The Grinhill Mk2 RC-motor drive

[BenMoore]

Go Grinhill!
Your original RC motor drive had already inspired me to start procuring parts for a 'Moore Mk I'. I love the ultra-light, inexpensive and innovation of your system designs
Its great to see continuing development here.

I hope to join in with a build thread of my own efforts and collected ideas from all the good Forum folk soon as I think the RC motor route has a lot to offer.
Coming from the virtual silence of my Crystalyte hub motor to fully opening the throttle of my 'cute' new RC motor at 48V on the bench , my main design concern is now noise reduction. I'm looking at reconfiguring the motor's wiring from Delta to Wye to lower its kV and increase torque so that lower motor speeds can be used. Also, with access to a lathe the bell (and axle) could be rebuilt/replaced so as to create a mini hub style motor - the rotor becoming supported on both sides. If its worth the effort, I expect it whould minimise the screeching resonances of the original bell rotor and perhaps achieve better conductive cooling through a thicker and stationary axle as well... anyone game to try?!

BTW, speaking of noise, don't you get sick of the same, bolted-on album on your integrated stereo? :lol:

 

[liveforphysics]

BTW, speaking of noise, don't you get sick of the same, bolted-on album on your integrated stereo? :lol:

LOL!


I also love your work Grinhill. Your designs are very clever in the simplicity of them. I also respect that you have the ability to make rational choices about how much power is enough, and escape the perpetual need to push everything to the point of breaking in the endless quest for more power.

Very clever stuff! I love it all!

Keep up the good work!

Best Wishes,
-Luke

 

[recumpence]

BTW, speaking of noise, don't you get sick of the same, bolted-on album on your integrated stereo? :lol:

LOL!


I also respect that you have the ability to make rational choices about how much power is enough, and escape the perpetual need to push everything to the point of breaking in the endless quest for more power.

Keep up the good work!

Best Wishes,
-Luke

Luke, say it aint so! You cannot give in to this. More power I tell you!

I wholeheartedly agree. I still love my recumbent. That bike rarely pulls huge current. I love seeing how mauch range I can pull from each charge. I am also building two trikes right now. One is crazy powerful, and the other is much more modest. Moderate power is sooooo much easier to build and contend with. I bet my smaller trike will see more use than the crazy one. But, heck, a good blast of adrenalin is needed every once in a while!

Matt

 

[liveforphysics]

BTW, speaking of noise, don't you get sick of the same, bolted-on album on your integrated stereo? :lol:

LOL!


I also respect that you have the ability to make rational choices about how much power is enough, and escape the perpetual need to push everything to the point of breaking in the endless quest for more power.

Keep up the good work!

Best Wishes,
-Luke

Luke, say it aint so! You cannot give in to this. More power I tell you!

I wholeheartedly agree. I still love my recumbent. That bike rarely pulls huge current. I love seeing how mauch range I can pull from each charge. I am also building two trikes right now. One is crazy powerful, and the other is much more modest. Moderate power is sooooo much easier to build and contend with. I bet my smaller trike will see more use than the crazy one. But, heck, a good blast of adrenalin is needed every once in a while!

Matt

Don't get me wrong Matt, I personally MUST always push things as hard as possible, which ensures continously breaking everything. But I do often think about how nice life must be for the folks who don't have that need constantly pushing them.

 

[Grinhill]

I also respect that you have the ability to make rational choices about how much power is enough, and escape the perpetual need to push everything to the point of breaking in the endless quest for more power.

Thanks, Luke!

I have to admit my last ride was using an 8S pack instead of the 6S. It allowed my uphill speed to increase from about 35 km/h to about 38 km/h. The peak power is still around the 1200W mark.

BTW, which controllers are you running on your beast at the moment, Luke? Have you found one that works for you?

 

[Grinhill]

Here's my most recent refinement, a wiring tidy-up. It was prompted by the need to increase battery capacity, so I will be going to two water bottles in parallel.

