Shredding E-MTB in bike parks

Mobutusan · August 17, 2020, 8:15pm

@rich As always, I’m loving your videos and insight. That bike park looks amazing and looks like so much fun! I really wish there was something like that around my part of the world. It’s crazy how much vibration you’re dealing with even on 9" tires. Was not expecting that.

One thing I was wondering is if you think spring trucks would help on those trails, since the springs try to return to center, or if you think they would be detrimental? Also, how do you think a board would ride with a Matrix 2 non-spring type truck on one end and a Matrix 1 spring truck on the other end? I just picked up a Comp 95x with Matrix 1 trucks, but only have motor mounts for my Matrix 2 trucks, so I was thinking of using a Matrix 2 in the rear, and Matrix 1 in the front (or vice versa=FWD), but I’m not sure how one spring truck would influence the maneuverability/stability, and whether it would be better on the front or rear (or neither?).

Keep up the awesome “work” and watch out for those trees.

rich · August 17, 2020, 11:27pm

Thanks bro, I was afraid the video is boring because I ride quite slow

Meanwhile I realized that Austria has the longest flow trails in europe and possibly in the world. Both trails are about 3-4 hours away. The longest flow trail is almost 16 km (10 miles) and the other one 11.5 km (7.1 miles), so sick! Just as reference the flow trail (Wexl trails) which I’m riding in the video is “only” 4.5km (2.8 miles).

The tires are part of the problem, the MBS T2 tires are quite hard and made of nylon.

The same DWII deck with 8" T1 tires feels much better. T1 tires are super soft and made of rubber, they smallow a lot of vibrations. I wish 9" T2 tires would be the same rubber compound.

No because often you need to turn more than is possible with springs in tight curves (or berms). You can compress elastomere further than springs, therefore you can achieve tighter curves. I would hurt myself with springs on this trails

Regarding your truck dilemma IMO there is only one solution, you need to buy a second Matrix II truck, better than springs . I like the trucks (if the motor mounts don’t shift) and they are versatile. They can be super carvy or super stiff.

BTW the Matrix II trucks on my jump board are super stiff (heavy compressed red shock blocks). I can’t turn proper but I need the stability for jumping. I would like to ride the “jump line” in the bike park that would be so great but then I can’t ride the flow trail which would be necessary to get there and down the hill. Maybe I should try it with orange shock blocks.

All the people already stared at me with 1 board, it can be worse with 2

SimosMCmuffin · August 18, 2020, 1:20pm

What are your motor kVs, gear ratio, wheel size and pack voltage?

EDIT: + Are your motors how hot?

rich · August 18, 2020, 2:06pm

about 220kv (officially 200kv), 1:6.25, 9" wheels, 12s6p (each motor @ 80A and 50A battery)

The main problem is riding (uphill) in summer at 30°C (86°F). Normally the Vesc 6 are about 60°C (140°F) when the motors reach 80°C (176°F) . When riding slowly uphill it seems the opposite.

At 30°C (86°F) on flat I can ride maybe 5-7 km (3-4 miles) before the motors need a break, uphill it’s 2.5 km (1.5 miles) before the Vesc6 's need a break.

Unfortunately the APS V2 motors have broken or wrong temp sensors so actally I measure it by hand. I might cook them one day.

From my experience there is always a temp border depending on the setup. For example at max. 24°C (75°F) I can ride like a maniac and drain the full battery at once. Just 2-3°C (35-37°F) more and I get heat problems.

SimosMCmuffin · August 18, 2020, 5:11pm

What’s the max speed that you like/need to have versus what your setup can do?

The VESCs hitting their temp limits could be remedied with lower kV motors, so the VESCs can operate at lower motor currents for a given torque (reduces losses in VESC), although if you’re already starting to also cook your motors, then that will worsen. Then if you have the possibility of increasing gearing ratio (although possibly not possible with gear drive) and you can do with lower top speed, your could increase your gearing ratio to get more wheel torque at lower motor amps, so the motors generate less losses.

Copper has a resistance temp coefficient of roughly 0.4%/Celsius, so for example if a cool motor at 30C has a total of 200 Watts of copper losses at a given current, then if it has warmed up say to 80C, then you have 20% more loss in the copper, in the area of 240 Watts at the same current. So it has a positive feedback loop. Then the VESC’s fets will also have warmed up and now they are also having more losses conducting. Then you will also get less cooling due to the ambient air being hotter.

rich · August 18, 2020, 6:32pm

Thanks a lot for your explanations.

