CIM Motor Strength

[Ether]

Originally Posted by Kevin Sevcik

OR, they could see about making their robot better. That's no crime.

To answer your question, it depends on the gearing and efficiency of your current system. Gearing is easy to determine, efficiency much less so. Luckily there's a simple way for you to answer your question experimentally.

Grab a clamp on Ammeter and measure the max current draw on your CIM while you're lifting. Whatever current you're currently drawing, a second robot of equal weight will likely double it. So if you're currently pulling 30 amps, a second robot would make 60 amps or so. So then it's a question of if you can actually give the CIM that much current. The Jaguar will happily pump 40 amps to your CIM for quite a while. 50 amps for much less so. 60 amps for not very long at all.

So, one measurement and a little math should give you an answer.

Great suggestion.

If they don't have access to a clamp-on ammeter, they can measure how fast the bot is lifting when the motor sounds like it is under the most load, then calculate how fast the motor is turning. Then use the CIM torque vs speed curve to estimate the torque, then use the CIM torque vs current curve to estimate the current. This assumes, of course, they are applying 100% command to the motor, and that there is 12 volts at the motor. The actual voltage at the motor will be somewhat less than 12V of course, because of voltage drops across battery resistance and external resistance - which is why this is only an estimate.


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[Kevin Sevcik]

Originally Posted by Ether

Great suggestion.

If they don't have access to a clamp-on ammeter, they can measure how fast the bot is lifting when the motor sounds like it is under the most load, then calculate how fast the motor is turning. Then use the CIM torque vs speed curve to estimate the torque, then use the CIM torque vs current curve to estimate the current. This assumes, of course, they are applying 100% command to the motor, and that there is 12 volts at the motor. The actual voltage at the motor will be somewhat less than 12V of course, because of voltage drops across battery resistance and external resistance - which is why this is only an estimate.

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Oooohhh. Good point. That's a reasonable assumption to make in absence of a clamp-on ammeter. In fact, if they're using a straight up winch style lift, it should have a reasonably constant load on it after the first second or so. You could probably just figure the motor speed on the average lift time and go with it. It'd give you a built in bump to the low-speed, high-torque side so it should be pretty safe.

[dtengineering]

If you can afford a clamp-on ammeter, though... they are really, REALLY useful tools.

Make sure the one you get measures DC amps. We found a nice one for less than $100 that has two ranges for DC Amps... 4A and 80A. It is PERFECT for FRC work. We use it many times each year and it has got rid of a lot of "guess work" for us.

Jason

[Ether]

Originally Posted by dtengineering

If you can afford a clamp-on ammeter, though... they are really, REALLY useful tools.

Make sure the one you get measures DC amps. We found a nice one for less than $100 that has two ranges for DC Amps... 4A and 80A. It is PERFECT for FRC work.

Please provide brand and model number? Available at Home Depot or Lowe's ? Or did you get it on-line ?

Thanks.

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[dtengineering]

It is the JET 310021, as shown on page 112 of http://www.jetequipment.com/products...HT_109-113.pdf

I think we bought it at KMS Tools a few years ago... which doesn't do you a lot of good as far as a "lets just run out and get one" point of view*... but here is the closest thing they have to it http://www.kmstools.com/darson-instr...amp-meter-1868

I notice it says it is manufactured by "Darson" rather than JET and has a different part number, but it looks exactly the same and has similar specs.

I don't remember paying anything near that much for it, though... KMS Tools has awesome sales for a couple days every month, though, so it is possible that I could have picked it up at 50% off.

Hope you're able to find something useful in your price range... I'd recommend all my "local" sources... Lee's Electronics has one that costs less, but is less sensitive (http://www.leeselectronic.com/catalo...oducts_id=7847) and RP Electronics (http://www.rpelectronics.com/) has a selection, too... but the JET/Darson one is nice because of it's lower 4A/80A settings. These stores do sell on-line but maybe you can access similar stores nearer to home?

Jason

*after being sent out in search of various parts essential for the construction of the robot field that are only available at American Home Depots, or at non-existent chains like Lowes, or where the part number is different in Canada than the states, I know how this feels... believe me!

[Ether]

Originally Posted by dtengineering

It is the JET 310021, as shown on page 112 of http://www.jetequipment.com/products...HT_109-113.pdf

I think we bought it at KMS Tools a few years ago... which doesn't do you a lot of good as far as a "lets just run out and get one" point of view*... but here is the closest thing they have to it http://www.kmstools.com/darson-instr...amp-meter-1868

I notice it says it is manufactured by "Darson" rather than JET and has a different part number, but it looks exactly the same and has similar specs.

I don't remember paying anything near that much for it, though... KMS Tools has awesome sales for a couple days every month, though, so it is possible that I could have picked it up at 50% off.

Hope you're able to find something useful in your price range... I'd recommend all my "local" sources... Lee's Electronics has one that costs less, but is less sensitive (http://www.leeselectronic.com/catalo...oducts_id=7847) and RP Electronics (http://www.rpelectronics.com/) has a selection, too... but the JET/Darson one is nice because of it's lower 4A/80A settings. These stores do sell on-line but maybe you can access similar stores nearer to home?

Jason

*after being sent out in search of various parts essential for the construction of the robot field that are only available at American Home Depots, or at non-existent chains like Lowes, or where the part number is different in Canada than the states, I know how this feels... believe me!

Hey thanks for taking the time to share all that. I've been meaning to pick up a clamp-on ammeter for years and it's about time I did something about it.


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