How many 393s do you (tentatively) plan to use?

[Phyrxes]

Fully expecting to use 6, on a related note anybody catch what exactly the spray was so I can duplicate its impact on tiles in our shop?

[Thorondor]

Originally Posted by bgambsky

It was just the new mats at worlds, no other mats gave me a problem.

I would highly doubt that its the mats that are causing the problem. During round up we were having a similar problem and we blamed it on the mats. We went to Ricky Torrence and he told us that often its because at World's people tend to drive more sporatically. We started driving smoother and it solved the problem (for the most part). I would say that its either because you have worn down you motors too much so they tend to trip easier, your driving was a little crazy, or your gear ratio is too agressive and should be geared down more. And as murdomeek said, even if it is the mats, you should probably come up with a way to fix that problem because they probably aren't going to be changing the mats.

[xwon3]

We are expecting to use 6 HS due to possible tripping of the cortex.

[Ephemeral_Being]

We are currently planning on using 10, some geared.

We'll have to see how safe that ends up being.

[Sayanthan]

since the sacks are heavy
i plan to use 4 hs motors for my lift alone

[jpearman]

One thing to bear in mind is that the HS motors don't use that much more power. Lets look at two situations.

Gateway rules maximum motor use
4 x 393 + 6 x 269

Sack Attack rules maximum motor use
10 x 393

Case 1, Worst case condition, all motors stalled

Gateway
4 x 3.6A + 6 x 2.6A = 30A

Sack Attack
10 x 3.6A = 36A

Either way is going to quickly trip breakers somewhere.

Case 2, all motors running below the trip current for their internal PTC

We know that the 269 has a PTC (HR16-075) with a hold current of 0.75A and a minimum trip current of 1.5A. The 393 has a PTC (HR30-090) with a hold current of 0.90A and a minimum trip current of 1.8A. Lets consider the situation where each motor is running half way between the two, 1.35A for the 393 and 1.125A for the 269.

Gateway
4 x 1.35A + 6 x 1.125A = 12.15A ... right at the limit for the cortex and power expander.

Sack Attack
10 x 1.35A = 13.5A ... A bit more but not that much, the system will still handle this but with reduced time.

This is a hypothetical analysis but gives you an idea that we are not talking about doubling the power needed but rather increasing it by perhaps 20% in most situations.

[The VEX Raptors]

Originally Posted by jpearman

One thing to bear in mind is that the HS motors don't use that much more power. Lets look at two situations.

Gateway rules maximum motor use
4 x 393 + 6 x 269

Sack Attack rules maximum motor use
10 x 393

Case 1, Worst case condition, all motors stalled

Gateway
4 x 3.6A + 6 x 2.6A = 30A

Sack Attack
10 x 3.6A = 36A

Either way is going to quickly trip breakers somewhere.

Case 2, all motors running below the trip current for their internal PTC

We know that the 269 has a PTC (HR16-075) with a hold current of 0.75A and a minimum trip current of 1.5A. The 393 has a PTC (HR30-090) with a hold current of 0.90A and a minimum trip current of 1.8A. Lets consider the situation where each motor is running half way between the two, 1.35A for the 393 and 1.125A for the 269.

Gateway
4 x 1.35A + 6 x 1.125A = 12.15A ... right at the limit for the cortex and power expander.

Sack Attack
10 x 1.35A = 13.5A ... A bit more but not that much, the system will still handle this but with reduced time.

This is a hypothetical analysis but gives you an idea that we are not talking about doubling the power needed but rather increasing it by perhaps 20% in most situations.

I'm definitely showing this to my team mates. What are your calculations for 6 393s and 4 269s?

[jpearman]

Originally Posted by The VEX Raptors

I'm definitely showing this to my team mates. What are your calculations for 6 393s and 4 269s?

Well using the same condition it would be

6 x 1.35A + 4 x 1.125A = 12.6A

Understand this is completely hypothetical, the robot does not run the motors at a constant current, it's fluctuating as the load on the motors changes, you need to figure out where in the speed/torque curve you are operating and make design decisions based on that. You could also add software to limit power to say the drive if other parts of the robot are operating.

[Team5119]

we only plan on using 2 393 motors, because we have 10 269s and 2 servos that are only 7/8 months old, so our major plan is to use the following cortex setup:

2 X 393
1 X Servo Module
2 X 269 via 2 wire motor ports
5 x 269

[Thorondor]

Originally Posted by Team5119

we only plan on using 2 393 motors, because we have 10 269s and 2 servos that are only 7/8 months old, so our major plan is to use the following cortex setup:

2 X 393
1 X Servo Module
2 X 269 via 2 wire motor ports
5 x 269

just curious, why a servo? Servos don't really give you any advantage over a normal motor.