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6WD with suspension? (Robomagellan)

#1

Anyone consider a 4WD rover with suspension?

I’m not familiar with all the off-road R/C stuff, I’m told something like a “Revo with TRX 3.3 (Model 5309)” can be made into a great off-road 'bot, but it’s a little pricey to buy it complete and throw away about half the stuff as DPA did:

geology.smu.edu/dpa-www/robo/jbot/jbot.html

Using this R/C (or E-Maxx, out of production):

traxxas.com/products/models/nitro/5309revo33-downloads

What I really want is just the suspension parts. Even make my own if I could get a good look at the parts, and how they work. GHM16 motors and TRC-01 tires would probably work. The electronics, motor control and computer stuff I’ve got covered. I can pick out mostof the parts in the exploded vidw. Just try to pick them out of a catalog page!

This would be an autonomous 'bot for Robo-Magellian.

Anybody familiar enough with the Traxxas Revo type chassis (or similar) to be able to identify (and select) the suspension parts?

I’m kinda looking for a used R/C on E-bay, but I’m just not that familiar with the R/C stuff.

Would LM be interested in a set of parts to make the above motor/wheels “full suspension”?

Thanks!

Alan KM6VV

06/29/12 EDIT:
I did figure out the parts available on E-Bay, after ordering a set of wheels. Key is to look for sellers of the particular model you are looking for, as “4907 Traxxas”. Then you just keep bidding on parts until you get all you’re looking for.
Got 'em!

#2

It’s very cool looking, but as you suspect it is not going to be cheap. I have an account with Traxxas, so getting the parts would not be an issue. But I’m betting beyond the cool look it’s no better than an articulating chassis with a motor on wheel configuration. It does look cool!

#3

DPA has basically “beefed up” with an aluminum chassis, and used 24V Pitman motors driven with universal shafts.

I’m not involved with all the R/C stuff, so even 'tho I might know a little about suspensions, I’d have a hard time pulling the parts needed. I can machine a chassis and similar parts as DPA (I’d discussed it with him even).

I really hate to spend $400-500 for an R/C, and then rip it apart…

You’re saying articulate a motor/wheel combination? I considered that. Do you have an example?

Thanks!

Alan KM6VV

#4

A Revo would be nice for robotics, but an overkill for your needs. However, using an R/C car chassis would save you a lot of time as looking at the 4WD1 it would be very difficult to add suspension to.

The picture you have posted looks like someone has made a custom shock tower and chassis plates to hold Traxxas upper and lower A-arms, the shocks and wheels. It looks like a pretty simple setup, and to be honest you could get these from any RC car, I’d perhaps search for “roller” under R/C on eBay and see what you come up with. Go for an electric chassis, as it will have things like slots for batteries etc. which a nitro chassis does not have. If you’re keen for Traxxas, a Stampede (which is what the picture seems to show, or a T-Maxx) would be a better option as it is simpler and wouldn’t need a great deal of modification. If you need lots of articulation, an R/C rock crawler might also be suitable, but you’d want to retain the transmission (in fact for a smoother ride factor in keeping the R/C car transmission).

Good luck!

JB

#5

I’m thinking mostly I’d do my own chassis, and add the suspension parts, and shocks. I just haven’t followed the R/C stuff to know what to look for.

DPA did a LOT of work to design/build the chassis. I don’t know if I want to take on what would be a BIG project right now.

I can certainly look for “roller” and the Stampede. I’ve already learned something!

DPA uses a pair of motors to drive the two sides of the 'bot. They are driven through timing belts. Not sure how I’d use the existing transmission (and differential) with two motors.

You’re certainly right about the 4WD1 not being easy to add Traxxas-type suspension! Although it might be a good place to try out a 4WD bot across the grass/sidewalks/etc. of a RoboMagellan course. I just discovered today that the Traxxas is built for a gas engine, so yeah, an electric model would be better. To bad the T-max isn’t readily available now.

Thanks!

