How many CIMs in your drivetrain?

[pfreivald]

Originally Posted by CryptoStorm

I started as a FIRST student in 2004. to my knowledge we've always used 2 CIMS per side on the standard "tank drive" type setup. We used mecanum wheels once which required independent drive of 1 CIM per wheel.

Does anybody have any (scientific) input on using only 1 CIM per side? (2 total)

how about 6 CIM drive?

We prototyped a 6 CIM drive during the offseason using VexPro's dog shifting dual-speed gearboxes, and it works fantastically.

We also did octocanum for about five years, and could beast through just about everyone...except for 6 CIM drivetrains, despite being geared down about as preposterously low as you could get, and with great traction.

I would strongly recommend not going to one per side--you'll lose every pushing match you get into with a four-CIM drivetrain, and each of those CIMs are going to draw more current, work harder, get hotter, and drain your battery more than four or six. The only advantage is weight, and it's not a good enough tradeoff.

[MaGiC_PiKaChU]

has anyone ever done a drivetrain with more than 6 motors? (not including steering for swerve)

[Ether]

Here's a quick calculation using MCALC to compare

one CIM drawing 60 amps at 12 volts
vs
two CIMs each drawing 30 amps at 12 volts:

Motor Calculator  build MCALC_2014d 2/3/2014 1255pm


Select motor:
1)CIM     6)FP0673   d)FP2719  f)FP9012     g)FP9015    h)FP9013 j)MiniCIM
a)am-0912 b)am-0914  7)DensoL  8)DensoR     c)Denso0160 k)BAG    u)UserDefined
2)RS395   3)RS540    4)RS550   e)RS775-12   5)RS775-18  m)RS555  n)am-0915
r)am-2193 s)am-2235  t)RS390   v)RS545      p)am-2161&2194
w)VEX2177hi  z)VEX2177std  1


CIM FR801 001, AM802 001A @ 12.00 volts:

@ free (no load):
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
     0.0   0.000    5310   100.0     2.7         0.0        32.4     0.0

@ stall:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   343.4   2.425       0     0.0   133.0         0.0      1596.0     0.0

@ max power:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   171.7   1.212    2655    50.0    67.8       337.1       477.1    41.4

@ max efficiency:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
    42.8   0.302    4648    87.5    18.9       147.1        80.2    64.7

Select input:
1)oz-in  7)watts_in    3)rpm    5)amps   b)rpm&amps  8)eff%
2)Nm     6)watts_out   4)rpm%   9)volts  a)rpm&ozin  m)main menu   x)exit 5


enter amps: 60

CIM FR801 001, AM802 001A @ 12.00 volts:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   151.0   1.066    2975    56.0    60.0       332.2      387.8    46.1


Select motor:
1)CIM     6)FP0673   d)FP2719  f)FP9012     g)FP9015    h)FP9013 j)MiniCIM
a)am-0912 b)am-0914  7)DensoL  8)DensoR     c)Denso0160 k)BAG    u)UserDefined
2)RS395   3)RS540    4)RS550   e)RS775-12   5)RS775-18  m)RS555  n)am-0915
r)am-2193 s)am-2235  t)RS390   v)RS545      p)am-2161&2194
w)VEX2177hi  z)VEX2177std  u


Enter the following motor specs in the order and units indicated,
separated by spaces or tabs:
volts   stall_ozin      free_rpm        stall_amps      free_amps
12       686.8           5310             266            5.4

UserDefined-> 12.0 686.8  5310 266.0  5.4 @ 12.00 volts:

@ free (no load):
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
     0.0   0.000    5310   100.0     5.4         0.0        64.8     0.0

@ stall:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   686.8   4.850       0     0.0   266.0         0.0      3192.0     0.0

@ max power:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   343.4   2.425    2655    50.0   135.7       674.2       954.2    41.4

@ max efficiency:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
    85.6   0.605    4648    87.5    37.9       294.3       160.4    64.7

Select input:
1)oz-in  7)watts_in    3)rpm    5)amps   b)rpm&amps  8)eff%
2)Nm     6)watts_out   4)rpm%   9)volts  a)rpm&ozin  m)main menu   x)exit 5


enter amps: 60

UserDefined-> 12.0 686.8  5310 266.0  5.4 @ 12.00 volts:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   143.9   1.016    4197    79.0    60.0       446.6       273.4    62.0

one CIM drawing 60 amps at 12 volts:
332 watts output mechanical power
388 watts waste heat

two CIMs each drawing 30 amps at 12 volts:
447 watts output mechanical power
273 watts waste heat

[GeeTwo]

We did a 2 CIM drivetrain last year, but Recycle Rush was definitely a special case; you didn't want to accelerate quickly or drive very fast. We're starting with 4 this year, and if we change it, we'll be going to six.

