pic: Omniwheel Minibot

[Scott Kozutsky]

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[magnets]

That's kind of cool. What on it makes it cost $500? $150 for the talons, $50 for the CIMs, and $300 for the aluminum/wheels?

[nathannfm]

Edit: ignore my post

[Scott Kozutsky]

Originally Posted by magnets

That's kind of cool. What on it makes it cost $500? $150 for the talons, $50 for the CIMs, and $300 for the aluminum/wheels?

I actually parted out every part and pre-tax and pre-shipping it works out to $465. Those gears, pulleys, belts, bolts and tube nuts really add up. 4.5 in bolts are expensive.

[BBray_T1296]

I think with something of that weight could get away with a significantly higher top speed.

Recall that a 150lb robot with 6 cims could top out at ~18fps, and that only because they can only travel 50ft before stopping.

If you were running it down a street or something you could push a full FRC robot to 25+fps over a hundred feet.

An antweight in comparison with just 2 cims should have no problem reaching 30 fps in 15-20 feet or so.

Then again, if you are operating in more confined places like classrooms or such, you would gain a control advantage topping out slower.

Also be careful, CIMs produce a significant amount of noise in the FM band. We converted a kitbot to run on a FM system and had control problems when we got 30+ feet away. We decided to seriously isolate our antenna from the CIMs, by putting the antenna higher and also wrapping the motors in layers of aluminum foil in an attempt to Faraday cage them.

[mman1506]

Originally Posted by BBray_T1296

Also be careful, CIMs produce a significant amount of noise in the FM band. We converted a kitbot to run on a FM system and had control problems when we got 30+ feet away. We decided to seriously isolate our antenna from the CIMs, by putting the antenna higher and also wrapping the motors in layers of aluminum foil in an attempt to Faraday cage them.

We use a 2.4 GHZ system on our V1 minibot and have had no issues. We're currently looking at running it on a 14.8V to 22.2V lipo so it should be faster than 21 ft/s that was estimated at 12v.

[ToddF]

Originally Posted by Scott Kozutsky

I actually parted out every part and pre-tax and pre-shipping it works out to $465. Those gears, pulleys, belts, bolts and tube nuts really add up. 4.5 in bolts are expensive.

If you post your BOM, we might be able to help you find less expensive sources for your components.

[Scott Kozutsky]

Originally Posted by ToddF

If you post your BOM, we might be able to help you find less expensive sources for your components.

1/2" OD Round Tube Axle Stock (3 feet) http://www.vexrobotics.com/vexpro/ha...ock.html?lulz= $11.99 2 $23.98 VEXpro
VersaHub (1.125" Bearing Pilot, 1/4" Thick, w/ Plate Sprocket Mount) http://www.vexrobotics.com/vexpro/wh...ubs.html?lulz= $2.99 6 $17.94
60t Gear with 1.125" Bearing Bore & VersaKeys http://www.vexrobotics.com/vexpro/ge...ars.html?lulz= $21.99 2 $43.98
4" Omni Wheel http://www.vexrobotics.com/vexpro/wh...els.html?lulz= $17.99 4 $71.96
VersaPulley Kit (HTD 5mm) - 42T, 18mm wide http://www.vexrobotics.com/vexpro/be...ley.html?lulz= $4.99 4 $19.96
14t CIM Gear (Steel) with Mounting Hardware http://www.vexrobotics.com/vexpro/ge...ars.html?lulz= $7.99 2 $15.98
Timing Belt (HTD 5mm) - 170T, 9mm Wide http://www.vexrobotics.com/vexpro/be...ts9.html?lulz= $10.99 2 $21.98
Flanged Bearing - 0.500" x 1.125" x 0.313" http://www.vexrobotics.com/vexpro/ha...ngs.html?lulz= $2.99 8 $23.92
tube connector*25 http://www.mcmaster.com/#94290a510/=sdvhn7 $15.13 1 $15.13 McMaster
4.5in bolts-1/4-20 (pack of 5) http://www.mcmaster.com/?lulz=#91251a089/=se2p5q $8.26 3 $24.78

total $279.61

This was copy pasted from my spreadsheet so sorry about the formatting.
the first number at the end of each line is the cost per unit then the quantity then the total. It's mostly vex stuff because it's cheap, available and simple other than maybe a different source for belt i doubt it. We're also from Canada so that cuts down options. And honestly we will be making McMaster orders and Vex orders anyways so it's very little trouble.

[Alan Anderson]

That looks like a very clean design. Well done.

But I can't understand the reason for using identically-oriented omniwheels in all four corners. Won't that let the 'bot slide sideways uncontrollably?

[AdamHeard]

Originally Posted by Alan Anderson

That looks like a very clean design. Well done.

But I can't understand the reason for using identically-oriented omniwheels in all four corners. Won't that let the 'bot slide sideways uncontrollably?

Essentially 33 ran this drive this year.

Quite a few teams have run "butterfly" drives that have this + drop down tractions as a second mode.

We found that the robot tracks straight as on carpet the omnis still have appreciable lateral rolling resistance.

Our driver quickly figured out how to drift with it, and how to control those motions roughly.

In summary, it's more far more controllable than people assume.

[JohnFogarty]

Originally Posted by AdamHeard

Essentially 33 ran this drive this year.

Quite a few teams have run "butterfly" drives that have this + drop down tractions as a second mode.

We found that the robot tracks straight as on carpet the omnis still have appreciable lateral rolling resistance.

Our driver quickly figured out how to drift with it, and how to control those motions roughly.

In summary, it's more far more controllable than people assume.

I've made several FTC robots in my day that incorporate this drive. It's completely controllable and it's pretty fun to drive. I'm almost certain FTC 3864 has used it 5 years in a row now.

[Orion.DeYoe]

Originally Posted by Alan Anderson

That looks like a very clean design. Well done.

But I can't understand the reason for using identically-oriented omniwheels in all four corners. Won't that let the 'bot slide sideways uncontrollably?

Controllability is relative. If you want to slide sideways then it does exactly what it's supposed to. Have you not seen 33's drive train (inspired by the JVN Build Blitz team I'm sure)?

[mman1506]

Originally Posted by Alan Anderson

That looks like a very clean design. Well done.



But I can't understand the reason for using identically-oriented omniwheels in all four corners. Won't that let the 'bot slide sideways uncontrollably?

Sliding sideways uncontrollably sounds like a lot of fun. It's designed to be brought around to demos but the vex parts make it easy to switch the omni-wheels out for something less silly.

[nathannfm]

If you do go to 4 CIMs I would gear them 1 to each wheel. If you keep the control system and batteries in the center I bet you could get it to flip and keep driving "upsidedown", that would be a pretty cool trick for demos. (added benefit, no belts)

[AdamHeard]

Make sure the lipos you get can handle the potentially huge currents 2 CIMs would cause. Trying to draw too much from them can cause thermal runaway and fire.

In terms of size and weight, I think you'd get a more satisfying performance by switching to 550's or 775 sized motors as you can shave a lot of size and weight off, without a large power loss.