Your favorite pneumatic robot wheels/tires? (6" - 8")

[Patrick Goebel]

So I'm back to the wheel issue for Pi Robot.  Turns out that the BaneBots tires, while very nice and soft, still allow for a fair bit of bouncing/shaking of the robot when traversing rough patches of asphalt or brick inlay.  I will be installing the pneumatic Parallax rear caster which should help a bit.  But I'm wondering if others have used pneumatic or semi-pneumatic tires/wheels on their robot. There seem to be quite a few out there for hand carts and wheel chairs, but the question is how to mount them to a standard DC motor axle?  I would like a 6" diameter--8" is probably pushing it with my current motors.  The Parallax Eddie pneumatic wheels look almost perfect but it seems you have to buy the entire drive kit (wheels, motors and controller) just to get the wheels.

Any recommendations?

Thanks again!
patrick

[KM6VV]

I've built one or two robots with I guess what you could call pneumatic tires.  Actually off-road tires. 

The first 'bot had hard-shaft through a bearing to drive the wheel (see Superdroid).  The tires are some sort of hobby R/C tire. 

My current 'bot uses tires,wheels and suspension from a T-Maxx Traxxas off road R/C.

Seems we discussed mounting this type of wheel at the last SIG.  I've got a 'bot like that too.  Big 8" wheels, I machined an approximately 1" aluminum rod to fit the wheels after I punched out the bearings.  The rod had a slight lip on one end, and was bored to fit my shafts.  A set screw (usually two) secure the aluminum rod to the steel shaft on flats.

A bearing supports the load of the shaft near the wheel, and the proximal end of the shaft can joined to the motor with a suitable coupling, or often bored to take the motor shaft.  I usually use a timing belt pulley of proper size on the shaft between two bearings, and drive the pulley with a belt from the motor.

Sometimes you can leave the bearings in the wheel, slide up a large timing belt pulley; drill it and the wheel in three or four places (ring circle) and secure the shaft that way. 

Let's see your chosen wheels/tires, and figure something out!

Alan  KM6VV

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[anfederman@comcast]

Try AndyMark.

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[Alex Sy]

Patrick,

Using pneumatic wheels probably not solve the bouncing and shaking.  Instead you would need some form of shock absorber.  You would use a spring to do this.  This assumes that the mass of the robot is much higher than the mass of the motor and wheel, so when you hit a bump, the spring takes up the bump while the inertia of the robot keeps it stable.   You do have to select the spring and pretension it so that it is near the middle of it's travel when the robot is static, and make sure that the motor assembly never hits either stop (end of travel).to maximize the shock absorption.  Of course when the robot is off the ground, it will hit the lower stop.

In terms of the spring, it can be coil springs like seen in some RC trucks or leaf springs which is used in old trucks.   You can also mount the motor assembly on a pivot point and use a torsion spring.

This would also improve your odometry as well as vision systems and make the robot last a lot longer.  Even then, on outdoors, you may also need to add stabilization on the video if you are moving fast and the camera is far above the ground.

Alex

[Patrick Goebel]

Thanks Alan, Alan and Alex,

I had not seen the Andy Mark site before--really nice stuff.  Unfortunately he only has an 8" pneumatic wheel (7.65" to be exact) which is probably too big. Too bad he doesn't have a 6" version which I think would be perfect.  (I've attached the current design of Pi's new base plate.  The pairs of wheels are the BaneBot's 4 7/8" wheels and the larger wheel off to the right is the 7.65" Andy Mark wheel.  You can see how big it is by comparison.  The base itself is 38cm x 38cm or roughly 15"x15".)

I like Alan and Alex's idea of using suspension.  Since my motors and motor brackets are mounted under the base plate, I wonder if I could start by using the appropriate springs around the mounting bolts so that the bracket is essentially sprung off the bottom of the base plate.  Anybody have a good source of springs of different lengths, diameters and stiffness?  I think the diameter would be around 1/4".  The motor bracket I am using is shown here.  As you can see, you could use as many as 14 springs per bracket/wheel but I was thinking more like 6 springs/bolts per bracket.  Pi Robot's current weight is about 18.5 lbs including laptop.

--patrick

[Butokim]

Patrick,

 

Most of them tat I "interviewed" are on the heavy side.  Not sure how well they will work out with smaller motors.

