Motor Used for Shooting [Archive]

kitare102

18-01-2016, 21:02

We've so far been pretty successful using 775pros on a 4:1 versaplanetary gearbox with 4" wheels at ~4500RPM (max rpm for this setup). Once the stages come in we'll be upping that to 3:1, for a shooting speed of around 6000RPM.

If I had to give any advice, it would mostly be that versaplanetary gearboxes with low reductions are wonderful, not only for powering your wheel, but mounting it to your frame. A helpful note, using a CIM adapter on a versaplanetary and gearing it 1:1 (no reduction stages) is a wonderful way to easily and sturdily drive a flywheel with a CIM or Mini-CIM. This setup on a Mini-CIM nets around the same top RPM (~4500) as with our setup mentioned above. See Ri3D Greenhorns for an example of this use case.

I'd suggest using the 775pros (or 775s from Banebots), as opposed to BAG motors, CIMs, or Mini-CIMs, for the higher top RPM and power-to-weight ratio, seeing as a shooting mechanism is very unlikely to torque-stall and burn out the motor during regular operation. However, I'm sure there are ways to make any of those power a successful shooter.

bEdhEd

18-01-2016, 21:10

We've stuck with mini-cims our entire prototyping process and have been pleased with the results. I posted a video of said results in Robot Showcase. Our final design incorporates this motor. Actually, almost all our high power motors in the current design are mini-cims, including the drive system.

Ether

18-01-2016, 21:14

We've so far been pretty successful using 775pros on a 4:1 versaplanetary gearbox with 4" wheels at ~4500RPM (max rpm for this setup). Once the stages come in we'll be upping that to 3:1, for a shooting speed of around 6000RPM..

Reading between the lines, it sounds like you are not planning to control wheel speed, is that right?

dkavanagh

18-01-2016, 21:21

Been toying with the need for encoder to get consistent speed. Parts for prototype should be here tomorrow, so snowstorm-allowing, we'll get going with a prototype and hopefully find out.

Boltman

18-01-2016, 21:22

Can someone do a quick rundown of plus and minus of each (Mini Cim, Bag and 775 Pro) for shooters thanks.

s_forbes

18-01-2016, 21:24

At the moment we're planning to use one of these motors:

http://i.imgur.com/9imwK6V.jpg (http://www.andymark.com/product-p/am-2005.htm)

CalTran

18-01-2016, 21:26

At the moment we're planning to use one of these motors:

http://i.imgur.com/9imwK6V.jpg (http://www.andymark.com/product-p/am-2005.htm)

Pneumatic punching option, a la 2014? Sick. I like it.

bEdhEd

18-01-2016, 21:28

At the moment we're planning to use one of these motors:

Hmmmm.... Is this a hint at a catapult? Or maybe a linear puncher?

carpedav000

18-01-2016, 21:33

A miniCIM... In a vex pro ball shifter :yikes:

R.C.

18-01-2016, 21:39

Hands down, 775pro!

Collin Stiers

18-01-2016, 23:02

We made a prototype 2 wheeled shooter with 6 inch wheels and 2 mini-cims direct drive. For the final design we are going to switch over to the 775pro's with a 3:1 versa Planetary

Anthony Galea

18-01-2016, 23:31

Hands down, 775pro!

Hm. I wonder why you would say that :rolleyes:

But in reality, I would have to agree. 775pros have been our best motor to shoot the balls.

kitare102

18-01-2016, 23:56

Reading between the lines, it sounds like you are not planning to control wheel speed, is that right?

Both sides of our shooter have an in-line versaplanetary encoder which allow us to control the speed of each wheel. Funny story, we remembered when we were setting different RPMs for testing that 4500 is the max for our setup because we set the system to 6000 and the when we measured our speed with a tachometer, it never got above that 4500. Hopefully that speed will be achievable with the new gearbox stages.

R.C.

19-01-2016, 00:01

Hm. I wonder why you would say that :rolleyes:

But in reality, I would have to agree. 775pros have been our best motor to shoot the balls.

Not biased at all... :cool:

But in all seriousness we used it to test our 6" wheeled shooter and loved the performance. The power per weight is unmatched at this point in time.

Sperkowsky

19-01-2016, 00:14

We are using 3:1 versaplanetarys with 775pros on a greenhorn style 2 wheel horizontal variable angle shooter.

Cims and mini Cims do decent at 1:1 bags don't work at all unless you go for a 5:1 or higher gear ratio.

Ether

19-01-2016, 00:42

Both sides of our shooter have an in-line versaplanetary encoder which allow us to control the speed of each wheel. Funny story, we remembered when we were setting different RPMs for testing that 4500 is the max for our setup because we set the system to 6000 and the when we measured our speed with a tachometer, it never got above that 4500. Hopefully that speed will be achievable with the new gearbox stages.

If you are operating the wheel at max motor speed there is no headroom to do closed-loop control.

