and even slight deformation is avoided.

Looks good tho, I'm excited to see the newer drive style, will love to see how it works out.

[TVan]

Looks great, I would consider a flexible shaft coupling on each side. If it looks like your frame will flex, you would not like teeth on the field

Tim