High speed tracked vehicle....something different

[Chi-el]

Hi All,

As I've announced in some other posts I'm working on a build that kind of qualifies for being on this forum solely for having tracks. It's doesn't have much with actual tanks to do. Maybe if I paint it green and stick an APC kind of body shell on it.....

I have been bashing truggies around and though I like working on them I do find they break easily with so many moving components in the suspension, steering and drive train. Mainly due to their enormous power to weight ratio, the plastic components easily give and the alternative is to upgrade everything to aluminium.
So instead of doing that I thought I'd better build something myself, in the form of a "tank", a bit like the ripsaw.

Just started sketching and drawing a bit and spending god knows how many hours (mainly at work) in mind visualizing and form the various design solutions.

I'm currently abroad for a few months, but when I get home I continue the build, in the mean time, more and more components have arrived and I took the drawings with me to do a bit of designing while I have tonnes of time to spare.

Here are some of the specs
- Chassis plate is 4 mm aluminium 700 x 360 mm
- Sprockets fwd and rear 80 mm diameter
- Running wheels are sprockets 65 mm diameter
- Suspension is total 18 pcs 105 x 21 mm springs 2,2 kg each max stroke 30 mm
- About 40 bearings in it.
- Track is 08B1 rollerchain with wings
- Track shoes/pads will be 24 x 55 x 2 mm aluminium plates with rubber profiles on them
- ESC's are 2 x ZTW Beast pro sl 200A
- Motors are 2 x Rocket 56112 780 kv motors 7,35 kW each
- Driveline is made of 15 mm 5M HTD timing belts rated 20.000 rpm 10kW
- Batteries will be 4 x 4s LiPo's
- Cooling with 2 x (speed controlled) fans piped directly on to the motors doing max 200 CFM each
- Controls by means OPEN PANZER TCB WHICH I STILL HAVEN'T FOUND

She still needs to go on a bit of a diet as she now weighs in at around 21 kg....ideally go below 20. There are plenty weight saving and optimizations, but is just prototype 1 so to say.

Open for suggestions! See attached pictures of where I'm at right now

[Jarlath]

Ambitious project. I assume that the Riptide was a source of focus for this endeavour?

Be aware of a couple items if using the riptide as a basis.
1. Tracks on the riptide are ultra-light so to minimize the centrifugal forces as they are rotated around the sprocket and idler. More mass = more forces trying to make the track fly off the driveline.
2. The riptide also has a spring loaded idler for when all the road wheels collapse (during a jump, hard banking turn at speed). Otherwise the road wheel suspension collapses and the track slack makes the above issue more pronounced.
3. 13000 RPM motors when @ 14.8V? What looks to be a 18:1 belt drive, 80mm drive sprocket. That = 181.5m/minute or ~3m/s or nearly 11 kph.

A scale speed version of a Panther @ 1/16th is 46 kph/16 = 2.9 kph (and most stock 1/16 rc tanks go a bit faster than that....).

[tankme]

I have used ANSI 2060P chain with K1 attachments like that for my 1/6th scale Sturmtiger set up for paintball combat. I used aluminum rivets to hold the track pads on. You do have to leave the space between the track links like I did or the track will not be able to flex up as things go under the tank. The gap doesn't have to be as large though. I made it larger so that less small debris would get caught in them. Here's pics of my original track design and the new one using the attachment chain. The attachment chain version worked better due to the stiffness and because it only had to interact with one set of sprocket teeth and not two. Being a double pitch chain also helps.

[tankme]

Forgot to mention that putting rubber pads on the tracks has advantages and disadvantages.

Advantages: improved grip climbing
Disadvantages: improved grip turning - will make the motors work harder turning the tank

[Chi-el]

Hi guys,

All good pointers, thanks!

@ Jarlath:
I was indeed a little bit concerned about the track weight and slinging it off the sprockets. I will be adding spring loaded idlers yes.

As for the speed, my calcs show quite a bit more speed, hopefully I didn't miss anything here:
Motors running on 8s = ~30v x 780 kv = 23.400 rpm max.
The gearing is 1:2 ( have some other ratios to play with) => drive shaft max rpm 11.700 = 195 rotations per second
This bring the circumferential speed of the 80 mm drive sprocket to 3,14 x 0,08 x 195 = 48,98 m/s = 176 km/hour
The motors have a torque of 3 Nm -> geared to 1:2 = 6 Nm on the sprocket, with an 80 mm sprocket this gives a track pull of ~75 N each side. So I'll see what that does, can always gear down a bit because the theoretical speed calcs seem way too fast to achieve.

Thanks!

