Out vs In runner
 

Hi everyone.

Short description of planned project.
ripsaw/sentry robot tracked platform.

Weight 40-60 pounds
Speed 0-15 mp/h
runtime - 2-3 hours.

Esc - flipsky 200 amp dual motor.
Motor - no idea.

My problem is the following. I am not sure which motor will work better for low end torque applications being used as a direct drive without any gearboxes.
Ive heard outrunners have heat issued but seeing that e-boards run 40 mph with a 80 pound person on it made me wonder if they cant be utilised better in this type of platform.

Please share your thoughts.

Kind regards

It's a bit off the beaten path from what we usually see around here but it looks like a very cool project. I'm familiar with the ripsaw style chassis, will you put a body on it? FPV? Make it waterproof? What will be its main function, besides making you laugh? You might want to take a look at my 1/6 scale hetzer project. I used electric scooter Motors in that and I run them on a 6S lipo. I had to dial back the endpoints on the transmitter because it was way too fast, probably an actual speed of 8 to 10 miles per hour. I'm using 350 watt 24 volt motors with the built-in transmission and a chain drive but I'm sure you can find something similar that will give you the top speed you're looking for. I'm using a sabertooth 2x32 dual motor controller. Will this thing ever carry a human?

if you just joined, you need to make 10 posts before you can start posting photos. That's to help keep the spammers out. Anyway, I'll be looking forward to the time when you can post some photos of what you have in mind.

Thanks for the reply Crius. Yes its a bit of a odd project. But the original plan was as follows

Tracked platform with good ground clearance.
Fpv with nightvision.
Long range controls.

I always run into the same snag.
getting a sized motor that can get the job done. Direct drive or through a geared system doesnt matter, ill be able to fine tune ratios using sprockets.

I dont think it will carry a person but being able to pull some weight would be nice.

My biggest concern is the motor size vs the controller and do i just add the tx/rx to the sabertooth?

i have never done a installation with mixed parts from differend manufacturers.

With a weight of 60 lbs and a speed of 15 mph (thats 15 m a second!!) for a runtime of 3 hours......that is a big battery pack! Assuming 12V and two motors.....thats around 250 Ah!! On totally flat ground it would be around 150 Ah. A car battery is probably around a 100 Ah or therabouts.

With 24 V motors that would probably be less i Guess.....but still substantial.

With one motor you would need one that can deliver nearly 15 Nm of torque.

In general, I doubt you would have troouble finding a motor (scooter motors, treadmill motors etc) but fitting enough batteries to keep it going for close to 3 hours at the speeds mentioned would be a lot of weight.....

P

Whatever motors you use....

Well thats why i was hoping that itll be able to "pull" a payload because then i just add batterries to w/ever its pulling OR i will have to make it longer to leave enough space for extra batteries.

I think after the motors the only other problem might be the type of tracks i use.

Either sprockets with chains. (Readily available but heavier)
Or rubber tracks (harder to source in small sizes, lighter)

Ive done a larger tank once with chains as tracks (motor bike chains) but the weight was collossal. I dont know what rubber tracks would suit.

My only advice is not to underestimate how heavy these things can be....... motors alone can be up towards a kilo each without gearboxes, chain tracks are easily 5 kg more, ... it gets very heavy very quick ..

p

Ok so first of all I love the ESC, but I think you are overthinking it a bit for that. I'm not sure of your budget but that is a very expensive ESC and it looks to just be an ESC. If you are going to put that kind of money in it I would consider a flight controller instead from a drone ($20-50ish) and instead use that as a control board. Use iNav as the software (check it out) and then you can still use any ESC you want. You can direct drive the ESCs from the FC (at a WAY faster rate than you could via old slow PWM if you are using sBus/crsf/serial/etc) or passthrough and do whatever. FCs have OSD built in, 5V regulators, filtered power, on/off switching power for video transmitters, and some even have PDBs built in. There are options for things like lost model alarms, gps, autonomous functions such as return home, bluetooth, multiple camera support, etc.
When you start getting that big in weight the easier and cheaper way to drive the motors is going to be brushed. Brushless motors have cogging at slow speeds but work great once spinning. Since you will be spending most of your time starting and stopping due to how tanks steer you will probably need a sensored brushless motor to help with smoothness. At that point you need a special ESC and for that type of amps/volts it can get expensive. The scooter motors that Crius spoke of earlier are actually meant for ride on scooters and he has 2 of them on a 24V (6S) setup. I've seen that thing almost wheelie due to that much power, I believe they would be some great starter motors or at least a form factor to look into. 24V/350W=14.5A is the "average" power it is going to pull. I personally like to always at the very minimum double the maximum amp rating on the motor for the ESC so 30-45A ESC would be great. The Sabertooth 2x32 will do all that board above will and is much cheaper and is great quality. I ran the 2x5A on our metal tanks and had no issue. I also personally use the 2x12A and 2x25A Sabertooth ESCs on my own builds. I would really try to stick with brushed motors if possible, they are cheap and easy to work with for our slow speed applications.
Please feel free to ask away, I've done a few rovers and I almost always seem to fall back to the Sabertooth and either direct wiring or a flight controller to handle all the other functions. iNav is an open source app that will let you change everything on it and is made to run things like rovers, cars, planes, etc instead of just drones.

