AM FP Gearbox...feedback?

[Justin M.]

Last night we had our robot together, nearly 100%. However, the dual 64:1 FP 42mm gearboxes didn't have quite enough torque to lift our manipulator, it's pushing about 30lbs. This is without the claw and additional chain so lets say a safe 40lbs max (this is before shedding weight - we might be replacing the 80/20 1515 for 1515 lite). The 256:1 gearboxes are sold out, and wont be back for this FIRST season.

So this brings me to the AM FP Planetary gearbox. I did some searching but I was wondering if anbody had some feedback concerning my application. Also if someone could recommend another motor, or idea that would great, we are sort of stuck right now.

Thanks

[Rob]

Hi,

That sounds like a pretty heavy arm...depending on the length you are going to have to do ALOT of reduction to get the FP motor into acceptable range. I hope that you have 2 FP motors available to use.

The AM planetary is probably a good start, I have never used it but I think it is supposed to reduce the FP to about the same free RPM as a small CIM (approx 5500 RPM).

One area you might consider is already attached to the motor: the plastic FP gearbox. Consider these possible advantages: They are free, very light and reasonably simple to interface with and mount. Another "advantage" that many dont consider when doing an arm application is that they are pretty inefficient...What you say, how is that an advantage? They are hard to backdrive. If you have 2 of them on your arm the amount of force required to backdrive might be more than the torque on your arm joint from the weight of your arm. This is a huge advantage because your arm can then hold position without applying power to the motors and sparing you from smelling a stalled FP burning up. If you gear your arm right they will always be at high RPM when moving and not need any power to hold position (although with a 30-40 pound arm that may not be the case).

Just something you may want to consider. Best of luck!

RAZ

[Justin M.]

Originally Posted by Rob

Hi,

That sounds like a pretty heavy arm...depending on the length you are going to have to do ALOT of reduction to get the FP motor into acceptable range. I hope that you have 2 FP motors available to use.

The AM planetary is probably a good start, I have never used it but I think it is supposed to reduce the FP to about the same free RPM as a small CIM (approx 5500 RPM).

One area you might consider is already attached to the motor: the plastic FP gearbox. Consider these possible advantages: They are free, very light and reasonably simple to interface with and mount. Another "advantage" that many dont consider when doing an arm application is that they are pretty inefficient...What you say, how is that an advantage? They are hard to backdrive. If you have 2 of them on your arm the amount of force required to backdrive might be more than the torque on your arm joint from the weight of your arm. This is a huge advantage because your arm can then hold position without applying power to the motors and sparing you from smelling a stalled FP burning up. If you gear your arm right they will always be at high RPM when moving and not need any power to hold position (although with a 30-40 pound arm that may not be the case).

Just something you may want to consider. Best of luck!

RAZ

We are using two to get the most torque possible.

I was considering re-using our monster 2005 FP gearbox with worm gears, that don't backdrive...is this legal? It was custom built...

[Rob]

Originally Posted by Justin M.

We are using two to get the most torque possible.

I was considering re-using our monster 2005 FP gearbox with worm gears, that don't backdrive...is this legal? It was custom built...

That would not be legal unless you remade all of the custom parts. Off the shelf purchased parts of it such as the worm gears may be legal to use (if they are unmodified).

Good luck,

RAZ

[Justin M.]

Originally Posted by Rob

That would not be legal unless you remade all of the custom parts. Off the shelf purchased parts of it such as the worm gears may be legal to use (if they are unmodified).

Good luck,

RAZ

The whole gearbox was constructed with off the shelf parts, gears, sprockets, and shaft. No custom machining was done. So basically to use these again, we would need to re-cut shaft, re-cut the aluminum casing, and re-tap a few holes?

[Rob]

Originally Posted by Justin M.

The whole gearbox was constructed with off the shelf parts, gears, sprockets, and shaft. No custom machining was done. So basically to use these again, we would need to re-cut shaft, re-cut the aluminum casing, and re-tap a few holes?

I am not going to claim to be any kind of expert regarding the rules of using unmodified COTS parts bought in past years because my team is not doing this. If my team was considering it, I would make myself an expert.

If you are thinking of going down this path then VERY CAREFULLY review all of the rules and Q & A responses related to this subject.

I still think that your best bet is to use the plastic FP gearbox.

Best of luck

RAZ

[Justin M.]

Thanks everyone...is there any place to get a new gearbox/motor assembly? We sort of got rid of the plastic gearboxes.....Also the original gears are a bit mangled from getting them off, and the FP motor shaft was grinded down to fit in the Banebots gearbox.