Alan KM6VV

#6

Hi Alan,

You could always put bigger, softer wheels (+ foams) on the 4WD1 to give it that extra bounce :slight_smile: Those into R/C rock-crawling remove the foams and cut it into a “star” shape to give more flex and traction to the wheel. Looking at the DPA chassis, certainly it looks impressive all CNC milled like that, but a similar job could be done using hand tools.

I’m looking at putting the requisite R/C shocks on my Johnny 5’s waist soon, as recommended on a couple of threads here. That’s where I’m coming from - I’m a radio control car fanatic first, robot novice very distant second :smiley:

JB

#7

I hesitate to mention competitor’s products here, but since this chassis is not available on Jim’s website I guess it is okay: pololu.com/catalog/category/88
I know that it is direct drive, like Jim’s chassis, but the suspension tension is adjustable.
Did you check out Steve Norris’ six wheel drive explorer from Minds-i? Pricey, but to the point and not an R/C conversion: norrislabs.com/
Regards,
TCIII

#8

Hi JB,

That’s a thought. I’m not looking to climb rocks, just a big grassy field and a few concrete walkways! I think just the 4"+ size tire with treads (like DPA) would work.

I have no problem coming up with the CNC made parts (well, time), but that’s a LOT of work! I was toying with the idea of making the GHM16 motors and TRC-01 tires work by building the control arms, tie-rods, links, etc. and a bearing for the axle. Of course, some sort of CV joints would be needed as well. This is getting more complicated all the time!

Alan KM6VV

#9

Thanks for the 2nd link (couldn’t follow 1st). OK, I’ll bet you mean the “Thumpers”. I hadn’t seen those on that website. I’ll investigate.

EDIT: The Thumper uses what look very much like simple ‘T’ ABS fittings to allow the 1" dia motors to be pivoted behind their tail shafts, thus giving some ground compliance. Nice trick! a simple SES metal bracket to hold an LM motor by the body could just work…

the MINDS-i 6-Wheel Kit would certainly get things started. But $600+ is up there!

Could go a little further, “Rocker Bogie”:

http://api.ning.com/files/P5iTPuh2G05ZPGiPLysMRQ8RJawnCPpetYZ56B0QeJHaMxRUS68IZIlRpYQI4PIA7Jv*jmxBGDfSMUkSKJshgpi42MwTk4/Rockerbogie.jpg

I think some suspension parts made with LM wheels/motors could work. Might make the 4WD1 chassis a bit more complicated!

Alan KM6VV

#10

Alan,
Fixed the link to the Pololu Thumper. Thanks for catching it!
I too have been looking for a reasonably priced independent suspension rover for a while and have still yet to find one.
Like you I have thought about buying the components for an independent suspension system and attaching them to a suitable chassis. However, the costs quickly add up for the individual parts and any necessary custom machining. Also, since the suspension is independent, you have to have differentials for each pair of drive wheels and drive shafts to couple the differentials to an appropriate motor or motors. Here is a typical E-Maxx chassis on eBay: ebay.com/itm/3908-Traxxas-E- … 58911187f8 The price is $269 and you still need wheels, motor, etc.
You will notice that Steve Norris added the second motor to his six wheel rover according to his article in the latest issue of Robot mag. Also, these rovers are not truly water proof and it would take some effort to make them so.
The Thumpers are some what reasonably price, but the motors have sleeve bearings and the wheels do not stay parallel to the ground as the wheel moves vertically up and down like a true independent suspension with universal joints.
Is the six wheel rover in your picture the one that was built and run in Australia or is it the one from a university in the Mid-West US?
Regards,
TCIII

#11

Is the suspension idea based on having four or more driving wheels on the ground even on rough uneven ground? If so then one might want to make long springy travel suspension arms with possibly the motors mounted at the wheels. Maybe something like a continous rotation servo wheel mounted on the end of a springy hacksaw blade. I think shocks on a bot is a waste providing nothing more than looks, and increased complexity and expense.

#12

Hi Tc,

Yes, it would be costly to machine all the suspension parts. I did come up with an idea to use two motors, and miter gears. No universals, if a very simple single pivot per wheel is used. Still thinking about that.