I would agree with the brushed over brushless setup, but that's because I've also used the brushed scooter motors in my 1/6th scale 150lb KV-2 paintball tank. It's actually really hard to control a tank at high speed with slick tracks. So for your purpose you will need to have a lot of grip on your tracks, but that also hurts you when you need to turn.
https://cimg7.ibsrv.net/gimg/www.rcu...f4704cf464.gif
40 pitch sprocket on 450W 24V motor.
https://cimg9.ibsrv.net/gimg/www.rcu...34fdcd204e.jpg
Direct chain drive.

That looks a lot like the setup in my hetzer, scooter motors with the chain drive. Those Motors are ridiculously powerful, I'm using a 2 x 32 sabertooth and a FlySky I-10 radio and I set the endpoints for throttle at just 50% and it still has loads of power. I've got some video of it in action somewhere, if you want to see how it performs let me know and I'll post a video or two when I get home from work tonight.

I got my motors from these guys (http://tncscooters.com/index.php?route=product/category&path=52_55) and 24V 450W (watt) is the maximum size you can get that is already geared down, but they have motors all the way up to 1000W @60V that are ungeared if you go up in voltage. Keep in mind that the more voltage you run the more efficient the motors become. It works like this...say you run a 12V motor and it pulls 15A from your ESC. An equivalent motor wound to accept 24V will pull like 12A from your ESC, but your ESC will also need to run 24V. Usually when you start getting up into the higher voltage ESCs, the parts (motors, batteries, and the ESCs) start getting quite expensive. 24V is a nice middle ground between good power and lower cost. All you really have to keep in mind mixing BRUSHED components is to remember to match your voltage range of your ESC and your motors while staying within the amp rating of the ESC. Typically I like to oversize my ESCs or if that isn't possible I will put in an inline breaker/fuse to keep the motors from drawing too many amps from the ESC. Although these motors normally pull around 15A under normal use, you can stall a motor of this size and easily pull more than 100A which can damage your ESC.

As far as BRUSHLESS goes...I'm with Erik and don't recommend it for your application. I've toyed around with brushless motors on a smaller scale in tanks and they didn't perform as well as brushed motors did.

For tracks you need to keep in mind that the faster the track moves the more likely it will be to come off. As your tank like vehicle turns, there are tons of side stresses put on the tracks. Rubber tracks deflect A LOT. Without some sort of a rigid center you will lose your rubber tracks in high speed turns. To compensate for this you would need to increase the track tension, but more track tension leads to more drag on your motors and less run time. I use steel tracks on my 1/6th KV-2 and they are heavy as hell (4" wide at around 25lbs each), but they don't come off as they are so stiff that they don't deflect side to side hardly at all. Having an active suspension will also complicate things. Having no suspension will actually help keep your tracks on better. It's a tradeoff.

I will also chine in being for brushed vs brushless being better for our tracked vehicles. Years back I'd purchased and rebuilt an Aeromate tiger I ( 1/16th scale) that had been originally brushless. As part of the rebuild I changed to brushed can motors with reduction units and I was able to get wonderful performance out of it. The original seller had sold it due to disappointing performance ( but he also hadn't taken the time to maintain the model or understand the issues..actually he abused it ); none of which an issue for me..

I'm using tandem 540 brushed motors in my heavy ( 50+ pounds) trucks. no issues.

Jerry

Im thinking of putting my drive gear in front, also will it be possible to not use a break function to turn but rather run one track forward and one track reverse to turn?
Stresses on the track will be alot less then.

