Grinhill's Medium-power RC-Motor Hardtail build

[Grinhill]

Some great news on the motor controller front - I no longer have a problem with the ESC losing sync.

In an earlier post (19 April) I mentioned that I bought a new hobbycity ESC, the HV 100A model, but it was D.O.A.

Last week a replacement finally turned up (the turnaround wasn't that bad, it took a while for me to package it up and post back to Hong Kong).

Yesterday I re-wired the bike, and had to add a 5V supply to work with the opto-coupled throttle signal, and then tweaked the settings.

Strangely, the "Normal" start gave the best performance. "Very Slow" start was very jittery and hard to get moving.


Now for the road test. In a word, fantastic.

So much better, now I don't have to fiddle with the throttle just to accelerate. Smooth, constant power!

Well worth the extra money.

 

[Grinhill]

I had a mechanical failure yesterday - motor shaft spinning and no drive. It was the one-way bearing. Last week I did notice that on full throttle acceleration from lower speeds, there was an intermittent slipping, which I thought was the belt, but in hindsight it was probably the bearing on its way out.

I had been running pretty close to the maximum torque rating on this bearing (3 Nm), and lower speed means higher torque. The failure occurred on takeoff from traffic lights - I usually pedal up to higher speed, but on this occasion I was in a bit of a car sandwich which I was keen to get away from.

I had only clocked up about 200km use, as my commute is only 6km each way. I have been pushing the system fairly hard, with an average speed of 32 km/h.

Anyway, this gave me the incentive to get the Grinhill Mk2 on the road. It uses a bearing with an 8 Nm torque rating.

 

[paultrafalgar]

Great stuff, Grinhill! A tiny point: could you make the bottle "modular" by fitting a plug/socket in the neck. Then you could carry a spare and switch batteries en route.

 

[Grinhill]

Way ahead of you, Paul.


Actually, I think my next purchase will be another set of batteries. But I will probably run them in parallel. At the moment, my average current draw is around 25A, with peaks up to 75A. This means the 5Ah battery is warm by the end of a ride, and I have used 4Ah of it. By running two in parallel, the batteries won't be working as hard, and may last longer.

 

[recumpence]

Running two packs in parallel will give you more pack life (more cycles) for sure as well as more power because the voltage drop will be reduced. If you are warming up Lipos, you are using them pretty hard and dipping into their internal resistance a bit too far.

Two packs will do you a world of good.

Matt

 

[Grinhill]

I did some test rides with the Mk2 drive, but some further tweaking was required. So, a few weeks back I managed to convert my broken one-way bearing into a fixed shaft without much effort.

I didn't really think this through before launching into it, but it turned out OK.

My pulley can't be easily pulled off the shaft due to the bearings mangling it - it slips towards the end easily for a few mm then wedges solid. So I thought I could try and drill through the pulley (in beween the teeth) while still assembled, to insert a pin or two, using a 1/8 drill bit.

A squealing noise as I was drilling made me realise I had hit the hardened rollers (slap forehead here). However, by mangling the bearing shell on the way through, it effictively locked the bearing solidly onto the shaft. I Repeated this on the other side of the pulley for good measure.

Installed back on the bike, it's a goer. I can now answer those questions about what it would be like to ride without the freewheel.

My riding style is normally full throttle all the way uphill and on the flat, then coast down down hills and approaching intersections. My throttle is a non-spring-return thumb throttle. With the fixed setup, it's a lot more work on the throttle beacuse I have to speed match more, and gradually wind back the throttle when decelerating. That's probably the biggest downside. The resistance to pedalling isn't all that noticeable.

 

[Grinhill]

Here's another bad news / good news story from last week.

I had ordered a $5 servo tester as a quick fix to my throttle signal drifting off in cold weather. It worked a treat, nice and smooth, with the on-board pot, but I wanted to make use of my existing thumb throttle setup. Luckily they were both 20K, all good so far.

I stripped the servo board of all lumpy bits, such as pot, pushbutton (this is used to select different modes, the default mode is the one I need), power wires (I supply 5V via the output signal connector). Still looking good.



Hook up the pot, fire it up, and the thing is terrible. Stutters and jolts, while starting or at high speed, sounds like someone is bashing the motor with a hammer a few times a second!

Obviously some EMI (electromagnetic interference) happening somewhere. I tried running the pot wires through a ferrite torroid, didn't really help. Then I tried it on the supply/signal side. Best improvement came with one turn through the ferrite, however it was still not good enough to be rideable.

Back to the old throttle (555 timer). Fitted a new 3-pin connector to make it easy to swap. Adjusted the stopper on my thumb throttle to give a wider range of pot travel. This seems to have fixed the temperature problem. Happy ending.

 

[EVTodd]

I wonder if you just got a bad servo tester. I'm using the same one and haven't had any problems with it yet (knock on wood).

You said the servo tester made with the timer ic solved a heat issue. Was the issue with the controller or motor?

 

[recumpence]

This is a little off topic, but worth a mention.

In relation to servo tester throttles, if a switching BEC is used as a 5v power supply, the switching RF (I am assuming it is RF) can wreak havok with the servo tester giving funky behaviour. Separating the 5v power supply from the servo tester usually cures this. Insulating, then shielding the BEC (wrapping in foil) normally solves it too.

This is not your issue, I know. But I figured it was worth bringing up here.

Matt

 

[Grinhill]

Todd, the temp issue was just related to the circuit not being temperature-independent. In cold weather the pulses were too wide to be recognised by the ESC as zero-throttle, so it didn't start.

The servo tester worked fine with the on-board pot, no trace of interference. I even soldered the pot back on to confirm this.

Matt
My BEC is a small DC-DC converter (Amtex brand) which is a pcb-mount type in a rectangular metal can, about 50mm x 25mm x 10mm. Specs probably exceed the RC BECs.

 

[mikhail-bar]

Great fantastic job!
Grinhill, tell please, I am not understanded: after installation 100A HV controller can you open throtle at deadstop?

 

[Grinhill]

after installation 100A HV controller can you open throtle at deadstop?

My advice would be don't do it. I have occasionally used full throttle from low speed, say 5km/h, and the Cycle Analyst has recorded peak amps as 200A. So the system didn't fail, this probably lasted less than a second, but I don't think it's good for any of the components. I am only using 12 gauge wire, which doesn't like this much current.