So if I need to use both bottle cage mounts, the power switch and other bits will need to move. The top tube would be ideal, except for the gear cables being in the way. Maybe a long channel for the wiring to sit in, hanging from the tube. What can I find in the garage...


It's a diffuser off an old fluoro lamp. The size and shape seems ideal for the job. Stuff can sit in it and be kept clear of the moving cables. So I relocated the switch box, and added a bit of paint to match the bike.



Now with everything reinstalled, a few dabs of hot-melt glue to keep it in place, a few cable ties, it looks pretty tidy.

 

[Grinhill]

Here's some data since I've been using the 8S2P battery pack: (I did post something about this a few weeks back but have since found that I wasn't running at full speed!)

New top speed on the flat (unassisted):
55 km/h (35 mph) at 1300W power cunsumption

New top speed up 10% grade (with assist FWIW):
45 km/h (28 mph) at 2000W power consumption

For my return commute (12 km) I use around 6Ah of the 10Ah.

I have had some slight movement of the sliding plate mounting arrangement after hitting potholes. Although only a few mm, this has reduced the belt tension sufficiently to allow some belt jumping at high power. I will have to add a couple more bolts to lock it in place.

 

[grwsaltspring]

I'm following your build with great interest as I'm curious as to how the "simple" build will turn out compared to some of the more exotic ones here.

Cheers Greg

 

[Grinhill]

I locked the plates together with two additional screws, just a couple of the self-drilling sort.

Still had belt slippage at the 2000W mark, it's just some very quick skipping, not continuous.

Maybe I'm just reaching the power limit in this configuration. The long belt and small motor pulley are less than ideal for this type of belt. You can see the belt slapping around a bit at high speed.

 

[grwsaltspring]

Any idea on the direction you will take this next in your ongoing refinement?

Greg

 

[swbluto]

I locked the plates together with two additional screws, just a couple of the self-drilling sort.

Still had belt slippage at the 2000W mark, it's just some very quick skipping, not continuous.

Maybe I'm just reaching the power limit in this configuration. The long belt and small motor pulley are less than ideal for this type of belt. You can see the belt slapping around a bit at high speed.

I had continuous belt slipping at 2 kW from a start and ended up busting the belt. I'm thinking that somewhere around 1.5-2kw is the limit for 5mm 15mm HTD belts in conventional direct drive configurations, but I think that my axle oscillations probably contributed to the slipping. It seems that also matt had belt slipping at 3kW, so it's definitely somewhere in the 1.5kW - 3 kW region. I've heard it's actually a torque limit and a belt can transmit more power than this, but it has to be spinning at a high RPM to ensure that it stays below the torque limit (As power = torque * (RPM, or technically, angular velocity)).

 

[Miles]

Ratcheting point (for a given belt) depends on static tension and torque/teeth engagement on the driver pulley.....

 

[swbluto]

Ratcheting point (for a given belt) depends on static tension and torque/teeth engagement on driver pulley.....

So true, but generalities are sufficient as guidelines as not everyone has the resources readily available to calculate the ratcheting point for their particular belt. And "conventional direct drive" seems to be narrow enough a category to generalize.

(Although, I'm driving an 8 inch wheel and he's driving a 24+" inch wheel. Maybe not.)

 

[Miles]

The point is though, that it's essential to take into account the number of teeth engaged on the driver pulley.....

 

[swbluto]

The point is though, that it's essential to take into account the number of teeth engaged on the driver pulley.....

True, but for conventional direct drives on bikes, the amount of engaged teeth doesn't vary by that much, does it?

I assume that people need to maintain a gear ratio of at least 10 for this configuration and that the "chordal angle"(Just taking a guess here) is usually between 45 and 60 degrees. Since the driving pulley isn't likely to be less than 14, and the wheel pulley isn't likely to be more than 200( Or would it?), it seems that there's probably a variation of upto 2 or 3 out of a mean of 6 engaged teeth.

So, what's the difference between 5 teeth engaged and 8 teeth engaged?

Ok, so it seems it might matter by a little bit. I guess it's a linear relationship and 8 teeth would have 60% more static loading capability than 5 teeth?

