3d-print e-mountainboard motor issues

[pckinzley]

Hi All,

I just built an electric mountain board but am having some problems in the power or torque or gearing of my rig. I listed out the components/specs below and had thought that I had somewhat over built this system but I cannot seem to any get good inital speed. I am using a sensorless brushless motor with an ESC that came with a sensor cable(but I dont think that matters right?) do certain ESCs required sensored motors?

Basically, as I attempt to throttle up it seems like the motor does not have the power to turn. I can see it struggling to turn, it makes a chuck chuck chuck type sound and it will move forward(at less than a few feet a sec) but it is laboring bad and cannot get up to speed. Even when I try to give it a bit of a push before throttle I cannot seem to avoid this, perhaps if I got to speed this would go away but I am not sure as I cant get there.

I can see that the belt is not skipping and I have tried numerous timing changes(up and down) soft start, and load changes on the ESC with no major change. I also rewired the ESC to directly connect the motor contacts in case there was a connection issue to no avail. I have wired the batteries in series to get 12s with my setup and I do see that people warn against long power wires to the ESC, which I do have. I understand that this could cause premature ESC failure but could this cause my motor struggling issue as well?

Could this be a bad motor? should the motor be able to easily overcome my grip and take my weight for the start? Any input is greatly appreciated!

I attached a couple pics of my first prototype(it is a little more robust now) 3d-print motor mount for your entertainment. Unfortunately, I tore the whole board down today but if we can get the thing moving I will post more as it comes back together.

specs:
-Turnigy Aerodrive SK3 - 6374-149kv Brushless Outrunner
-TURNIGY K-Force 120A-HV OPTO V2 5-12S
-17 tooth pully 5mm HTD
-62 tooth wheel cog 5MM HTD
-80 tooth belt 5MM HTD
-2 x 6s 5.0A 20s lipo
-SBEC Hobbyking YEP 20A HV (for receiver)
-frysky receiver

 

[WeeChumlee]

Hi
Hmm, bit perplexed myself there.
I have no experience with that particular ESC so cannot advise on timing or setup there, maybe somebody can help as it would seem to be a viable ESC.
There will be a bit of cogging at start-up but this should go away as soon as the wheels start turning, just a very slight kick push should alleviate it - especially with that motor and voltage.
That motor at 12S and your gearing should be able to pull trains. I have a board with the 6374 168kv motor, so pretty similar, running on 8S and with the slightest push start there is no cogging at all.
I really hope others can help you out here - without having to resort to purchasing a new ESC. (If you do, go VESC would be my advice)
Good luck man.

 

[nowind]

Hey.

I dont know the ESC but i can point out something else.

Your Gearratio is really bad. 3.65:1 is far away from good for an EMTB.

You geared your board with the 12S Lipo for 43mph or 69kmh

I use the same Motor with a 6:1 Gearing and it pulls like hell.

Go at least down to a 12tooth pulley.

Greetz.
Jenso

 

[pckinzley]

Thanks for these reply's sorry for my slow response. For some reason I thought the forum would email me but it must not be default.

Weechumlee: I did start to worry about my ESC. It does have braking and timing stuff despite being a heli design but I had a bad feeling on it and went out and put an order down for two of the enertion VESCs the day before yesterday.. unfortunately, they wont get here for more than a month! The mountain board I have as foot straps and so it is really hard to get foot speed prior to engagement with out it being really awkward so I was hoping for a smoother start. A second point, when brakes are enabled there is no coast so I cant really use my foot - more reasons for VESC.

Nowind: I thought I read somewhere that a 3:1 was an ok ratio for this type of application, but it is interesting to hear that your 6:1 is giving good results. I did find all of the speed and gearing ratio calculators but I am struggling with assessing the real power of a particular motor. I want to design for 200lb load. How do I know if this is the motor or the load that is the issue, how can I factor in weight in this calculation? I was using SDP/SI for pulleys and gears and the smallest 8mm bore is 17 I looked around and found some 12 tooth 8mm on ebay though so maybe I will try it out. I dont trust my drill press skills on the small pulley...

Also what about teeth in mesh, the smaller pulley would bring me down to 4 from 6. I read 6 was a good amount for teeth in mesh and lower might not be good. Any thoughts here?

thanks all for your responses!

 

[nowind]

Hey.

Yes its a problem if to less teeth in mesh.

I´m using a roller to use this problem.

My reduction from 12:72 is without the roller not workable.



Greetz
Jenso

 

[pckinzley]

Does anyone have any comment on calculating for power of a given motor or system? I want to design for a given total weight 200Lbs. How do you calculate whether a given motor KV/amp/gearing ratio will work?

Nowind: how much stress would you say is on the roller in your case? Is most of the strain in the system still bearing on the big and small pulley? I have concerns about adding this into my 3d print mount.

thanks all!

 

[nowind]

Hard to tell, there will be some stress of course.
Just try it (-;

 

[randyc1]

Hey.

Yes its a problem if to less teeth in mesh.

I´m using a roller to use this problem.

My reduction from 12:72 is without the roller not workable.



Greetz
Jenso

Nice !! Where did you find that roller , how wide?,.. i opted for (3) 4mm wide bearings side by side for a 15mm belt.

 

[nowind]

The roller is from maedler.de
https://www.maedler.de/Article/14087200

It has 30mm diameter, its 35mm long.
I have shorten it about 3mm.

Fits nice with the 25mm width Belt.

Greetz
Jenso

 

[pckinzley]

Finally made some progress on this project but ran into a snag. I ended up going with a similar solution as randycy1 for the roller. However, I notice the bearing are eating the belt a little so may 3d print a covering that will hopefully be smoother. I did end up transitioning to a 12 and 72 (6:1) pulley system + a VESC and was able to get an amazing 10 blocks including some uphill.

2 problems though, one catastrophic, that I hoping those here can help with!

The first is that I am getting some cogging at about mid throttle persistently and then again while on hills. I noticed that I got a few cogs on start up which I might expect but I basically also get a persistent knocking cog after getting up to maybe 5-10mph as well as braking and it seems to be very consistent as speed increases.

The second problem is my set screw. I have now destroyed 2 small pulley's threads for the set screw. My pulley was 6mm bore so I used a lathe to bring it to 8mm bore to match the 149kv turnigy motor Im using. This leaves my pully with about a 1-2mm worth of metal around the motor shaft. I dremel cut a flat spot on the motor shaft and used lock tight etc. Howeve, I think the combo of the cogging(think I need to deisgn for this anyway) and torque basically killed the threads and ejected the set screw. I now feel like drilling a hole through the shaft and using a pin design might be best? What are people's thoughts here? Nowind: your small pulley looks very robust can you share any information about it.

thanks all!

 

[Pylonflyer]

Timing on the esc for that outrunner may not be ideal. You might check for timing settings for that motor. From your first post, I was also going to suggest double checking your motor to esc connections because it sounded like you were missing a phase.