Author Topic: Robot Wheel Hack... (Read 5877 times)

Nyx · « **on:** June 15, 2007, 09:52:08 AM »

Turns out it's very difficult to find affordable motor-gearbox-wheel setups for heavier robots (mine will weight about 100 pounds). So I decided to improvise...

I bought these two items from the electronic goldmine:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G15885
http://www.goldmine-elec-products.com/prodinfo.asp?number=G13889

The motors seem good quality and the wheels are solid... The only problem is that there is no way to screw anything on/into the axle of the motor... So I proceeded the hack-ish way... I sandwiched a motor-wheel pair between two catalogs and fitted the motor's axle into the wheel's mounting hole with a hammer. I then proceeded to generously apply a very solid glue I have to make sure it wouldn't get off... I also made a small wooden frame to which I attached the motors... Tonight I will add the front and back caster wheels (it's a differential drive setup, like on Shakey the robot) to my little frame... And tommorow I plan to finally mount my robot base onto my support frame.

I *hope* this will hold together. My main worry is that the wheels could just break off, or bend under all the weight. I might just try to add more glue before I install the robot base on my little setup! Anyways, the glue is strong, as it can hold several hundred pounds... So that's some encouragement.

I will give you news and show you some pictures of the completed rig soon. Pray for me (and my robot

).

ed1380 · « **Reply #1 on:** June 15, 2007, 03:38:39 PM »

those motors are from windshield wipers. yes they'll be pretty mowerfull, but now efficient
waiting for pics

Nyx · « **Reply #2 on:** June 15, 2007, 05:37:09 PM »

Quote

those motors are from windshield wipers. yes they'll be pretty mowerfull, but now efficient

What are you trying to say?

This is the wooden robot base

The wheelchair battery I recently bought

The wheel base I recently built

The robot base will be installed on top of the wheel base, which has two casters and two independent motorized wheels.

ed1380 · « **Reply #3 on:** June 15, 2007, 07:30:12 PM »

the motors will use more electricity per work unit compared to efficient motors.
like in cars, it'll go just as fast it'll just need more gas to get the same distance.

Nyx · « **Reply #4 on:** June 15, 2007, 07:33:32 PM »

Well that's not a problem, I can supply them 25 amps at 12V.

Nyx · « **Reply #5 on:** June 17, 2007, 09:22:23 AM »

A little update... I will permanently install the wheels on the base, but here is what it looks like together (upside down) with the cut-outs I made for the wheels:

http://i207.photobucket.com/albums/bb16/Nyx095/PDR_1309.jpg

Ro-Bot-X · « **Reply #6 on:** June 17, 2007, 10:32:34 AM »

Nice and clean! I love it! Looks like an upside down R2D2...

Eco19R · « **Reply #7 on:** June 17, 2007, 06:23:20 PM »

I got a question - what happens when it tries to drive over a small obstacle or even when it transitions from carpet to hard floors - wont the two casters bottom out and it will get stuck since both of the drive wheels would be in the air?

ed1380 · « **Reply #8 on:** June 17, 2007, 06:25:27 PM »

Quote from: Eco19R on June 17, 2007, 06:23:20 PM

I got a question - what happens when it tries to drive over a small obstacle or even when it transitions from carpet to hard floors - wont the two casters bottom out and it will get stuck since both of the drive wheels would be in the air?

yep, that's true if all 4 wheels are on the same level. I think that's why the carts at home depot have 2 big cener wheels and smaller ones on the edges

Eco19R · « **Reply #9 on:** June 17, 2007, 06:35:48 PM »

So wouldn't it be better to have two powered wheels either in the front or the back so that can't happen. ?

Nyx · « **Reply #10 on:** June 17, 2007, 07:32:00 PM »

I don't see what you mean. It's kind of hard for the two drive wheels to be "in the air" at once, since the casters are on a central axis, the robot would become inclined on one side or the other and one of the drive wheels would touch the ground.

Eco19R · « **Reply #11 on:** June 17, 2007, 08:08:56 PM »

Well if it didn't tip over and the motor was strong enough to get the two casters un-stalled I guess thats what would happen, but I think there might not be sufficient weight on the wheel that touches the ground to give it enough traction to pullout of that position.