Also, whats the best way to attach a sprocket to the FP gearbox?

[Andrew Blair]

As another option, depending on your arm's setup, can you add a counterweight or gas spring to help to offset the load of the arm? If you can design it in, you could potentially reduce the overall average load of the arm by a large amount. Just in my head, I'm imagining close to 30% of the arm's weight. With some clever counterweight/force work, perhaps with constant force springs, you could completely eliminate the weight of arm more or less, and leave your gearboxes to deal only with the acceleration of the arm.

[Rob]

Originally Posted by Justin M.

Also, whats the best way to attach a sprocket to the FP gearbox?

Here is a link to a page showing what we have done in the past (and this year):

http://www.joemenassa.com/robotics2005day29.html

You will have to look through and find the images of the FP gearbox and adapter. the shaft goes through the hole in the gearbox and is supported on the backside as well as the front. The metal adapter in the white FP gear is an octagon and has a keyway in it to interface with the shaft. The octagon is just under 1.5" fact to face.

I'm not saying this is the best way, just something that has worked for us.

Best of luck

RAZ

[Justin M.]

Is there anyplace we can buy a whole new motor/gearbox setup?

[AdamHeard]

Originally Posted by Rob

Here is a link to a page showing what we have done in the past (and this year):

http://www.joemenassa.com/robotics2005day29.html

You will have to look through and find the images of the FP gearbox and adapter. the shaft goes through the hole in the gearbox and is supported on the backside as well as the front. The metal adapter in the white FP gear is an octagon and has a keyway in it to interface with the shaft. The octagon is just under 1.5" fact to face.

I'm not saying this is the best way, just something that has worked for us.

Best of luck

RAZ

Team 60 (and us copying them) machine an octagon that is 1.490 face to face. Then hose clamp the plastic output of the FP tightly around the octagon to prevent slipping. The Hose clamp doesn't take the torque of rotation, just prevents the octagon from slipping. We have run these without the clamp before, but the hose clamp increases reliability.

[AdamHeard]

Well, the AndyMark gearboxes only have a 3.67: 1 reduction, So those won't work.

The KOP fisherprice gearboxes have a 124:1 reduction.

Also, you say 40 lbs but we need more information to do calculations. Is it lifted straight, is it a lever arm?

Is the shaft of the BB directly driving the arm, or is chain? If there is chain, you can easily add more reduction in the sprockets.

[Justin M.]

Originally Posted by AdamHeard

Well, the AndyMark gearboxes only have a 3.67: 1 reduction, So those won't work.

The KOP fisherprice gearboxes have a 124:1 reduction.

Also, you say 40 lbs but we need more information to do calculations. Is it lifted straight, is it a lever arm?

Is the shaft of the BB directly driving the arm, or is chain? If there is chain, you can easily add more reduction in the sprockets.

It's a forklift. It's going to move by a chain system, with a sprocket mounted on the shaft and also directly overhead. We're bolting the chain directly to the forklift, so when the motor turns, the forklift goes up. I was thinking about reduction, but the torque needs to be transferred directly to the chain "pulling power", not the sprocket on the other end. Also the chain needs to be somewhat straight, so the two sprockets need to be about the same size.

I was thinking about reducing the gearbox directly by using some gears or something...like a gear mounted on the output shaft of the 64:1 gearbox, turning a larger gear mounted directly to a sprocket, which in turn transfers the torque to the right place.

[AdamHeard]

Originally Posted by Justin M.

It's a forklift. It's going to move by a chain system, with a sprocket mounted on the shaft and also directly overhead. We're bolting the chain directly to the forklift, so when the motor turns, the forklift goes up. I was thinking about reduction, but the torque needs to be transferred directly to the chain "pulling power", not the sprocket on the other end. Also the chain needs to be somewhat straight, so the two sprockets need to be about the same size.

I was thinking about reducing the gearbox directly by using some gears or something...like a gear mounted on the output shaft of the 64:1 gearbox, turning a larger gear mounted directly to a sprocket, which in turn transfers the torque to the right place.

How many teeth are on the drive sprocket?

If you have 20 or so, you can probably get all the additional reduction by going to a smaller sprocket.

[Justin M.]

Originally Posted by AdamHeard

How many teeth are on the drive sprocket?

If you have 20 or so, you can probably get all the additional reduction by going to a smaller sprocket.

We are using 10t sprockets on either end, for now.