How Best To Overkill A Rover Design?

Lynxmotion Rovers, Sumo, and Tracked
1

I’ve been thinking over building a car for my biped to drive around my house in.
Now… being who I am, I won’t just be content with a little toy that can zip around with my biped crammed into a cutout on top.
No, siree.
:stuck_out_tongue:

I’m looking to make a rover that’s powerful enough to push any human out of it’s way (I’m going to make it hate everyone but me, hehe), slow enough to have enough time to read sensors and navigate without smashing my house appart, but fast enough to be interesting to watch/able to catch fat humans (a.k.a. most Americans).
:laughing:

So, as usual, I’m going the overkill route.
I’ve picked out a couple tools from Harbor Frieght that I’d like to convert to drive this sucker:
harborfreight.com/cpi/ctaf/D … mber=43331
and
harborfreight.com/cpi/ctaf/d … mber=90798

Right now I’m leaning towards the winch for a few reasons.
The biggest reason is that this bugger will require me to speed it up, instead of slow it down (the wrench’s 1400 is way too fast).
As far as I can tell, it’s usually safer and easier to speed up, since you’re gears/sprockets/whatnot won’t have to deal with the shock of quickly multiplying the input torque.

This means that I’ll be able to use some nice big tires to take care of much of that (probably the 10" solid rubber tires from harbor freight).
After that, I’m estimating that I’ll still need between a 1:2 and a 1:5 gear ratio on the output to speed it up to where I want it
It’s only an estimation because the 6’ of rope per minute doesn’t tell me much, since I don’t know if that’s measured when the line is totally out (just wrapping around the shaft) or when it’s almost all the way in (wrapping around a big thickness of cable).

I might even be able to get away with removing some gears from the housing to get the right speed, but I can’t tell for sure from the sketchy assembly diagram they give.

The cons?
Big 12V car battery necessary (not really a problem, since I can easilly pull 2 around with 2 motors.
Big amps (about 30 starting).
Big MOSFETs should be able to handle that well.
Lots of modification necessary to make it useable.

I’m thinking that the vibration of the impact wrenches is going to be too much.
The vibration combined with the big starting torque that I’d have would probably make it difficult to gear reduce.
Does that sound right?

The impact wrench does have a lot of pros, though:
Nice inline design makes mounting a lot easier.
It comes with it’s own batteries which saves me money.
Doesn’t draw nearly as much amps, so a speed controller will be easier to make.

I’ve also checked other motors, but dismissed them for various reasons:

Regular 18V drill motors: lots of people use them, just too wimpy for me 8)

Planetary winch: much easier to convert to what I need, but the average current draw for the cheap one at HF is above 100A, which is too close to the limits of even the best MOSFETs.
By the way… I remove some gears to get the speed I want from this bugger, will the motor draw significantly less amps?

Starter motors: my brother is a mechanic, so these come free. However, I’ve got the same current problems with them as the planetary winch.

I haven’t got my heart set on any one motor, yet.
My current favorite is the winch mentioned at the top, mostly because of it’s badass image.
The only thing that I’m set on is the image of my biped rolling over poor little peasants.
:smiling_imp:

Opinions, anyone?
Motor suggestions?

Many thanks.

^.^

2

You might save some time and $$$ by using a kid’s battery powered ride-on toy. Wal-Mart has some inexpensive ones below.

walmart.com/catalog/product_ … p?cat=5353

3

Hmm…
After browsing them, it seems like only the ones around $200 are worth looking at.

It would indeed be nice to stick with the premade plastic frame, but that just doesn’t tickle my fancy.
If I’m going to be rolling over family members, it’s got to withstand a 200 pound guy falling on it as well as the kicks and swearing that will undoubtedly follow closely.

As for just buying them for the motor, I’ve no idea what they’ve got inside, but I imagine that it’s not going to compare to a winch or an impact wrench.
And, if all I’m getting out of it for $220 (the price of the neat ATV) is two motors and a battery, I might as well go with two 18V drills, which means two motors and two batteries for under $100.

Thanks, though, for the suggestion.
^.^

Any other takers?