Thank you for the photos. They are reqlly helpfull!

Why would you believe the stress is lessened by running the tracks opposite directions?

Running the tracks in opposite directions will result in a neutral ( in place pivot) turn. No matter how you do it
to make a 'normal' turn you need to create a difference in rotational speed between left and right tracks- in the same direction.
with brakes, controlled ( dual) differentials or two esc controls. A controlled differential transmission as used in Tamiya's Leo 2 and I believe
their other modern tanks is an example without brakes.

If you want to explore some of the background of tracked vehicle mechanical steering read this article: https://www.semanticscholar.org/pape...980b6cf21?p2df

Look for the .pdf document reference and open it. Attachment 2270489

Jerry

If you go brushless motors you are going to need some hefty very expensive brushless motors to get the torque you require.
Some really low kV and high wattage motors.
I think i would tend to agree with others above that getting a brushed motor with some type of gearing would be more suitable for your application.

I have got some brushless direct drive units on cars etc and they are awesome at speed, but low down there is a lack of control, they would tend to jump into action rather than give a smooth transition of power. Then due to the nature of the drive would get hot real quick.

I've seen video of some of your cars, Will, and they truly are little beasts. If I wasn't in the hobby myself it would make me think you're just a little bit crazy. Of course, they say that you have to be crazy to be an RC tanker, as a normal person would go insane. :p

Like it's been said, no matter how you turn the vehicle the tracks will try to slide sideways off the sprockets and under the roadwheels. It's the nature of the beast. Friction is trying to keep the track in place on the ground when the motors are pulling it in a different direction. The more grip your tracks have, the worse it will get. Even a real life Abrams tank that has had millions of dollars of development work will shed its tracks if you do a neutral turn (one track going forward and the other in reverse) too fast or for too long. There are ways to try and keep the tracks on though. You can use large high center guides (which only work with large sprocket and idlers due to the need to wrap tightly around them), you can use really stiff tracks like I did, you can use tracks with guides on the outside of the track (like the M5 Stuart tracks), or you can use "track retainers" on the sprocket and idler (basically rings mounted on the outside of them that reduce the chance the track will come off). The original Abrams used a track retainer on the outside of the sprocket, but no longer does. It's all a balancing act.

https://cimg7.ibsrv.net/gimg/www.rcu...59e261b316.jpg
Abrams retaining ring - will only stop the tracks from riding over and off the sprocket if the tracks don't have enough room to as shown. The sponsons are close enough to the ring so that the tracks can't ride over it. If there is enough room for the track to come over it, they will when something gets drawn into track and over the sprocket. Not compatible with the M5 track type below. Pretty much only works with center guide type tracks.

https://cimg8.ibsrv.net/gimg/www.rcu...f9959e7b41.jpg
M5 Stuart type tracks with guides on the outside.

https://cimg1.ibsrv.net/gimg/www.rcu...cefb7d2af8.jpg
Very stiff center guide tracks.

https://cimg2.ibsrv.net/gimg/www.rcu...db21f64a9b.jpg
Very stiff with almost no left to right deflection. My tracks are off the shelf Rexnord 1864K4 conveyor chains with a K1 attachment. In this case the track type is Rex 1864. The K4 in the model number means K1 attachment, 4" width.

https://cimg4.ibsrv.net/gimg/www.rcu...5f54324d69.jpg
Very slick surface which helps reduce friction with turns, but causes the tank to turn too quickly at high speed. Tracks will actually break free if you gun the throttle.

I think all us seasoned tankers are in agreement here with the brushed versus brushless, I think we have all tried at one point honestly and wanted it to work. Brushless motors are much more common these days and getting different spec motors is much easier than brushed motors. The prices aren't too terrible either really. Just for our heavy slow speed application brushed is better ATM until sensored brushless motors/escs come down in price.
Also just a heads up controlling the tank is the easy part, almost all the aftermarket boards out plus the Taigen board allow you to run your own ESC/Motor combos and if you just need to control the main motors without a controller you can always program your radio to a delta wing mix and connect each drive motor to the respective channel output. The transmitter will mix the input and output a signal perfect for driving tanks and doesn't require a control board at all. Heck if you want to get real brave you can always retrofit a current gearbox out now to run a chain, that is what I did. I had a friend make me a set of sprockets to go on the TG gearboxes to adapt a chain and use that to power a mower. That project didn't get finished but I do have everything to finish it when I find another dead mower to play with (I got a rider now so the RC lawnmower took a backseat).

