Robot Linear Speed

I have done some rough speed calculations. Given that we decided to go with a 4 wheel holonomic drive, I can start to choose parts.

I have been targeting 12 feet per second linear speed, that is forwar, backward, sideways. Diagonal movements will be 30% faster because of the angle that the wheels are mounted (45 deg, using 1, 1, sqrt(2) triangle). I can explain the math in greater detail tomorrow if you wish. but sqrt(2) = 0.707

I was looking at single speed VexPro gearboxes. (AndyMark website is down/slow)

Assuming normal load speed for the CIM motor (4320 RPM).

Using a 4" diameter omni wheel (assuming no slipping on the floor) and a VexPro single speed gear box with a reduction ratio of 4.17:1 produces a linear speed of 12.8 ft/sec and a diagonal speed of 18 feet per second. This is one quick robot.

we can reduce the speed slightly by using a 5.67:1 gear box and a 4" diameter omni wheel produces a linear speed of 9.40 feet per second and 13.30 feet per second diagonal speed.

Please comment below about what speeds we should be using and if you think we can or can not use a single speed gearbox IE. no shifting.

- Ben

I think speed is important, but the slower speed you suggested would work fine. Being able to move 9.5 feet/second will allow us plenty mobility, I believe. The game is generally based on alliances so moving from one spot at one end to the opposite side terribly fast is not a huge concern, due to the zones as our assist limitations.

But in contrary if we are as the "1 robot" as described in the video, moving across the field is important, but the passes may be, thus not always needing the full power.

But overall, having the faster one is not a bad idea, since we do not always have to go the full speed, but the advantage is there if we need it.

sorry, the passes may be slow*

i am for having low and high gear for the reason that although even our low gear wont win us pushing fight a quick robot may be harder to align to shoot than a slower robot unless our drivers think they can do it on high gear and will has ramping code to make the control easier for small touches id rather this since i know that those double speed cost the big moneys

In 2011 we had a top speed of 14 feet per second and it felt more than adequate for an open field. Gearing for 12 feet per second should be sufficient and being able to suddenly go 18 feet per second diagonally would be beneficial to avoiding defense.

The only benefit i can think of with more reduction while using omniwheels would be more controllable movement. Also traction with omniwheels is less than that of a "regular" wheel so lower gearing might result in wheel spin, ie if the robot were to be pushed by an opponent.

Sorry I missed the "Single Speed"

In that case, the slower one would work better I think, because of sudden changes of position to catch a ball, due to miscalculation of where it will land, or any other problems.

I believe the defense in this game is very minimal, so defense is not a top priority

I like these gear boxes.

They are significantly cheaper than the AndyMark ones.

http://www.vexrobotics.com/vexpro/gears-and-gearboxes/ball-shifter.html

The High Gear (3.66 reduction) is a little faster than the 4.17 gear box and the Low Gear is 8.33 reduction which should give us around 6.5 linear feet per second.

- Ben

I think that Holo is going to give us an advantage only when catching, if we decide to catch.

You rarely see Holo drive in first these days and I think there is a reason behind it. If we are catching, holo could make sense. but if we aren't catching, tank all the way.

If we go holo and catching we're weighing a decent chunk of our success on a big risk.

Sebastian, we don't need a low gear if we aren't planning on pushing. What we need is a low speed. This can easily be changed in the CODE by adding a multiplier. We could fine tune the exact speed that we would like.

Will to the rescue.

Therefore we should be looking at the single speed gear boxes that I originally specified.

- Ben

I have uploaded a sample drive platform to the DropBox, in a folder called Holonomic Drive.

This is a .stp file that can be imported into Inventor.

Note: I am aware that we are not allowed to have 8 CIM motors. The files for the gearboxes already had two CIM motors mounted to them. When we assemble the Gearboxes we will only use one CIM each.

There may be smaller and cheaper gearboxes available. The ones I used are from Vex (made by West Coast). These are two speed shifting gearboxes.

Comments?

- Ben

i dont see the need for shifting gears with a holonomic drive
in terms of moving at higher or lower speeds ben already explained that can be done by move diagonally, and as far as pushing goes the fact of the matter is we wont be winning any pushing battles, seeing as omni wheels are meant to roll in every direction

on a related note, our only way of dealing with defenders is going to have to be to dodge around them with holonomic's mobility, which i bring up because riley has only ever driven tank before, so hes going to have challenge enough practicing the holonomic drive, thats why i dont think going crazy fast is in our best interests at the end of the day...also eriks post about how us moving fast wont matter too much if we have to wait for the others

in conclusion, single speed, with the higher reduction (5.66:1? something like that, i cant remember the exact number)

also ben, the folder for the holonomic platform is empty, try reuploading it?

Adnaan, 

Good points. I also agree that we don't need shifting gear boxes. In terms of cost, we cant afford 4 shifting gear boxes because of the cost limitations in the rules. The robot can not cost more than $4000.

I updated the Dropbox folder last night. You must have been looking at it at just the wrong time. The new model that is uploaded also has some of the control system parts included on it.

- Ben