[Jarlath]

Hi guys,

All good pointers, thanks!

@ Jarlath:
I was indeed a little bit concerned about the track weight and slinging it off the sprockets. I will be adding spring loaded idlers yes.

As for the speed, my calcs show quite a bit more speed, hopefully I didn't miss anything here:
Motors running on 8s = ~30v x 780 kv = 23.400 rpm max.
The gearing is 1:2 ( have some other ratios to play with) => drive shaft max rpm 11.700 = 195 rotations per second
This bring the circumferential speed of the 80 mm drive sprocket to 3,14 x 0,08 x 195 = 48,98 m/s = 176 km/hour
The motors have a torque of 3 Nm -> geared to 1:2 = 6 Nm on the sprocket, with an 80 mm sprocket this gives a track pull of ~75 N each side. So I'll see what that does, can always gear down a bit because the theoretical speed calcs seem way too fast to achieve.

Thanks!

Ahh. OK I assumed that you had a single ESC and battery driving each motor which is only a 4cell for each motor... But if you are driving both ESC's off the series connected Lipos then yes, my voltage is off by a factor of 2. And yea, I dunno what happened with my ratios (I can see 15mm vs 33mm radius, I must have fudged a number accidentally in my head).


From my calculations using your Surpass Hobby 56112 Brushless Motor (http://www.surpass-hobby.com/index.php? ... duct_id=92)

Brushless Motor Efficiency Calculations
Voltage (V) : 38V
Current (A) : 195A
Resistance Rm (ohms) : 0.0061 Ohms
No Load Current Io (A) : 2.6A
Voltage Constant Kv (RPM/V) : 780 Kv

Power In (W) : 7410W
Copper Losses (W) : 232W
Iron Losses (W) : 98.8W
Total Losses (W) : 330.8W
Power Out (W) : 7079W
Efficiency (%) : 95.5%
Torque Constant Kt (mNm/A) : 12.243 Kt

So I'd say that your max torque output of the Motors is about 2.3Nm @ 195A inrush current.

Like I said, ambitious project! Looking forwards to it.
Finish a side's driveline and test it Make video!

[Chi-el]

Hi,

Thank you for the detailed torque calcs!

I'm currently in China for work so will not be able to start the building again until mid May, when I get back.
Will keep you posted.

Regards,
Chi-el.

[Chi-el]

Hi All,

It has been quiet for a long time, too quiet. I've in te meantime progressed with the build till the point of having it running.
However, have run in to some unexplainable control issues. I'll post some pictures soon!

Chi-el

[Chi-el]

Ok, a bit faster than planned, see attached some images of the current state. In case you wonder what happened to the ESC and motor cables....one of the cats thought they made nice chewing toys...

So I had some trial runs with it on the test stand and to be honest, it was scary. Super fast, like a chainsaw on nitro or so....looks promising.
Oh yes, the Open Panzer boards. I had some made here in China, sent them the plans, had 6 made and couldn't get on any of them the flashing done. Too bad, but whatever I've tried I couldn't get them to work. So instead I bought a FlySky - I6s and a IA-10B receiver. My dream would still be to use a pistolgrip controller, but that'll have to wait.

Made a small test run on the ground, indoor, way to fast! The motor accelleleration was way too fast and too aggressive to control.
So here the problems started, what seemd as just a minor adjustment on the end points, motor timing and throttle curve adjustments turned in to a nightmare.

After making the adjustments the whole control is messed up.
Issues now:
- response to stick movements only happen in one direction, either forward or reverse
- motor speed control is not visible at all, goes to max power whilst limited both on ESC and in the FS-I6S

Attempts made:
- Full reset of TX and RX, binding again, start from scratch
- Firmware upgrade on the ZTW Beast PRo 2--A ESC's and the ESC programming card
- Re-program TX, as what I remembered of if it (previsous setting I did ages ago.
- perform ESC throttle calibration

Does anybody have a bright idea where this could come from? It used to work just fine, just needed to temper the motors a bit.

Regards,
Chi-el.

[tankme]

Most brushLESS ESCs have built in reverse lockouts and deadbands built in for cars. Both of those things are bad for tanks. If you run it forward and then reverse nothing happens? What happens when you run it forward, then push reverse, release and reverse again? Does it reverse? That would be an example of how a reverse lockout function works. The deadband is at the beginning of the stick travel. When you push it forward just a little, it probably doesn't move at all. I experimented with brushless motors some, but could never get over the limitations in my ESCs and I tried several different kinds. A person better versed in brushless motors suggested I use a drone controller instead of ESCs for cars. I never tried it though.