 

J

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From: hbrob...@googlegroups.com [mailto:hbrob...@googlegroups.com] On Behalf Of Patrick Goebel
Sent: Saturday, October 06, 2012 8:58 PM

To: hbrob...@googlegroups.com
Subject: [HBRobotics] Your favorite pneumatic robot wheels/tires? (6" - 8")

[Arthur Wait]

Hey Patrick,

I found the pneumatic tires on Eddie are pretty good, though you need to play around with the PSI. I'm surprised Parallax don't seem to carry the wheels separate from the motors--you might try calling them directly and see if they've got any extra stock lying around. I think they actually manufacture the wheels themselves.

Art

http://gplus.to/artwait

[Michael]

Patrick,

Item TIR-6X1.25 on this page appears to be what Parallax uses for the Eddie drive system: http://www.electricscooterparts.com/tires.html#6

I didn't see matching wheels on that site, but it might give you some leads.  Another idea, although I am not sure they will have load capacity for handling Pi Robot, Dubro and Dave Brown are both brands of RC airplane wheels that have foam core tires in 6" sizes.  You still would have motor drive shaft mounting issues though, as they would not be bolt-on. My bot is indoors only with BaneBots wheels, so I haven't tried any of these myself yet.

Regards,
Michael Sprague

[Butokim]

Patrick,

 

Art has the right idea.  Parallax is great about coming up with things like that.

 

Jim

 

James M. Geidl, K6JMG
D.B. Cooper, you have  a message.
 

---

From: hbrob...@googlegroups.com [mailto:hbrob...@googlegroups.com] On Behalf Of Arthur Wait
Sent: Sunday, October 07, 2012 12:11 PM
To: hbrob...@googlegroups.com
Subject: Re: [HBRobotics] Your favorite pneumatic robot wheels/tires? (6" - 8")

[Tim Craig]

This site has a lot of tires and wheels for lawnmowers which fall into your size requirements.  Some are pneumatic.

http://www.jackssmallengines.com/

You could mitigate some of the jarring by running pneumatic tires a little "soft".  Cost you a bit in energy though as the same warning applies as driving with underinflated tires.

Another option to have some compliance would be urethane rollers similar to the blue one on this page.

http://www.fairlaneproducts.com/

I wanted to try these in my FIRST mentoring days but never had a way to attach and drive them.  Look sort of like the spoke arrangement on Spirit and Opportunity.

Tim

On 10/6/2012 8:57 PM, Patrick Goebel wrote:

[Alex Sy]

Patrick,

Ace hardware has a selection of springs that may work.

Alex

----- Original Message -----

From: Patrick Goebel

To: hbrob...@googlegroups.com

Sent: Sunday, October 07, 2012 11:11 AM

Subject: Re: [HBRobotics] Your favorite pneumatic robot wheels/tires? (6" - 8")

[KM6VV]

You should really check out the off-road (Traxxas, etc) parts, ready-made shocks w/ springs, upper/lower A-frame suspension parts, drive shafts, hubs, wheels, tires etc.

Alan KM6VV

[Steven Nelson]

Question: How much does the robot and it's payload weight? Also what surfaces do you intend to operate it on? Indoor

outdoor, dirt, carpet, asphalt etc..

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[Patrick Goebel]

Thanks Art--I sent an email to Parallax to see if they will sell the
wheels separately. They seem to have a special keyed axle/hub setup but
I'll wait to see if they're available before worrying about that.

--patrick

[Patrick Goebel]

Thanks Michael--it didn't occur to me to look at airplane wheels.  There seem to be a pile of options out there like this one that would allow fairly easy mounting using a standard wheel hub like this one.

--patrick

[Patrick Goebel]

Thanks Tim,

The rollers look like an interesting alternative to springs though I'll give the springs a try first since they should be fairly easy to mount.

--patrick

[Patrick Goebel]

Hey Alan,

I might be able to go that route if I could figure out exactly what I would need.  Not being an RC car person, I can't make sense of all the parts that seem to be listed separately on the RC sites.  Do you have a link to a picture and/or kit that I would need to suspend the two front wheels?  I would need to use my current Pololu motors with 6mm axles.  Also, I don't think knobby tires are what I want since if they're anything like mountain bike tires, they tend to "rumble" on hard surfaces like asphalt and tile.

--patrick

[Patrick Goebel]

Hi Steve,

The robot weighs 18 lbs including laptop. It will run on low ply
carpet, linoleum, asphalt and brick inlay. So nothing particularly
rough--no grass, dirt or gravel.

--patrick

[Alan Marconett]

Hi Patrick,

 

I went through the same process.   About a year ago, after talking to DPA, I wanted to use R/C parts, but did not have a clue as to what to buy.  And I didn’t really want to dig that deep into that hobby.