Steve N’s two-motor build puts a motor on each side, or fore-aft? It still amounts to an expensive kit + more expensive parts. Haven’t seen his article.

Thumpers are a little less expensive, but then you need six motors, and all that weight is un-sprung. Not the best choice, and the motors aren’t the best, as you’ve observed. Also, Zoomcat observed that the wheels don’t stay parallel to the ground. Also desirable.

DPA (David Anderson) in the link given is often at the Dallas robotics club. Just gave a really great two hour presentation on his 'bots.

Thumper is clever. Instead of using six motors, two motors and miter gears driving shafts to each wheel. Wheels wouldn’t be parallel (could add a universal joint or two) to fix that. A lot more parts!

Still thinking!

Alan KM6VV

#13

Mostly for better traction on grass and on/off concrete. Probably won’t get into water (hopefully)! Looking for something a little more robust then a continuous R/C servo for outside (avoiding the really big and expensive ones).

Probably just cut two wishbones and a hub plate, and make up universal joints. Or buy some of the stuff. (thinking only at this point). I’m not an ME and especially not an automotive engineering expert, so that would be quite an engineering project. Not out of the question, but…

Thumper could be made, if one wants some compromises. Good experiment. Maybe just do four wheels, and use LM parts. But I like the idea of making a parallelogram (four-bar) wishbone, and the hub and universal joints. I might draw it up and make just one…

Alan KM6VV

#14

Hi Alan,
I think that the bare bones E-Maxx chassis for $269 on eBay might be the most cost effective approach. The suspension (dual wishbone), the dual shocks, the differentials (fore and aft), the transmission (there are dual motor and two speed upgrades available), and the basic chassis are all included in the price. All you need is the wheels/tires, motor of choice, controller, battery and electronics. However, a thorough review of this bare bones chassis (E-Maxx 3809) indicates that the Castle Creations brushless motor, controller, and associated battery is going to be very expensive in relation to the cost of the bare bones chassis. So this option is now off the table.
Regards,
TCIII

#15

I think there is a way to make the E-Maxx chassis AWS, rather than just steer the front alone. Basically rebuild the rear end with parts for the front, and add a servo. An E-Maxx with 4WS would be that much more agile, right? And we’re not worried about top-end speed anyway.
A nice side benefit of 4WS is you can ‘crab’ the vehicle as well as do super-tight turning circles. Put some oversize plush tires on, and it may never get stuck again!

#16

kdwyer,
The E-Maxx 3809 chassis is a way to go if you have the bucks for the chassis/motor/controller combination. I suspect that this chassis/motor combination will be approaching $600 even if you buy it piece meal off of eBay.
Regards,
TCIII

#17

That’s getting closer, I think. I wouldn’t be buying E-Maxx parts (motor, ESC, etc) anyway, and would be mostly just using the suspension parts, a la DPA. Idea is to use two DC motors, one driving each side through timing belt and universal joint drive shafts. See DPA’s 'bot in first post of this thread.

But I really appreciate the comments. found an E-Maxx chassis anyway!

Thanks!

Alan KM6VV

#18

Hi Alan,
Might want to consider the Tamiya TXT-1: pololu.com/catalog/product/123
The $359 price tag is not too bad. However, the suspension is not truly independent, but the front and rear axels can flex (rotate) around the center of the differential. Also it can be made into four wheel steering.
Regards,
TCIII

#19

Hi TC,

Wow! More and more choices! But I see (suspect) that one motor drives the front wheels, and another the back wheels. we want Left drive and Right drive, and we don’t need steering.

I searched this time on E-bay for “E-Maxx”, and really started seeing a LOT of stuff!

Thanks!

Alan KM6VV

#20

If you DIY the continous rotation servos, there are some big ones that aren’t too expensive.

hobbyking.com/hobbycity/stor … 16sec.html

hobbyking.com/hobbycity/stor … _103g.html

hobbyking.com/hobbycity/stor … 21sec.html

hobbyking.com/hobbycity/stor … tegory=291