Genex's Build - Why so slow?

I’m going to post my boar specs here and ask for help.

I just got my board built, and it is massively slow. Lets start with specs.

SK3 5065 236kv motor

120A x-car beast series esc

14t motor pulley, 40t wheel pulley, 70mm wheels. pulley’s, belt, ect are all 5mm

2x 5000mah zippy 3s lipo batteries (series for 6s2p, 24v)

some cheap $20 quanum 3ch rx/tx

I managed a max speed around 6-8 mph max. I ran it for probably 3/4 mile full throttle at that speed to see if it heated up, and it was barely warm. Am I missing something? My end points on my controller seem fine, 24v should theoretically with 70% efficiency give me a bit over 10mph. I am shooting for 20mph, as you would expect. I’m not sure how I am supposed to achieve this. My motor seems to have plenty of torque, so should I be looking at something like a 15 to 36 tooth gear ratio? (fact is, it occasionally jumped the belt at something like half throttle, shame on me for having a loose belt :P) 3-5k rpm seems low for an e-longboard but at the same time the motor itself is max rated for 10s. I would prefer at all costs to stay at 6s since I have 2 sets of batteries and an esc that is rated for 6s.


Here is the list of stuff in the same order I listed them above.

Also, that theoretical top speed is from a calculator (can’t post more than 2 links :wink:)

alright, heres my stuff. Only the two most important right now since I can only post two links.

Please dont buy the quanum receiver and make the same mistake as me. You will probably regret it! Some guys say that this receiver is good but i really dislike it.

I had many problems to connect it to the esc… it is not durable too…

I would recommend the (FlySky, Hobbyking or what else vendor…) GT2B or GT2E (newer version). It is much more reliable!

It seems a bit slow but that is your decision! I would use at least 9mm width for the belt etc…

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it also seems like the belts are going to hit the dirt. I wouldn’t use a 40T pulley on anything smaller than a 90mm wheel.

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Yea, im using 9mm belt. The 5mm is the pitch. I purchased from 83mm flywheels and am going to use those instead. I also am 3d printing a 36T insert for the flywheels so I can get my wheel pulley perfectly centered. Since I last posted I came upon a few things. I’m pretty sure the problem is from two root causes. One being a highly imbalanced wheel. The bolts I put in are WAY off center and I can tell it is off balance. I think that is slowing down my top end enough to give me the results im seeing. Also, my pulley is slightly off center, moving about 2-3mm up and down at it rotates when viewed from the parallel. I think those two things are causing the low top end. The off center bolts are probably the main cause, since at the higher rpms that get us to 15-20mph there is much less torque to work with, and even the smallest problem like that can slow us down. Not 100%, mabye 95% sure, but we will find out.

see above^ :stuck_out_tongue:

14:40 ratio is too short in my opinion. try going for a 30T wheel pulley. thats one reason you are slow, but what about the settings on your ESC? have you set up the low/high voltage shut down correctly? if you go over/under the thresholds set in the ESC it will just cruise along very slowly.

I agree on the ratio, Im going to shoot for a 14/15 - 36 to start with and then go from there. I haven’t messed with my esc at all, and the stock values it comes with are pretty good for what I can tell. Here they are.

Cutoff voltage at 3.0v/cell (there is no high voltage shut-down) Motor timing at normal (on a scale of very low, low, normal, high, very high) I would make this very high but I don’t have a programmer. Initial accel at high throttle percent reverse at 60% (have this disabled on the controller) 0% throttle limit 50% braking 0% drag brake (would also change this to 12 or 15%) Normal motor rotation 4% neutral range (doesn’t really apply to anything) 6v BEC output.

None of these really ring a bell.

Try changing to 3% neutral range

could just be gearing then…

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I think the wheel pulley being off center in combination with the less than perfectly weighted wheel are causing me problems. I get my 83mm flywheels tommorow and I will throw those on with a new pulley that is centered to see if that is the root.

Fix your alignment/balance issues first, for sure. And a 16/36 gearing with 97mm wheels should theoretically get you right up around the 20mph mark.

Our of curiosity, how did you check your esc settings without a programming card? Cause I’d definitely get one of those. I thought I’d only use the card once to initially program it, but I actually find it to be a great tool that I use somewhat often to tweak settings, especially when changing setups.

The esc comes with a manual that lists its default settings along with all of the other available settings. I would buy a programmer but the x-car beast has a specific plug and the programmers are out of sale constantly. I haven’t seen one for sale anywhere.