 

Then six months later, I decided I wanted a set of tires.  Found them all right on E-bay.  Figured out that the “4907” model was a good search term for the parts I needed.  Turns out, (I suspect), some shops buy up overages, or buy complete cars for parting out.  So searching for “traxxas t-maxx 3.3”  on e-bay got me offerings for all the shocks w/ springs, upper/lower A-frame suspension parts, drive shafts, hubs, wheels, tie-rods, tires etc. I wanted!  I even got some steering parts and servos, although it’s a little tough to fit in these parts with my current design.

 

Yes, I can do that.  Here’s a link to a set of exploded views of the Traxxas chassis.

 

http://traxxas.com/products/models/nitro/4907tmaxx33-downloads

 

Traxxas Suspension Arms, Lower: T-Maxx, 2.5R, 3.3 by Traxxas

Bulkheads, FR, L & R: TMX3.3 by Traxxas

Traxxas 5451X Assembled Driveshaft by Traxxas

 

Actually, the “traxxas t-maxx 3.3”  line that had a glut of parts two or three months ago appears to be drying up (old model).  You might have to set your sights on another model.

 

You “Shop by the pictures”, you won’t find the part numbers in the exploded views as easily.  I can show you the parts, if you’re interested.  I think if you saw the parts up-close, you’d quickly figure out if it would work for you.

 

The driveshafts I used take a 6 mm with flats shaft.  I went from ¼” shafts, so I machined a mating shaft to take my pulleys. 

 

Buy a used R/C stampede or similar car/truck?

 

Alan  KM6VV

 

 

 

On Behalf Of Patrick Goebel

 

Hey Alan,

[Patrick Goebel]

Turns out Jim is not kidding about weight.  I checked out a pair of 6" lawnmower wheels at Ace Hardware today and even the ones with the plastic hub weighed a ton.  Furthermore, the rubber was as hard as a rock so definitely no softening of the ride with these guys.

So I ordered a couple of sets of airplane wheels thanks to Michael's suggestion.  One set is this Dave Brown foam filled model and the other is this Dubro pneumatic design.  Probably take a week to get 'em and then I'll report back.

--patrick

On 10/07/2012 11:24 AM, Butokim wrote:

Patrick,

 

Most of them tat I "interviewed" are on the heavy side.  Not sure how well they will work out with smaller motors.

 

J

[Steven Nelson]

The Dave Brown Lite Flight tires are very good they should support the 16 lbs of weight you mentioned. You can enhance their traction (if needed) by applying RTV Silicone automotive gasket compound to their  traction surface with a popsicle stick while rotating the tire with your motor(s). That will provide a durometer of about 30-35 which is really really good on slick surfaces like linoleum, wood, plastic or even bare steel. Dave Browns are completely RC combat robot proven and of course RC aircraft proven as well. I didn't know about the Dubro pneumatic tires please review them when you get a chance. I like new builder data points and stuff...;) At 16 lbs you are getting close to the need of considering a bearing on both sides of the wheel for maximum strength especially if you are driving the wheel from a small gear box or directly from a small motor shaft. Overhang or a cantilever design can cause bearing failure if you push the gearbox or motor too hard. Of course I tend to over build a bit for everyday purposes. Strong like Tractor Smart like Bull. I'm still working on the Bull part...

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[Steven Nelson]

I got to wondering why you couldn't Boost a WiFi signal and what the limits are without a radio operators licence.

http://wiki.robotz.com/index.php/FCC_Regulations_on_WiFi

http://en.wikipedia.org/wiki/Long-range_Wi-Fi

Also I am glad that it was mentioned that using higher frequency only allow  for more  bandwidth (DATA per second) and usually decrease range, reliability, safety for precise control because of the permeability and reflections of the unpredictable stuff between the transmitter and receiver. Basically the higher the frequency of the carrier wave the less reliable it becomes. Low frequency Light waves wiggles trough matter better than high frequency RF Light waves (aka the Radio wave spectrum). That unfortunately is the nature of RF Light waves. I'm often amazed that it even works at all... Hmm now if we could only use Gamma Ray transmitters.. Mwa ha ha and stuff.. Well maybe not..

On Tue, Oct 9, 2012 at 5:18 PM, Patrick Goebel <pat...@pirobot.org> wrote:

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[Steven Nelson]

Oop's I posted the radio stuff in the wrong thread. I blame my dirty glasses...