Nyx · « **Reply #12 on:** June 17, 2007, 09:32:40 PM »

What position are you even talking about

Eco19R · « **Reply #13 on:** June 17, 2007, 10:19:05 PM »

As soon as your robot tries to go over something small the two powered wheels lift off the ground, you said it would tilt so one powered wheel would be on the ground - which is true but depending on how top heavy it is it may tip over, that aside if it is able to tilt so one wheel touches the ground that wheel still won't have the majority of the pressure on it - the main weight will still be on the casters, I just pointed out that it may not have enough traction to move it out of the stalled position.

Don't get me wrong your base looks good - your wood working skills are far far above mine, I am just exploring certain issues that may arise - the best way to tell is to finish it and see how it performs.

Nyx · « **Reply #14 on:** June 17, 2007, 10:56:09 PM »

We will see. It's obviously not made to travel on rough terrains, but I think it should do fine in an office environment. As for the weight distribution, it's designed to be bottom-heavy, as the battery goes on the first level, just above the motors....

I will be flipping it rightside up tommorow and trying the motors to see how well it fares.... May post a video

Ro-Bot-X · « **Reply #15 on:** June 17, 2007, 11:41:34 PM »

In american houses or offices rarely there is a transition between 2 different floor levels. To compensate, one of the caster wheels has to be mounted on spring. I don't think it will loose traction on both side wheels, since Nyx said it's weight will be around 100 lb and the motors are realy strong, I have used motors like those an a similar base and worked fine. The only thing I didn't like about that type of base is the dificulty of getting on/off ramps. But for a level floor it's perfect.

Nyx, take a look at http://leafproject.org/. They are using a base like yours.

Nyx · « **Reply #16 on:** June 18, 2007, 08:35:00 AM »

Oookay. I've done the first test this morning. The good news is that the stuff stays together, and the base seems to be level when up right. It even moves when powered.... And does so pretty fast (faster than my usual walking speed). What's rather disappointing, however, is that one of the wheels seems to skid a bit at some points. I think this might be because the casters are slightly too elevated and the robot is actually tilted to one side slightly... But I will have to evaluate. The use of all-plastic wheels may have been a bad strategy and I may have to at least get one of those rubber traction bands you can install around plastic wheels.

Nyx · « **Reply #17 on:** June 18, 2007, 01:49:44 PM »

Does anyone know where I could find wheel hubs for a 9mm axle (0.35"), or something close to that? It seems people only sell wheel hubs for tiny robots...

Ro-Bot-X · « **Reply #18 on:** June 18, 2007, 02:22:42 PM »

http://www.robotmarketplace.com/marketplace_hubs.html

Nyx · « **Reply #19 on:** June 18, 2007, 02:37:31 PM »

Those hubs don't seem to fit the dimensions I specified (9mm axle)... They're way too large. That, and the prices on everything they sell on that site are plain abusive.

Admin · « **Reply #20 on:** July 17, 2007, 07:45:14 PM »

Just curious on the progress on your bot . . .

As for wheel hubs, they are pretty easy to make with a drill and bandsaw.

Yea the problem you have with the wheel skidding is because 3 contact points are guarenteed to contact the ground, but 4 arent (highschool geometry).

You just need some form of spring shocks on at least one of the wheels.

On my Fuzzy robot I used a flexible thin aluminum frame to counter this problem.

cooldog · « **Reply #21 on:** December 08, 2007, 06:53:16 PM »

i was wondering how is the torqe on the windsheild wiper motors

ed1380 · « **Reply #22 on:** December 08, 2007, 07:46:44 PM »

i think pretty powerful

cooldog · « **Reply #23 on:** December 08, 2007, 07:56:10 PM »

what ESC did you use?

also was it rc

ed1380 · « **Reply #24 on:** December 08, 2007, 08:54:45 PM »

he probably used a motor driver

looks like a balancing robot, so MCU controlled (methinks)

airman00 · « **Reply #25 on:** December 08, 2007, 09:00:34 PM »

Quote from: ed1380 on December 08, 2007, 08:54:45 PM

looks like a balancing robot, so MCU controlled (methinks)

not a balancing robot , it has two casters in front

it gives the illusion of balancing

News:

Author Topic: Robot Wheel Hack... (Read 5877 times)

Related Topics