Originally Posted by MaGiC_PiKaChU

has anyone ever done a drivetrain with more than 6 motors? (not including steering for swerve)

I've read about people considering 4 CIM + 4 min-CIM designs for Mecanum and 4-wheel Killough, but was unable to find any examples that had been built and played.

[dellagd]

Originally Posted by GeeTwo

I've read about people considering 4 CIM + 4 min-CIM designs for Mecanum and 4-wheel Killough, but was unable to find any examples that had been built and played.

Here you go

That year we ran 4 CIMs + 4 Mini-CIMs in our shifting 8in Mecanum Drivetrain. Looking back, mecanum probably wasn't the best choice that year with the heavy defense (), but we sure tried our hardest to make it work. For the most part it did, and we were able to handle many defensive situations with the great traction of the extremely wide wheels, but the cons far outweighed the benefit.

With 8 CIM-motors, we had the potential to run 320 Amps of current into our drivetrain before any of the individual 40A breakers would trip. Even operating well below that, there was incredible risk for popping the main breaker, not to mention browning out components, both of which happened in matches on multiple occasions. In high gear, any defensive situation was almost always a brown-out and radio reboot on the field. In low gear, we had maybe 10 seconds before a brown-out. With the current sensing capabilities of the new PDP, careful software could allow a team to more safely run this kind of setup, but back then, it was far more risk than the team could effectively manage or I would ever recommend.

[CryptoStorm]

We talked about using 6 cims for a all terrain off season robot. I've got a couple 36v motors I'm going to donate though.

The team is considering 2 CIM drive this year. I'm not recommending that, especially with tank treads. I think they will change their minds when they see how poorly it performs after the chassis is built. Hopefully we can drive it this weekend.

Maybe I'll be proven wrong though..

[CryptoStorm]

Originally Posted by Ether

Here's a quick calculation using MCALC to compare

one CIM drawing 60 amps at 12 volts
vs
two CIMs each drawing 30 amps at 12 volts:

Motor Calculator  build MCALC_2014d 2/3/2014 1255pm


Select motor:
1)CIM     6)FP0673   d)FP2719  f)FP9012     g)FP9015    h)FP9013 j)MiniCIM
a)am-0912 b)am-0914  7)DensoL  8)DensoR     c)Denso0160 k)BAG    u)UserDefined
2)RS395   3)RS540    4)RS550   e)RS775-12   5)RS775-18  m)RS555  n)am-0915
r)am-2193 s)am-2235  t)RS390   v)RS545      p)am-2161&2194
w)VEX2177hi  z)VEX2177std  1


CIM FR801 001, AM802 001A @ 12.00 volts:

@ free (no load):
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
     0.0   0.000    5310   100.0     2.7         0.0        32.4     0.0

@ stall:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   343.4   2.425       0     0.0   133.0         0.0      1596.0     0.0

@ max power:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   171.7   1.212    2655    50.0    67.8       337.1       477.1    41.4

@ max efficiency:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
    42.8   0.302    4648    87.5    18.9       147.1        80.2    64.7

Select input:
1)oz-in  7)watts_in    3)rpm    5)amps   b)rpm&amps  8)eff%
2)Nm     6)watts_out   4)rpm%   9)volts  a)rpm&ozin  m)main menu   x)exit 5


enter amps: 60

CIM FR801 001, AM802 001A @ 12.00 volts:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   151.0   1.066    2975    56.0    60.0       332.2      387.8    46.1


Select motor:
1)CIM     6)FP0673   d)FP2719  f)FP9012     g)FP9015    h)FP9013 j)MiniCIM
a)am-0912 b)am-0914  7)DensoL  8)DensoR     c)Denso0160 k)BAG    u)UserDefined
2)RS395   3)RS540    4)RS550   e)RS775-12   5)RS775-18  m)RS555  n)am-0915
r)am-2193 s)am-2235  t)RS390   v)RS545      p)am-2161&2194
w)VEX2177hi  z)VEX2177std  u


Enter the following motor specs in the order and units indicated,
separated by spaces or tabs:
volts   stall_ozin      free_rpm        stall_amps      free_amps
12       686.8           5310             266            5.4

UserDefined-> 12.0 686.8  5310 266.0  5.4 @ 12.00 volts:

@ free (no load):
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
     0.0   0.000    5310   100.0     5.4         0.0        64.8     0.0

@ stall:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   686.8   4.850       0     0.0   266.0         0.0      3192.0     0.0

@ max power:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   343.4   2.425    2655    50.0   135.7       674.2       954.2    41.4

@ max efficiency:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
    85.6   0.605    4648    87.5    37.9       294.3       160.4    64.7

