This is our current climber. It uses two RS 775 motors connected with 256:1 gear ratio gear boxes. We are using a wrench to stop the robot from back driving so that we don’t have to stall the motors.
We are now learning that while the math works out this may not be an optimal solution because the gearboxes aren’t the strongest. We should be fine in terms of the required torque given the size of our drum, but it may be a situation in which parts do not perform as advertised. We’ll have to test things out over the next few weeks and hopefully come up with the best possible solution.
I think you can be almost completely certain that those gearboxes will not last you the entire season. I’m sorry to be the one to tell you this, but they are just not that strong and are not robust enough for this application.
I would recommend replacing them with a pair of Vex VersaPlanetaries, and using the JVN Mechanical Design Calculator to figure out a ratio that will allow your robot to climb well. I bet you can climb nearly 4 times as fast as this setup is geared for without much of a problem depending on the diameter of your winch and weight of your robot.
Unless I am missing something in the picture, It looks like you are putting some significant side load on those gearboxes. You most likely will want to support your shaft with something other than the output shaft of the planetary gearboxes, such as a plate with a bearing in it that the shaft runs through.
From Andymark’s Website:
“Mounting a large load to the end of an unsupported shaft may damage the gearmotor. The shafts on these motors are supported by two ball bearings making them fairly rugged; however, we do not recommend them to be used with large overhung loads. We recommend using a design that supports the end of the shaft. If it is not possible to support the end of the shaft, we recommend mounting the load as close to the face of the gearmotor as possible and cutting the shaft to length.”
I speak from experience when I say: Nothing breaks planetary gearboxes faster than side load! ::ouch::
Those aren’t 775pros or rs775-18’s, they are 775-125 or 775-5 so factor of 10 difference in power output. They are going to struggle the lift the robot in under 15 seconds.
The torque output at the motor shaft is divided by the radius of the drum to get force. Bigger drum, less force.
You’d be better, as mentioned above, using a lower gear reduction on a more powerful motor.
We’ve tested 48:1 reduction on a CIM and a MiniCIM just driving a shaft, and they pull 120lb fast enough.
I was thinking they might be Rs775-18s? They look just like them, and they’re attached to Banebots gearboxes. How can you tell that they are not RS-775-18s?
This is why we post stuff like this, so it isn’t bad news, on the contrary bad news would be having our gearboxes blow up in our first match of our first competition.
We thought we had done the math on these motors and gearboxes, but have yet to test them.
Thank you all for the input. I’ll have the team do some research and once we decide on something we’ll post an update.
Banebot gearboxes have significantly improved in the past couple of years. In fact they are commonly used in high power 1500+ watt direct drive combat robot drive applications. I wouldexpect them to preform better than VPs in the same (un-optimal) setup.
I like the way your drum (at least it looks like) rotates so that you get a couple of wraps before there’s load on it. But I gotta ask, what kind of bolts are you using. Because it looks to me like to get that rotation on your drum your entire climber is held onto your frame with two bolts.
This means to me that the failure point of your climber is those two bolts, if those bolts aren’t strong enough they will shear and it will be a really bad time. 150lbs of robot on two bolts seems like a likely failure scenario to me. You should be able to buy bolts with that shear strength, so it should be a (relatively) simple fix.
Seeing as those are P60s and Banebots themselves lists the maximum torque as 35 ft-lbs, versus 115 ft-lbs for a VP 1/2" hex shaft (or 72 ft-lbs for a 7:1 or up stage) I’d say you’re only about 50% correct there. The P80s at 85 ft-lbs are about on par with the VPs, but then again they’re twice as big.
eedoga, go with the Versaplanetaries. Banebots gearboxes in high torque applications are just asking for heartbreak. And VPs are MUCH easier to tweak into different motor or gearing configurations.
These are P60s, not the new upgraded Banebots gearboxes (BB150s or BB220s). They have not been updated since 2009 and have the same (lack of) load carrying capability we all “know” and “love”.
The VersaPlanetary is stronger than both the P60 and the P80 series of gearboxes.