I also had temp problems (thermal throttling) with SK8 149kv or closed Maytech 150kv motors with 1:5 gearing on 8", same with closed Maytech 220kv with 1:6.25 gearing on 220mm wheels (9").

Just thermal throttling of the Vesc6 is new to me. But if the Vesc 6 would stay cool then the motors would overheat anyway and I need to take a 10 min. break. . The actual 6384 motors have more copper than any other motor I’ve had before so maybe they just draw more amps.

Someone suggested to replace the heat pads of the vescs, they are about 2 years old but I don’t know if this would help.

I need 50km/h top speed, the top speed of the actual setup is 52km/h (only with full battery, later it’s about 46 km/h).

SimosMCmuffin · August 18, 2020, 7:00pm

More copper in the windings should reduce any resistive losses. Higher running RPMs do result in higher core hysteresis losses as the ferrous stator material has to flip it’s magnetic field more often with higher RPMs + there are the eddy current losses induced by the changing magnetic fields, which are also RPM dependent.

You run your system hard and there is only so much what the components can soak up before overheating and being that they are generally smaller in the esk8 application, just means that dissipating that heat is harder (less surface area) and there is less mass to soak up with (aka heats up faster). I don’t see really anything else than getting a rotor fan to move air through the motor to increase convective cooling, but that can be tricky with closed motors. VESCs would have less heating with lower kV motors.

Motor related losses are talked about in great detail in this video by Justin Lemire-Elmore, although in e-bike context, but applicable in many ways to to our use cases as well.

Kornum · August 20, 2020, 4:56pm

What i have found to work best is the mbs Dylan Warren pro deck…
Other things that imo is key to mountain bike trail success is:
PPM! Uart is fine for most, but you loose the ability to define your ramp time.
On my unity I run 0,02~0,01 it gives you the needed aggression to start up on the uphill parts after braking, AND ESPECIALLY THE ABILITY TO START UP WITHOUT WHEELSPIN WHEN NEEDED

Back truck looser than front truck… it’s the trick to get thru hairpin turns (there are limits to what it makes you Abel to do, but you will clear more than before)

Loose back truck also works like traction control on the rough surface… it will keep you from lifting a drive wheel on hard turns…

Mbs matrix II trucks… they are far less bouncy than trampa… witch on off-road translates to more control and better traction

LOW TYRE PRESURE I run 1,5bar (I’m 94kg) it will give you a more settled board. And better grip… and will stop your wheels bouncing on high speed on rough terrain like roots…

LOW KV and big motors 170kv and 6396 motors work for me… 150kv would be even better, you get all start up momentum you will need fare mor than top speed! (My gearing is 15t 72T) 6384 motors will also be fine, I would not go smaller…

F5 bindings ESPECIALLY THE HEEL STRAP! It allows you to be relaxed, loose And low to better absorbing bumps and follow the terrain!

Helmet back protection knee pads and elbow is a given! MAKE SURE YOU CAN RIDE AGAIN TOMORROW!! The most important thing!!

Venom121212 · August 20, 2020, 6:18pm

I’ve never agreed with a statement more. I’ve been loosening my rear trucks more and more recently when offroading and have been curious about a looser rear than front setup.

How does it fare on road?

rich · August 20, 2020, 7:37pm

Interesting, that’s the first time I hear this. It sounds weird but I could give it a try.

The rear truck carries all the weight of the drivetrains and motors and starts to wobble on hard acceleration or higher speed and feels way to soft for me right now. Compressing the dampers 2mm helped a bit but not much.

The problem with the stiff deck is that often the rear gets lifted or twisted when riding over roots or bigger stones which is awful and I had several falls because of this. With the Trampa deck this never happened.

Yeah just came back from dirt park with cranked down red shock blocks. It is super stable off-road and I feel very safe. Unfortunately I can’t steer well which I would need for trails. With orange shock blocks I don’t feel safe when jumping, too soft.

I would consider Matrix II trucks but the motor mounts shift which is annoying. Furthermore the black ones are always out of stock in EU

seaborder · August 20, 2020, 7:51pm

@rich we need to make a ride with the emtbs there onetime

bavaria where Iam from isnt that far

rich · August 20, 2020, 8:19pm

Yesterday I’ve visited another trail park but it was a bit disappointing.

I rode the uphill flow trail but it was quite difficult to ride with narrow tight curves and it was pretty steep. Several times I lost balance and fell.

It was only 25°C outside but the Vesc6 did overheat within minutes. I had to take many breaks.

I recorded some short logs to see what’s going on. Well after a break it took 2:42 minutes from 65°C to 80°C

Here the currents

After a long brake I rode 3:15 minutes and the temp climbed from 52°C to 67°C.