Select input:
1)oz-in  7)watts_in    3)rpm    5)amps   b)rpm&amps  8)eff%
2)Nm     6)watts_out   4)rpm%   9)volts  a)rpm&ozin  m)main menu   x)exit 5


enter amps: 60

UserDefined-> 12.0 686.8  5310 266.0  5.4 @ 12.00 volts:
   oz-in      Nm     rpm    rpm%    amps   watts out  watts heat    eff%
   143.9   1.016    4197    79.0    60.0       446.6       273.4    62.0

one CIM drawing 60 amps at 12 volts:
332 watts output mechanical power
388 watts waste heat

two CIMs each drawing 30 amps at 12 volts:
447 watts output mechanical power
273 watts waste heat

Wouldnt a 1/4 hp motor and a 1/2 hp motor consume the same amount of power if the continuous load only required 1/8 hp. Amperage being based on load.

I know that 2 cims will be capable of more torque, I'm just wondering how noticeable it will be from the perspective of the driver.

[Ether]

Originally Posted by CryptoStorm

Wouldnt a 1/4 hp motor and a 1/2 hp motor consume the same amount of power

Take a careful look at what I posted:

one CIM drawing 60 amps at 12 volts:
332 watts output mechanical power
388 watts waste heat

two CIMs each drawing 30 amps at 12 volts:
447 watts output mechanical power
273 watts waste heat

332+388 = 720 total watts consumed (one CIM)

447+273 = 720 total watts consumed (two CIMs)

They both consume the same power @ 12 volts @ 60 amps, but you get more output mechanical power and less waste heat with two CIMs.

So you don't need as many amps with the 2 CIMs to get the same output power as 1 CIM.

[MrRiedemanJACC]

Originally Posted by Ether

Take a careful look at what I posted:



332+388 = 720 total watts consumed (one CIM)

447+273 = 720 total watts consumed (two CIMs)

They both consume the same power @ 12 volts @ 60 amps, but you get more output mechanical power and less waste heat with two CIMs.

So you don't need as many amps with the 2 CIMs to get the same output power as 1 CIM.

So if I may add to that and continue the idea with a 3 CIM gearbox and 60 amps total load on the the three motors, you use MCALC at 20 amps per CIM and get this:
CIM FR801 001, AM802 001A @ 12.00 volts
oz-in=45.6, Nm=0.322, rpm=86.7, amps=20, watts out = 155.3, watts heat is 84.7 and eff% = 64.7


So I'm seeing the three CIMs each drawing 20 amps at 12 volts:
465.9 watts output mechanical power
254.1 watts waste heat

vs these two choices that Ether's calculations from before.

one CIM drawing 60 amps at 12 volts:
332 watts output mechanical power
388 watts waste heat

two CIMs each drawing 30 amps at 12 volts:
447 watts output mechanical power
273 watts waste heat

So not as much of a gain in efficiency improvement as I had hoped, but the package is still capable of much more.

[Andrew Schreiber]

Originally Posted by Ether

CIM FR801 001, AM802 001A @ 12.00 volts:
oz-in Nm rpm rpm% amps watts out watts heat eff%
151.0 1.066 2975 56.0 60.0 332.2 387.8 46.1

Probably not the right place to mention this but the thread on MCalc is actually closed.

In your MCalc32 equation sheet you say power_out = speed * torque. Given your Speed (2975) and the torque (1.066) I'm confused how you get 332.2 W out.

Edit: admittedly the only reason I noticed this was I don't have a windows machine and liked the concept of MCalc so started a Go version. (I also needed to learn Go for a project at work and this seemed like a simple program)

[Ether]

Originally Posted by CryptoStorm

Given your Speed (2975) and the torque (1.066) I'm confused how you get 332.2 W out.

Convert everything to SI units to do the computations.

Convert 2975 rpm to 2975/60*2pi = 311.5 radians per second

311.5 rad/sec * 1.066 Nm = 332 Nm/sec = 332 joules/sec = 332 watts

[Andrew Schreiber]

Originally Posted by Ether

Convert everything to SI units to do the computations.

Convert 2975 rpm to 2975/60*2pi = 311.5 radians per second

311.5 rad/sec * 1.066 Nm = 332 Nm/sec = 332 joules/sec = 332 watts

Ah, that's the part I was missing. Thank You. Now I'm only off by ~0.01 which I mostly attribute to using the motors.vex.com numbers which might be different.

[Ether]

Originally Posted by Andrew Schreiber

Probably not the right place to mention this but the thread on MCalc is actually closed.

I didn't close it. That happened a while back when the server crashed or got updated or re-hosted or something. I'll ask Brandon to re-open it.