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-   -   Best HH motor for my custom project. (http://www.rccrawler.com/forum/electronics/608856-best-hh-motor-my-custom-project.html)

SnoopyBG 05-21-2019 03:49 AM

Best HH motor for my custom project.
 
Hello people, totally new here. I hope you'll be able to help me with my VERY specific issue. I'll try to describe it as well as I can.

- It's a custom project that is not a crawler, BUT what I need is the smoothest and finest low speed control. I need to have the rig start from a dead stop with no jerking and virtually like a real car-smooth and confident.

- Right now I have a 45T 3-slot (10 000rpm 7.2V) chineseum motor that is not terrible at low speed (better than the 27T I had before).

- The problem is I need about 20 000rpm max speed because of the 20:1 ratio I have between the motor and wheels. I am running it at 2S, but I can go 3S easily. I can also fit a 550 motor.

-Max speed is secondary to low speed control.

- It has to be brushed, I have a quiet 60A (80 peak) ESC.

- I've focused on the HH motors and would like some guidance on which one is the best for my application.

And here are my questions

1. It seems the cralwmaster pro 540 is a popular choice. Would a 13T crawlmaster have a smoother start than a 45T cheap motor?
Would going for a 13T increase the initial jerk and reduce low speed control compared to a 20T?

2. What about the puller series? Is the skewed 5 slot armature superior for a smooth start? Does it have disadvantages to the straight armature?

3. Would the increased torque of the 550 crawlmaster result in a smoother start compared to a 540?

4. What about the custom PRO 540. Is it worth it to go there for a smooth start and 20 000rpm?

5. Which motor will have the absolute smoothest start disregarding the max speed requirement? The 27T 540 PRO? The 20T crawlmaster? The 16T Puller 500? The 45T torquemaster PRO?


As you can see I am a bit lost with all the options. All in all is there a way to have the smoothest low speed while ALSO reaching 20 000rpm?

Voodoobrew 05-21-2019 03:07 PM

Re: Best HH motor for my custom project.
 
My simple suggestion for best low end speed is get a fast brushed motor, use a 3 cell lipo, gear it down until you are ok with the top end speed.

550 motors have bigger magnets that increase minimum rpm but add torque
Puller motors use stronger magnets but they are thinner which may end up about the same as standard wet magnets, plus a skewed armature. that reduces torque and minimum rpm. I'm not sure how these compair other than they are lighter.
The crawlmaster 540 13t on 3s and more reduction would be my suggestion.

SnoopyBG 05-22-2019 01:41 AM

Re: Best HH motor for my custom project.
 
Quote:

Originally Posted by Voodoobrew (Post 5936577)
nd minimum rpm. I'm not sure how these compair other than they are lighter.
The crawlmaster 540 13t on 3s and more reduction would be my suggestion.

Thanks for the tips.

I can't add anymore reduction. Do you know if a 20T crawlmaster will have a lower minimum speed and smoother start than a 13T or 16T? I reckon with voltage I'll get close to the speed I need.

Voodoobrew 05-22-2019 08:16 AM

Re: Best HH motor for my custom project.
 
The higher turn motors produce more torque per volt. The torque helps them to overpower the magnets and achieve a lower initial startup speed I believe. But at the same time they have less amp draw which causes them to bog down and stall under load easier. So as long as there is very little resistance aganst the motor, yes. These effects may be too subtle to notice. Some of the 45t motors can probably handle 4s too, if your esc can handle it. If you don't mind burning up your current motor to find out.

Another option is getting a revolver motor and a sidewinder 4 esc, it's not that expensive considering you asked about puller motors. Revolver motors are really smooth and produce a lot of torque.

Is this for a vehicle? Are you using planetary reduction? 20:1 reduction is not very much reduction (as far as crawlers go generally 40:1) and I run 100:1 reduction for buttery smooth low end crawling. Perhaps if you shared more we could figure out a better solution, because motor differences are more subtle then mechanical reduction if you want low speeds.

Also see if there is a way to add some sort of a throttle curve to your setup, so you have finer low end throttle control at the throttle trigger.

SnoopyBG 05-22-2019 01:34 PM

Re: Best HH motor for my custom project.
 
It's a custom vehicle based on a drifter chassis. I'm 3d printing a station wagon shell and the point of the whole thing is to make it behave true to life in scale. Meaning the top speed should be comparable to 1:10 of the top speed of the real counter-part.
The real trick is I've made a custom active suspension controlled by an arduino, an accelerometer and 4 servos which makes the chassis wobble, lean and rock like a real 70s land yacht. Therefore any sudden jolt like from a choppy start makes it spazz out unrealistically.

The gearing stock was a pinion and spur gears and then a rear differential (also a front but that was removed quickly). Right now I have a belt connecting 2 custom pulleys with a 8:1 ratio and the the stock diff with a 2.6:1 ratio. The reason was to make it quieter-gears really make a rattle.

It's not impossible to have a different type of gearing installed but it'll be hard given the chassis type and how much into the project I am already.

So with my 7cm custom wheels and 20ish :1 gearing I'll get about 13km/h at 20k rpm, which isn't the best but okay for 130km/h at 1:10 scale (the actual scale is more like 8.5:1).

The throttle signal gets processed by the arduino and yes I've made it exponential for better low speed control. Then it gets fed into a 60A brushed motor driver that runs at 20khz to eliminate the coil whine (or at least make it inaudible to humans).

I also have an audio module that simulates the engine tone, hence the need for quiet mechanics.

So, right now I think 5 slot motors are the best for low speed and I gotta pick the right turn count. There won't be much resistance to the motor, in fact the response curve is VERY slow so it doesn't jump off the start but pick up speed like and old wagon. It will be driven on smooth surfaces and the wheels are even designed with only a narrow strip touching the road for reduced grip.