Even when the temp was at 60-70°C the power felt very limited, strange.

Then I reached the top and could choose between blue, red or black line.

I chose the flow line and looked forward to ride it but it was disgusting I mean it was steep and veeeeery rough, many roots and stones but the worst was the trail itself. Everywhere massive crossways grooves hard as a rock which made it very difficult to brake or even ride, awful. I had several falls, sometimes it was too steep for my brakes and I flew off the track in the middle of a berm. Jesus what a dangerous ride.

Then I climbed the hill again including breaks and then I recognized the drag, the T2 tires deformed again and got shaved.

I don’t know why but this happens only with the “new” swapped tires. Last week a part of the side wall deformed and scratched on the bolt of the housing. After de- and inflating it worked again but now the full side wall moved outward. The other side is the same just not that bad.

The rubber shaved the stainless steel bolts as well, sick!

At the end of the day a motor mount came loose which also never happened before.

I wanted to drive to Wexl trails today but that didn’t work, both boards under construction.

It is weird how damaged the hanger looks.

Meanwhile I put everything together and have to wait for the thread locker to cure… boring. 3 days left then I’m back at work and can ride less.

Sounds like a plan, I’m ready

JoeyZ5 · August 20, 2020, 9:07pm

The settings for UART aren’t under the UART tab, they are under a tab that I think is called VESC Remote or something.

rich · August 23, 2020, 5:41pm

I switched to 9" Primo Strikers, never had them before but they look tiny in comparison.

Big advantage is the large gap between tire and mount, no more tire shaving…

compared to T2 tire

I tested them yesterday and visited Wexl trails a second time.

They worked well when riding on hard packed dirt, grass or gravel. I guess in muddy conditions they are not the best.

The first time I rode the uphill flow trail and then the flow trail downhill. I was faster than many bikers and had to brake a lot until they could clear the trail. The carvy trucks are really hard to handle, several times the rear truck buckled to one side which lead to falls or almost crashes. I hope I can get used to it.

Then I took the bus shuttle the second time. After very long waiting I was trapped with many people with masks in the sizzling hot bus in full armor. Then on the second ride the board stopped working and I couldn’t brake. Then it worked again but happend twice again. It’s not a good feeling losing the brakes on a trail where you need brakes to survive. The loop key was 100% inserted so I started to investigate further. Every connection/cable looked good so I inserted the loop key again and heard humming / popping noises like a short, that was scary. So I had to walk down half of the way and was sweating like a pig.

Today I checked the loop key and could lift the wire, the connector is burnt

I guess that happened when the XT90S got loose last week where the board also shut off several times. I’m thinking about going back to anti-spark switch where I feel safer because vibrations are no problem at all…

taz · August 23, 2020, 5:56pm

I doubt that was the cause. I would stick with the loop key if I were you and find a way to keep it in place if this is a problem

rich · August 23, 2020, 6:48pm

Any other ideas? Would be interesting.
I just read several times that XT90S get very hot and can melt if they are not 100% plugged in Mine was 10% plugged in when I recognized it and before I rode with a loose loop key for some time.

TBH I don’t like loop keys, for me it is annoying. I just made the loop key because a cable of the AS switch broke and it’s a tiny 5pin connector with 1 mm pitch, need to research where to buy. I have 3 boards and all of them have anti spark switches. I run 10s and 12s on standard AS switches and the MTB 12s on direct FET AS switch (before the wire broke). The switches are from 2016, 2017 and 2018 and never failed. I know many switches failed but not mine. The only problem with the cable break was that I had to wiggle the wires to switch it off. But that was not dangerous. I also switched to a loop key because I thought it’s much safer. Meanwhile I lost several times control of the board when going downhill due to a problem with the loop key.

AFAIK a broken AS switch just gets stuck in ON position which is better than losing control.

Pickled_Monkey · August 23, 2020, 8:10pm

the blackening is from the connection sparking, most likely it was a dry solder joint and the vibrations just made it finally fail.

taz · August 23, 2020, 8:16pm

Although that is true, in order for the solder to melt, you would have to reach temperatures that would probably melt the plastic part first.
Like @Pickled_Monkey said, it could have been a cold solder joint.

JRJoe · August 23, 2020, 8:38pm

I had a loop key for a long time and after it was connected halfways only like in your case once it started to smoke and some days after it came of.

Mainflow · August 23, 2020, 8:44pm

One time I broke my as switch wire during a ride. (on/off) (Battery was the traitor…)
Shuts off immediately. But since the rework, no issues so far.