4

I don’t know what kind of motors would really fit, the power u claim to need is enourmous, I think if this car needs to withstand 200lbs of falling mass the frame alone would be heavy to challenge the motors to move at anywhere over 1300rpms (huge guestimate don’t quote me)

5

No worries there.
I’ve got the design of the frame all worked out, and 13,000rpms is way too fast for my purposes.

I’ll make a rough rectangle of 1" square hollow steel stock, with a few crossbeams, and then plate only around each internal.
That way, I save on weight by only shielding the stuff I need to (like the motors/electronics) and the shielding will also provide a nice flat surface to bolt everything to the frame.
I’d be very suprised if the steel outer frame was more than 20 pounds.

I’m looking for around 100 rpms.

With 10" tires, that’s over 4ft per second, which is quite fast, indoors.

6

I am talking about motor rpms and u are talking about final drive axle rpms? right?

7

If you really want to be able to run over 200 lb people, you are going to need more power, and more mass for traction. For the frame I mght use a kid’s large steel wagon. Replace the rear axel with a strong tube steel one with low pressure riding lawn mower turf tires mounted on it. Drive the axel with one or two car engine starter motors via a go cart chain and sprocket. Mount two large lead acid deep cycle batterys in the rear over the drive axel for traction. The front axel might be be turned/steared via a 1/4 scale servo, or a reversing drill motor. It would look something like robot driven car in the movie “forbidden Planet”.

8

Woopsies!
Quite true, Hydro.

We were indeed talking about different sides of the coin.

Zoom, I like the sound of some of that.
I’d probably stick with the 1" bars for the frame, since it’ll allow me some welding practice, which I enjoy, and I can get the material from a local shop pretty cheaply.

I checked out some turf tires on ebay and they look very nice, if a bit expensive.
The only problem that I have with them is that, like all pneumatic tires, they can be punctured.
That’s not really a big deal, though, since it takes quite a hit to pop any tire.
The only reason that I care is that I might use this bugger once in a while for local competitions.
If they’re worth the traction, though, I can always shield them.

In that case, are solid rubber tires worth the added weight, or is it more cost-effective to go with pneumatic and protect them?

You raise a good point that I had forgotten about:
Ackerman steering.
Skid steering a heavy bot probably isn’t the way to go, especially on carpetting (since the bot will be indoors most of the time).

I’ve got a 1/4 scale servo on my biped as the waist rotate, and I’m quite impressed with it’s power.
Still, though, I’ll probably tack on a gear reduction from ServoCity, just in case.
Now that I think about it, I might indeed steal the front axle from a wagon, since I’ll be hardpressed to design my own.

I did plan on mounting two 12V’s right over the drive wheels, so I’m glad that I got that right…

The only real problem I see with your suggestion is the starter motors.
How am I supposed to make a speed controller for them?
I’ve heard that they can pull over 100A at stall, which is pretty dangerous for even the best MOSFETs.

9

Sounds like you want to build one of the RC controlled “battle bots”. There is probably a lot of info on these on the net. These don’t appear to use any speed control, just foward/stop/reverse. Wheel chair motors and controls may be what you need for more control. As always with these types of ventures, make sure you have good health and liability insurance.

10

Oh, no I don’t wish to build an RC vehicle.
It’ll be fully autonomous, except for some input which will come from the biped.

If I use it in a local competition, it will remain autonomous, since I’d only be doing it for fun.

I have indeed researched battlebots, since they’re outwardly similar to what I’m planning.
homepages.which.net/~paul.hills/index.html is a great resource for it.
There’s even a part about building speed controllers for starter motors.
I emailed him and asked if starter motors would be useable in a longterm robot, and he said definitely not.
They work well for short duties, but anything longer than a few minutes runs the risk of overdrawing and overheating the MOSFETs.

I could get away without a speed controller for this bugger, since I’ll have him going slow enough that he could function well indoors at top speed.
However, I want to build a speed controller simply for learning purposes.

Wheelchair motors are great… but expensive.
I think I’ll borrow from your design ideas, but pick up those winch motors.
They’ve got all the gears inside that I could ever need, and even a relay that I’ll be able to use until I’ve got a working speed controller.
I’ll probably have to build my own housing for the gear reduction, but that’s not too big of a deal.
The winches aren’t the most ideal way to go, but they are a lot of parts for a little $.
They’re rated for intermittent duty of 2,000lb pulling, so rolling around 100 lbs or so continuously shouldn’t bother them.

