Lynxmotion Tech Support

Hello everyone. I am getting back into 3kg sumo. I have a score to settle and have been inspired to make a new killer sumo. Many people build these bots with a wheel directly connected to the gearmotor. This approach limits the motor size, specifically the length. Some have created custom wheels and gearboxes to get around this restriction. My approach will use an MXL timing belts to allow one largish motor per side. Because the motor lies on top of the drive wheels it can be much larger / longer. The motor used in this mock up will be replaced by a much larger motor and gearbox. I've just started really, but parts are starting to arrive. I have some progress to report. The parts will eventually be aluminum. This is a very early stage prototype.

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Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

Are the black round parts on those wheels? If they are what kind are they?

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Decode this secret ASCII message:
$52 $4F $54 $46 $4C $4F $4C

*Avatar is me after I laughed out loud too much.

Jim,

I feel sorry for the poor guy that you are out to beat.

Rick Brooks

Looks very good, nice, clean and professional!

I'm just wondering though what your plans are in regards to connecting the wheels to the gearmotor? In the setup you have pictured it looks like you'll use drive belts that are half the width of the timing pulleys in order to use two belts on each pulley? ie. belt from motor to wheel 1, belt from wheel 1 to wheel 2, belt from wheel 2 to wheel 3?

It'll be a real nice setup. I'm curious whether such narrow and fine pitched belts can handle the torque. I've never used MXL, but am familiar with XL size.

Good luck, looking forward to seeing the progress!

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[color=red]Team Terror[/color]
http://www.angelfire.com/blog/teamterror/

I dunno Rick, he's pretty good... I have a lot of catching up to do!

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Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

They are indeed wheels.



They are made from a two part polyurethane. My supplier is no longer making them. I'm looking for another source. They have a lot of traction.

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Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

If the tires are multisegment rings on a hub (or could be), you might be able to make a simple mold and produce your own using silicone sealant (which reportedly has good traction qualitys). DIY tires might also allow some experimentation for traction improvement. Hmmm, now I'm thinking of thick o-rings on a large tubing hub.

The tires are not multi segment, but one piece molded polyurethane cast directly onto the wheels. The marks on the surface are from the mold itself. It was a stack of 1/4 inch steel plates. Their CNC mill couldn't cut anything thicker. They even degassed the polyurethane after it was mixed to eliminate small air bubbles.

The polyurethane tires (ShoreA 20 as I recall) are about 50% better than silicone sealant and, perhaps, too soft. Good luck trying to come up with better tires for sumo. You will need it.

Rick Brooks

Sorry I forgot to answer this yesterday. The wheel and motor pulleys are aligned and can accept a 1/4" wide belt. My plan is to use 4 idlers to position the single 1/4" wide belt to have the required pulley contact. This is going to put a pretty good amount of tension on the belt. It may not last very long, but it doesn't really have to. I may have to replace them after each event. There are some impressive MXL belts with Kevlar that are very strong. I hope we can hit them hard and fast without slipping. We will see.

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Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

Here is an update. I got the bearings in for the idlers. Everything is lining up well. I need to remake the motor mount panel to add a way to add tension. It works!



Here is an image of one of the motors I am considering. If it's not got the umph I need it has two larger brothers in the catalog. hehe!

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Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

Considering the length of the motor housing, are you going to make the other wheel assembly identical as the first so that when you flip it around, one motor is toward the front of the sumo and the other motor is toward the back? This configuration will allow you make it more compact width wise anyway. Only thing though is one motor will need to be reverse biased or the sumo will run in circles.

Great job. I love the stout compact look of this thing.

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Mike

The robotics nut.

Yes that's the idea. The timing on the motors is adjustable so we can either set them both for neutral or adjust them both for optimum performance in one direction.

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Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

Jim,

It looks like a Promax "400" or similar. I'd go with the "05" big brother from the start. Remember too much power is never enough.

As you correctly pointed out, adjustable timing is mandatory.

The belt drive appears to be about 1:1 ratio, so the gear box should be about 25:1 or 30:1, but not outside of that range. Plan on using more voltage than the motor rattings. Add batteries until you get the speed that you want. Also figure on a speed control that can safely handle 40 to 50 amps per side. Again, overkill is necessary.

I've never done anything with belt drive, but you may be loosing a lot of power in the idlers. Perhaps removing the idlers and eliminating the center wheel will be an improvement. Experimenting is required.

Wait. Why am I telling you all this? Forget this post.

Rick Brooks

If he removes the center idler, wont he be loosing power to the center wheel? If all the wheels are to be belt driven, the I would guess there would be a need for all the idlers.

I would not be surprised if I am missing something.

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Mike

The robotics nut.

Hi Rick, keep talking buddy... lol

OK I'm coming clean. Here is all the data so far. I've been meaning to do this anyway...

The pulleys are all 32 tooth and can accept belts up to 0.289". I'm using a standard 0.250" wide MXL belt. The idlers are 0.125" ID, 0.375" OD and 0.156" wide, I'm using two of them per position. The tires are 2.125" diameter and 1.5" wide.

I completely expected comments about the timing belts. This is uncharted territory for many. If I were building for Japan rules, vacuum and or magnets, then it would be out of the question. But with just 3kg pushing down on the drive train the bot is likely to bounce before anything breaks. Off the forum I have received comments ranging from "Those timing belts will not be a problem at all" to "The thing will fly apart!"

Here's the information on the cobalt motor.

Maxx Products PMX4812.
Diameter 1.14"
Length 2.13"
Weight 4.1 oz.
Shaft 1/8"
Winding 12/#22.5
Typical voltage 8.4-9.6vdc
Test voltage 8.0
Static RPM 15,600
Static amps 19.2
Static Power 154W

I believe static means not flying?... These motors are for airplanes. The current demand is what made me want to try these before going to the 05 model.

The gear box is a planetary box with 27:1 reduction and dual planetary gears, just double the height of the current planet gears for more strength. Dual ball bearings on the final gear of course. 15,600 rpm with 27:1 is 577 rpm at the wheels. Which is 64.2IPS! We can slow it down from there if necessary.

I agree to some extent that 4WD has inherent advantages over 6WD, especially in my situation, but I really want 6WD...

I hope to have it moving under it's own power in a few days.

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Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...