So if you have a 775Pro geared at 3:1 and want to control the wheel speed at 6000 RPM you won't have a lot of battery voltage left to work with.

kitare102

19-01-2016, 02:53

If you are operating the wheel at max motor speed there is no headroom to do closed-loop control.

So if you have a 775Pro geared at 3:1 and want to control the wheel speed at 6000 RPM you won't have a lot of battery voltage left to work with.

I'm not the one behind the controls for the robot, but I believe we're more interested in using the encoders for 1) making the two sides of the shooter differ by set amount to see how spin will affect trajectory and 2) monitoring when the flywheels get up to speed so that we can move the ball into the shooter the moment it's up to speed.

GeeTwo

19-01-2016, 05:38

We're planning to pull our catapult with an AM PG71 (motor is a 9015), taken down another factor of 3.6 (at initial design) with sprockets and #25 chain. The encoder is already in place on the COTS assembly.

We'll probably use another PG-71 (no encoder, just limit switches) for our mechanism to lift the ball over the bumpers and into the launcher.

Roller pickup TBD.

Nick.kremer

19-01-2016, 05:45

If you are operating the wheel at max motor speed there is no headroom to do closed-loop control.

So if you have a 775Pro geared at 3:1 and want to control the wheel speed at 6000 RPM you won't have a lot of battery voltage left to work with.

I have seen you posting the same thing in a few other threads. I was wondering if you have a minute to explain/have a link to a thread that explains how operating voltage is tied to using control loops, to someone who knows very little about such things?

GeeTwo

19-01-2016, 07:11

I have seen you posting the same thing in a few other threads. I was wondering if you have a minute to explain/have a link to a thread that explains how operating voltage is tied to using control loops, to someone who knows very little about such things?

The control works by varying the voltage supplied to the motor. The motor controllers cannot put out a higher voltage than they take in from the battery. Without getting into PID theory, essentially if it's going too slow, the voltage is increased; if it's going too fast, the voltage is decreased. If you're running the motor at top speed (giving it full voltage), you can only adjust down. Far better to have your nominal operating speed at say 75% of top speed, especially later in the match when the battery voltage is reduced.

lark95

19-01-2016, 07:56

We have been using bb550 motors on versa planetary 3:1 gearboxes with a four inch wheel. It has been working great for us. We have used these motors in the past with great success and I am surprised i haven't seen anybody else using these motors.

D_Price

19-01-2016, 08:03

Our team has tested both the miniCIMs and the CIM's. We are using two CIM's to "launch" the boulder. Good luck to all teams this year!

Just curious as to what motors people are using to siege the opposing towers with. With the unlimited-ness of non-CIM motors, what are people going for?

popnbrown

19-01-2016, 09:05

We're also looking at using a 775pro at a 3:1 but I'm having trouble figuring out how to attach a longer shaft to the VersaPlanetary Gearbox shaft.

I figure in order to gain efficiency it would be better to drive the shooter wheels directly from the gearbox, without adding a second set of gears, belt/pulley or sprocket/chain set-up. We don't have a lathe, so is our only option to not directly drive the shooter wheel?

Mike Schreiber

19-01-2016, 10:25

Can someone do a quick rundown of plus and minus of each (Mini Cim, Bag and 775 Pro) for shooters thanks.

For a shooter it really doesn't matter too much. The main thing that matters is your RPM and compression, I'm not convinced torque has a large impact on the shot as much as it has on spin up time / slow down after a ball is shot (which doesn't matter in this game). You want to get the wheels going at a specific repeatable speed to get an accurate shot - generally between 3000-8000 RPM with a 4" wheel(s) and depending on the distance / angle etc.

The advantage to a Mini CIM is that you can direct drive and be at around the right RPM, the disadvantage is that you can't really go any faster than free speed unless you gear up - which is silly. The Bag, 775, or 550 all have high free speeds and require some gearing down, but a versa planetary box makes that really easy. 550s are a little weird this year since you can't get them from VP or AM. Also consider packaging and where your motor / shooter will live inside the robot.

JesseK

19-01-2016, 10:37

We're using 775Pro's through a Versaplanetary, geared to appropriate reductions for the wheel size (still not determined). Other than power:weight as has been stated, I like the open air cooling that's perfect for a high duty cycle use case like what a shooting wheel does. For shooters that use low compression on the ball, it's perfect.

Ether

19-01-2016, 11:32

I have seen you posting the same thing in a few other threads. I was wondering if you have a minute to explain/have a link to a thread that explains how operating voltage is tied to using control loops, to someone who knows very little about such things?

What Gus said:

The control works by varying the voltage supplied to the motor. The motor controllers cannot put out a higher voltage than they take in from the battery. Without getting into PID theory, essentially if it's going too slow, the voltage is increased; if it's going too fast, the voltage is decreased. If you're running the motor at top speed (giving it full voltage), you can only adjust down. Far better to have your nominal operating speed at say 75% of top speed, especially later in the match when the battery voltage is reduced.