 

[swbluto]

Well, I'll go out and say that I was putting in 1.8 kW into the system while probably engaging 5 or 6 teeth. According to my simulator, it appears the motor was probably putting out 10.5 N.M. when it continuously slipped and broke. It seemed like it didn't continuously slip when it was 4 N.M. and less.

(By the way, before people go "Oh, that's a sucky torque", consider this: It has a gear ratio of 4, that's 42 N.M. at the wheel. Also, the wheel is 8" which about three times less that of a 24" wheel, so the torque that would correspond to a similar force on a 24" inch wheel is about 126 N.M. According to ebikes.ca's simulator, that kicks butt, but it seems the 530x are similarly powerful in the 40-50 volts region at 100 amps. My scooter is consuming 60 amps at 33 volts.)

 

[grwsaltspring]

Are the number of teeth on the drive pulley and ones ability to successfully mate this pulley to the RC motor of choice the limiting factors with a build like this one (IE Grinhills build)? Particularly if we are trying to use off the shelf components for the most part.

 

[Grinhill]

A little more info to add to the debate.

My belt is the 9mm wide one, limited by the large pulley, which has about 12mm between flanges. My estimate of the tooth count on the large pulley is 266 (422mm diameter, 1330mm circumference divided by 5).

An unusual feature of the large pulley is that the teeth aren't full profile, they are fairly shallow ridges at 5mm intervals. Then, the pulley is divided into quadrants around the circumference, and only two of the four quadrants have the ridges, the other two are smooth. Apparently the friction from having such a large contact area reduces the need for having all teeth.

I'm not able to determine whether the slipping is occurring on the small pulley or the large one.

 

[Miles]

Grinhill,

It will almost always slip on the small pulley. What size is yours?

The sections with the missing teeth are probably there because of the need to separate the four mould sections radially in order to be able to mould the double flange.

 

[Grinhill]

20 teeth. (ratio = 13.3).

 

[Miles]

A 20t pulley should be able to handle at least 5Nm torque (around 4kW at 8000 rpm) with a 9mm wide high-torque belt. How are you setting the tension?

The problem is usually the high torque levels you can get when accelerating at low speeds ......

 

[Grinhill]

A 20t pulley should be able to handle at least 5Nm torque (around 4kW at 8000 rpm) with a 9mm wide high-torque belt. How are you setting the tension?

I have the M6 screws slackened a little, push the motor assembly upward with one hand then drill some smaller holes for the locking pins using the other hand. The belt had about 10mm movement with light finger pressure (in the centre of the chord). I repeated this process yesterday and managed to get some more tension, now only about 5mm deflection.

The problem is usually the high torque levels you can get when accelerating at low speeds ......

I don't use WOT from low speeds, I always ease the throttle up gently.

I still had a few slips this morning on the steepest hill section, but this time I noticed it coincided with bumps in the road. I think the whole drive unit is flexing ever so slightly, which is releasing the tension enough to let a few teeth slip. Another factor is this was towards the end of the ride, so the belt would be warmer. Does this make a difference?

This morning was a good test - a headwind of around 40 km/h.

I was burning 2400W to maintain 50 km/h on a level road! (note no slipping during this section).

 

[heathyoung]

Yep it was crazy windy this morning! Seen your bike a couple of times around Cardiff, I'm usually in the car otherwise I would say hello.

 

[E-Ride]

...
This morning was a good test - a headwind of around 40 km/h.

I was burning 2400W to maintain 50 km/h on a level road! (note no slipping during this section).

So how much amps? (2400/22.2 ~ 108?)

 

[Grinhill]

So how much amps? (2400/22.2 ~ 108?)

I have the Cycle Analyst set to Watts, and I wouldn't take a hand off the bars to press the button at that speed. :wink:

This is while running on 8S (29.6V), so say 80 A.

I checked the peak amps recorded on the CA, it was 116A. Probably during acceleration.


Heath, you are welcome to PM me if you would like to take a closer look some time.