Help Selecting Motors/Chassis/Motor Controller/Battery pack
DavidZemon
Posts: 2,973
I've had a $256 SparkFun gift card burning a hole in my pocket for a long time. I think I figured out how to spend it: the 6WD Wild Thumper. This thing looks like a total blast.
Introduction
My fiance wants some extra-curricular programming experience to supplement her Java day job. She wants to program an autonomous robot. If I'm going to use my gift card for her project, I want it to be something fun to play with, not just fun to program. Henceforth the massive overkill Wild Thumper linked above. Because the Wild Thumper consumes the entire gift card, that means there will still be some out-of-pocket expenses (which I will pay for since they will cost way more than what she actually needs), including a motor controller, battery (and likely charger), and sensors. I suspect a Raspberry Pi with a high-res camera (and maybe a compass) will give her exactly what she wants in terms of easy-to-program, tracking accuracy, and price.
Questions
Wild Thumper
Ignoring the fact that it is overkill, is there any reason the Wild Thumper would be a bad choice for an autonomous robot?
Would the RoboClaw 2x15A be a good motor controller? Do you have other suggestions?
Would a 2,200 mAh, 7.4V 30C LiPo battery work well? I did some math (motors = 7.5V/5.5A stall current) and came up with ~23 minutes minimum run time. Maybe 30 minutes average?
4x4 ATV
This platform is a lot cheaper and smaller. Looks like there is probably room for a Pi, camera, compass, and battery.... hard to tell though. This would be better suited for indoor use since it would be able to get into smaller places in the house. Do you see any problems with this platform (other than the fact that it won't carry a potato cannon)?
What would I use as a motor controller? Does this little board look good, if the two motors on each side were connected in parallel?
Could I use the same LiPo for this guy instead of 5 AA batteries?
Other platforms
I didn't see any other options that look reasonable on SparkFun. Are there any other kits you would recommend for an autonomous, RPi-controlled robot?
Introduction
My fiance wants some extra-curricular programming experience to supplement her Java day job. She wants to program an autonomous robot. If I'm going to use my gift card for her project, I want it to be something fun to play with, not just fun to program. Henceforth the massive overkill Wild Thumper linked above. Because the Wild Thumper consumes the entire gift card, that means there will still be some out-of-pocket expenses (which I will pay for since they will cost way more than what she actually needs), including a motor controller, battery (and likely charger), and sensors. I suspect a Raspberry Pi with a high-res camera (and maybe a compass) will give her exactly what she wants in terms of easy-to-program, tracking accuracy, and price.
Questions
Wild Thumper
Ignoring the fact that it is overkill, is there any reason the Wild Thumper would be a bad choice for an autonomous robot?
Would the RoboClaw 2x15A be a good motor controller? Do you have other suggestions?
Would a 2,200 mAh, 7.4V 30C LiPo battery work well? I did some math (motors = 7.5V/5.5A stall current) and came up with ~23 minutes minimum run time. Maybe 30 minutes average?
4x4 ATV
This platform is a lot cheaper and smaller. Looks like there is probably room for a Pi, camera, compass, and battery.... hard to tell though. This would be better suited for indoor use since it would be able to get into smaller places in the house. Do you see any problems with this platform (other than the fact that it won't carry a potato cannon)?
What would I use as a motor controller? Does this little board look good, if the two motors on each side were connected in parallel?
Could I use the same LiPo for this guy instead of 5 AA batteries?
Other platforms
I didn't see any other options that look reasonable on SparkFun. Are there any other kits you would recommend for an autonomous, RPi-controlled robot?
Comments
You're really need help deciding between the super awesome Wild Thumper and the wimpy 4x4 ATV?
If you're not going to get a Wild Thumper at least get a Rover 5. It has quadrature encoders which the Prop can easily read.
I don't have a Wild Thumper myself but I've read a lot good things about it.
Edit: I don't really see anything wrong with the 4x4 ATV. It just suffers when compared with the Wild Thumper.
The one bad thing about the wild thumper is its size. It will be much harder to navigate in our tiny apartment. For that reason, I'm getting a lot of push back against it. And this is, after all, supposed to be her hobby project not mine.
I only use & recommend gear ratios over 100:1, even indoors for better control & accuracy..
I was about to say that I like the treaded rescue platform, of which Bat-Gorilla-Santa mentions stair climbing ability:https://www.sparkfun.com/videos#all/sWFcxb-ghr0/231
But that only has 2 of those too-fast 1:48 gearmotors to drive 6 wheels and 4 treads. That's REALLY underpowered and undergeared. Treads take like 3-4 times as much power as wheels. That would make the four-motor 4x4 ATV look powerful in comparison.
My ultimate goal is a small 4 wheeled robot for cruising under the house with a wireless camera and electric pump for ant/spider spray (Raid Max Bug Barrier with battery powered pump) so I don't need to crawl around on my belly this year when the time comes.
Robots from Inspector Bots are my inspiration, but way overkill/overpriced for my needs.....
I am looking at replicating the Dagu Rover 5 by making my own utilized a waterproof enclosure from Polycase, Openbeam extrusion pieces, and small gearmotors from Pololu. The only thing I need to by are the gearmotors. My plan for the remote control are two Propeller/XBee setups (again, because I have it all)
http://www.ebay.com/itm/111811054792
I have an article in the next SERVO mag about this and 2 Wifi drone cams. Should be out this week.
How do I select new wheels for the robot? I'm not too keen on buying wheels that cost as much as the entire chassis/motor kit. If we go with the Rover 5 (which is a 99% probability right now), then it will be purely used for roaming around inside the house. No need for those awesome Wild Thumper wheels. The most it needs to do is drive over carpet and the little bump between carpet and tile. Does this wheel look good?
