HELP!!!!!!!!!: Arm Lifting

[4404 PCH Colts]

We are having problems raising our intake arm. We have it directly hooked to a CIM motor attached to a 64:1 BaneBot gearbox. Looking for teams with similar designs to provide stall torques and/or gear ratios that are working for them

[PayneTrain]

Without knowing your whole system and wanting to give you the fun of learning this stuff yourself, you'll want to download JVN's Design Calculator. It helps even the most helpless like myself understand what we need to make our robots run and supports the fragile facade of it looking like I know what I'm doing. By comparison, you'll probably be a natural.

[Ginger Power]

What Wil said. But for reference 4607 is running a 725:1 ratio with a Cim motor in a 4 stage Gem 500 gearbox from AndyMark, and we have a 4:1 reduction after that with #35 chain. Oh and we have 2 of those setups. I like to say we have infinite power

[billbo911]

Originally Posted by PayneTrain

Without knowing your whole system and wanting to give you the fun of learning this stuff yourself, you'll want to download JVN's Design Calculator. ...

Getting and using the JVN design calculator is the best advice you can get!

We are using a Mini CIM and 90:1 reduction on a 24" arm.

[JamesCH95]

At first blush a CIM connected 64:1 to a collector mechanism doesn't strike me as scary.

0) Counter-balance the mechanism with a spring or air cylinder (one should generally do this no matter what else you find IMO)
1) Check your battery, main power connections, and other electrical connections
2) Check for binding/asymmetry/drag in the mechanism
3) Make sure you greased the BB transmission
4) Make sure there's not a stupid coding issue limiting power
5) Check JVN design calculator to make sure you're not insane

Originally Posted by Ginger Power

What Wil said. But for reference 4607 is running a 725:1 ratio with a Cim motor in a 4 stage Gem 500 gearbox from AndyMark, and we have a 4:1 reduction after that with #35 chain. Oh and we have 2 of those setups. I like to say we have infinite power

You have a maximum of 337*2 watts of power

That overall reduction is... unneeded. At some point you're simply slowing yourself down, risking damaging mechanisms, and adding weight.

[Ginger Power]

Originally Posted by JamesCH95

You have a maximum of 337*2 watts of power

That overall reduction is... unneeded. At some point you're simply slowing yourself down, risking damaging mechanisms, and adding weight.

I know it's overkill, and I know it's not "infinite power", but it's more than we'll ever need. We have the weight and room for the gearboxes any they move the arm at a favorable speed, so I see no reason to change. With that said, we could easily remove a stage on the Gem and lower the gear ratio if it becomes a problem.

[4404 PCH Colts]

Thanks for all the advice folks! We did some back of the envelope estimations, and are also looking into other options like the ones you listed above, but wanted to make sure we weren't going crazy. The JVN calculator will be EXTREMELY helpful as well. Thanks again!

[Kevin Sevcik]

The single best way to figure out how much torque you need to hold a rotating arm is to buy yourself a luggage scale or a fishing scale or something.

Disconnect the arm from any gearboxes or motors so friction won't throw off your readings. Tare the luggage scale, put the rotating arm horizontal to the floor, hook the scale onto the arm somewhere and measure the weight. Multiply the weight by the distance from the pivot to the hook and you've got a fairly accurate measurement of the torque you need.

Note that you want your transmission to stall at something like 4 times this torque or better to account for losses, actually moving the thing, and not blowing breakers. JVN's calculator can help you more with this aspect of things.

[DaveL]

Most of our lifting arms have been pneumatic. But when I first became a mentor, we didn't know how to do pneumatics and we used a motor to power our arm in 2012.
I learned 2 things really fast; 1) don't rely on your motor's bearings for arm support and 2) any arm faster than full range of motion in under 3 seconds is very dangerous and unlikely to be accurately controlled by humans.

In the off season, we went and rebuilt that arm with a 250:1 Banebots transmission and a 2:1 sprocket reduction. (500:1 total reduction).

We learned the arm is so stiff, we needed to run the motors to move it. What's going to happen when a robot hits it or your robot runs into a wall?

We are trying AM's 50:1 transmission with a 5:1 sprocket on a 2 foot arm (250:1). This transmission has large steel gears that should back drive if hit. Hope that's slow enough without running it at 3 volts!

[Hgree56]

Our team was having a similar problem. Most of what we did has already been said before but springs help with lowering the arm more slowly and getting that original push into the air. Good luck guys!!!

[DaveL]

Update: tested the arm last night. With 3 volts it moved at a reasonable speed and was able to lift 30 lbs. placed 12 inches in front of the frame!

The arm can be back driven by hand, yet there was enough friction to hold the arm in place.
Dave

[JamesCH95]

Sounds like more than enough!