Prototype transmission for potential use this year

[sanelss]

https://www.youtube.com/watch?v=uUyp...ature=youtu.be

[Nate Laverdure]

Looks great. Do you think you could eliminate a lot of this play with a hex hub? You could try to broach the bronze gear to the same shape.

[sanelss]

well the play isn't on the bronze gear, that mating is actually pretty good. it's specifically between the andymark hub, keystock, and axle. Also we don't have the tools for hex shafts and it would be a major pain to deal with the bearings considering how it has to be assembled. but even then there would be some inherent play anyway. One option would be to setscrew the key in place. or get the 3/8 hubs and then bore and broach it ourselves for a tighter fit. The axle was sanded down though so maybe whoever did that went too far. may not be worth messing with though

[avanboekel]

Are you able to turn the wheel by hand on the new version?

[sanelss]

Originally Posted by avanboekel

Are you able to turn the wheel by hand on the new version?

not a chance in hell. this drive is 1 way only(cim to wheels). Trying to go the other way will be met with extreme resistance and would cause something to break if you actually could turn the wheel. But in our case this is actually a desired trait. It allows us perfect control of motor speeds at all times and provides extreme braking when someone else is trying to push is around when we don't want them to(providing the wheels grant enough traction)

[Richard Wallace]

Nice work aligning the worm and minimizing lash in the gearmesh.

Have you measured the free current?

[sanelss]

Originally Posted by Richard Wallace

Nice work aligning the worm and minimizing lash in the gearmesh.

Have you measured the free current?

it's about 3.5 amps

[nicholsjj]

This looks great guys. I think that this version will help you in many of the pushing battles that you all faced last year. Your omni-directional drivetrain was very fun advantage to pair up with last year during the elimination rounds and I wish we would have provided you all with some more firepower. Thanks again for selecting our team last year and I hope that we get to work together in Saint Louis again in 2014.

[AdamHeard]

Originally Posted by sanelss

not a chance in hell. this drive is 1 way only(cim to wheels). Trying to go the other way will be met with extreme resistance and would cause something to break if you actually could turn the wheel. But in our case this is actually a desired trait. It allows us perfect control of motor speeds at all times and provides extreme braking when someone else is trying to push is around when we don't want them to(providing the wheels grant enough traction)

I don't follow this logic.

[sanelss]

Originally Posted by AdamHeard

I don't follow this logic.

Well just think about it. Any wheel drive where you can move the motor by turning the wheel you will have drifting wheel speeds depending on what else is going on. for example another robot is trying to push you around or you want to slow down but the inertia carries your robot further. With this setup where the wheel can't move the motor. If we tell the motor to go at 100rpm, then it doesn't matter what else is going on that motor is going to draw up to 100A or apply extreme braking to make that motor turn at 100 rpm, not any slower and not any faster. That means if u want the robot to stop, it's going to come to a complete dead stop instantaneously. Also if we meet some resistance(another robot) then the PID loop will keep increasing force to the absolute limits to try to make that motor turn at the set speed. Also if another robot tries to push us around, even if we don't have enough power to overpower them, simply not trying to do anything will provide tons of force and keep them from pushing us around, well as much resistance as the friction of the omni wheels provide. With this design we don't need the force to over power other robots, we just need enough traction and that will prevent anyone from pushing us around.

[AdamHeard]

Regardless of gearing method, the motor will shift up and down it's curve as the applied load changes (being pushed is an applied load).

If your statement were true, the gear train would magically be creating and dissipating energy.

Originally Posted by sanelss

Well just think about it. Any wheel drive where you can move the motor by turning the wheel you will have drifting wheel speeds depending on what else is going on. for example another robot is trying to push you around or you want to slow down but the inertia carries your robot further. With this setup where the wheel can't move the motor. If we tell the motor to go at 100rpm, then it doesn't matter what else is going on that motor is going to draw up to 100A or apply extreme braking to make that motor turn at 100 rpm, not any slower and not any faster. That means if u want the robot to stop, it's going to come to a complete dead stop instantaneously. Also if we meet some resistance(another robot) then the PID loop will keep increasing force to the absolute limits to try to make that motor turn at the set speed. Also if another robot tries to push us around, even if we don't have enough power to overpower them, simply not trying to do anything will provide tons of force and keep them from pushing us around, well as much resistance as the friction of the omni wheels provide. With this design we don't need the force to over power other robots, we just need enough traction and that will prevent anyone from pushing us around.