If you still have questions, please do ask.

roystur44

19-01-2016, 16:36

Reading between the lines, it sounds like you are not planning to control wheel speed, is that right?

Since the target is a hole in the wall and not a hoop. I think getting your shooter to have a fairly straight trajectory is needed. Let the motor rip and throw a fastball into the hole. It's all about aiming.

Roy

CalTran

19-01-2016, 16:39

Since the target is a hole in the wall and not a hoop. I think getting your shooter to have a fairly straight trajectory is needed. Let the motor rip and throw a fastball into the hole. It's all about aiming.

Roy

So what's your plan if your battery runs low, or (hopefully not) you forget to switch it between rounds? Pray that it still makes it?

Ginger Power

19-01-2016, 16:43

So what's your plan if your battery runs low, or (hopefully not) you forget to switch it between rounds? Pray that it still makes it?

"Letting the motor rip" could still mean controlling for voltage fluctuations. Just gear your shooter such that at 80%-85% speed you're still shooting much harder than you need to.

billbo911

19-01-2016, 16:52

We have have exceptional results with our prototype using a single RS 775-18 geared 2:1 driving a pair of 4" wheels. We run the motor anywhere between 8.5v and 10v.

Our intent is to run a pair of 775pro's geared 3:1 (60:19 to be exact) and (This is for you, Ether) Bang-Bang to control the rate of the wheel.
Our plan is to use a single retro reflective section and just measure the period to determine the rate the wheel is spinning. We may end up with two sections to preserve balance in the wheel.

Boltman

19-01-2016, 17:02

For a shooter it really doesn't matter too much. The main thing that matters is your RPM and compression, I'm not convinced torque has a large impact on the shot as much as it has on spin up time / slow down after a ball is shot (which doesn't matter in this game). You want to get the wheels going at a specific repeatable speed to get an accurate shot - generally between 3000-8000 RPM with a 4" wheel(s) and depending on the distance / angle etc.

The advantage to a Mini CIM is that you can direct drive and be at around the right RPM, the disadvantage is that you can't really go any faster than free speed unless you gear up - which is silly. The Bag, 775, or 550 all have high free speeds and require some gearing down, but a versa planetary box makes that really easy. 550s are a little weird this year since you can't get them from VP or AM. Also consider packaging and where your motor / shooter will live inside the robot.

Cool Thanks!

lark95

19-01-2016, 22:08

550s are a little weird this year since you can't get them from VP or AM. Also consider packaging and where your motor / shooter will live inside the robot.

We have plenty left over from previous years so it is not a problem for us. However you can order the 550's directly from banebots.

We have done some more testing of the 550's on a 3:1 with 4 in wheels and are able to get a very straight shot at full speed.

timytamy

19-01-2016, 22:23

We're also looking at using a 775pro at a 3:1 but I'm having trouble figuring out how to attach a longer shaft to the VersaPlanetary Gearbox shaft.

Try http://www.vexrobotics.com/vexpro/motion/217-4008.html

triumph69

20-01-2016, 10:59

carpedav000

20-01-2016, 11:54

We are using a miniCIM to power a ratcheting shift-to-freefall gearbox.

Monochron

20-01-2016, 12:56

We are using a miniCIM to power a ratcheting shift-to-freefall gearbox.

Can you describe your reasoning for this? What is the pupose of a ratchet on your shooter? And why the need to shift to neutral?

CalTran

20-01-2016, 13:07

carpedav000

20-01-2016, 18:19

Catapult?

Close, spring-powered linear puncher. :yikes:

billbo911

20-01-2016, 19:46

Close, spring-powered linear puncher. :yikes:

Shades of 971 in 2014!

PowerfulKitty

21-01-2016, 00:52

We're also looking at using a 775pro at a 3:1 but I'm having trouble figuring out how to attach a longer shaft to the VersaPlanetary Gearbox shaft.

While that coupler should work, there is a way you can do it for almost free. Versaplanetary shafts come with a tapped 1/4-20 hole, so you can tap a matching hole in a shaft and secure them together with a short (~1in) piece of all thread. We also put a regular old hex shaft collar over the joint just for good measure, but I can't say whether it's really necessary. It's a pretty straightforward job if you have access to a lathe.

Considering we are making 4 of these joints, that would be $80 for the couplers. :eek:

GeeTwo

21-01-2016, 06:45

Since the target is a hole in the wall and not a hoop. I think getting your shooter to have a fairly straight trajectory is needed. Let the motor rip and throw a fastball into the hole. It's all about aiming.

Roy

Our target was to have the ball traveling nearly horizontally through the goal, to increase the goal's effective cross section. This isn't feasible with the bumpers over the outer works. We'll probably have two good ranges for shooting, one on the way down (at the outer works, when a defender is active) and one on the way up (near the batter, preferred if no defender present). This trajectory will also give us a rather high launch angle, which should be better to get over defending robots.