Update #1

Changed out the wheel pulley for a 36T which fits into a 83mm flywheel.

This definitely made it faster. The centered pulley and slightly higher gear ratio has brought me up to a much better 9-11 mph range. I even got around 13-14 down a very slight hill. I am convinced from here on now that my issues reside around my gear ratio. I am 150 pounds, so weight isn’t really an issue. Even at full power for a good 10 minutes the motor is probably at around 100F max. Heat isn’t a problem. I plan to switching out my 14T motor pulley for 18T or 20T and keeping my 36T wheel pulley, or possibly changing to a 32T pulley. If anyone has suggestions please let me know. Gear ratio’s are my weakness here, since I have no idea what people use. I feel like my motor simply does not have the rpm’s to manage high speed at lower gear ratio’s, so I will have to suffice with losing efficiency to gain speed and go for a lower rpm with more torque using a higher ratio.

The calculator hasn’t been accurate yet; it has been about 3-4 mph under. As is, with my stats, it says I should be getting a 13.8mph speed with 70% efficiency. (70% is the suggested efficiency) but I am only around 9-11 max.

So, basically, what do you guys think of these ratio’s? Also, what do you think I should be changing if it isn’t ratio’s? Motor on left, wheel on right.

14T to 32T

16T to 32T

20T to 32T

16T to 36T

20T to 36T

Btw, you were right about the ratio being too short. I listed some ratio’s; take a look at them and see what you think. I am willing to buy a new aluminum motor pulley, but am using 3D printed wheel pulley’s, so my options are limited to 40T,36T and 32T.

Obligatory pics coming soon once I get the right ratio and don’t have duct tape holding the batteries to the board :smiley:

How fast do you want to go? Personaly id probably go 14:32 from that selection However you might want to go faster than me… The calculator is a rough guide. Its reasonably accurate but doesnt account for real world situations. Wind, hills etc.

I probably wouldnt go too tall on the ratios id keep it above 2:1 for the sake of your esc.

Its a trial and error game, find the speed you like and the electronics that can support it.

Update #2

I’ve changed the motor pulley to a 20T, and the wheel pulley to a 30T. This gives me a 2:3 ratio, meaning 3 motor rotations to 2 wheel rotations.

This yields me about 14-16 mph. I am very happy with that right now. That speed is as fast as I would like to go, but I have encountered another problem. I would like more torque. Which requires me to lower the ratio, and lose speed. I am keeping the 20T motor pulley as it gives me enough teeth in mesh to never worry about belt skipping. I am planning on moving to a 40T wheel pulley just to see what happens.

I am confused, because I am seeing people with 5065 SK3’s at 245 kv (ever so slightly higher kv over mine) having no problems getting my speed and higher on a much lower ratio. 15-36 seems common, which is WAY lower than what I am running to get that.

I would like to get more torque out of the setup. Anyone have any idea’s what could be causing me to have to use such a high ratio to achieve this speed?

i made a video about this topic, check it out:

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Yea, I had watched that when I was beginning my build. I went with a 236kv SK3 as I was running 6s (24V).

The problem I am having is that other people with nearly identical specs are achieving the speeds I am seeing with a lower ratio than I use to get the same speed.

As a good example:

This guy is running a 245kv 6364 and 6s and achieved a 41 kph top speed (25mph)

I cannot even achieve 20 (im getting 14-16) with a higher ratio that he is using. He is using 15-36 and I am using 20-30. My motor is a 5065 SK3 236kv.

He seems to be having torque issues as well, but the fact remains than he is achieving a higher speed with a lower ratio. While I have not have the chance to try a lower ratio since I started using a 20T motor pulley, I can’t imagine it is going to magically produce me enough torque to get me over my current speed.

My only hints as to why I am not achieving those speeds is one of two things. One, the roads I ride on are pure crap, fairly rough. There isn’t potholes and land mines by any means, but it isn’t glorious fresh paved road either. The second being that the ratio is so high that I am losing so much torque that I cannot get to the higher speeds. Doesn’t make any sense to me but who knows. Also, is having a 5065 motor going to limit my top speed that much compared to a 6364?

Any suggestions would be great. Thanks in advanced.

Edit: Sorry read more of the post, my bad

Another thing that might be the issue are your batteries, if you have a voltage meter it wouldn’t be a bad idea to check and see if you’re actually getting the correct voltage out of your batteries. If it’s not that, then it either has to be a fault in your ESC or wonky settings

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