[sanelss]

Originally Posted by AdamHeard

Regardless of gearing method, the motor will shift up and down it's curve as the applied load changes (being pushed is an applied load).

If your statement were true, the gear train would magically be creating and dissipating energy.

indeed it will. I never said it wouldn't however with this system is such that it makes the job much easier on the cim. For example if we were moving forward at a certain speed. A robot behind us is attempting to push us forward faster. It's not going to happen. All him trying to do so would REDUCE the load on our drive motors and the extra force would be directed into our chasis. If we wanted to remain stationary, and someone tries to push us, provided we have enough traction our robot will move absolutely nowhere regardless of how hard they push. or we can advance forward at the rate we want to advance at and not any faster than we want, due to this type of setup. Now granted if we faced head on against another robot, if we don't have more force than they do we won't be able to push them back, but at the same time they wouldn't be able to push us back either and all the cims simply have to do is not move and all the force is transferred into the transmission structure

[Madison]

Originally Posted by sanelss

indeed it will. I never said it wouldn't however with this system is such that it makes the job much easier on the cim. For example if we were moving forward at a certain speed. A robot behind us is attempting to push us forward faster. It's not going to happen. All him trying to do so would REDUCE the load on our drive motors and the extra force would be directed into our chasis. If we wanted to remain stationary, and someone tries to push us, provided we have enough traction our robot will move absolutely nowhere regardless of how hard they push. or we can advance forward at the rate we want to advance at and not any faster than we want, due to this type of setup. Now granted if we faced head on against another robot, if we don't have more force than they do we won't be able to push them back, but at the same time they wouldn't be able to push us back either and all the cims simply have to do is not move and all the force is transferred into the transmission structure

Forgive me if I missed this, but what kind of feedback are you receiving that allows you to measure actual velocity versus desired velocity?

With an encoder on the worm, you're only able to measure the CIM's speed; you can't empirically determine whether or not the rotation of the worm is actually being transformed into linear motion along the ground. The presence of (or lack of) backlash between the wheel / worm gear / worm doesn't change that.

[sanelss]

Originally Posted by Madison

Forgive me if I missed this, but what kind of feedback are you receiving that allows you to measure actual velocity versus desired velocity?

With an encoder on the worm, you're only able to measure the CIM's speed; you can't empirically determine whether or not the rotation of the worm is actually being transformed into linear motion along the ground. The presence of (or lack of) backlash between the wheel / worm gear / worm doesn't change that.

Yes you are right. I was talking from a more theoretical viewpoint rather than a practical one where assumptions like wheels not slipping aren't necessarily accurate. Although thinking about it, since we know how much and in what direction force is applied to the motors, we can have a feedback loop with the accelerators which would indeed tell us actual acceleration vs attempted. so if wheels are moving but robot isn't well we know we arn't actually going anywhere or if the proportions are off what they should be.

[magnets]

Neat idea. However, I am fairly certain that your worm wheel will loose teeth when you have the weight of the robot behind it. If your robot is going fast, and suddenly you stop applying power, the worm wheel won't be to turn the worm gear, so you'll just snap a tooth off. It will be different than just testing it on a table.

In the video you talked about having to use a smaller worm wheel in order to get the same reduction. These are pretty fragile, so you could switch to a bigger worm wheel with a two-start worm.

A few other recommendations. Be sure to lubricate your gears! Make sure there isn't any play sliding the worm or worm wheel up and down on their shafts and that the unsupported drive axle doesn't wiggle around, but a little play in rotating the gears (like you showed in the video) is really important. That backlash makes the transmission operate more smoothly, and helps with lubrication, especially when you're using gear like this, than "slide" instead of "roll" on each other.