[Patrick Goebel]

Just an FYI that I haven't heard back from Parallax so I don't know if
they will sell the Eddie wheels separately. I'd probably have
difficulty with the mounting anyway so I'll wait to see how I do with
the airplane wheels that are on their way.

--patrick

[Butokim]

I have seen them close up and they are pretty brutal.

James M. Geidl, K6JMG
D.B. Cooper, you have a message.

-----Original Message-----
From: hbrob...@googlegroups.com [mailto:hbrob...@googlegroups.com] On
Behalf Of Patrick Goebel

Sent: Thursday, October 11, 2012 11:24 AM
To: hbrob...@googlegroups.com
Subject: Re: [HBRobotics] Your favorite pneumatic robot wheels/tires? (6" -
8")

[Patrick Goebel]

Good news for FloorBot lovers.  This morning I tried the 6" Dave Brown foam airplane tires on Pi Robot, as well as the Parallax caster wheel.  (By a happy coincidence, the larger drive wheels now give me just the right amount of clearance to mount the new caster.)  The Dave Brown wheels are really light--just 100 grams each.  The BaneBots 4-7/8" wheels are 149g.  And the Dubro pneumatic wheels (which I now have but haven't tried yet) are 360g.

Anyway, the foam wheels and pneumatic caster work really nicely on asphalt and mildly rough brick patio.  I don't think any kind of spring suspension is going to be necessary.  Also, the larger wheel diameter (compared to the BaneBots) definitely makes going over door thresholds a little less precarious.  Fortunately, my drive motors don't seem to have any trouble turning over the bigger wheels even when motoring up a wheel chair ramp.

I will bring Pi and his new setup to the SIG tonight as well as the Dubro pneumatic wheels.

--patrick

[Michael]

Patrick, that is good news.  How much compression of the foam tires are you getting on Pi? Also, could you post a couple of pictures on your wheel/hub/motor mechanical mounting? I don't mind waiting for a blog post because I am months away from any possible usage, but I am not in CA so won't get to see it in person.

Regards,

Michael

[Patrick Goebel]

Hi Michael,

The foam is really pretty dense so I can't see any noticeable depression under Pi's 18 lb weight while rolling.  However, there is some noticeable flattening of the contact point after the robot has been parked for a while.  (You can see it in one of the attached photos.)  I have a feeling the foam will also get torn up fairly quickly with a lot of outdoor use--we'll see.

The wheels were dead easy to mount--even for a mechanically challenged person like me.  I had a couple of these 6mm universal hubs lying around and I was able to self-thread a pair of hex bolts into the plastic wheel hubs after drilling a slightly smaller hole.  The fully pneumatic Durbro wheels are much heavier and one would likely want to install a separate axle through the entire wheel hub, then use a bearing mount like Wayne and others do and move the motors further in.

--partick

[William Bowers]

I'm just curious. Is weight a problem in your robot design? Solid rubber wheels can get very heavy. Air/foam filled wheels are lighter than solid wheels and do not tend to not have deformation problems and better durability. Or is weight not a big factor, the wheels were just the right size.

--

[Patrick Goebel]

Hi William,

Yes, I always have weight in mind for several reasons: (1) battery life,
(2) being able to get up gradients like wheel chair ramps and (3) having
to carry the robot from place to place. Pi's geometrical dimensions
were chosen so that he can fit in my car behind the passenger seat. The
T-slot makes a great handle to carry him using one arm.

The Dubro air-filled rubber wheels are 360 grams each compared to the
Dave Brown foam wheels at 100 grams each so yeah, a lot heavier. But
it's only a little over a pound extra to use the rubber wheels and I
suspect I will ultimately choose the grip of the rubber and the ability
to adjust the air pressure over the weight penalty.

--patrick

[Steven Nelson]

I like the Dave Brown wheels too. I did a motor test one time with a small 1 lb. Antweight robot that was 2WD using standard Futaba S3004 servos (of course Team K.I.S.S internally modified and overvolted to 12 VDC) with a 3 inch Dave Brown Lite Flite wheel mounted directly to the servo shafts. I set a 13 lb. Sealed Lead Acid battery on the little robot and drove it around. The tires held up fine even when doing hard skid steer turns they folded a bit but not too much. Of course this was an extreme test and not for normal usage. I was actually more concerned with the servo motor shafts than the Lite Flite wheels. I'd still like to hear about hoe the dubro air filled tires compare. Also foam or pneumatic tire do provide a nice amount of cushioning for shock loads.

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