Voodoobrew 05-22-2019 03:20 PM

Re: Best HH motor for my custom project.
 
Firmer tires will also reduce grip if you don't like the visible line on the tire.
Are you aware of the holmes hobbies motor recommendation page it lists the apromaxate speeds of each of his motors (shown below).
masicaly multiply the KV by the battery voltage for the max motor RPM, you know how to calculate the rest, so for 20,000rpm at the motor

3s or 12.6v you would want a 1587kv motor (CrawlMaster Magnum 540 16t, CrawlMaster 550 12t, CrawlMaster 540 16t or CrawlMaster Magnum 540 13t)

2s or 8.4v you would want a 2380kv motor (CrawlMaster 540 13t, CrawlMaster 550 10t)

you can approximate others based on the chart

SnoopyBG 05-22-2019 04:30 PM

Re: Best HH motor for my custom project.
 
Yes, I was looking at it, but I'm not sure how much low speed fidelity I'd be sacrificing by getting a 16T compared to 13T for example.

P.S. The tires, are also firm, yes. Still have a lot more grip than I'd like though.

Voodoobrew 05-22-2019 05:28 PM

Re: Best HH motor for my custom project.
 
I forgot to mention I think holmes hobbies is currently making a YouTube video comparing between these 2 motor setups, it is high turn high voltage vs low turn low voltage. Might be worth waiting for.

Are you using 3d printed pully/gears, that could easily be reduced if you can add a double pully in the center no? Double the 8x reduction, or something less drastic with bigger pinion pulleys.

Voodoobrew 05-22-2019 05:29 PM

Re: Best HH motor for my custom project.
 
Also if you get a trx4 rear axle it has like 8:1 reduction.

HumboldtEF 05-22-2019 05:43 PM

Re: Best HH motor for my custom project.
 
Quote:

Originally Posted by SnoopyBG (Post 5936902)
Yes, I was looking at it, but I'm not sure how much low speed fidelity I'd be sacrificing by getting a 16T compared to 13T for example.

P.S. The tires, are also firm, yes. Still have a lot more grip than I'd like though.

I can say the difference in low speed startup between a 11T, 13T and 20T (motors that I have) are hard to discern. They are all good and so close to each other its likely gonna be difficult to feel the difference.

Setting up some exponential on the throttle is helpful but I think a throttle curve can do more as it can be fine tuned and shaped exactly to your liking, not sure if thats possible with your electronics or not.

Voodoobrew 05-22-2019 06:57 PM

Re: Best HH motor for my custom project.
 
What if you set the lean to work off a % of throttle change with a fade of a few seconds. Instead of an actual accelerometer. It won't be as realistic but it will limit that shake in the beginning

SnoopyBG 05-23-2019 01:12 AM

Re: Best HH motor for my custom project.
 
Quote:

Originally Posted by Voodoobrew (Post 5936944)
What if you set the lean to work off a % of throttle change with a fade of a few seconds. Instead of an actual accelerometer. It won't be as realistic but it will limit that shake in the beginning


That'd be kinda hard to implement and I'd rather do it the right way and smoothen the start.

SnoopyBG 05-23-2019 01:13 AM

Re: Best HH motor for my custom project.
 
Quote:

Originally Posted by HumboldtEF (Post 5936926)
I can say the difference in low speed startup between a 11T, 13T and 20T (motors that I have) are hard to discern. They are all good and so close to each other its likely gonna be difficult to feel the difference.

Setting up some exponential on the throttle is helpful but I think a throttle curve can do more as it can be fine tuned and shaped exactly to your liking, not sure if thats possible with your electronics or not.

Thanks, thats really helpful.

JohnRobHolmes 05-25-2019 07:43 AM

Re: Best HH motor for my custom project.
 
If smoothness is the big concern, I would build a custom pro 540 with a 16t skewed 5 slot arm ran on 3s. . Startup at 0.2v, which is the smoothest build I can offer without going too costly custom.

SnoopyBG 05-27-2019 08:17 AM

Re: Best HH motor for my custom project.
 
Quote:

Originally Posted by JohnRobHolmes (Post 5937731)
If smoothness is the big concern, I would build a custom pro 540 with a 16t skewed 5 slot arm ran on 3s. . Startup at 0.2v, which is the smoothest build I can offer without going too costly custom.

Well damn, I already ordered a Crawlmaster 16T (not from the HH site, because of shipping). I didn't even know there was a skewed 5 slot arm. How much would that've cost me?

JohnRobHolmes 05-29-2019 05:00 AM

Re: Best HH motor for my custom project.
 
Custom pro motors are generally $90ish depending on features.

SnoopyBG 05-29-2019 08:15 AM

Re: Best HH motor for my custom project.
 
Quote:

Originally Posted by JohnRobHolmes (Post 5938455)
Custom pro motors are generally $90ish depending on features.

Well, I'm getting the regular 16T soon, so I'll see how that works.
Is there a drawback to using a skewed 5 slot arm?

JohnRobHolmes 05-29-2019 12:31 PM

Re: Best HH motor for my custom project.
 
slightly lower torque density, but the added smoothness is generally worth it for why I design motors.

SnoopyBG 06-09-2019 12:02 AM

Re: Best HH motor for my custom project.
 
What's the voltage or power limit on a 16T crawlmaster? I can go up to about 30V. What's the theoretical highest rpm achievable?

JohnRobHolmes 06-09-2019 06:54 AM

Re: Best HH motor for my custom project.
 
I would generally recommend a 4s limit. Although the rotor can handle more speed the brushes start to blow out on 5s and higher due to the compound being turned for 12v.


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