https://cimg3.ibsrv.net/gimg/www.rcu...b015af91c.jpeg
https://cimg5.ibsrv.net/gimg/www.rcu...174a39bc3.jpeg
Pictures for reference. Pretty cheap this way and tons of gear reduction

You might have seen this before but there us a good overview of track systems for scratch built large tanks at this site:

https://www.rctankcombat.com/articles/track-systems/

bit out of date now probably but it still has some good ideas and pros and cons of each.

P

That's what my KV-2 and Sturmtiger in 1/6th were originally built for - paintball combat. That site is where I got the idea to build them. My tracks that I developed for the Sturmtiger are the ones labeled "Chain and Bolt Track" on that site. Although they worked OK, they would derail more often than I'd like. They have since been replaced by more reliable 2060 attachment chain tracks with ABS track pads which have never derailed. You can see the differences on both my tracks here: R/C Tank Combat - T065 (Page 2)

Those newer tracks are pretty nice. I have always fallen back on motorbike chains for larger scale tracks but they (1) weigh an absolute ton and (2) need the idler replacing with another sprocket - otherwise they just come off due to no "horns".

Here is a dual duplex track with crosspieces and a single duplex chain.

https://cimg1.ibsrv.net/gimg/www.rcu...0803b51e39.jpg
https://cimg4.ibsrv.net/gimg/www.rcu...0a9b1ecef4.jpg


I tried a few of the track types on the rctankcombat site but I could never get them to work. Some of the track types (like the hollow pin chains) I couldnt source and some like the door hinge track were beyond me. Part of teh problem being that I could never manage to make a sprocket.

But that site has always been a handy resource when it comes to larger scale for me..

P

I have been trying to link 2 motor setups.

1. 2k watt brushless motor from a e/bike or e/cart.
2. 350 watt motor with worm geaebox from a e/chair.

Both motors can move a human. Thats about a 100kg platform. So if i can get my robot to 50kg and still run 2 motors it should work according to my theory but i am still very noobish to these types of builds.

If anyone wants to chime in i would appreciate it.

Thanks in advance!

I'm not sure what you are trying to do at this point when you say "link 2 motor setups".

Are you trying to use one of these motors for one track and one for the other? Most of us use two matched motors/gearboxes - one for each track.

Or are you asking which setup would be better?

If you are trying to use one single motor to power both tracks you will get into building a complicated differential steering mechanism that would cost more than just getting two motor/gearboxes.

You can get away with low power motors (few hundred watts) for the speeds and masses you have been talking about as long as you are only driving on the flat.

As soon as you include hills (or even gentle inclines) those power requirements are going to skyrocket up into 4 or 5 KW per motor.

Reducing your speed requirements will drastically reduce the power requirement, widen your motor choice, shrink your battery requirement, lower your battery weight, increase your running time.

I said it before - those weights at those speeds for that long (original post) need more battery capacity than I think is feasible.

In addition - and I think its worth saying - if you hit someone or something with 30 kg moving at 15 mph - you are probably going to end up talking to the boys in blue (or whatever colour they wear where you are) and you would be better off with some insurance.

P

Yea I agree here, battery restraints are going to be a factor that needs to be figured out first. You can try some custom battery packs (check out Battery Hookup for specialty large packs) but density is a set thing of lithium cells. There is a max density value you can get from them and realistically you need to plan for that. Also packs start getting very expensive at that size unless you start making them. You can always chain a bunch of 3/4/6S packs and put them in series and parallel to get what you need but it gets dangerous and tedious to connect them all right. Just for reference, a high C rate battery (not that fake garbage nano puff stuff you get from hobby king) from CNHL is going to run about $110 for a 6s/6.2A/90C pack and that is on sale, usually runs about $170. You will need at least a few of those to get decent run time you are asking (2-3 hours is a pretty darn long time for batteries, especially with no cooling) and even then you are going to need a few in parallel at minimum. I would also look into a BMS, if you are running that big of battery and capacity. The motors will be fine with the brushed scooter type, they are meant to push a 150lb+ person on a 200lb+ scooter so you should have plenty of torque to get the job done. The main issue here is battery, space for the battery, weight, and safety.