If that's all you need then most anything will work OK, including the 4x4 ATV you first mentioned. I assumed you wanted outdoor functionality from your first post about compass & Wild Thumper.
Duane likes that Rover 5. It's nice that the encoders come with it. I'm not a big fan of treads though. They look cool but consume a lot of power and can jam easily if anything gets caught inside. So yes, you can change Rover 5 from treads to wheels but the costs does start to add up.
Note that 4WD bots are fairly "unstoppable" and more agile on rough terrain, but (speaking of compasses) their skid-steering ability for navigation/dead reckoning will probably be less accurate than a traditional 2WD bot with casters on smooth floors. Horses for courses.
I mentioned the Wild Thumper because I thought it would be fun to connect an RC receiver/transmitter to it when she's not using it and then go outside to have some fun. But seeing as how that isn't going to happen, it's likely not ever going to see a blade of grass.
The quaderature encoders might be a really good thing though. I remember her saying she wanted to be able to backtrack where it had previously traveled. I think the encoders would be a requirement of that (ignoring GPS for the moment)
This doesn't mean you can't put encoders on the wheels and derive at least something useful. But you will likely need to combine it with something else -- a compass, for example -- to help you navigate. A beacon to firmly indicate "homebase" doesn't hurt, either. Outdoor vehicles ideally need a combination of sensors to counter the vagaries of uneven terrain. For these types of vehicles, especially anything relying on slip for turns, encoders are best considered as a means to control the speed of motors, not for dead reckoning.
I suppose it's fair to say I "like" the Rover 5 but as I'm sure you'll recall, it wasn't always smooth sailing when I first started using mine.
Here's a thread about my treaded Rover 5. I initially had a lot of trouble keeping the treads on. My my present setup, I can't get the Rover 5 to throw a tread no matter how vigorously I drive it.
If you're going to add wheels to a Rover 5, add Vex Mecanum wheels. These things are a blast. It's always fun to see people's expressions the first time they see the robot drive sideways.
I have thread which was originally about my Mecanum wheeled Rover 5. The thread took a few detours but there are instructions on how to mount the Mecanum wheels to the Rover 5 in there somewhere.
In case anyone hasn't see my Mecanum wheeled Rover 5, here it is. Someone had asked how I controlled so the first two minutes is me talking. If you skip to the 2:00 mark you can see the robot in action.
The Mecanum wheeled robot takes the same control inputs as a quadcopter copter minus the throttle.
One possible problem with using wheels with the Rover 5 is the Rover 5 has relatively soft metal used on it axles. The normal Rover 5 wheels are partially supported by the gearbox. If you use wheels which stick out from the robot, the axles are more susceptible to bending.
Thank you all for the input
I am still wondering about wheels though. How do I know what wheels will and will not work with a given motor? Are they all standard? Are there multiple standards?
Since your aim is to use the vehicle outdoors, make sure the motors are sealed -- not necessarily air tight, but not open frame either (the dirt, you know).
I was thinking the same thing since all pics I see with treads show flexing of the motor/gearbox "leg" assembly. That is one reason I am planning on making my own version rather than buying a Rover5.
Thanks Erco! That's in my eBay watching and one will be grabbed soon. That should be perfect for my needs.
BTW, I never liked being in crawl spaces either. I used to be a cable TV installer and I've worked in 11 states. "What will I do if I see a critter in here?" I used a long stick with a hook in most cases.
Should be up by week's end.
Typically, half of the article is online and anyone can view. Naturally I saved the MD81 camera part for the end of the article, so can't be seen for free...
Outstanding. I've wanted to do wifi for a lonnnnng time but didn't have the guts to try to
kluge one up to my usual low standards.
Spectacular, I was thinking about going to visit my daughter tomorrow and hadn't quite made up my mind. There is a bookstore on the way down... makes it perfect.
If it isn't out... I'll just have to get something else and go back next week:)
Thanks
Incidentally, I got 2 more cams today, the ones I mentioned previously from http://www.ebay.com/itm/111811054792 . These are cheaper, come in a poly bag, not a nice retail box like my original. The bad news is excessive video lag, which is about a second compared to a half second from the first one I got, so I guess there are several verions of this camera.
Alternatively here's a complete REAL 5.8Ghz FPV system for $52, 4.3" screen included. No lag, good reviews. Trying not to buy but I'm weakening. http://www.banggood.com/Syma-X5C-1-X5SC-X5SW-5_8G-FPV-720P-Camera-with-Monitor-Real-Time-Transmission-p-980090.html
Addendum at http://www.servomagazine.com/index.php/magazine/article/february2016_WiFiVideoCameras
Related, I just ordered that Banggood FPV system too. Will comment after receipt.
As my daughter was disassembling my spare S2 the other night, I actually got thinking about cannibalizing it for the setup. It would be nice to put my remote control S2 concept to use. I would need to check on changing wheels and obviously doing something other than the tail dragger style for under the house travel, but much of the hardware is usable for my needs. I will need to look for some "re-purposed S2" pages.
Have you had an opportunity to check the FPV system out? What do you think about it?
Related: Everyone needs several of these zoomable 18650 flashlights: http://www.ebay.com/itm/1800lm-Zoomable-3-mdoe-CREE-XML-Q5-LED-18650-Flashlight-Focus-Torch-Lamp-Light-L-/281871144889
Agreed. I just bought 3 lol. We'll see how it compares to this guy which I bought a year ago and have enjoyed very much. Supposedly these ebay versions are three times the lumens? hmm... we'll see
Thanks for the flashlight link, that could work since I have 2 extra 18650 batteries right now.