Thanks for the input.
:smiley:

11

Sigh…

I’ve been spending the last few days searching for the parts that I’d need, and I’ve slow come to accept the current impossibilities of the above ideas.

First and foremost:
Price!
I had no idea just how much an average deep-cycle battery costs (the one I settled on was $80, and that was really cheap for it’s size).
Factor that into the hundred or so that I’m dropping on winch motors, the cost in steel to build it, the price of the tires, and then the price of the speed controller, and I’m already pushing 300.
Definitely not what I had in mind when I first began planning this.

Secondly:
The rover would have big difficulties turning around in my hallways.

Thirdly:
I’m just not willing to spend that much time on a rover, right now, even one that can squish my family.

So, I’m going to take it back down to the realistic notch.
I’ll be getting two of the good old $20 18V cordless drills.
At 900rpm max with 4 inch tires, there’s no way that I’ll ever be able to use the full speed (i’m betting it’d boil the tires), but it’ll do for now, since I’m not willing to find a matching gear reduction to wack on the front of it.

I’ll be welding 1/2" structural “L” channel for the frame and mounting the motors with wood.
I’m thinking that I can predrill too-small holes in the sides of each wood mount and then power in some nice thick bolts with a pneumatic torque gun.
That way, the bolts thread themselves and jam in very tight, which should hold the motor real well.

I’ll be making the speed controller with monster 350A MOSFETS from www.irf.com.
Those buggers are meant for automotive applications, so I’ll be able to reuse this speed controller when I finally get around to realizing my dream of family squishing.
In a full bridge, even at 125C, those monsters should supply enough amps for starter motors, which I’ve been itching to use.
:smiling_imp:

So, I’ll leave my plans for household domination on the backburner for now, and focus on paving the way for it in the future.
This should be a pretty fun project with the eventual goals of:
more welding practice,
learn a lot more electronics,
and get to see my biped zip around the house on his new wheels.

Wish me luck.
:slight_smile:

12

You’re gonna love the power/cost of the drills. I ran the 12V drill motors at 24 volts using the NiCad pack that came with the drills ( 4 packs in total 2x2 series to parallel configuration to drive 6 motors). A lot of fun until it ran into the sand of a local beach. What a pain in the ■■■■ cleaning. Good luck and keep us posted

13

You’re gonna love the power/cost of the drills. I ran the 12V drill motors at 24 volts using the NiCad pack that came with the drills ( 4 packs in total 2x2 series to parallel configuration to drive 6 motors). A lot of fun until it ran into the sand of a local beach. What a pain in the ■■■■ cleaning. Good luck and keep us posted. I used two OSMC’s with a Mob

14

nick, if you ever plan to build that battlebot family kill robot thing :smiley:, check this site out:

robotmarketplace.com

really powerful battlebot electronics and motors.

15

I’ve been there before and droolled for many an hour over their impressive selection.
But, like McMaster and many other great robotics resources, most of their parts are quite expensive.
If I pay $50 for a bearing, I’ll go broke very fast.
:stuck_out_tongue:

There’s been another slight change of plans.
While surfing HF, I came across these bad boys:
harborfreight.com/cpi/ctaf/D … mber=93449

After much debating, I’ve decided to go with them over the much cheaper 18V drill motors.
The nice part is that they’re low speed setting is about 400rpm, which is just about the max speed one can careen around the hallways when indoors.
I’ll be using them full-blast while I test the design, until I’ve got a working speed controller, so the low rpm setting is very helpful.
Of course, the real deciding point is the 25ft.lbs. of torque.
:smiling_imp:

I’ll probably remove the hammer mechanism, which will probably reduce the torque a bit, but it’ll still be quite a strong little bugger.
:smiley:

16

I know what you meen about the parts being expensive. I just mestioned it to give you some ideas. BTW what kind of electronic speed controller will you be working with for those bad boys of yours? Will any programming be required or is it plug and play hooked up to a radio controller??

curious to know. :smiley:

17

Is there ever going to be an update on this, it was soo cool back when Nick started this thread. I haven’t seen him since :open_mouth:

18

I doubt it. It had the usual earmarks of a general BS session.

19

I see :blush: